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Old 09-11-2017, 10:19 PM   #1
will740turbo
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Join Date: Jun 2006
Location: Arcata, CA
Default Could this HG rust expplain low compression leaking to crankcase?

Yo. So I pulled my L-block engine from my wrecked 744 to put it in my 89 gle 745 (POS timing belt broke in 240 miles).
Anyway, I did a compression test, found low compression on one cylinder, and have it on a stand with the head off. The compression readings were 120,120, 60, 120 from water pump to firewall. I added oil to the one with a low number, and it didn't help at all. Added more, still no help.

I did a leakdown test on it, and found that the bad cylinder was leaking down into the crankcase. I checked all the other cylinders and got no leakage and couldn't keep the engine from turning. My tester was jury-rigged out of fittings and a compression tester, so I don't have a %age.

The head gasket looks pretty beat up to me, and it seems to have rusted quite a bit. Pistons and rings look great from the tip.. maybe 0.010 inches play. I haven't gotten plastiguages yet, but don't think the rings are bad. There's a ridge of rusty looking deposits way up high, but the piston bores all show crosshatching and are polished with no apparent mars. They're so shiny that the crud on the piston crown reflects on the sleeves.

I think the headgasket is to blame. There is substantial rusting of the actual gasket around the coolant passages (using zerex g-05 for years, but the engine came with 147k on it). There is some of the gasket also eaten away very close to both the oil drains and the metal sealing surface where the sleeves meet the gasket.

Here are some pics (may have to edit later to add them; i'm on my phone.)

Headgasket installed on block


And separated



First rust I noticed




Here's one that looks good...




And less good...


OMG wut r u doing headgasket?




STahhhhp (this is the cylinder with compression down to 60psi)

Last edited by will740turbo; 09-12-2017 at 12:39 AM.. Reason: Adding photos
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