Pre-unit slickshift gearbox leaking oil - is there a cure?

slimlavud · Jul 8, 2015

Hello all.
I have a chopper (yes, some of us still do) with a Tirumph pre-unit slickshift gearbox - which is excellent but when leaned over on the side stand (it leans quite a lot), it dribbles oil down between the two gearbox shafts. I have checked the oil level and it seems safe even when oil has finished dribbling out behind the dry open clutch. But I know that SRM do a sprocket retaining nut that has a seal to stop this on BSAs, does anyone do one for the Triumph gearbox please? And maybe it is just not an issue? I use ordinary mineral engine oil in the gearbox, this seems fine? Thank you, Slim
here's a pic of the bike if it doesn't offend you all too much - 1954 BSA A7 frame, M20 forks (extended), Harlel 45 wartime (1945) engine.

Recycled Rocker · Jul 8, 2015

Yo Slim Nice chop, slickshift eh, think yer on right track with gearbox/drive sprocket, but some Triumphs had selector shafts the went through back of box as well. This started to leak on mine as was only press fit no seal which eventually leaked. A diagram of your year gearbox if yer aint got one would help as yer know. Failing that phone call SRM or Supreme, always found Supreme helpful on phone, very knowledgeable on Triumph spares.

camman · Jul 8, 2015

That is an interesting mix Slim....I have a friend (yes really) , although not chopper style, has fitted an Indian V into an M20 frame with BSA gearbox and girder forks....great fun to ride.
I should think the oil loss would be at least be reduced, if you used 90 sae grade oil, which I believe would have been specified for that gearbox......it is in T140, for sure.
I have always had a weep from my Bonnie when on side stand.....but dont mind as it keeps chained oiled

thebiglad · Jul 8, 2015

I'm with Camman, try EP 90 oil - it's readily available and it'll protect the gearbox better, plus as it's thicker it might not leak as much???

slimlavud · Jul 8, 2015

Thanks chaps, yes, it is definitely coming out between the two shafts, just a standard feature really when the sleeve bush gets a bit worn... If I can't get a nut with a seal, I shall try and engineer something, might even be a business opportunity! You might know though, is there a lockwasher on a pre-unit sprocket nut - I don't think so...?