I bought a m98 175 Alpina engine on the cheap last year to build for a trials bike thinking the trans gear ratios would be the same as a Sherpa T.They are closer to a Pursang ratios so I don,t think they would work to well for a trials bike.Would a m49 trans be a direct swap? I,m going to put a 250 top end on it so is there anything else I,m missing that would need to be changed?

Scott, Be sure its not already a 250 as 175s didn't sell and were swapped to

250 top end, ( this comes from a source other than me).

Just passing along news.

Larry

I would check the diameter of the barrel spigot on the 175 before you get too excited about using a 250 barrel. It might be OK but it would be a very thick sleeve in the 175 motor if they are the same OD

By the way, there are quite a few Sherpa Ts out there with Alpina bottom ends and they go fine in sections once geared down

There may be an issue with the mainshaft diameter on the clutch side between the two gearboxes. If I recall correctly, the diameter changed but can't remember exactly which year.

Also the M49 mainshaft locates the clutch hub by woodruff key, so if your M98 has the splined mainshaft you will have to use the M49 clutch hub and basket as well. There are differences in the length of the clutch hubs and in the thickness of the spacer that sits behind them so you have to get the right combination to keep the chain true to the crank sprocket

Thanks to all for the replies.I went out to the garage to check out the cylinder.

Larry,it is indeed a 175cc and thank you for the heads up because now that you have mentioned it I remember reading about most being swapped out for 250 barrels also.

David-also a good call on making sure a 250 would bolt up.I was going on what Hughs had told me,but it doesn,t hurt to check first.The O.D. on the barrel spigot of the Alpina measures the same as a set of 250 pursang cases that I have.It,s not a real thick sleeve,the spigot is extra thick to take up the space.It is also good to know that the Alpina gear box can work.

Woody, those are the things I was wondering about maybe being a problem.There is a complete m49 trans on ebay right now and thought it might just work.If I can make do with different sprockets it would be easier and a bit cheaper.If I were to buy a trans I would check with the parts suppliers here first.I would rather buy from them if they are not too crazy on prices.

Thanks to all of you for the help and quick replies.

Scott, Woody is spot on about the main shaft all the way. (Great knowledge).

The Alp I recently built (mod 85) had a very worn main shaft ( on the left side )

and was a spline for the clutch, I imagine you can use your main & the mod 49

gears & lay shaft.

Check with Lynn.

Larry

Edited November 3, 201411 yr by lbhbul

Hullo scot taco,I have just read your Sherpa gear ratios posting. I have completely re-built 2 Alpinas in the last 3 years & agree,the ratio difference to a Sherpa box is not too great,I think you will be O.K. At that. One thing to mention however,when replacing the crankshaft main bearings it is a good idea to use C3 rated bearings.These are extra clearance ones,& worth fitting because 2 stroke motors run quite hot on the main bearings.They are only a few pennies more expensive than standard ones. Finally a question,if the 175 barrel is not going to be used,is it avaiable for sale ? Can you p.m. Me on this. Thanks,John JSY .p.s. The bearings I use are SKF Explorer 6205/C3

P.M. sent John.Thanks for the help.