Bultaco Sherpa 198 Help

[rric]

Hey Guys,

i just got a 198 sherpa from a friend, which i'm currently trying to "restore" -- well, - at least to get it running good and fast again.

I'm currently at the stage that i've got most of the engine parts disassembled, splitting the cases is the next step.

The problem i've got is that my piston looks like ****, - one piston ring is stuck (i'm sure i can free it up or make a new one), but the piston still doesn't look very good. It's got various scratches, - a damn-hard-to-move pin and all the other stuff everybody fears when pulling the top end. one way of using it again would be to coat it using carbon which does cost about 100 euro (2/3's of a new piston i guess)

Now i'm not sure about (re)using this piston again, or calling it junk and get one off a modern bike and make it fit. On one hand i've got a 250 cylinder barrel where the liner doesn't look too bad, but on the other hand i'd like to give this bike some more power as i'm not planning to use it primary as a tractor but to get to work through the city, while having the choice to take the forest or the road, so thinking of bumping it up to 370cc, - or whatever piston i can get and make fit somehow. I'm not sure about the 250 cylinder regarding whether i can machine a new liner with a bore of about 85+mm and make the ports work (is there enough meat?) and additionally i guess i'll have to change the size of the bolt radius for the barrel and head bolts, don't i?

Did anyone of you think off stuff like this, or am i just crazy? Does anyone know of a modern piston from another engine which fits almost and is easy to get? (at least regarding piston pin?) i don't want to have to machine my own conrod- but if i'll have to i have to, i guess.

I attached some pictures of the tools i had to build so far for disassembly. Currently i'm building the crankshaft removal tool, and think about fitting a light generator with a small rotor which has a weight of 700 gramms, to get rid of the 1700g femsa rotor.

I'd highly appreciate any thoughts and ideas about this stuff i mentioned, THANKS!

Best regards, ricardo

[bondy]

hi to split the case first take the clutch basket off and weight then gear selector. also the magneto and igintion plate undo the 12 nuts on the L/H side then put the engin in the oven for 15 minets at 300f if a oven is not possibal use a blow torch.and concentrate the heat all around the middal of the crank cases shouldnt take long before you can split it. if the pin is stiff heat the piston up a littel then the pin should come out really easy. as for the piston if its damaged your probley better just buying a new 1 and get the barrel rebored.

[boghopper350]

In answer to one of your questions, yes I think you are probably crazy!

This bike is not built to go fast and should have plenty of power with a new piston and rebore.

[rric]

Hey Bondy,

thanks for your answer!

Splitting the cases doesn't look like a big problem to me, either. I got the piston removed, but while i've disassembled and assembled quite a lot engines so far, i never came across such a sticky piston pin. Even heat didn't help very much, - propably there was too much carbon and other dirt in the piston pin bore which's hard to remove prior to piston pin removal.

So i guess i'm right thinking nobody else tried to convert a 250cc engine to 350cc?

I gave this a lot of thinking and it's propably easier to use a new piston in this engine or even make the old work again and wait for a 350 to appear on ebay or somewhere else...

[bondy]

some times you have 2 heat the piston then tap it out with a drift. make sure you have took the sir clip out. if the piston isnt to bad you can use it.and clean the carbon off if you dont plan on buying a new piston i would at least buy new rings. as for making a 250 into a 350 am not sure about that 1 but if it was me i would wait and see if a 350 came up i have a 199A spare motor but plan on rebuilding it.