gordo Posted November 3, 2008 Report Share Posted November 3, 2008 Hi folks, I would like to know if a 1975 Bultaco Alpina 250 would make a good trials bike. If so, what are some things I should do to convert it? Thanks, Gordon Quote Link to comment Share on other sites More sharing options...
swooshdave Posted November 3, 2008 Report Share Posted November 3, 2008 About all I'd do it put the narrower tank/seat on and some good tires (assuming you've removed all the lights and crap). Quote Link to comment Share on other sites More sharing options...
peterb Posted November 4, 2008 Report Share Posted November 4, 2008 Hi Gordon, I used an Alpina motor as a basis for making a 352cc Sherpa (it was a 350 model that had a 64mm stroke), not so straight forward. The gear ratios are different to the Sherpa plus the overall ratio is higher meaning that you need both a very small front gearbox sprocket and a very large r'wheel sprocket to get the gearing low enough for a trial bike. The wheels are heavier than the Sherpa, the front is 1kg heavier but has a brake good enough to do nose wheelies - doesn't look right on an old bike somehow. Not sure what size carb is on the 250 but a 26 or 27mm choke size would be right for a trial motor. The Alpina forks have wider yoke centres with the bar clamps set further forward - a good thing I reckon. I guess that if you can experiment with the overall gearing (sprocket sizes) then it is worth a go. Bye, PeterB. Quote Link to comment Share on other sites More sharing options...
dfwilson Posted November 4, 2008 Report Share Posted November 4, 2008 I bought a 250 Alpina in 1970. I had two chains and two rear sprockets. The stock (as I remember ) sprocket was 36 tooth and I purchased a 48 tooth to ride in the hills. This worked pretty well. Cheers DFW Quote Link to comment Share on other sites More sharing options...
swooshdave Posted November 4, 2008 Report Share Posted November 4, 2008 Hi Gordon,I used an Alpina motor as a basis for making a 352cc Sherpa (it was a 350 model that had a 64mm stroke), not so straight forward. The gear ratios are different to the Sherpa plus the overall ratio is higher meaning that you need both a very small front gearbox sprocket and a very large r'wheel sprocket to get the gearing low enough for a trial bike. The wheels are heavier than the Sherpa, the front is 1kg heavier but has a brake good enough to do nose wheelies - doesn't look right on an old bike somehow. Not sure what size carb is on the 250 but a 26 or 27mm choke size would be right for a trial motor. The Alpina forks have wider yoke centres with the bar clamps set further forward - a good thing I reckon. I guess that if you can experiment with the overall gearing (sprocket sizes) then it is worth a go. Bye, PeterB. Correct me if I'm wrong but I believe the earlier Alpinas were much closer to the Sherpa Ts. Quote Link to comment Share on other sites More sharing options...
woody Posted November 4, 2008 Report Share Posted November 4, 2008 Yes they were, the Alpina changed in about '75, models up to then were Sherpas with different gearing and bigger tank. After that they got the Pursang type fork yokes. If you have the earlier version then changes are minimal, just the tank and gearing - there are plenty of Sherpa gearboxes on ebay so you could just swap the gearbox internals as long as it is from a compatible model as there were a few changes to the mainshaft and its bearing on the clutch side over the years and this will determine whether your clutch hub would still fit. If yo have the later type Alpina I'm not familiar with them so no idea how much work is involved but sounds like PeterB had the later version. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted November 4, 2008 Report Share Posted November 4, 2008 An Alpina sold in 1975 might be a M115(250)/116(350) or a M137(250)/138(350). The M137/138 is the type of Alpina that is furthest removed in design concept from the Sherpa T of the same year. I'm not sure about the M116/117 as the ones I have came with triple clamps removed and mixed up in a box. After the M137/138 Alpinas came Alpina models (M212/213) that went back to being very similar in geometry and design to the 1978 M198 Sherpa T. The M137/138 has the Pursang triple clamps as Woody mentioned and a long swingarm - I have a restored M138 Alpina and I can tell you it would make a poor trials bike compared with one of the Alpina models that are very similar to Sherpa Ts. The first Alpinas were the M85 (250) and M99 (325) and it is these models that are most like the Sherpa Ts of the same era, differing mainly in the internal gearbox ratios and the seat/tank. If you can advise the model (the M number is the first part of the engine and frame numbers) of your Alpina or post a photo it would help identify it. Quote Link to comment Share on other sites More sharing options...
john collins Posted November 4, 2008 Report Share Posted November 4, 2008 Yes - as others have said you need to be fairly carefull in finding which model you use - and do not get too hung up on engine numbers etc - as many seem to be doing with all things Bultaco - as over the years one hell of a lot of Bultaco's have been modified, had different gear clusters fiitted, cranks and top ends etc - I know becuase I have done probably hundreds. The 250 Alpina sometimes found in UK - is often one of a batch that came in - and Sammy Miller had quite a lot to do with them - and sold quite a few.( I think he also turned a few back into normal Sheropa's) To all extent and purpose they looked very similar to the blue 75 Sherpa shown on the front of the Bultaco haynes manual. The tank was larger and there were SOME differences in gear ratio's - but not as great as all that. Many of us at time thought of them as a sort of cross betweem trials and trail - and some of us - at least m- thought they make a basis for an Enduro bike ( I thought wrong). I bought one - and with a few mods rode it in Welsh Two days and a few British Champ Enduro's - but it was very much based on the trials bike than anything else - so excellent in mud/section type parts - but too slow and rather scary when flat out along the tracks - oh - and I stood up for two days! If you have this one - it is easy to use as a trials 0 change the ratios if you wish - I have loads of suitable gears both new and s/hand - although if you just play with sprox a little you will find you can use 1st & 2nd as is . A slimmer tank seat unit will be better as well. The " proper" Alpina - more common to Spain etc is a different beat - and probably left as it is as it will be worth more money in original state Quote Link to comment Share on other sites More sharing options...
gordo Posted November 4, 2008 Author Report Share Posted November 4, 2008 Hi Folks, Thanks for all the feed back. I am waiting on the model #s, but have the VIN # if that helps. PB13700550. I would assume seeing the 137 in the VIN, would make it a M137. And as feetupfun has advised, that model is the most removed from the Sherpa. That's unfortunate news. But that is why I posted this question. I want honest informed answers before I purchase a bike that might not be what I'm looking for. Thanks, Gordon Quote Link to comment Share on other sites More sharing options...
swooshdave Posted November 4, 2008 Report Share Posted November 4, 2008 Hi Folks, Thanks for all the feed back. I am waiting on the model #s, but have the VIN # if that helps. PB13700550. I would assume seeing the 137 in the VIN, would make it a M137. And as feetupfun has advised, that model is the most removed from the Sherpa. That's unfortunate news. But that is why I posted this question. I want honest informed answers before I purchase a bike that might not be what I'm looking for.Thanks, Gordon Yup. M137. Might want to wait for a Sherpa or different Alpina. Quote Link to comment Share on other sites More sharing options...
gordo Posted November 5, 2008 Author Report Share Posted November 5, 2008 I have found a 1978 Alpina 350, Model 213. Would this make a better choice? I would think I could get away with sprocket changes to begin with. And then look for a smaller tank and seat. Gordon Quote Link to comment Share on other sites More sharing options...
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