Engine stripped, need advice

[Flipatron]

OK, so I've removed the head off my Xr250 and so far I can't see anything that would cause a knocking noise. The head is A1 (apart from the stripped spark plug thread), the camshaft and followers look as good as new, the valves seem to be fine open/close ok and the cam chain seems ok.

What sort of play should I expect from the cam chain?

How can I tell if the big/little end is ok, would I have to remove the barrel and push/pull or can I check with just the head removed. I've had the piston up and down via the kickstart and can't see and evidence of a problem.

Bit of a mystery TBH, where should I look next? I've no choice but to re-build it should the piston check out ok and the thread is re-done.

[AIRWOLF]

Yes, you need to remove the barrel.

[holdk2]

You need to take off the head and bore and check if you have play in the big/small end, if thats ok it could be valve clearances. I have a workshop manual if you needed.
Kev

[Flipatron]

Ok the barrels off, should there be any play in the big or little end? I've taken the piston off and can hold the conrod and there is a bery small amount of play if you wiggle it, should there be no play at all?? Also the small end has a tiny amount of play, with the piston off and the little end inserted into the conrod I can wiggle the little end a little. Again should this be a smooth but wiggle free fit?

If this needs fixing then what the hell has caused it?

[holdk2]

Hi,

You need to lock the flywheel/crank at TDC some how, put the piston back on the con rod then see how play you have from both bearing together there is tolerances. “They should be no slogger in any of these two bearing at all”

Now if you have 2 shafted bearing I would look at the oil pump before you start replacing parts etc get a new 1.

How many miles has the bike done

Kev

[jasonbc]

OK, so I've removed the head off my Xr250 and so far I can't see anything that would cause a knocking noise. The head is A1 (apart from the stripped spark plug thread), the camshaft and followers look as good as new, the valves seem to be fine open/close ok and the cam chain seems ok.

What sort of play should I expect from the cam chain?

How can I tell if the big/little end is ok, would I have to remove the barrel and push/pull or can I check with just the head removed. I've had the piston up and down via the kickstart and can't see and evidence of a problem.

Bit of a mystery TBH, where should I look next? I've no choice but to re-build it should the piston check out ok and the thread is re-done.

I would have checked valve clearances before taking it apart in the first place and also the cam chain tensioner if it's the type that unscrews from the back of the cylinder if it isn't that type you would have to take the head of to unlock the blades on the older style cam chain tensioners to take pressure off the cam chain

[Flipatron]

Well I would have checked the tappets but after stripping the thread off the sparkplug hole I was kind of commited to stripping the head off anyway. Simply checking things now that it's apart, just don't know if the play in the big/small end is ok.

I'll try and video the play and post it up.

Bikes done 1500 miles BTW

Here's the vid

[AlanH]

There is a small amount of wiggle on a small end normally but that does look a bit excessive. I'd get that checked out by an engineer with an internal micrometer. They'll be able to see whether it's within spec and also whether it has gone oval. It's difficult to tell by feel.

[holdk2]

Hi,

Alan is right you could have a engineer look at it, at a cost £££

However the play in the bearing is not the wiggle as you put it. it's the vertical clearance your looking for, that’s why I’d advised you to put the piston back on then check the vertical clearance's

Or instead of wiggling it support both sides of the gudgen pin and check for clearance/play vertically.

Run your finger nail along the pin is they any ridges on the pin were the pin rides in the bearing.

If you could take a video of this it might help.

Kev

[AlanH]

Alan is right you could have a engineer look at it, at a cost £££

If 2 minutes with an internal micrometer costs more than a tenner, you're using the wrong engineer.

However the play in the bearing is not the wiggle as you put it. it's the vertical clearance your looking for

Yes, quite right. I was commenting on the amount of wiggle shown in the video. If there is a lot of wiggle, it's a sign (not a definite sign but a probable sign) that the small end may be out of spec as the more worn the more wiggle there is. It's difficult to know whether a wiggle is normal or excessive. It's also sometimes difficult to detect vertical clearance too especially if you've not had lots of experience.

As your decision to rebuild the crank will be based on the outcome of the test, it would be better to bung a few beer tokens at someone with the correct kit as the only 100% reliable way to tell is by measuring it.