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d2alfa

Loss of Compression

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Hi Folks,

Just noticed rattles from the rocker cover and on checking found that three cylinders had compressions around 160 but one was only 90.

My assumption is that a valve is leaking and my intention is to replace the offender.

The sump always seems wet so I intend to install a new gasket.

The engine has probably done about 130k miles.

Are there any other things I should consider with the sump and head off?

Regards

David

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Hi David ~

 

This might be a good time to renew the big end and main bearings as well as the oil pump? Check the crankshaft end float. (new thrust washers).

 

Tom.

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To change the rear main bearing of a 4 pot with the engine still in the car you have to remove the gearbox and flywheel first, but all 4 big ends can be done, no need to remove the pistons from the bores if really pressed, just make sure the liners are secured before turning the crank.

Cheers rob

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Hi David

 

You might find its a broken valve spring or bent valve. When running is there any excessive blue smoke from the exhaust?

 

It might be worth removing the rocker cover first to check the springs and then clearances using a feeler guage, if not just to rule it in or out.

 

Regards

 

Kevin

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Hi David,

when you say the sump always seems to be wet - what do you mean.

Is there water in the oil - if so this could be corroded Fo8 seals at the bottom of the liners :o

 

If you have the head off do not rotate the crank unless you have clamps on the liners.

 

Roger

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Hi,

Thanks for the advice.

The oil pressure appears ok.

There is plenty (probably too much) blow back gasses around.

No water has been found in the oil but the perimeter of the sump gasket shows plenty of oil around.

I was hoping to avoid the big ends and pistons and would probably hand over to a specialist to carry out.

Regards

David

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Before dismantling, try the 'oil test'. After chev king all the compressions, repeat after tipping a teaspoonful of engine oil down the spark p!ughole. The oil will always increase the piston ring seal, unless they have fallen apart, but will not affect a poor valve seal.

 

Do that while you can turn the easily, and your diagnosis is confirmed, or denied!

John

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