removing barrells

Albervin

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The crankcase halves do not grip the liner symmetrically (if you have an interference fit)! You will get a slight ovalling (?) effect. At least the muff is (should be) concentric with the liner.
 

Howard

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New pictures make it look like the piston was rocking sideways on the gudgeon pin, what sort of fit was the pin in the piston and small end (or was it too badly damaged to know)? It looks like it was too slack to me, but van Drenth has had the problem with tight pins, so that's probaly the place to start.

H
 

jellywrestler

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New pictures make it look like the piston was rocking sideways on the gudgeon pin, what sort of fit was the pin in the piston and small end (or was it too badly damaged to know)? It looks like it was too slack to me, but van Drenth has had the problem with tight pins, so that's probaly the place to start.

H
The gudgeon pin came out unscathed as did the piston crown the piston does rock side to side, haven't had time to take the front one off and check it out to compare it all
No real marks on the inside of the piston either
 

Howard

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I assume you've checked oil holes in small end and piston. The only other thing I can think is that the barrel is barrel shaped - don't believe I just wrote that, but you know what I mean. I can see that the crancase might cause ovaling at the bottom of the liner, but as Alyn says it won't affect the top, so it's not very likely.

H
 

mercurycrest

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Just a thought....... did someone turn an oversized piston to size on a lathe with a three jaw chuck so it's round instead of oblong?
 

Bracker1

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Replace with JE pistons from California. Have them sized to the muff. They do custom sizes and designs. I have heard JP from Aus tend to sieze. JE has a pretty good rep.
Good Luck, Dan
 

tatty500

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Have I missed it or has someboby stated the obvious?
This damage is caused by break-up of a circlip.
The ends of the gudgeon pin are shamfered for use with a wire circlip....or if a flat circlip was used then the pin ends should have been flat. Either missmatch will cause a problem.
Even a properly fitted correct size circlip can be forced out of its groove by axial movement of the gudgeon pin. The circlip ears down against the bore and eventually breaks up. Some pieces reach the other side through the pin. The inertia of the pieces against the piston soon wear it away.
This axial force on the pin can be caused by: a bent or twisted rod: or a small-end bored not in line with the crank axis: or even a badly worn big-end...but not in this case
Simply though, suspect the circlip.
 

clevtrev

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If a circlip was the problem, you would see a score mark throughout the range of the stroke, not just at the top and the bottom.
 

clevtrev

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So what do you think it was Trev', Did the piston just Melt? I have never seen anything like that, Good Luck Bill.
The only others, repeat, others, have been Omega pistons that have suddenly gone out of shape. That is bigger across the pin, than fore and aft.
 
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