Phoenix from the Scrap Pile.: 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!