Panther 1935 Model 50. 7. The Engine

 As noted before this 500cc engine was incomplete and badly mauled. The crankcases and rocker box are the only parts I can reuse and the former needs some work.

On the timing side the lug that holds the dynamo chain cover had been sawn off. I carved one from a piece of aluminium and screwed it to the case, finishing off with some aluminium solder. The magneto drive bush was badly worn so this was replaced.

Missing lug and broken out mag stud holes.

I made two stepped studs for the magneto fittings on the drive side case where the holes were badly damaged. These were tapped out oversize and screwed in place. The seating for the U-bolt saddle was rather mashed and uneven; this was filed flat.

The original flywheels were scrap as they were cracked between the two tapered holes. I considered them irreplaceable, or at best very hard to find as they have a throw of 90mm for this 500 cc motor. I decided to build it as a 600cc and use flywheels from the M100 wreck that I had previously rebuilt. Although rusty they cleaned up well. They also had balance holes in what appeared to be logical places, unlike other pairs of flywheels I had to hand.

Usable flywheels? Of course.

I dismantled the rusty flywheels and soaked them in vinegar to kill the rust before wire brushing and checking for cracks. The shafts were removed; the timing side shaft is shorter on this engine compared to the later motors so I fitted that from the Model 50 flywheels. The driveside shaft was damaged and replaced with a new one.With clean flywheels I fitted the new big end pin without the conrod to check for endfloat and found that the cases would not close. This I expected as the pin has slightly oversize tapers to allow for stretch in the flywheels. I machined the faces of the wheels around the bearing bosses to achieve an endfloat of about 20 thou before taking it down again.

The bigend race was pressed into a standard M100 conrod. (The original M50 rod is the long type for a two ring piston and I intend to use a three-ring slipper piston. The original rod is also scrap as the race is so loose it just drops out.) The bearing was then assembled and turns sweetly with no tight spots. The flywheels were assembled, the nuts torqued up  and the lock washers bent against the nuts. I had come across a stand for truing the crank and this proved to be ideal. With judicious belts of a heavy copper mallet I felt satisfied with a run-out of 2 thou.

Crankshaft on the truing jig.

Although as found this engine had two ball races on the crankshaft I decided to fit single-lipped rollers as specified in later Panther engines.These MRJA11/8 bearings can be very expensive but I found some on the internet made by NKE of Austria. The use of cheaper bearings brought forth much lip-sucking in engineering friends but they look fine although the true test is in how they perform. Time will tell; certainly their website looks quite impressive but that is of course no guide. 

The driveside case was heated to drop out the old race and fit the new. On the timing side the race just fell out so the new one was fitted with Locktight bearing fit. With the cases closed and tight an endfloat of 12 thou was obtained and the crankshaft rotated quite sweetly, dropping  to neutral under its own weight so all seems well.

With the bottom end in its cradle I made up the missing engine studs in stainless before final assembly with sealant, I also bent up some new U-bolts in 3/8" stainless.

Bottom end in its cradle.
Note the new lug at the top.

I put the assembled bottom end into the frame and this allowed me to assemble the clutch and primary drive starting with the chaincase back. The one that came with the bike is for the post 1935 crankcase where a large opening in the chaincase fits over the boss on the crankcase. This early crankcase has no such boss so I turned up an aluminium adaptor, fitted it with an oil seal and screwed it to the chaincase with sealant. Normally these cases are bolted to a lug on the engine but here the lug has been broken off so I plugged the redundant hole with a nut and bolt. Finally the rear case was bolted back to the engine plates.

 

Chaincase rear with adaptor

Adaptor from the back

The clutch was then assembled and the engine sprocket (26 teeth for solo gearing) and primary chain fitted.

The slipper piston I had to hand was +30 so I chose the best cylinder I had and got this rebored to suit. With new rings gapped to 10 thou the piston and cylinder were fitted to the cankcase and bolted down with spacer tubes on the U-bolts so I could turn the engine over without the cylinder lifting.

The reprofiled cam followers eventually arrived (thanks Foxy) and I could assemble the timing chest and time the engine. I rigged up dial gauges on the piston crown and on the inlet pushrod and bolted a timing disc to the engine sprocket. These come with two handy threaded holes for a puller but have a secondary use here. A wire pointer provided a reference and top dead centre could be found with accuracy.

Timing disc and dial gauges

Dial gauges

The book gives valve timings for this engine starting with inlet opening 10 degrees before tdc. I set the cam to this and put the crankshaft pinion on after, using the keyway which gave the best fit to the camwheel teeth. The two keyways give you half a tooth leeway. I checked the rest of the valve timings and they were miles out. I tried again using the inlet setting for later engines, 25 degrees before tdc and everything fell into place, with all the other timings close to published figures.

I had no magneto with the bike and approached a friend who builds magnetos and has a vast stock. He offered to build me a BTH from bits and soon wished he hadn't. Apparently there are three different lengths of armatures in these instruments and he rewound the wrong ones twice. Eventually though he produced a very smart BTH magneto; not cheap but showing a very healthy spark. This needed.a 10mm thick mounting plate and another friend made one for me on his mill, copying one off my Dowty rigid. He made a lovely job of it but sadly it didn't fit as my pattern was for a Lucas mag and the mounting holes were in the wrong place. I set to with a lump of 12mm aluminium plate, the lathe, angle grinder, hacksaw and files and made one that does fit. I could't bear to ask him to make another.

The BTH has a small taper and I didn't have the magic POC adjustable coupling so had to revert to adjusting the timing on the taper. I timed the magneto to TDC at full retard and when checked on full advance gave 38 degrees before TDC. This is the quoted figure for 1935 but P&M reduced this to 35 degrees after some big-end failures. This though is controllable at the handlebar lever. Later I replaced the dog with the adjustable type which makes timing the ignition so much easier.

I now turned to the cylinder head and rocker box.

The head that came with this machine is the wrong one, and is for an earlier model. I have passed this on. I had the right head to hand and another one on the spare engine I have for my 1936 M100. I also had two rocker boxes, one that I had sold to the previous owner of this bike, this has come back, and one along with the head on the spare engine. I had a good look at both.

Both heads were fine so I cleaned up one, painted it and fitted the valves. These are open and use large diameter springs and associated fittings. I had most of this but was short of one spring seat so I turned one up.

Cylinder head.

Both rocker boxes were ok but the shafts and rockers less so. The push rod end rocker is part of the shaft but the valve end is separate, it is keyed to the shaft and retained with a nut and spring washer. The shafts are hardened and tend to break away at the keyway. I had a mixture of valve end rockers, three late type and an early one which has a screwed tappet adjuster, this runs against the valve. As this engine will have adjustable tappets at the bottom of the pushrods I need the later type rockers without an adjuster. One of the pushrod end rockers has been broken and welded so my choice is narrowed as I don't want to use that.

Rocker box

Broken keyway on rocker shaft

Welded rocker, pushrod end.

Rocker parts, note early type adjuster

Picking all the best bits I assembled the rocker box. I had no pushrods so took those from my spare engine and fitted head and rockers to the cylinder. 

One part I didn't have was the oil filler cap which sits on the rocker box but I recalled that I had given a broken one to Sherb when he bought my 1933 M100. He generously sent it back and I fitted a new threaded part which I had clumsily broken off years ago. This completed the build of the motor so I filled it with straight 40 oil, fitted a temporary exhaust and a small fuel tank and fired it up. It started easily and ran well so I could now sort out the final stages of the build.

Oil filler cap

The completed motor.

Panther 1935 Model 50. 6. The Wheels

 The wheels were in a rusty condition but appeared to be sound. I dismantled the brakes and removed the bearings from both. The back wheel had several bent spokes one of which I managed to unscrew as a pattern. Central Wheel provided some replacements in butted 6 gauge steel zinc plated. I then had both wheels, the front brake plate and the speedo drive gear powder coated in silver.

Front wheel as received

Back wheel as received.

        The front wheel has a WM2 rim and 40 spokes as per Panther wheels but it doesn't look Panther to me although it may be earlier than those machines with which I am familiar.

Front wheel powder coated.

      It took a while to remove the bearings as the whole assembly seems rather unusual. There is loose half-inch diameter axle inside a sleeve which carries the bearings. These are taper rollers which face outwards, the cups being fitted last. Adjustment is provided by a sleeve threaded into the hub and this is held in place by a lock ring. I had to make a special tool to remove the sleeve. Grease is retained by felt washers, large steel washers and a circlip.

Front wheel bearings.
Top, axle, centre, lock ring, threaded sleeve, bearing cup,
taper rollers on inner sleeve
Bottom, felt seals, washers and circlip/

       The threads on the axle are also odd at 24 tpi on 1/2 inch diameter. I could find no standard reference for this and had to screw cut the nuts, something I find fairly difficult. Having taken ages to do that I though to check Tracy Tools website. They of course can supply taps and dies. Apparently the thread is UNS, Unified Special.

The brakes I had relined at Villiers Services. The shoes came back beautifully cleaned with bonded-on linings.

Front brake parts

Speedo drive gear, screws, plates and locknuts.

     The back wheel has a standard 1930s Panther rear hub but it is laced to a WM3 rim. No real problem. I can use either a 3.50 or a 4.00 tyre. To set up the wheel I needed to check the chain lines and to do that I had to start with the engine sprocket which is on a taper and not adjustable sideways. I have yet to build the engine but I did have an assembled crank so I put that into the cases and slid it between the engine plates. With a clutch basket and centre fitted to the mainshaft of the gearbox I could align the sprockets and make spacers to locate the gearbox laterally.

       With the rear wheel bearings and axle in place, and the rear sprocket fitted temporarily against some cush rubbers I could align the rear chain. Everything looked fine until I noticed that the rim is half an inch off centre. This is a real pain as I know that the spokes are not adjustable as most of the nipples are rusted tight. The wheel will need to be cut apart, new spokes sourced and the wheel rebuilt so back to Central Wheel for another set of spokes. One step forward, two back!

The rebuilt wheel ended up centred in the frame and this gave me a rolling chassis.

Rear wheel complete and centred

Front wheel.

Speedo drive, front wheel.

     The large speedo drive gear came attached to the front wheel and I found I had the gearbox in the cupboard.where it had lain for many years. This had a large fibre gear attached which gave the wrong gearing. I calculated that I needed a twelve tooth gear to give the right ratio having run the speedo head at a known speed in the lathe and noted the reading. I cut this from a piece of Tufnol, a similar material to the original gear and time will tell if it is man enough and if the gearing is about right. The mounting bracket was made up to fit a handy lug on the forks.

      I needed to press ahead with the engine but was stalled as the cam followers were badly worn. These had to be built up and reprofiled but this of course took time; all praise to our Mr.Fox. To keep on track I turned to the electrics which would originally been Miller. However  as with all things this machine I turned to what I had, generally Lucas stuff.

        I had a dynamo with the correct tapered shaft for the chain drive sprocket, cleaned and tested it and ran it up in the lathe whereupon it produced about 18 volts, so all well there. A Lucas CVC unit with regulator and cut-out also proved to be functional and when connected to the dynamo, an ammeter and a headlamp produced a good stable output at 7.8 volts. Hopefully it will perform similarly on the bike. I made up a loom and checked out a Klaxon horn I had. This proved to be a bit reluctant but eventually emitted a satisfying squawk. 

The new pattern parts I needed for the lights proved to be a real problem and took ages to solve. The new eight inch headlamp takes a prefocus bulb and I found that the bulb holder fitted to the reflector could rotated which messes up the dip. Also the pattern Lucas prefocus bulbs were crap. I bought a box of ten and they all have the same fault. the ring which locates them in the holder is a press fit but it is not tight and can rotate on the bulb which means the terminals in the connector miss those on the bulb. Also some of these rings are slack enough that pushing on the connector against the springs in the terminals can push the bulb into the lamp. I soldered the ring in place once I realised what was going on but still could not get a connection. The problem only revealed itself when one of the terminals in the connector fell off and I saw that it was crimped over the insulation! How the Chinese got a rocket into space is beyond me!

      I then spent ages making a rear lamp based on the Miller two lens effort. Finally everything works off the battery, lights, stoplight, and horn. I'm sure some of this pattern electrical stuff will self destruct once the engine is running, so that is the next step.

Rear lamp based on a Miller design.

Panther 1935 Model 50. 5. Assembly of the Frame.

The main frame is in good condition although the black paint is badly chipped and showing many areas of pink primer. I rashly decided to srtip it chemically, a decision I greatly regretted as it took nearly a week of intermittent work until I had the main frame fairly clean. The black paint gave up easily to the cheap stripper I had but the undercoat was very resistant and needed Nitromors. Some parts such as the engine plates I stripped mechanically. 

Parts partially stripped.

As noted before, the chain stays had been cut at the wheel end and had lost the mountings for the rear stand. I set to with the trusty angle grinder and a piece of 8mm plate and carved out two pieces using a wheel lug from a Model 100 rigid as a pattern. These were drilled and tapped for two tubes to mount the stand, and two pieces for the stand rubbers were turned and trimmed to fit. The parts were then assembled and welded together by ace welder Rex.

Rear stand fittings.

The sidecar fitting present on the right hand chainstay appeared to be brazed in and was immovable. I cut off the ball and drilled out the rest using increasing sizes of drill until I could drive out the thin wall of metal remaining, ending up with the original hole undamaged. There is no thread in the twin down-tube frames unlike the later rigids.

At a Solent Section meeting, the first I had been to for a year, someone mentioned a local powder-coater who came well recommended for being quick and cheap. I packed all the bits into a box and went over there on the Monday. I had it all back clean and beautiful on the Wednesday for a cost of £80, an absolute bargain.

Powder coated, all this for £80 in 3 days!

New rear stand mount.

 .Although lacking many parts I decided to start on repairing the Cycle Parts that I had to hand, namely the mudguards. The rear one, an Indian pattern one, was new and unused so this needed nothing more than a quick rub down. The front one, donated by Rex, was cracked and had a few spare holes so these were patched using my limited ability with the gas welding set. The tinware was then sprayed with cellulose primer followed by top coat which was matched to a green panel on the petrol tank. The label on the tin says this is a Lada colour, but so what!

Tinware in Lada green.

I calculated the radius of the rear mudguard using a program on the internet and set it up in the frame at the right distance from the centre of the axle using the lifting loop and the lower front cross fixing as fixed points. This enabled me to measure the length of stays required and these were made from half inch diameter steel tube. The ends were crushed in the vice against a shaped steel block to give the correct transition from round to flat. I used a similar process for the front stays.

Mudguard stays, front and rear.

As these girders are a bit odd Pantherwise I only had three fixing pints for the headlamp stays so I made these to suit from half inch diameter steel tubing.

Headlamp stays.

Other sundry parts that needed making were a rear mudguard to frame bracket with cleats for the CVC unit, a speedo bracket, front brake cable stop, steering damper stop and a top bracket for the front mudguard.

Sundry parts.

I had no footrest parts so used those on my 1936 M100 as patterns. Whilst I could cut and bend plate and turn bar the serrated ends that bear on the engine plates are more difficult. I made these by cutting and turning a pair of inner footrest brackets from a post-war heavyweight and the parts were welded up by the indefatigable Rex. Finally all these bits were powder-coated black.

Footrest parts

I needed some tool boxes and as these are hard to find and expensive I decided to have a go at making a pair. Sherb kindly lent me an original box for this model of Panther.

Original toolbox.

The main problem for my limited ability working with sheet metal was the front around the lid. This has a joggle for the lid, is curved along the top and has a return on all sides. Easy with dies and a press, less so by hand, so I broke it down (figuratively) into separate parts I could form from strip. Firstly though, I needed a bender so I turned to Youtube and made a simple roller bender.

Roller bender

This enable me to curve the strip for the top and I cut pieces for the sides and the returns of the front. Using 1mm thick sheet I cut a long length to cover the top, bottom and sides in one piece providing a joggle for the lap joint on the underside. I assembled a wooden former from layers of plywood screwed together and used this to form the returns on the back for attaching the long strip. For the front I welded the prebent and cut strips together and cut a lid from 2mm sheet. The whole lot was then soldered together and  clips sourced from Ebay riveted on.

Toolbox parts, top and sides strip, wooden former, lid, back. strips
for the front and the hinge.

I was quite pleased with the result but then had to do it all again to make the second one, bearing in mind that they are handed.

Completed box.before painting.

As noted before I had a set of girder forks with this machine which, although clearly not the same as Panther ones, appear to be Webbs. The basic girder and the yokes are sound and have been powder coated. The distance between the upper and lower spindles on the girder was quite a bit more than on the set fitted to my 1936 Panther so I made some suitable spacers for the headstock. these keep the links more or less parallel. Head races and balls I had to hand. I had replaced the top links and made a new set of spindles using EN24 steel. Luckily the yokes and girder appeared to be unworn at the pivots. I also sorted out the friction damper using a knob I found in a box of bits. 

The spring was too long and had to be cut down in length slightly. I roughly measured the spring rate using a bathroom scale in my hydraulic log splitter which gave a value of about 100 pounds per inch. With a load at the front wheel on my M100 of 200 lbs I cut the spring so that the links were roughly level at two inch deflection. 

Girder fork spindles and steering damper.

Headstock with spacers.

With all the fork parts ready I assembled the headstock and the girder fork followed by the rest of the frame, mudguards and toolboxes. Even though every part was assembled before painting to check fit nothing goes together easily during final assembly. Some local touching up will be required.

Front end.

Back end.

Gearbox detail

Number plate

The number plate I have had laying around for years. I think it came with a bike I bought from Sid Wilkinson but I don't know who did the artwork.

Just needs wheels for a rolling chassis.

Panther 1935 Model 50. 4. The Gearbox.

Although it is not essential to have the gearbox ready before assembling the frame it makes life easier to have it to hand rather than struggling to fit it around the rear mudguard, engine plates and battery carrier. So I turned next to the gearbox.

This machine uses a Burman BAPH four-speed gearbox with bottom and front mountings and these are not that easy to find. As I have mentioned before I obtained most of one from Shaun Meaney in Australia and found a kickstart case cover on Ebay. 

The Australian BA box

It turned out that the Australian box had been mishandled as an attempt had been made to drive out the bearing at the kickstart end by bashing the mainshaft. This had resulted in a mushroom end to the mainshaft at the clutch end and a broken-out circlip groove to the bearing housing of the inner kickstart case. The mainshaft damage was not difficult to rectify but the broken circlip groove was a problem. I also found that the inner bush in the sleeve gear had partially worked its way out during its life preventing full engagement of top gear, a common fault with these boxes. This had led to damage to the dogs on the sleeve gear and the mainshaft sliding gear. Note that the kickstart shaft is different on the BAPH to that on the BAP box although both are in short supply.

Luckily another BAPH box turned up, this one with top and bottom mountings so, although the main case is not suitable, the inner kickstart case and all the internals are the same. This was fortunate as I could replace the damaged gears and use the inner kickstart case to replace the damaged one. After cutting some gaskets I had all the parts needed to build the gearbox.

Gearbox casings.

Kickstart case parts

Internals. Note that the oil seal shown does not fit the BAPH
as the recess is not as deep as that on the BAP.

With new bushes fitted to the replacement sleeve gear and reamed to size and the mainshaft thread for the clutch nut repaired the gearbox went together well and clicks sweetly into all the gears - on the bench at least. Time will tell if it works in service..

Finished box.