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sherpated

Bultaco Flywheel Woes

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Hallo .

This is my first post. I would appreciate it I could pick your brains guys. I´m in the process of

stripping my Alpina type 188 350 engine down which is sitting in a 159 chassis. I bought it about a year ago and had a fair

bit of trouble getting it to run properly since. I have done several trials on it so far but its constantly giving

me starting troubles. Over the last year its broken a woodruff key on the ignition side (fitted with electronic) Then another

time, a primary chain tensioner broke. Now, again it has stopped running...possibly due to the flywheel on

the clutch side? Im pretty sure it was in one piece the last time I checked! I am starting to wonder if something

is off balance? I know the bearing race on the ignition side behind the flywheel looks a bit ragged could the

crank be vibrating and throwing stuff off balance. Is it at all the right flywheel?

The first picture shows the flywheel hanging on the shaft .

Any help appreciated!!

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Yes, it should all be in one piece (both flywheel cheeks with the sprocket in the centre. It looks like your outer flywheel cheek has been machined down -ts smaller than a sherpa which has both cheeks the same diameter - I may be wrong as ive never worked on an Alpina. It also looks like they tried to balance it - see the holes drilled in it. Suggests they knew what they were doing.

I'd just get another one - reasonably easy to find..

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Can't tell you if that's the right weight for an Alpina as never had one, but on the Sherpa double weight, the inside weight is welded on. I have one that the weld has broken on and it's in two pieces like yours.

Can't see any trace of weld in your pictures but maybe that's what's happened. If the inside weight was loose then it could have caused vibrating which may cause a problem with your crank and may give an air leak through the ignition side seal?

A 250 Sherpa weight looks as though it would be about the same weight as yours, they are often on ebay, you could try one of those, or a 325 Sherpa weight (not sure what a 350 Alpina is supposed t perform like but obviously, the lighter the weight, the quicker the engine picks up)

I'd replace the crank seals, sort the weight and try it again. You'll soon know if you have to strip and replace mains.

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I wondered if it had been machined down but the holes threw me. Never thought they might be to balance it.

I tried machining a Sherpa one down recently. Nothing came off it and I just got a squealing noise... Pays to know what you're doing I guess before trying to machine what is probably case hardened (what ever that means) metal...

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thanks guys for the quick feedback.I think ill try and pick up a sherpa flywheel. Funny its broke but Im in doubt whether to get a heavy sherpa flywheel or one the same weight.Woody, You said that the lighter the flywheel the faster the pick up. That sounds logical, bur are there any advantages of a heavier one in the sections and are there any disadvantages for the balance of the crank?

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In respect of different weights and crank balance, I can't answer from an engineering aspect as I don't know. I've not had any issues swapping them from one bike to another, that's about all I can comment on that one

As for the weight suitable for your bike, I don't know as the Alpina 350 is a longer stroke and bigger capacity than the big Sherpa, and I've never ridden one. I've no idea what the power delivery is like, whether they have any similarity to the 325 Sherpa, so I can't even make a guess as to the effect of different flywheels.

The Alpina is a trail bike, different gearing from the trials bike, so not sure what it would be like in trials sections, especially more nadgery ones.

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I go along with the general consensus that the outer part of the driveside flywheel has been machined down, although I don't know what a model 188 flywheel should look like, either.

However, I don't think the holes drilled in it will balance anything - least of all a plain circle flywheel that shouldn't need balancing anyway (i.e. it's not a crankshaft flywheel with bobweights, etc.) - surely the holes are for lockwiring the crank end nut.?.....

As already pointed out, the two parts of this flywheel were originally welded together - I have a number of driveside weights in the shed (including a Sherpa 325 item that has what looks suspiciously like a crack through most of the weld); don't recall any signs of balancing on any of them.

Disclaimer : my memory's not what it used to be !!

Edited by lorenzo

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I know the M213 primary flywheel is the same as the 325 Sherpa and the early 250 Alpina ones are the same as the Sherpa so you would think M188 would be the same as the 213 and the 325 Sherpa`s. I also have a broken M151 flywheel too.

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Thanks for feedback andthe suggestions for different flywheel models that I can possibly use .I have been looking around the net and found a couple of pictures of Alpina engines with their flywheels exposed. It looks like the standard flywheel is a lot heavier than I have, with the two sides on it being roughly the same size like a double disc. I will try and track down an Alpina one as first choice.

Im suprised to hear from some of you that the splitting/breaking of the wheel is not an unheard of problem. That surprises me with it being such sturdy hunk of metal! Love old bikes..always full of suprises!

I hoped I would be up and running for the easter hols, with just a quick crank seal change but I guess Ill have to be a bit patient until I track down a flywheel...I ll keep you all informed.....:)

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I've got some 350 alpina drive-side flywheels but I suspect the postage would be pretty steep unless you also live in Australia

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Thanks feetupfun! i would kindly accept your offer but alas I am in europe and agree with you on the postage, because its quite a heavy object. I will try to track one down here first. The kind chaps at Bultaco uk are already onto it today so we 'll see how that goes.Thanks very much for the offer though I might get back to you on that one yet!:)

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If it is the big double weight it will be the same as the 325 Sherpa, or 250 models from around '68 to '70

The thing to watch out for is the profile of the outer edge of the outer weight. There are two types, one has a flat, sharp edge, the other is rounded off. If I remember correctly, the weight with the sharper edge will foul the inside of the earlier clutch case - ie: the one fitted prior to 1975 that was up to the M150/151 which had the later style case.

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Thanks Woody,good tip. I'll bare that in mind when shopping for one. Being an m188 ,as far as records go, its from 76/77.? By the way, I took the motor out of the frame today and will split the casings tomorrow and fit new bearings. That will be fun. The wifes out too tomorrow so Ill pop it in the oven to heat it and air out before she gets back!.....?

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stick em in the dishwasher first, get them really clean, dont want to stink the oven out. oops misses is looking over me shoulder, gonna get frisked every time i come in from the workshop. ha ha. if you get stuck, i have one out of a m92 325 or is that too early?

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This is an M92 weight

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This is from an M49

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Looking at the M92 weight, it has a more square edge than I remember but without seeing the weight from a later bike I can't remember how different they may be now. All I can remember is that when I tried to fit a casing with to an engine it fouled on the weight - but I can't remember which combination of case / weight it was now... not much help unfortunately.

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