Isetta gearboxes

[Bob Purton]

I plan to swap over my gearbox later this month for another one I recently bought. I know these gearboxes are very tough and give cause to very few problems.  However my old one has badly worn splines on the input shaft that the clutch plates goes onto and I'm sure this is causing a little drag in between gear changes. Is there anyone out there with experience with these gearboxes? The replacement one has unworn splines but are there other parts I should renew before I fit it? Obviously I will replace the two oil seals on the shafts input and output and the clutch rod piston seal. Any advise welcome.

[Big Al]

The push rod / clutch pin mechanism has caused me issues in the past. They can prevent release or engagement unless they are a good clean working fit. Clutch plate contamination is possible if the seal has weeped. Most of the linings can be boiled to clean them up, not so sure about modern stuff - mmm asbestos.

Biggest thing is to get the engine in line with the top spider drive of the chaincase on good tough engine mounts. As long as the drive is in line there is little power loss through the rubber donuts. As soon as that alignment is lost the amount of energy lost, and wear on components, is inversely proportional to the miss alignment. Given that the BMW single can dance round like an Indian looking for rain good mountings a balanced and well tuned engine is important. All of that jigging about will effect the gearchange too and accounts for some of the really nasty Isettas I have attempted to drive. Add in Holywood steering and gearstick action and it can be an deeply unpleasant experience. But then I probably do not need to tell you all that as you have been around long enough to have found that out.

[Bob Purton]

Thanks for that Al. I had underestimated the significance of the engine alignment but yeh, power would be sapped out if working against the rubber donuts all the time. I will give that due attention. You are right, an ill set up Isetta is no fun to drive. Mine was truly awful when I first got it. My steering is as good as it will ever be now that every bush and bearing has been renewed apart from the actual steering worm which I'm told do not wear because of being enclosed in grease all the time. Not sure thats true though. The radial tyres made the biggest single impovement. All the small improvements I have made to the car over the few years I've owned it are now stacking up and its getting to be a nice car. Still not as good as I remember my original RHD but that wasnt very old when I owned it in the the early seventies. Also I believe it had the late model carb with fuel squirter and the square cut steering worm.   

[Big Al]

I was going to say there are several differing steering worms. No idea which is best. The front geometry on an Isetta is not too clever which is why the needed a steering damper on some of them. Of course as a four wheeler the car is very much more directionally stable. The Trike is something of a compromise and is what it is.

No knowledge of carb changes but it is certainly possible to get the engines to run nice and smoothly. I think there might have been a few soft engine mountings about back in the day. The Trojan can get resonance on the mounts too if the slotted mounts are aligned incorrectly. I prefer the solid Heinkel ones but more vibration comes through to the rest of the car.

I believe the rear drive shaft is another source of probs as the course splining wears. No idea if there is an engineering answer now. It used to be super glue compounds.

I saw Marcus has advertised DUF. Bit sad.