The Panther Page

Technical Tips

This part of the site contains an ad-hoc collection of technical tips. Most are as offered and there is no attempt at completeness. Over the years Sloper has published a wealth of information. Also the email list archives are steadily amassing useful tips. When I have time I extract these to this page. All additions welcomed.

Disclaimer All advice and tips are provided in good faith. Neither I nor the originator of the tip accept any liability for problems arising from following this advice. It is your responsibility to ensure that the advice is sound. If your local laws do not allow this disclaimer then you are not permitted to read this section.



Transmission Cycle Parts Misc

Technical Tips - proto-manual


  • Pistons
  • Cord piston rings
  • Cams
  • Main Bearing Conversion (M75)
  • Exhaust
  • Oil Levels
  • Oil Leaks
  • Oil Consumption
  • Starting
  • Carburation
  • HT Electrics

  • Pistons

    Volvo (& other) pistons can be machined to be suitable for the heavywieghts.

    Here are the details of one way of doing this, using a Volvo piston; details kindly supplied by Dai Lloyd-Hughes:

    As you know the standard bore of a 120 is 88mm. If we take for our starting point the gudgeon pin size of a 120 panther piston (G) we find that it is 22.230mm dia. (approx). There appears to be no Volvo pistons to this spec.

    In the frame however is AE part no PI 033 22 08 from engine set AE1424 with G @ 23.5 and a bore of 88mm. The distance from the centrepoint of G to the top of the piston is 38.250mm which will reduce the compression ratio by about .5:1, (ie to about 6:1 instead of 6.5:1) but this shouldn't affect the performance. I cannot tell you if the oil control ring will come to rest above or below the oilway in the barrell. If it comes below you can blank it off at the seat of the barrel and beneath it drill a 1mm dia oilway from the crank case "so that it spurts vaguely in the direction of the bigend." (acknowledgement, Will Pyke, 1990). The piston appears to have a wider top land than P&M, a good thing. It seems to come in 2 oversizes.

    The application for this piston is for the 1974-1980 Volvo model 246TE, GL, GLF etc range  which you might find in a breakers' yard, or you might find an auto factor to sell you one, as opposed to an engine set of 6 which a Volvo dealer almost certainly would tell you you had to buy. The 88.9mm bore AE3706 Volvo piston looks like more fun, having a variety of piston crown heights giving diffrent cr's, more versatile oversizes and G@24.00mm.  It seems what you have to do to make these pistons fit is to reamer out your little end (Le) a bit, bore your barrel to match or use a liner.

    The piston may weigh more than the P&M which will lower the balance factor of your engine which is currently probably in the region of 51% to maybe about 46%.  This shouldn't matter either and doesn't mean you will snap the rod, a common mistaken belief. If you wish you can lighten it using rotary files etc and it's never a bad idea to reduce the skirt of a piston to a near knife edge to reduce friction and increase oil control. You may even have to file the piston internal gudgeon boss ends if they won't quite accept the rod. If the bosses are a bit wider than P&M then again this shouldn't matter.

    I will be interested to know If I am right about the part no. quoted and to hear what the oil consumption is like with it from those that have used one.

    There are other pistons that seem to have applications for Panthers but I have only researched those with G22.230, the rationale being that if my piston failed I could have interchangeability without worrying about the dimention of Le. Fruitful sources are Austin, Bedford, Daimler,  Land Rover, Triumph and Jaguar, but all need modifications of some kind. Owners of model 100 may do better. It is astonishing that amongst thousands of pistons so few are of G22.230. Interestingly the 120 Con rod is very similar to big HRD Vincents. One may conjecture that the same forgemasters supplied both companies and that whoever made P&M pistons might have suggested G22.230 to achieve an economy of scale. I wonder who else they supplied.  Form in this case may have followed fashion, function or hard business sense.

    My source is the AE Auto Cylinder Components Catalogue pt no 68231 / 01 which I recommend for a good read. Regretably no-one seems to do a similar one for motorcycles, persumably because we have allowed them to become fashion accessories, but I doubt such a catalogue, if it existed, would have a piston of such large dimention as to be suitable.

    Finally, it might be asked why one would seek an alternative piston for M120. One reason might be unavailability, another that the top land is compromised when this engine was 'stretched' and another might be the quest for better oil control. On the other hand one may be buliding s 'special' or just like experimenting. My motivation stems from all of these reasons (except for unavailability) but was triggered several years ago by what to do with a wrecked barrel on it's last oversise. In the end I chose a Jaguar Series 3, 4.2 piston because it too is a big cat. The spigot dropped off the barrel when we bored it to size but it stays in place ok when it's bolted down. Oil consumption is no better but the main thing is that I and the bike seems to like it.  I'm now experimenting with one we have cut a second oil control ring into, ie it now has four rings, but it is too soon to say what this has done to improve matters. The exercise has again compromised the top land.

    Paul Kellet describes an alternative using a Jaguar piston:
    I don't know the Volvo part number, but if you want an alternative I have a Jaguar piston fitted to my M120. I have done about 3,000 miles with double adult sidecar without problems (exhaust valve guide excepted). Oil consumption is about 600 miles to the imperial pint (no, it's true!). My experience tends to confirm Rollo's opinion that the oil finds its way past the piston. The piston I use is Hepolite part number 21433. Modifications needed are

    1) bore out cylinder to approx 90mm, I used piston to bore clearance of 3 thou.

    2) the gudgeon pin diameter is larger, you need to ream out the little end bush

    3) the piston is a bit heavier than the standard part, mainly because the gudgeon pin is almost solid. You can taper out the gudgeon pin hole at the sides using a sharp tool in a lathe to get it to the same weight.

    I did not have Dai's problem of the spigot breaking, though I can believe it might be a problem under some circumstances as it is getting a bit thin with 90mm bore.

    Cord piston rings

    There is great debate about the merits or demerits of fitting Cord piston rings to Panthers. Some owners have experienced rapid destruction of the bores, others swear by them. I make no comment other than suggest that you look for advice if considering this. There does seem to be a growing consensus that Cord rings should never be used in a newly re-bored barrel and are only appropriate for squeezing a few extra thousand miles out of an already badly worn barrel.


    There was plenty of discussion in early Jan 2000 on the email list about cams. Paul Kellet provided the following interesting data and information...

    All the Panther cam figures I have seen have the peaks approx symmetrical about top dead centre within experimental error (which is about 7 degrees) so I don't think it is necessary to identify the cam. This is ignoring the asymmetry of the valve lifting mechanism but I don't think this makes a lot of difference. My belief is that any of these Panther M100cams can be timed symmetrically in terms of peak position.

    If you can get within 7 degrees of symmetry I am sure it will run really well, I would be a bit worried about 28 degrees asymmetry on my fine M120 thoroughbred.

    In Open In Close In Peak Ex Open Ex Close Ex Peak
    Panther All 4 stroke 37 10 45 107.5 65 15 115
    Panther M100 49/53 25 55 105 70 30 110
    Panther M100 49/54 25 55 105 65 30 107.5
    Panther M100 55/59 20 50 105 55 25 105
    Panther Springer 57/59 21 54 106.5 67 23 112
    Panther M120 59- 25 54 104.5 63 20 111.5
    MC data book M100 23 54 105.5 63 21 111
    MC data book M120 25 58 106.5 63 20 111.5
    Haycraft 1930s M100 25 55 105 70 30 110
    Tuning for speed 25 70 112.5 70 30 110
    Haycraft later edition 25 55 105 70 30 110
    Haycraft 49/54  25 55 105 65 30 107.5
    Haycraft 55/57 20 50 105 55 25 105
    Modern MC Mechanics 25 55 105 70 30 110
    POC manual M100 25 55 105 65 30 107.5
    POC manual M120 25 54 104.5 63 20 111.5
    Average 23.1 54.6 105.8 64.9 25.6 109.7

    Main Bearing Conversion (M75)

    I have had to replace main's on M75s before for just this problem. I used a much more low-tech solution (overside plain bearings) and took it to an engineering workshop. For those wanting a to tackle a higher-tech solution themselves, here's a suggestion from Graham.

    First point to make is that I have done less than 1000 miles on this setup so far, so I would not make any great claims for it yet! Having said that, it seems to run ok and doesn't make any (unusually) nasty noises.

    The incentive for modifying the main bearing setup was the demise of a replacement driveside bush. I have had problems with the driveside bush ever since getting this bike running about ten years ago. I eventually discovered that the oilway drilled into the driveside crankcase to feed the bush did not intersect the groove machined in the bush to carry the oil around the bush, but not before the bush had siezed to the mainshaft and spun in the crankcases (more than once and in spite of being pinned). This had worn the bush housing in the crankcase, which I suspect was the cause of the last bush failure I had, which resulted in the bush breaking up. I was left with a crankcase with an oversize bearing housing which was not even round!

    The standard main bearing bush is 1.25" OD, 1" ID, 1.25" long(+the thickness of the flange), and made of lead-bronze. The flange allows it to resist end thrust as well as controlling radial motion. The crankcase does not have much material to spare around the main bearings, so ball bearings would not be an option. I decided to use a 1.5" OD caged needle roller bearing with an ID of 1.25" and is 1" long. The part no for this is B2016 (I am 99% certain that these are INA parts, but there is a chance that I am wrong - I can't find the data sheet at the moment!). The imperial range is available in 1/16" steps, so the part number is B(for bearing), 20(ID, x1/16"), 16(length, x1/16"). I also used a 1.25" OD, 1" ID, 1" long inner race, part no IR1616. This fits straight onto the lightweight mainshafts if they aren't too badly worn. The total cost of bearings and inner rings was about 40GBP for both sides.

    I also bought a 1.5" reamer which made the machining easier, but was not entirely necessary. This cost 10GBP as Navy surplus. I think it would be damned expensive if you bought a new one!

    Four other parts were needed. Two 'flanged washers' to take the end thrust (Phospor bronze, flange 48.5mm OD x approx 4mm thick, spigot 1.5" OD x 5mm long, ID 32.0mm), and two spacers to sit against the crank wheels and space the inner races to the correct positions (Steel, 31.75mm OD x 1" ID x 9mm long). The exact thickness of the flange was determined by trial and error to set the crankshaft endfloat without having to use spacers.

    To machine the crankcases I bolted the timing side crankcase to an angle plate attached to the cross slide of my lathe and aligned the timing side main bearing housing with the lathe centre as accurately as possible. This took a LONG time! I then bolted the drive side crankcase onto the timing side and checked that the drive side housing aligned (as best I could given the damage it had sustained).

    I got seriously nervous at this stage and unbolted the driveside again to recheck the timing side. After re-bolting and re-checking the driveside, I was left with no option but to start machining the whole thing. I used a fairly short boring bar mounted in the lathe chuck and machined the drive side housing fractionally undersize before removing the driveside crankcase and machining the timing side crankcase (again fractionally undersize). I then used the 1.5" reamer mounted in the lathe chuck to run through both sides in one operation (albeit a very slow operation).

    If you are still reading this, you will have guessed that I have a fairly big lathe in my garage, but if I had the option I think it would have been easier on a milling machine. I don't have one, so I used the lathe...

    Having completed the machining, the assembly was pretty straightforward. I used Loctite Stud & Bearing Fit to secure anything that wasn't a good tight push fit, and also pinned the flanged washers into the cases with a single roll pin.

    Now for the admission; first time I tried it out, it ran for about 20miles before siezing. I had made the fit between the flanged washers and the steel spacers a little too tight and the spacers were simply mild steel. One of the spacers had picked up on the inside of it's flanged washer and locked solid. I opened the ID of the flanged washer a little and it hasn't given any trouble since. The dimensions given above are the original dimensions, not the modified ones. The only good news was that the roll pin trying to stop the flanged washer from rotating worked perfectly! Jumping up & down on the kickstart would not budge it!

    I have some CAD 'sketches', but not complete drawings if anybody wants them. DXF etc.

    Well, that is how I did it. If the crankcases had not been damaged I might well have considered a different approach. The same range of bearings includes some which could go straight into the Panther crankcases with no  machining. The thrust washers could be cut down from the original bushes if  required. These bearings would run directly on 1" shafts without inner  races. The only problem I can see is that the standard mainshafts have oil  scrolls machined into them which would probably mean getting special shafts  made. I suspect that this would be the simplest and cheapest option.

    Let me know if you try it. Anybody want to borrow a 1.5" reamer??


    The threads for the exhaust nuts on Panther heads corrode or wear badly and as heads are scarce and expensive it is important to salvage the threads. Stuart Penfold offered the following advice in response to a question from Markus:

    And from Knowles Mackay:
    If you  need copper sealing rings for cylinder head to exhaust pipe connection for M100 engines, they are a Kawasaki part KP11060-1689.
    Oil Levels

    Panther dipsticks cause no little confusion (I have been the victim of it on a M75). Markus asked:

    To which Stuart Penfold replied: Oil Leaks

    Mark Nazer offers the following tip:

    Oil Consumption

    Big Panthers are legendary for high oil consumption (see relevant part of Panther Lore). There are a number of suggested technical solutions. Below are some email posts which discuss the various merits.

    From Grahame Sherbourne comes the following views on the oil-weir and piston skirt oil hole adjustments.

    Most of this stuff can be atributed to some of the very good development work done by the much missed Will Pyke. I think that the general view is that lowering the wier by around 1/2 inch and then extendin  the weirs edge into close proximity with the fly wheels is the solution.

    I do have an engine that I once started to modify in this way but it is still in the workshop and has not yet run (don't hold your breath)  Reports in Sloper have all been favourable and it makes sense to me.  The 650 has smaller diameter flywheels and so this idea does two things to improve the situation. Lowering the weir gives the fly wheel, flinging the oil forward a bigger target and bringing it closer to the surface of the wheels allows a scraping effect.

    Another idea of Will's was to lower the oil feed hole in the rear of the barrel (or even to block this and put a hole in the oil gallery in the crank case)

    My own M100 runs with the oil hole 1/2inch lower than standard.

    I'm sure that these ideas DO have merit but in my opinion a very good piston to bore (ring) seal is the answer to oil problems particularly on the M100.

    If you are new to these engines do not expect oil comsumption to parallel those of BSA or others a constant 200miles to a pint is a real achivement (yes I know there are those who claim much better but this figure realistic and attainable)

    Paul Kellett followed up with these comments.
    My M120 runs fine with no scraper blades and standard weir height, has done at least 200mpp for the last 5,000 miles or so with a Jaguar piston, it was ok before this on a mk1 owners club piston (I took it out because they sometimes detonate).

    I can't see how scraper blades would make much difference except at very low engine speeds. Lowering the weir gives a bigger target but the percentage increase isn't huge so it's not going to make the difference between 30mpp and 200mpp is it? I would be nervous about doing this as my M120 definitely consumes more oil if I have the oil level too high, presumably it tends to slurp back over the weir as the bike bumps along. Also I have met people that have done these things and not really cure the problem (Jonathan Jones??).

    Last summer Rollo was telling me that he has measured the position of the oil feed hole and it is right on top of the oil control piston ring, he thinks some engines have it too high so that they pump out the oil. This sounds likely to me, if I had a problem engine I would try lowering this first. In fact I wish I had one to experiment on! For a quick and dirty tryout you could just fit a base gasket the wrong way round to block up the oil feed for a few miles.

    PS an old man I was talking to years ago told me he cured high oil consumption on "an old P&M" by fitting a baffle across the bottom of the barrel to stop so much oil being flung up it. He assured me that it worked well for a long time, this was on a machine fitted with a "float" and used by a bike shop to carry other motorcycles. No idea of the practical details or whether it is possible on an M120.


    Starting the big singles can be daunting. They have reputation for tearing achilles tendons. The following is extracted from a discussion on the email list on the topic.


    Amal Concentrics can be used as replacements for earlier Amal carbs which can be hard to find and maintain. Rollo offered the following advice:

    and followed it up on how to set the things up: There seems to be substantial confusion about the specifications for carbs for the Model 120. I copy some of the discussion below. I have no conclusion, but the information here may throw light on your problem. The discussion followed a question from Les Kellet:
    My 1965 M120 combo has a 389 Monobloc, set up as per the POC Engine manual (and "The Book of the Panther Heavyweight") viz 280 main jet, 30 pilot jet, 106 needle jet, cutaway 3, needle groove 3 (ie the middle one). It runs a bit rich around 1/4 throttle which makes it 8 stroke a bit around 30mph, it gets much worse if I raise the needle a notch. Away from 1/4 throttle it runs ok and it does about 60mpg with chair. Yes I have tried a new needle jet.
    I notice on the website there are two different settings given for the M120, one with cutaway 3 and needle groove 4, the other cutaway 4 and needle groove 2.
    My understanding is that the top groove on the needle (ie the weakest setting) is number 1 in which case the website settings don't sound right to me. My M120 appears to want to run with cutaway 3 and needle down a notch from the middle (groove 2?) but it pulls a big chair and gets pretty hot already, I don't want to burn the piston. I feel tempted to try a 105 needle jet and leave the needle in the middle notch. It's not too easy to dick around with cutaways because the slide has been sleeved.
    Can anybody confirm what the "correct" factory setting was?
    Jordan Princic offered the following advice:
    For the M120: The carburettor type is Amal Monobloc 389/33. All sources I found agree on that. The P&M Spares List states MJ 280, and bore 1 3/16 inch (which is wrong, it's 1 5/32). The P&M Maintenance Manual says MJ 280, throttle valve cutaway 3, which means 3/16 inch, and needle position 3, that is 3rd groove from the top. Amal parts list (dated 1961) says MJ 280, PJ 30, NJ 106, needle position 4. Modern Motorcycle Mechanics (J. B. Nicholson) says the cutaway should be 3 1/2, otherwise as per Amal list. This is a Canadian book. Pitman's The Book of the Panther (H/WT) 1938-66 seems to suggest the CA is 3 and the needle position 3, but is ambiguously combined with specs for the M100. As on the table on the web site, the 1962 on specs are different, in that the cutaway is 4 and the clip position 2. I regret I don't know from what source that particular 1962- entry came, possibly from an Amal list that passed through my hands. (Note: these are the settings I'm using on my M120 solo, that seem to give good results, albeit I haven't clocked up many miles yet.)   Does anyone have a later Amal Monobloc list? To summarise, the main jet is consistently stated as 280, the cutaway ranges from 2 to 4, and the needle clip position is from 2 to 4, according to source, all for M120.

    It's not rare that settings vary between bikes, markets, geographies. Things that affect them are quality of fuel, altitude, whether or not an air cleaner is fitted (suggest MJ 320 if no air cleaner), ambient temperature, etc, and that's for a new standard bike. Engine and carb condition counts, too, and fuel recipes are changing. According to Amal list, needle jet should not have bleed hole. I guess this refers to the cross drillings sometimes seen on these jets. Worth checking? Do you have the correct needle fitted? It should be a D, not a C which is for 376 carb. Air leaks at flanges? For confirmation, smear some grease around joints. What does your spark plug look like? If too lean, the porcelein would be bone white, rather than a light brown of a correct mixture.

    Robert Shaw added:
    I have in my Carbie file, a 7 page printed document of unknown author that suggests that form 1958 to 1961 the M120 had a 389/33 1 5/32 " amal with 280 main jet, 30 pilot jet, 389/3 throttle valve, .106 needle jet and a needle position of 4. From 1962 to 1966, the throttle valve was changed to 389/4 and the needle position to 2, everything else remaining the same. On my M120 I have cheated and put on a mark 1 concentric, which is a much better and bigger carbie. Panthers are a bit strangled and can, in my opinion, benefit from better breathing.
    Les followed up with a question about the cross drilled holes which Jordan answered thus:
    To follow up on Les' request for my Monobloc settings, I have checked the needle jet, and it does indeed have the two holes. As I said, it seems to run quite OK, but I will probably experiment with a NJ with no holes at some time. To sum up, the settings presently are:
    Standard Panther cast aluminium bodied air filter with oiled cotton element.
    Amal Monobloc type 389/33, bore 1 5/32"
    Main jet  280
    Pilot jet  30
    Needle jet  .106, with two holes cross drilled
    Jet needle  D, position of clip 2nd groove from top of needle.
    Cutaway  4
    HT Electrics


    Many Panthers are fitted with Lucas Magnetos. Some specific tips follow. There is a good web page on Lucas Magnetos.

    Magneto Retiming

    I paraphrase Rollo Turner's advice on two ways to retime the magneto; a difficult task due to movement on tightening

    You can retime the mag more easily if, when you offer the mag up to the engine, you put a bit of loctite or similar on the tapered shaft and, with both parts of the mag dog in position, slide the mag in. Then wait ten minutes. The loctite will have set, the mag can be withdrawn and the nut put on and tightened with no movement.

    Another way of doing it is to leave the mag in situ all connected up. Take off the timing side case. Take out the oil pump idler wheel. Set the mag by rotating the mag pinion to the points just open with full advance and the engine a bit before tdc. (By
    the way exactly the same effect is achieved with engine on tdc and timing on full retard). You then replace the idler wheel. It never quite meshes with the teeth so if you need to rock the mag pinion half a tooth do it so that you have slightly over advanced the engine. Then alter the position of the lever to give the exact point of full advance and mark where the lever goes. Thats where you run it at.

    Magneto Coupling

    The following is condensed and adapted from a discussion between Grahame Sherbourne and Dai Lloyd Hughes regarding the Magneto coupling / auto-advance-retard drive on a Model 100. Apparently there are two different types. "The auto advance type coupling ... is a real pig and is just not as obvious to dismantle as the shaft is hollow and the sprocket screwed Left Hand thread to the shaft." The advice from Grahame for this type is...

    If your bike is pre 52 you ain’t got a magdyno but two separate instruments. A bolted down mag and a high level chain driven dynamo. As you are experiencing trouble I also guess that you have one of the very troublesome auto advance devices in the timing cover.  These are pretty rare because everyone junks them (including Panther themselves after a very short{by their standards} production run). The sprocket is held to the hollow shaft by a left hand thread of about 11/16 dia.  Now how do we get it to let go? If the sprocket is Knackered and they often are use a drift on the teeth.  You must leave the timing gears in place to lock the engine so don’t remove the autoadvance until the tight fitting thread has at least moved. Although this would be the method most (me included) would use albeit applying a little heat and using a brass drift, a more workmanlike way would be to fashion a strap wrench from a bit of the correct size chain and thereby protect the sprocket.
    And from Dai for the other type...
    This job is easier if you have the engine out of the bike, but same principle applies with it in. Remove the small split pin on the mag drive spigot, if it has one. Lock the coupling from the outside with say a flat steel bar, (you might get lucky with a broard tyre lever). Jaming the gears on the inside of the case say with a small screwdriver is not good practice. Remove conventional RHS nut. Using a small puller (or just possibly a soft drift and hammer) pull off the pinion or knock through the shaft, taking care not to loose the small woodruff key on the shaft. Coupling will now pull out with fingers. The bush can now be pressed out from the inside of the timing case. The counsel of perfection is to use/make up a puller with a spacer that just fits the id of the bush, again you might get lucky with a suitably sized socket. The last one I did  drifted  out with said socket, but as I had the engine out I took the precaution of supporting the casing on wooden blocks. The operation might benefit from a rag dipped in boiling water wrapped round the casing for a minute or two. Reverse to re-assemble.
    Magneto Conversion

    It is possible to convert a magneto to points and coil without it being obvious that this has been done. J.P.Lodge tells us:

    Kirby Rowbotham [UK] (01889 584758 and adverts in OBM) do an 'electronic ignition in a magneto' conversion. I think that they use the Boyer Bransden ignition unit (which is very good - I have it on three assorted bikes (not the Panther) and never had a problem)  I don't know what the cost is.
    I seem to recall the cost (from another, mislaid, email) is ~US$400. Rollo gave substantial details of the conversion:
    The magneto is basically a hollow shell with just a pair of rotating magnets. The spark is done via coil and Boyer ignition. I also fitted a car alternator at the same time to provide serious charging facilities.

    The conversion has some good and bad points. Personally I wouldnt go back but its all a matter of individual taste.

    Good things
    First kick starting under all but the very coldest conditions when I can't kick the thing over for the oil drag.

    Never, yes never, kicks back!

    Definitely smoother

    So far 100% reliable (except for operator error - I discharged the battery twice at the national last year by leaving the ignition on. That nice Mr Harvey lent me a battery and two welding rods to get going again!)

    I reckon its better at the top end as well. Whether this is because it has to be timed more accurately (you will need a strobe) or whether its just that the spark is more precise I dont know. I have had well over 70 out of my 100 and it will do more but being a rigid and given the state of the roads, advancing years and general lack of bottle I run out of nerve above this speed as the any bumps in the road cause the saddle to behave like an ejector seat! My friends 120 was on sidecar gearing but would fairly rocket up to 60 to 70 and was very comfortable at that speed. In figured much over 70 on sidecar gearing was not a brilliant idea...! But I know it really goes because after I had done it I had an anguished call to say it had failed in the middle of the night. My name mud! Closer inspection revealed a few minor problems not connected with the ignition (phew!) but since it had failed at high speed I thought I ought to check it out. Fastest Panther to 70 I have ever ridden I think.

    Bad things
    Leave the ignition on and it flats the battery in no time at all resulting in a search for jump leads because it wont start without! needs one of those Power box thingies really that enable it to start without the battery I suppose.

    The electronic ignition takes a surprising amount of current and needs over 12 volts to function correctly. So your charging circuit has to be absolutely wonderful or you can stop in the middle of the night to read yourmap with the lights on only to find the damn bike wont restart. This is embarrassing.

    Anybody can start your bike!

    This is a mod you could do yourself though I got Kirby to build the rotating magnets into my magneto. Once you have done that fitting is easy. Coil and electronic box fit under the tank or in the toolbox or wherever you like. Mines under the tank. Wiring is pretty straightforward and thats it. You will need a timing circle thing and a strobe to time the set up since the electronics control the advance/retard and give exactly 10 degrees I think. So if you dont get it right you take your foot off, or it wont start at all!

    Alternatively there is a D.I.Y. method published in Sloper some time ago, which Grame Sherboune refers to:
    I’m another satisfied coil ignition user.  Along with John Shaw and John Sykes I converted using the info. from Sloper but with a Softer (lower resistance) carbon brush.  The results are startling the bike Starts Ticks over and generally runs better .  A good Mag is a wonderful thing but a dodgy one is a pain in the bum this conversion made me realise that I had never had a good Mag.

    Most people seem to use the original Mag pickup but this means that the wire (now low tension) has to turn through 90 degrees. This is attached to the spring loaded carbon brush and sometimes results in a stiffness of movement so I fabricated a replacement from a lump of tufnel that allowed the wire a more direct route.

    I have used this system for many thousands of miles and only had trouble once when an unrelated wiring fault discharged the 6volt battery (I still use a standard Lucas dynamo ) , I wouldn’t go back to Mag unless Originality was a real concern.

    Spark Plugs

    Similarly spark plugs. I use B6HS or B7HS NGKs. Bosch range is different with one plug covering a large range of NGK. Original was, if I remember rightly an FE80. Old books of plugs will give you the conversions. The Green Spark Plug Company can or used to be able to supply all manner of interesting variations with platinum tips etc. When they burn oil like crazy a harder plug helps. I used a B5HS I think which lasted a lot longer than the softer ones, but still the machine eat plugs about as fast as it drank oil. Now I have solved my oil problems I have gone back to B6 or B7. So again there is no one correct solution and I doubt the factory ever worked to a single correct solution either! (Rollo Turner)


  • Clutch centres
  • Clutch Recorking
  • Gearbox Adjusters
  • Gearbox Lubrication
  • Gear-changer
  • Sprockets



    Clutch centres

    The heavyweight Panthers have a tendency to the stripping splines syndrome. There is a solution: a conversion is possible and again I quote from Tom Norman:

    Dave Thornber advertises in OBM and some other UK classic motorcycling magazines.

    Jordan Princic offers the following tip:

     Grahame Sherbourne offers the follow-up comments: Clutch Recorking

    Grahame Sherbourne offers the following tips for recorking a clutch:

    Jordan Princic has some excellent pictures and description of the recorking process, starting from raw cork

    Gearbox Adjusters

    Jordan Princic offers the following tip:

    Gearbox Lubrication

    Early gearboxes specified grease as a lubricant. This can cause some confusion when initially faced with the gearbox. There are various alternatives. The following is extracted from a discussion on the email list on the topic.

    And how to get the lubricant in and out... Gear-changer

    Sundry advice on how to sort out problems with setting up the gear-chager (gear-shifter) - normally only a problem afeter being disassembled...


    Cycle Parts

  • Frame
  • Dowty forks
  • Wheels
  • Paint
  • Transfers




    I paraphrase Rollo Turner again: Frames springing apart are always a problem on Panthers because the frame is stressed. Everything should go back together quite easily with a jack under the crankcases after slackening the engine mounting bolts a few turns. It always takes some leaning on and fiddling with but the bobbins do go in. I expect it is to do with the frames being slightly twisted after all these years probably from pulling sidecars.

    Rebuilding Dowtys

    I have rebuilt mine a few times. All the seals are (were a couple of years ago) available - most from the POC except the main seal which are legendary for being difficult to find. A friend located some in 1993 in a bearing shop (Ashley Bearing Co, Ashley Road, Upper Parkstone, Poole) on the south coast (of England). I do not know what he asked for - I think he took in one of my old ones. These had a code number on them of PR12-20DR C30 LID (note that the 3 and O are over-written). The total costs were a couple of tens of pounds I believe (maybe much less 120p each?) and the forks have stayed up for five years (but with little use to be honest). Subsequent enquiries I am told (early 1999) indicate that they cannot supply these seals. However Derek Milne has located an Australian supply. Ludowici Seals, Unit 1, 36 Tikalara Street, Regency Park, SA, Australia sell part number SU 18 for about A$9 each. They can make seals from drawings at ~A$15 each. The POC and Derek have drawings.

    I will tidy the following up some time, but here is a quick brain-dump on overhauling Dowtys. This relates to my experience with lightweight Dowtys on a 1949 Panther M75. Other models may differ.

    There is a manual available for the forks (Panther Dowty Oleomatic motor Cycle Forks - Service and Maintenance Manual). I imagine that either the POC or Bruce Main Smith would be able to provide a copy. They are not very detailled though, but worth a read.

    I believe that there are two major modes of failure - damage to the chromed legs and seal failure. The legs can be (straightened,) rechromed and ground but I recall that the axle lugs pose a problem, requiring removal and reattachment (maybe this was for straightening by rolling). It is not immediately obvious but a small amount of pitting is tolerable since the chrome surface is not actually the most important working surface. The seals are the typical problem. They seem to last a very long time - I had 44 year old seals (at least I believe that they were original) which were fine unless I bottomed the forks where they would lose all air rapidly. Around town though they were good for a few days between inflations. However, you don't have to live with even that - I rebuilt mine in early 1993 and put air in them just once since then.

    There are six bits of rubber in each leg, all of which harden or perish with time.

    1) The top filler plug has a simple O-Ring obtainable easily.

    2) Next down is the main static seal for the top part. This makes the top of the upper fixed leg air-tight. This is available from the POC for 150p (part R668)

    3) Next down is the really crucial bit - the moving seal on the piston. This makes the sliding joint between the upper fixed leg and the lower moving leg air-tight. My recollection is that surprisingly (to me) the movement is over the inner face of the upper leg and not over the chromed face of the lower leg. This seal is rather a rare beast. In Jan 1993 a mate found suitable seals at Ashley Bearing Co, Ashley Rd, Upper Parkstone, Poole, Dorset, UK for about 130p each. He took the old ones in. They had a code number on them (the old ones) of PR12-20DR C* ID (where the * is either a 3 or a 0 or one overwritten on the other). It may be that any decent bearing factor can come up with replacements but this is where I got mine. Unfortunately my mate, whilst being very helpful and knowledgeable, is a pretty untogether sort of chap (Hi Dai!) and failed to provide any details of bearing type other than he thought they were off the hydraulics of a JCB. (Anyone with more concrete info please let me know.)

    4) Next down is the main static seal for the piston. This makes the top of the sliding/lower leg air-tight. This is available from the POC for 150p (part R666)

    5) At the very bottom is a big end-stop rubber cusion which I imagine is not too critical in dimensions just the material must be able to stand continuous oil immersion (dimensions approx 18.5mm tall, ID 10mm, OD 24mm).

    6) There is also a sliding seal at the bottom of the fixed leg which moves against the chromed leg. This is not so important. It does not hold air it just scrapes dirt of the leg so that it does not find its way into the main moving seal. Well I suppose it is important that it does this function. I do not recall where I got these or whether I just greased up the old ones and put them back (resolving not ride through fine sand). Actually I think this is available from the POC at 350p (part R669)

    What else do you need to know?

    a) The filler valves can fail and I understand that ordinary tyre ones don't last well because the oil attacks the rubber in them. I don't know about this - both mine work.

    b) Also in dismantling the forks one special tool is needed. Basically it is a C-spanner needed for the top of the piston. I fabricated one from a piece of ~2mm scrap metal (dexion shelving I think).

    c) Be very very clean when reassembling - wash everything scrupulously in something appropriate (such as clean parafin).

    d) Smear all the rubber bits with a little grease on reassembly and be extra careful when inserting the piston/lower-leg assembly that you don't damage the lip of the main seal.

    e) Disassembly is perhaps not very obvious. Unscrew fillers and drain, then replace filler tightly. The top assemblies are joined by a rather flimsy pressure balance pipe and initially stay in the top yoke. You need to have the bottom yoke removed or the pinch bolts so loose that the upper legs can rotate. Rotating and pulling downwards should free them from the upper assembly. Pushing the lower leg fully up should now reveal the top of the piston/lower-leg assembly where the special spanner comes in. Once that is undone (many turns I seem to recall) the lower leg will drop away followed by (together with?) the upper leg. The bottom nut may be removed to remove the piston. Finally undoing the two filler plugs will relaese the rest of the assembly.

    Please excuse the legalistic tone of the following disclaimer - as I hand out more advice I get more nervous that some day I or the recipient will make a mistake and in this litiguous world try to clobber me when I am only trying to help... I provide most of this information from memory/notes as an unqualified amateur enthusiast and I provide it for free. As such I will accept no resposnsibility for inaccuracies or errors or the consequences of such inaccuracies or errors. Remember that you are working on a motor vehicle on which your or others' lives may depend. It is your responsibility to ensure that what you are doing is correct. If in doubt seek the assistance of a qualified specialist, who will presumably guarantee his/her work at a price.

    Also note that parts are available from the POC to club members only.

    If the forks are beyond recovery or you want to go to a simpler and presumably more reliable system I pass on the following information that Tom Norman sent me:


    Here's an excellent sketch of the front wheel hub (British Hub Company) of a 1952 Model 100 by Stuart Penfold (click on picture to get greater than full screen version which should print clearly)...

    {36m100wheel.gif, S.Penfold, 32kb}



    Andrew Wilson in the Jan 2000 issue of Sloper reports that British Leyland Damask Red (Code No DSBM9) is an extremely good match for the Red Panther colour.


    Jim Rushton informed "Re tank transfers, copyright probably belonged to Phelan & Moore and has therefore probably entered the Public Domain definition of copyright on the demise of the company.  Any legal eagles out there that can confirm this? If so, do you all know that you can buy Ink Jet Printer water slide transfer paper from ." There are scanned transfers on the Panther Pictures Page and on Grahame Sherbournes website.


    Threads and Fasteners

    John Fergusson provided the following explanation of threads and fasteners and their relevance to Panther's:

    For the definitive web resource on threads and fasteners see Kjell's Gjengetabell Tommer (soon to be translated in to English but quite comprehensible even without).

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