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Engine Specific Info and Questions => IDI Engine => Topic started by: dave friday on April 08, 2015, 03:54:33 am

Title: low compression on one cylinder
Post by: dave friday on April 08, 2015, 03:54:33 am

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.

Title: Re: low compression on one cylinder
Post by: air-cooled or diesel on April 08, 2015, 04:18:31 am

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.

Title: Re: low compression on one cylinder
Post by: RabbitJockey on April 08, 2015, 04:44:25 am

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.

Title: Re: low compression on one cylinder
Post by: manehfr on April 08, 2015, 05:20:44 am

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

Title: Re: low compression on one cylinder
Post by: dave friday on April 08, 2015, 05:41:01 am

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]

Title: Re: low compression on one cylinder
Post by: dave friday on June 06, 2015, 04:36:02 pm

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?

Title: Re: low compression on one cylinder
Post by: Dakotakid on June 07, 2015, 06:33:46 am

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

This sounds terminal.

Title: Re: low compression on one cylinder
Post by: dave friday on June 07, 2015, 08:44:41 am

How do I attach the pictures?

Title: Re: low compression on one cylinder
Post by: Dakotakid on June 07, 2015, 06:47:28 pm

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

Instructions there.

Title: Re: low compression on one cylinder
Post by: libbydiesel on June 07, 2015, 09:09:05 pm

The head is scrap. 

Title: Re: low compression on one cylinder
Post by: dave friday on June 08, 2015, 01:45:26 am

Thanks both...

Title: Re: low compression on one cylinder
Post by: dave friday on June 12, 2015, 12:55:22 am

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.

Title: Re: low compression on one cylinder
Post by: vanbcguy on June 12, 2015, 08:30:25 am

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.

Title: Re: low compression on one cylinder
Post by: dave friday on June 12, 2015, 12:54:10 pm

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