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Discussion Starter · #1 · (Edited)
Greetings. I have an engine I put together, my first and only, about 10 years ago. Car's been a slow project.
It's a '77 first gen 350, bored .060 over, Scat 383 rotating assembly with KB dimpled alum. pistons - 9.5/1. Heads are GM performance ("fast burn") mild port and polish, MSD 6-A through an HEI cap. Wolverine "Blue Racer" wet cam, intake is ~ '63? ~ Hilborn re-ported for MegaSquirt 2 EFI.
After a bit down the line (wiring disconnect through firewall issue), it fired right up!. But idled fast ~ 2200-2800+ ~ fiddled with TunerStudio and got it to stay about 2200 for break-in. A few years later ... that's another story ... fired right up and idled nice - 800-900. Ran rough and stinky, but ran a few 2 mile turnarounds, up to 3200. But the last little trip to test stiffer rear coils, it seemed extra noisy, I thought I may have heard a faint little snap ~ and it seemed to run a bit rougher that last 1/4 mile home. I shut it off, but restarted to pull it in garage and noticed a lot of "smoke" out the pass. side exhaust (separate exhausts). I'd seen some smoke before, part of the over-rich-ness. Pulled rocker covers ~ nothing broken. Pulled pan and ~ dirty grey soup ~ water in the oil. Pulled plugs and #8 leaked clear water out - for about a 2 hour drip.
My novice head says, head gasket, or cracked cylinder. Compression check this morning - all 153#+/- but #8 is consistent 149# over several rounds of checks.
Is that enough of a difference to indicate gasket?
 

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The fact that it has sat a lot with low run time and it is one of the 4 corner cylinders says check the intake manifold-to-head gasket first.

The compression test results aren't enough to jump right to a head gasket or cylinder crack assessment....I'd need to see 25+ psi difference to make that call.
Your difference is not any different than any other healthy engine....they are never all completely the same.
Most mechanics guidelines are: No problem unless the difference exceeds 15 or 20% or more compression loss....you're not even 2.5%
 

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Discussion Starter · #4 ·
The fact that it has sat a lot with low run time and it is one of the 4 corner cylinders says check the intake manifold-to-head gasket first.

The compression test results aren't enough to jump right to a head gasket or cylinder crack assessment....I'd need to see 25+ psi difference to make that call.
Your difference is not any different than any other healthy engine....they are never all completely the same.
Most mechanics guidelines are: No problem unless the difference exceeds 15 or 20% or more compression loss....you're not even 2.5%
Well ~ that's a great Idea, eric. But I was thinking like Blazer and took the manifolds off before I saw your comment - dang. Might have been a whoooooole lot simpler. :LOL:
 

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1977 is inside the era of thin wall castings, sixty over is pushing it on these blocks if you haven't had the bores sonic tested for thickness.

A similar issue with porting where you’re removing material from Chvy’s already crack prone head castings. This is especially critical with the exhaust ports where operating temps are rather extreme compared to elsewhere. A compression test will not show this as the failure generally occurs to the manifold side of the valve.

You need to skip the screw around motions and pull the heads, coolant inside the engine is a bad omen. It doesn’t matter if it’s a casting crack or a gasket it has to come apart.

Bogie
 

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Discussion Starter · #6 ·
1977 is inside the era of thin wall castings, sixty over is pushing it on these blocks if you haven't had the bores sonic tested for thickness.

A similar issue with porting where you’re removing material from Chvy’s already crack prone head castings. This is especially critical with the exhaust ports where operating temps are rather extreme compared to elsewhere. A compression test will not show this as the failure generally occurs to the manifold side of the valve.

You need to skip the screw around motions and pull the heads, coolant inside the engine is a bad omen. It doesn’t matter if it’s a casting crack or a gasket it has to come apart.

Bogie
"Chvy’s already crack prone head castings" - does that also pertain to their Performance aluminum heads? Yeah, I'm a little worried about the thin cylinder wall - no sonic testing - one of the last overbore jobs the old shop did before closing .... If after pulling the head, and it appears that the head gasket is not breached, how would I go about having the cylinder wall tested? I'll also look very closely at the manifold gasket and see if there's an indication it failed on the intake side. Thanks*
 

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Discussion Starter · #9 · (Edited)
Awful ugly, what do you use for coolant?

Bogie
Water - sat in that engine for years. Could use a good flushing.
I'm not sure where to go next with this ~ pull the other head, engine out of car and full flushout, then rebuild? Pick up a comparable head gasket, put it all back together now and pray? lol
I really don't want to pull the rotating assembly if the block is good ~ I don't know that my bellhousing would fit a new short block if I bought one .......
 
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