Rebirth of a Lightweight Panther. 9.The Gearbox

         The gearbox in the Model 70 is a Burman 8HPB four-speed unit for which spares are very hard to find. Luckily the box I had on the shelf is complete but the one that came with the 'Game Changer' was missing the cover to the kickstart case and the contents, kickstart ratchet, spring and the selector components.

Complete Burman 8HPB gearbox

Part Burman 8HPB gearbox from the 'Game Changer'.

Burman 8HPB internals, missing parts ringed.

        I hunted through my boxes of gearbox bits but while I have built up the HP hand-change box for my Red Panther, two CP boxes for the Model 75s and several BAP boxes for heavyweights,  both pre and post-war, I found nothing remotely suitable for this box.       

        An appeal on the Panther Facebook page produced a response from Bruce Sharman in Australia who offered me parts of the selector and two covers, one broken but with the broken piece, and one complete but with the clutch operating arm and its mounting missing. Luckily having a complete box to hand meant that I knew what the missing pieces should look like. Certainly the parts that Bruce offered looked like they could be adapted to suit even if not strictly correct. They were soon on a plane heading my way. thanks again Bruce.

Parts from Bruce 1. foot change pawl, sector spindle, control
quadrant, sleeve and pawl, ratchet sleeve.

Parts from Bruce 2. Kickstart case cover, kickstart case cover
(broken) with clutch lever.

       The sector spindle I already had, it was sticking out of the box. the control quadrant appeared to be from an earlier box with a short sleeve, the ratchet sleeve seemed to be from a later BAP box. One cover looked to be new and unused but the clutch operating arm was missing but was present in the broken cover. All in all a very useful box of bits.

       The clutch operating arm was solid and at first I could not see how to access it. I realised its aluminium mounting was actually a separate part pressed in; a gentle tap on the outside saw it slide out so I could free off the arm and install the whole thing in the new cover.

Clutch operating arm and mount.

        Now I could turn to the selector parts. I cut the short sleeve off the control quadrant and the splined end off the ratchet sleeve, boring the quadrant to give a press fit onto the new sleeve. Luckily these components were not hardened. I backed up the press fit with some braze and cleaned the parts. This, along with two springs from Fingertip, gave me all the selector parts.

Splined section and short sleeve removed, long sleeve pressed into
quadrant and brazed.

Selector parts.

        I cleaned the cases and the internals of the box noting that there was only one worn bush in the sleeve gear, the second bush was missing. Also the mainshaft bearing at the kickstart end was badly worn. Luckily the sleeve gear bearing, a special, appeared to be ok once washed out. All the gears looked to be in good condition. All the parts are shown below.

Sleeve gear parts

Layshaft and gears.

Mainshaft, gears and kickstart ratchet.

Internal selector parts.

Kickstart spindle, quadrant and spring.

        The kickstart quadrant is from the other gearbox, I have so far been unable to find another; it is considerably smaller than those fitted to the |BAP gearbox, both pre-war and post-war.

Gaskets.

Cases, clutch operating arm mount not yet in position.

I obtained new sleeve gear bushes and a mainshaft bearing kickstart end from Bearing Boys and this meant I had all the parts to hand. The bushes were pressed into the sleeve gear and reamed to size and the gearbox was assembled. It snicked into gear satisfactorily so I installed it in the frame with new stainless studs and a pair of cams for primary chain adjustment. Spacers on the mounting studs ensure that the chain alignment between engine sprocket and clutch drum sprocket is correct.

Whether the gearbox works satisfactorily in service remains to be seen. Reports by users are not encouraging!

Gearbox installed in the frame

My thanks (again) to Bruce Sharman.

Rebirth of a Lightweight Panther. 8. The Engine

       Upon inspection it was clear that the engine was a bit of a mess. The head and barrel were off and it was very dirty so without more ado, and without really looking at it, I pulled it apart. This was fairly easy as the crankcase was only loosely bolted up. Clearly someone had been inside it as the crankshaft gear was missing. The other timing gears appeared to be ok and the cam followers came out easily.

Engine as received

     With the cases cleaned up I checked the big and little ends for play and found none. Also the timing side bush and the drive side roller bearing appeared to be  in usable condition. I therefore put sealant on the joint faces and gaily went ahead with assembly. WRONG! To my surprise the cases would not close. I was surprised as I hadn't changed anything and I had expected the crankcase would go together easily

    After cleaning off the jointing compound with difficulty I bolted the cases together against three feeler gauges spread around the perimeter, adjusting their thickness until the crank would turn sweetly with a little endfloat. This was achieved with a 70 thou gap between the cases! But how had this come about?

     Possibly a previous owner had fitted a new bush with a thicker flange and gave up when the cases wouldn't close but that's largely irrelevant, the problem was how to cure it. I didn't fancy removing the bush but the drive side roller race looked to be improperly seated so I heated the case in the oven, dropped out the race and reseated it.  This made no appreciable difference. I removed a shim from under the roller race, which luckily was a sliding fit on the crankshaft, again without improvement. Talking to Sherb I decided the only answer was to skim the flywheel faces behind the bearings. I put the crank assembly in the lathe between the 3 jaw chuck and a revolving centre and checked this would turn slowly and safely with the conrod sliding on the saddle. At my slowest speed of 43 rpm I skimmed the faces, 10 thou each side before trying in the cases. It took many goes before the cases closed with a satisfying clunk, giving me between 5 and 10 thou endfloat. I fitted all the bolts and tightened up dry to ensure the endfloat did not disappear before taking it down, cleaning everything off, and using Locktight Bearing Fit on the roller bearing. I then reassembled the cases for the final time, this time with sealant. The crank turns sweetly but I still wonder where that 70 thou came from. I put the engine bottom end into the frame and tightened up all the mounting bolts. The engine still turned over sweetly.

      The cylinder had lost a chunk of the top fin but many years ago I had put some pieces of fin from an old barrel in a drawer and to my surprise I found them straight away. I trimmed a piece to fit and brazed it on. The cylinder is on standard bore and a quick whizz with a hone cleaned it up nicely. I sprayed it with heat proof paint and popped it in the oven to cure.

Repaired fin before painting.

      The piston is of standard size but was dirty and without rings. I found a set of Hepolite rings in a box. These are labelled 350 Stroud but are the correct size. I checked the end gaps at the bottom of the bore and they all came in at 10 thou. I oiled the grooves and fitted the rings before heating the piston with a hot-air gun before sliding the gudgeon pin into the small end and carefully locating the circlips. Retrieving the barrel from the oven and with a new base gasket I bolted the cylinder down onto the crankcase.

Hepolite ring set.

Bottom end in the frame.

  

      I cleaned up the timing gears choosing the best of several heavyweight crankshaft pinions to replace the missing one. After close inspection I am confident all the gears are 20PA although not marked. I then put them into the timing case temporarily, they will need to come out to set the valve timing. The replacement pinion was very tight on the key so I eased that down a bit and the pinion slid on tightly to the shaft.

In fact my confidence re the crankshaft gear was totally misplaced. A document in the POC library shows that 20PA gears were not fitted until 1949 although KE805 material was used the year before and some gears are so marked. 

Ref, POC Library

I turned to the internet to see if there was a way to check the PA simply. The size of Imperial gears is defined by the diametrical pitch, DP. Panther gears have a DP of 20. A table on the internet gives the base pitch for a range of DP and PA values. For a DP of 20 and a PA of 14.5, the base pitch is 0.15208 inches, for 20PA it is 0.14761"

Use a digital caliper and measure across three teeth placing the anvil of the caliper on the tangent to the involute and not on the fillet or across the tooth corners. Note the reading then measure across four teeth. subtract the values  to give the base pitch.

Measure across the teeth about mid-height.

On a crankshaft pinion from a Red Panther bottom end I had on the shelf I got the following values. Over 3 teeth,  0.552" over 4, 0.400" difference  0.152" = O.152" = 14.5PA. For the late heavyweight pinion, taking similar measurements on the teeth, 3 teeth 0.5475", 4 teeth 0.3995" difference, 0.148"  close to 0.1476" = 20PA.

Close comparison of the gears shows that the 14.5PA gears are thinner at the root than 20PA.

14.5PA top, 20PA bottom

Gears may be found stamped 805 14.5PA. These were probably made as spares for early machines after the change to 20PA.

I removed the heavyweight gear and fitted that from the Red Panther engine.

Timing gears and oil feed pipes

Timing gears assembled in the case.

       The piston was set to top dead centre using a dial gauge on the piston crown and a timing disc was fitted to the drive side crankshaft. The engine was turned backwards to 10 degrees before TDC and the camshaft fitted so that the inlet cam was just beginning to lift the follower. As the cam is one piece for both inlet and exhaust all other settings follow naturally. I checked them anyway and they conformed more or less to the P&M data sheet I was using. This sorted the valve timing so the engine was turned a complete revolution to set the ignition timing at 38 degrees before TDC on the compression stroke. The ignition cam cannot be fitted until the timing cover is in place.

P&M Data Sheet

With the timing cover tight against a new gasket I fitted the cam to the camshaft and set it to just open the points on full advance, using a resistance meter to confirm the exact opening of the points. I then turned to the head.

The valves were ground in and the head painted before bolting it down onto a copper gasket. I had no pushrods for this engine although there were a pair in my other engine I could use as patterns. I had a spare pair from a heavyweight so I removed one end of each of these and cut the tube to the length set by the pattern. These tubes were of aluminium alloy, some earlier pushrods used steel tubing. The rockers are very similar to those in a late heavyweight engine, in fact the rocker spindles are identical.

The exhaust valve lifter and spoke are almost identical to those in a heavyweight engine although the arm is slightly shorter. I found a cable and installed that but it is poorly situated, coming up against the underside of the fuel tank. The engine now just needs an advance/retard cable and a lead to the points from the ignition coil.  Also a carburetter must be sourced and jetted correctly.

Completed engine.

Rebirth of a Lightweight Panther. . 7, The Tinware

The mudguards as found were in a fairly poor condition with a few dents and some major splits and holes in the blades. The stays were generally rusty and bent or missing altogether so I junked most of those. I had no toolbox, chain guard.or headlamp.

Rear mudguard and seat frames.

Front mudguard.

I welded the splits and holes in the mudguard blades and made new straps to be bolted inside the guards to carry the stays. Lots of filler and rubbing down was followed by a coat of rust converter paint and several coats of primer. I am too impatient or inadequately skilled to achieve that factory-fresh finish but as long as the final result looks a bit shiny I can ignore the many imperfections. I prefer trying out these things such as welding and paint spraying myself rather than paying professional help although this approach often results in indifferent results. In the end I can live with it.

The stays were made from 1/2 inch diameter tube with the ends crushed cold in a vice using a shaped steel block to give the curved transition from tube to flat. The mudguard blades were set the correct distance from the wheel spindles to find the correct lengths for the stays. They were painted using the Teckaloid I used on the frame. The two saddles were taken apart but I found I had a better pillion seat on the shelf, identical to that on this bike but in better condition and with a good cover. The driver's seat was treated to a new cover.

Shaped block for forming stays.

I had made a rear chain guard and the battery carrier earlier in the restoration although the latter had to be modified as I had made it too wide. I cleaned up and sprayed a headlamp that I found amongst my junk but I later realised there was nowhere to fit an ignition switch. This machine has coil ignition. I found another headlamp shell which had openings for an ammeter, light switch and an ignition switch complete with key that I found in a box. Not original but hopefully functional. Spares Guru Ian Fox gave me a rusty tool box so everything was coming together.

With everything primed and cut back the tinware components were sprayed with several coats of black cellulose which was cut back and polished. It is at that stage that all the defects show up.

Front mudguard and headlamp.

Rear mudguard and toolbox.

The fuel tank needs work and will be attacked another day.

My thanks to Old Foxy.