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low compression on one cylinder
by
dave friday
on 08 Apr, 2015 03:54
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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.
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#1
by
air-cooled or diesel
on 08 Apr, 2015 04:18
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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.
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#2
by
RabbitJockey
on 08 Apr, 2015 04:44
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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.
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#3
by
manehfr
on 08 Apr, 2015 05:20
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my guess... im almost sure its the piston rings...
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#4
by
dave friday
on 08 Apr, 2015 05:41
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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]
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#5
by
dave friday
on 06 Jun, 2015 16:36
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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?
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#6
by
Dakotakid
on 07 Jun, 2015 06:33
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This would be interesting to see.
Do you have a digital camera for a clear picture?
This sounds terminal.
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#7
by
dave friday
on 07 Jun, 2015 08:44
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How do I attach the pictures?
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#8
by
Dakotakid
on 07 Jun, 2015 18:47
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#9
by
libbydiesel
on 07 Jun, 2015 21:09
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The head is scrap.
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#10
by
dave friday
on 08 Jun, 2015 01:45
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Thanks both...
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#11
by
dave friday
on 12 Jun, 2015 00:55
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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.
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#12
by
vanbcguy
on 12 Jun, 2015 08:30
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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.
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#13
by
dave friday
on 12 Jun, 2015 12:54
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Thanks,i did have a go at knocking number 3 pre-cup out..i gave up![AMC Spanish head ]