Piston diameter puzzle

White_Disco · Jul 17, 2016

So I've stripped down the engine of my disco to try and locate an engine noise and steam leak. I've been measuring the tolerances today and found that 3 pistons are 90.37mm in diameter, but piston no1 is 90.05mm in diameter, I have checked and double checked. With the head off, No1 piston could be wobbled slightly with the fingers whilst fitted to the engine.
Is this just wear and tear does anyone know? or could someone have put in a smaller piston at some point. ( I have found some evidence that someone has had the engine apart before). The bores all seem to be the same diameter.

wammers · Jul 17, 2016

White_Disco said:
So I've stripped down the engine of my disco to try and locate an engine noise and steam leak. I've been measuring the tolerances today and found that 3 pistons are 90.37mm in diameter, but piston no1 is 90.05mm in diameter, I have checked and double checked. With the head off, No1 piston could be wobbled slightly with the fingers whilst fitted to the engine.
Is this just wear and tear does anyone know? or could someone have put in a smaller piston at some point. ( I have found some evidence that someone has had the engine apart before). The bores all seem to be the same diameter.

The bores appear to be .020" oversize somebody has fitted one standard piston. Naughty boy.

White_Disco · Jul 17, 2016

Sorry I should've mentioned that the cylinder bores are within tolerance for Standard diameter (90.47 to 90.647), it's like a smaller piston from another engine's been used

jamesmartin · Jul 17, 2016

White_Disco said:
So I've stripped down the engine of my disco to try and locate an engine noise and steam leak. I've been measuring the tolerances today and found that 3 pistons are 90.37mm in diameter, but piston no1 is 90.05mm in diameter, I have checked and double checked. With the head off, No1 piston could be wobbled slightly with the fingers whilst fitted to the engine.
Is this just wear and tear does anyone know? or could someone have put in a smaller piston at some point. ( I have found some evidence that someone has had the engine apart before). The bores all seem to be the same diameter.

were are you measuring pistons,bottom of skirt 90 degrees to gudgeon pin, 90.05 mm in thou is 3545 std is 3562 +20 3582

White_Disco · Jul 17, 2016

I'm measuring at right angles to gudgeon pin hole, half way between hole and piston skirt. Somehow it's less than std size, I'm confused!

jamesmartin · Jul 17, 2016

White_Disco said:
I'm measuring at right angles to gudgeon pin hole, half way between hole and piston skirt. Somehow it's less than std size, I'm confused!

should be the very bottom of skirt, bores and pistons are nominal size which means they are likely to be a few thou either way from stated nominal size,which is why you bore a block to the actual size of piston you have during a rebuild

White_Disco · Jul 17, 2016

Ok Thanks James, I'll measure again from the very bottom cheers.

Piston diameter puzzle

White_Disco

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wammers

No longer with us, RIP

White_Disco

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jamesmartin

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White_Disco

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jamesmartin

Well-Known Member

White_Disco

Active Member

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