Transmission mod - Prototype

[Phil Hyde]

Members knowledgeable of the Triumph C range 350/500 engine will be familiar with the removable plate that sits behind the clutch and affords access to the gearbox sprocket. The cover, part No. E3789, carries a small oil seal designed to keep oil in the primary chain case. A small amount of wear in the high gear bush soon renders the seal unserviceable.
So, I have come up with an idea to improve on the seal and provide additional support for the main shaft. Essentially a replacement cover, bearing, and adapter sleeve. Very much a prototype at this stage. It will be built into an engine in the coming weeks. Out of interest the plate was turned from 5.25” dia 6082 aluminium. I could only obtain a 30 mm thick slice and ended up with a lot of swarf. Future versions would be better made from 20 mm plate. Bearing choice was limited as the width was limited.

I have to say the basic idea is not new. Many years ago a guy by the name of Darren Snell produced a similar set up for BSA singles

[iansoady]

Looks good Phil. Could you not just modify a standard plate by making a top hat insert, possibly screwed in place? I assume the bearing (2RS type) fits in place of the bush although I can't then understand how the outer end of the sleeve gear is supported?

[Phil Hyde]

Ian, hi. The standard cover plate is a bit too flimsy in my opinion. Yes, it could be modded. For my prototype, the bearing carries the main shaft via a spacer sleeve. The standard bush in the high gear is foreshortened. As you will appreciate, very much a first go. A way of keeping my engineering head active. All being well i will keep the forum updated as it progresses.

[iansoady]

Thanks Phil, look forward to updates.

[druid]

Phil,
I have carried out a similar mod to my unit BSA singles. It seems to work well, however there is a drawback. The oil seal will tolerate some misalignment due to either incorrect machining of the cases or a slightly bent mainshaft. A proper bearing won't allow this.

Druid

[Phil Hyde]

John, you make a good point about the concentricity of the gearbox main shaft and its associated ball bearing in relation to the removable inspection plate. The engine i am working on is 66 years old. I am constantly amazed by how good the Triumph machine tools were, especially churning out machined casting to fine tolerances that afforded high levels of interchangeability. Notwithstanding updates and improvements this engine was in production from 1957 until 1973/4. I am looking forward to refining by design assembling the engine and getting it running. Will keep in touch.

[iansoady]

I agree about consistency - my engine has a T100 drive side crankcase and a 3TA drive side and they match perfectly. Re alignment a partial although inelegant solution might be to make a central bearing holder with a small amount of diametric clearance to alllow it to find its own alignment a bit lik e centring brake backplates.