low compression on one cylinder

[dave friday]

Hi all,as above..i have three readings of 370psi and one of 260psi!
I have checked that the valves are sealing by using an air line,no hiss from the inlet or exhaust but plenty from the valve cover/crankcase breather.
I think ive got a cracked on that piston.
Any thoughts/guesses?
Ta.

[air-cooled or diesel]

i had a couple of years ago shopped around and found pistons, meyhle, for around $130 a set, and other parts by shopping around, i say a re-head too, and other stuff.

[RabbitJockey]

not necessarily a cracked piston, and id highly doubt that anyway.  could be a cracked ring or that cylinder just wore more for some reason.  you won't know what u have till u pull the head, if the bores look ok, measure them, if theyre with in spec u can just hone and rering.

[manehfr]

my guess... im almost sure its the piston rings...

[dave friday]

Thanks both,I missed out "top ring" .I replaced the low cylinders piston+rings and re-rung the other three pistons 9000miles ago,I honed the cylinders but there was/is a bit of a ridge at the top of the bores!
This was done as a temporary measure!..the cylinders are bored to 77.51mm [maxed]

[dave friday]

Hi all, the rings on no 3 are ok but the head and gasket are not,all 4 pre-cups have cracks also there is a small crack between the pre-cup and the inlet valve seat on no 2 ...
what to do?
Is the head scrap,do I bolt it back together and hope for the best?

[Dakotakid]

This would be interesting to see.
Do you have a digital camera for a clear picture?

This sounds terminal.

[dave friday]

How do I attach the pictures?

[Dakotakid]

http://www.vwdiesel.net/forum/index.php/topic,13132.0.html

Instructions there.

[libbydiesel]

The head is scrap. 

[dave friday]

Thanks both...

[dave friday]

Hi all,i've been to two "machine shops" for advice on how to buy a new head, one said to reuse the head but that it might fail in the future ,the next shop said that the cracks weren't a problem but I should to have it pressure tested and surface ground!
I bought a "SB"engine so will start a new thread for that.

[vanbcguy]

Cracks around the prechamber area on the head make it very likely that it'll drop a prechamber in to the cylinder in the future with disastrous results. Doesn't sound like either shop is familiar with these style of engines.

[dave friday]

Thanks,i did have a go at knocking number 3 pre-cup out..i gave up![AMC Spanish head ]