#7 Cylinder looks... strange... Please take a look.

[oz]

Greetings,
Long story short, blown head gasket on my '91 GT (on RH side), replacing both... Took LH head off and found some strange marks in cylinder #7. See attached...

Scuffs with small gouges in the scuffs.

What could cause this?

(stock short block, go fast parts, blower... making over 475 hp w/ conservative tune. After tune I lowered rev limit to keep engine intact - 50k original miles on engine, less than 1k since boosted)

THANKS!!!
oz

 

[KZGUNS]

was this engine sitting for a while? kinda look like it was sitting and rusted where the piston was parked. Can you catch the scratches with your finger nail?

 

[oz]

was this engine sitting for a while? kinda look like it was sitting and rusted where the piston was parked. Can you catch the scratches with your finger nail?

Well, yes, I only drove the car a couple times last summer and the one time it overheated (and then I found the coolant was low). That's surely when the head gasket failed and started sucking in coolant... I didn't make the connection then so it sat all winter and spring - so yea, it sat 7-8 months.
Figuring out that it had a blown head gasket this summer, I used a borescope to check to see which cylinder had water getting in and #2 had a small puddle. I did not see any water in any of the other cylinders. #2 has no marks at all (it was only a couple weeks between the time it last ran and when I scoped it. I had also drained the coolant shortly after I last ran it... so not much time for water to pool.)
The spot in #7 does look like it could have been a little rust... My nail does just 'catch' a little when I run it over this area - and it's contained to the spot where a ring would have contacted the cylinder where water might have pooled...
So.... I'm thinking maybe the borescope didn't tell the full story and #7 had water in it over the winter.
I know there was water in at least one cylinder because when I started it the first time this spring it turned over strangely... started to turn then kind of paused and turned slowly then fired... I think it was purging water out of one of the cylinders. When running, the majority of the steam was out of the right side - so I was not surprised to see water in #2. #7 is more of a mystery...
THANKS!

 

[KZGUNS]

Its possible this happened long before you did any work, like before you owned it. If it was me and i wasn't ready to rebuild I'd probably just run it. Once together maybe do a compression and leak down test.

 

[oz]

Its possible this happened long before you did any work, like before you owned it. If it was me and i wasn't ready to rebuild I'd probably just run it. Once together maybe do a compression and leak down test.

I did have the heads off a long time ago and there were no marks in the cylinders. A compression test is a good idea as I do have numbers from before I put the blower on it. Should be a good comparison.
I was thinking of honing it a little... just push the piston all the way down (it's all the way down when #1 is at TDC so easy to do), put a 4" diameter piece of cork gasket material on top of the piston to protect it and just hone enough to remove the ridge that catches my fingernail... I just don't want to do more harm than good.

 

[Noobz347]

Clean it out, oil it up, and run it.


I wouldn't use any more harsh than steel wool. The rings knock off anything in the way within the first couple of revs.

 

[oz]

Clean it out, oil it up, and run it.


I wouldn't use any more harsh than steel wool. The rings knock off anything in the way within the first couple of revs.

Yea, that's my thinking too... My fear was combining this with boost and encountering an explosive event....

 

[Noobz347]

Nah... You'll run a compression and leak-down test before installing boost anyway.

--or if you already have it, run it light then check compression.

 

[oz]

Nah... You'll run a compression and leak-down test before installing boost anyway.

--or if you already have it, run it light then check compression.

Yea, compression and leak down was all good when I added the blower. I'll run it a bit and recheck it.