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Cylinder Head language

MortenBayliner

New member
Hi all engine guys.
I have recently changed my cylinder head on my OMC V8 5L small block 1988
The reason to this change was cylinder 7 who had a low compression (6.5bar)
Cylinder 1-3-5 was (9.5-10 bar)

Now can anyone help me to understand what the removed cylinder head are trying to tell me.
By looking at below picture, I would say cylinder 3 and 5 are looking just perfect,
Cylinder 7 is a little rusty, and I do also suspect the exhaust valve to be the reason for the low compression on this cylinder.
But what about cylinder 1, cylinder 1 had good compression (10bar) but it is very clear on the picture, it is very black and sodded.
Way?, bad mixture? any suggestions??
All the best
Mr Bayliner

IMG_8458 copy.jpg
 
A cylinder leak-down test would have been very helpful, but now that this head has been removed, that opportunity is gone!

Make sure that you replace this with the same casting number cylinder head.


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Ayuh,.... #1 is the coldest end of the block,....

If #7 is rusty, I'd suspect leakin' exhaust,....
 
do you know about how many hours are on the engine?... the photo shows very little, as opposed to what one could see from actually being there.

removing and looking closely at the valves could give a bit more information.....

without knowing how the engine has lived since it was new, its tough to give any advice without actually seeing..... how do the cylinder walls look?.... how much, if any sludge is built up in the valve covers, and valley?..... when was the last time the exhaust manifolds were changed?...

the exhaust manifolds are a big concern, because it doesnt matter if you rebuild that engine, or replace it with a new $5000 drop in motor, if you dont KNOW for sure the manifolds are good on the inside, they can be the express reason the motor is ruined on the next trip out. we care very little how new and shiny they look on the outside, but its the inside that is going to be the determining factor.

with the little bit of rust you mention, this usually indicates a problem somewhere, but sometimes an engine that has been setting for a long time can have slight signs of rust in the cylinder due to the valve in that cylinder being open.....
 
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