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cornishflyer

Sherpa T 250 Conrod sideplay

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I've just heard that around the time that this model came out the con rod was centered from the piston end using the small end spacers (which my bike has).

Perhaps this isn't an issue at all (embarrassed).

Edited by cornishflyer
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On 30/11/2017 at 11:44 PM, cornishflyer said:

I've just heard that around the time that this model came out the con rod was centered from the piston end using the small end spacers (which my bike has).

Perhaps this isn't an issue at all (embarrassed).

Don't even feel embarrassed asking a Bultaco related question on this forum. Simply because they are quirky and had loads of changes which happened during production and parts been later superseded.

Back in the day, I had from new a early red model 199 with fibre glass tank. Which had a duplex primary drive chain, tensioner and corresponding clutch basket, which I thought was standard equipment as this is how it came from the favtory. However, it wasn't until many years later that I found out these components were normally only fitted to the Pursang motocrossers and not the Sherpa's.

Edited by model80
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On 27.9.2017 at 3:53 AM, cornishflyer said:

Quick update.

I measured the play in the conrod and sideplay at the top is only 1mm. When pulling on the gudgeon pin I can't feel any play at all so I'm thinking the conrod might be quite new and is OK. 

What I would like to do is get some of the crank pin washers and just get the crank rebuilt. I'm not sure if I can get those without the conrod, or what the measurements/material is?

I also can see on the exploded diagram that there is supposed to be a washer that goes on the end of the kick starter shaft (that fits into the RHS engine case. Mine is missing. Any ideas what that washer thickness is?

Cheers,

Dylan

Hi Dylan, my play at the top is 1,5mm (its a 350, 183) and i can feel very, very little play up and down when totally dry. with 2T oil there is no play. In my Bultaco Book it says the limit is at 2,5mm... I will try to use it.. I think for me, its ok... a few days in the year in classic trials. the washer at the end of kick starter is important, cause kickstart gear and transmission gears can get into contact...and oil can leak out of the kickstart shaft. cheers

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On 23/09/2017 at 6:49 PM, feetupfun said:

That seal sleeve is normally a light push fit. I haven't had to heat one up to get it off.

Yes the big end should not have that much side play. Should be more like 0.5mm. Might have had the wrong conrod kit fitted.

Some Montesas do have the conrod kept central by the top end of the rod, but Bultacos like yours use the bottom end of the rod to guide the rod and depending on the piston used, also may have centralising spacers on the gudgeon pin.

Fairly standard Bultaco failure to shear the drive side key when something goes wrong. One Bultaco I bought recently had that nut welded to the crankshaft! Being a Sherpa T it was a slow process grinding the weld away inside the drive side flywheel recess.

It's hard to see how much clearance there is on the outsides of the crank wheels in your video, but is it possible that the crank wheels have moved apart to cause that side play at the big end?

Hi again,

After many different attempts I finally got the seal "bobbin" off by cutting it off. I suspected to find some sort of adhesive under there but actually it's that the shaft seems to be too tight. The new bobbin is the same tightness, if I push it on the shaft I'm never going to get it off again.

feetupfun, you said you find them to be a light push fit, have you ever seen them tighter? I'm thinking I'm going to have to get something machined, either the crank shaft or the inside of the bobbin. 

Cheers,

 

MVIMG_20180120_125345.jpg

MVIMG_20180120_125352.jpg

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I've pulled apart two more Bultaco engines since then and in both cases that seal sleeve came off without effort. The knowledge that a new seal sleeve jams on the shaft means that the problem is probably the shaft. Being a very close fit, it would not take much of an imperfection to make the sleeve jam, so I would probably study closely to see exactly where the new sleeve starts to jam and try and find what the imperfection was and then deal with it. It may just have something there that can be removed with a hand-held oil stone. If you heated the shaft when you were trying to get the old one off, there will be combustion deposits and maybe some oxide that should be removed (there are deposits visible in the photo). You should also clean the inside of the new sleeve of any rust spots. A scotchbrite scouring pad is good for removing deposits like rust, combustion product and oxide film.

I can see a lip about 12mm in from the flywheel shoulder that indicates that the shaft has been deformed a bit. It may not be that bit of deformation that is your problem area, but deformation of the shaft somewhere is likely to be the cause of the jamming sleeve. The high areas can be reduced or removed using an oil stone. If you have doubts about knowing which areas are high you can colour the shaft with a whiteboard marker or with chalk and do a test fit. The high bits where it jams will be wiped clean.

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1 hour ago, feetupfun said:

I've pulled apart two more Bultaco engines since then and in both cases that seal sleeve came off without effort. The knowledge that a new seal sleeve jams on the shaft means that the problem is probably the shaft. Being a very close fit, it would not take much of an imperfection to make the sleeve jam, so I would probably study closely to see exactly where the new sleeve starts to jam and try and find what the imperfection was and then deal with it. It may just have something there that can be removed with a hand-held oil stone. If you heated the shaft when you were trying to get the old one off, there will be combustion deposits and maybe some oxide that should be removed (there are deposits visible in the photo). You should also clean the inside of the new sleeve of any rust spots. A scotchbrite scouring pad is good for removing deposits like rust, combustion product and oxide film.

I can see a lip about 12mm in from the flywheel shoulder that indicates that the shaft has been deformed a bit. It may not be that bit of deformation that is your problem area, but deformation of the shaft somewhere is likely to be the cause of the jamming sleeve. The high areas can be reduced or removed using an oil stone. If you have doubts about knowing which areas are high you can colour the shaft with a whiteboard marker or with chalk and do a test fit. The high bits where it jams will be wiped clean.

Great information, thanks, I'll proceed with your advice and report back.

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Well I went at it with an oil stone and it soon appeared that I would need a lot more to get the sleeve onto the shaft, I ended up having to use a fine file. Hopefully, by working slowly and on the high spots I kept the thing round. I was careful not to touch the shaft under where the bearing fits.

Next, to check the crank webs are still true, heaven knows what this engine has been through to cause these things :(

 

 

MVIMG_20180121_143305.jpg

MVIMG_20180121_143313.jpg

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So, since doing the work to the crank I've been thinking that the crank I have must be from an earlier bully with two bearings on each side. The ridge visible must have been the line where the second bearing came up to. So now I'm worried that by taking off what ever metal I have I've put the shaft out of round, not to mention what ever else dimensions might be different with this crank. 

There is a friend of a friend that I will be able to take this to, hopefully I will be able to compare with the correct crank, and also check for run out on the shaft.

I'll keep you posted.

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On 31.1.2018 at 9:08 AM, cornishflyer said:

So, since doing the work to the crank I've been thinking that the crank I have must be from an earlier bully with two bearings on each side. The ridge visible must have been the line where the second bearing came up to. So now I'm worried that by taking off what ever metal I have I've put the shaft out of round, not to mention what ever else dimensions might be different with this crank. 

There is a friend of a friend that I will be able to take this to, hopefully I will be able to compare with the correct crank, and also check for run out on the shaft.

I'll keep you posted.

Hi Mate, I am nearly 100 percent sure, that there is no difference between cranks wit two or three bearings. I found them in several sherpa and alpine engines. The difference is the seal holder. on the picture left side for one bearing, the right one for two bearings drive side. there also exist different seal sleeves. a long and a short one...greets

 

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Edited by dr-alpina
wrong picture posted

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Talk to InMotion (Bultaco UK) they know these engines inside out etc. There are about 4 different con-rod and gudgeon pin types. It is important that you get the righ info and spec for your engine. I fitted new con-rod assembly to my M80 which had two bearings on drive side and one on the ignition side. The con-rod had no play up and down and very little sideways but as I was into it I wanted new parts so I knew that all would be good with my crank assembly. You will need a hydraulic press with 40 ton capacity to start the big end shaft moving in the flywheel halves. You will also need to be extremely careful how you do this. I used a few methods to ensure that there was no uneven pressure and to keep the flywheel halves aligned. The new connecting rod and big end bearing together with little end bearing had different diameters to the original but it all went together perfectly. On some Bultaco the little end spacers keep the con rod aligned while on others it is the big end shims that keep the connecting rod ‘in the middle’ aligned. My finished crank assembly has a small end with a larger diameter needle roller bearing but uses the original godgeon pin and two shouldered spacers. The big end bearing has a slightly bigger diameter roller bearing with larger big end eye but obviously the same diameter big end crank pin. Please get in touch with In Motion as they really know their stuff🙂👍👍👍If you would like I can email you photos of my crank before, during and after fitting new conrod etc. If you go for honing out and oversized rollers don’t forget you will be running on the old crank pin.

Edited by section swept
Added material
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Here goes pictures of old and new con-rods. The hydraulic press, this needs to be powerful enough to start the big end crank pin moving through the flywheel halves. The rest of the pic are self explanatory, old bearing removed, selection of tools and spacers (not all shown). New connecting rod with 20mm dia little end eye. Old piston spacers, new one were stepped to match larger little end burg. Very blocks on surface table (took pics after dti’s used to confirm flywheel alignment. Finished article 🙂👍

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Edited by section swept
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On 24/09/2017 at 0:38 PM, bullylover said:

It looks like there is a washer missing off the ignition side of the crank pin. That might be what is causing so much play. They are supposed to have a washer on each side of the bigend pin.

Some Bultaco crank assemblies or rather the big end did not always have any shim/ spacers/ thrust washers fitted but relied upon the con-rod being held central in the bore by the little end /piston spacers doing that job. Montesa used a similar approach but the set-up process was more fiddly involving selective fit little end spacers between the piston and little end eye. I call it a proper job when both ends are controlled by shims or call them what you will.

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