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Discussion Starter #1
Hello,

Well my motor was rebuilt 2 summers ago and I have probably put 500-1000 miles on the engine but because of a possible blown head gasket (engine is pressurizing the cooling system) I did a compression test and now I am wondering about the results.

Basically most of the cylinders were 145-155 on a dry test and one was 135 except for the cylinder that I think the coolant is leaking into. That one is 175, bang, right on the first dry test. So, that's why I suspect that cylinder has coolant sitting in it.

My main problem is that when I squirted oil in the rest of the cylinders, only the one beside the 175 shot up to 170-175. The reast seemed to max out at 155.

So why are only 2 of my cylinder up to 175 on a wet test? Is this telling me that my rings still haven't set yet or are the valves leaking 20% of my engine compression?

Are the rings still seating?

Just looking for your thoughts....thanks, Greg.:(
 

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Sounds like you squirted a bit too much oil in the one cyl. the second time around, raising the compression, you only need enough to seal the rings. A 10% difference is acceptable across the board, although I would look into the 135 and 175 cyl's, the spark plug should be clean from the wet cyl., likely the 175.
 

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I agree with Wrencher. What do the plugs look like? Has this been a problem from the start or did it just start ? A blown head gasket at a water passage usualy results in that cylinder burning water. A heat crack in a cylinder head (one that opens up as the engine warms up) usualy pressureizes the cooling system.
 

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The Smell of Nitro in the morn
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I agree with brainsboy, drive it a little more then do a leak down test next.
 

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Discussion Starter #6
I don't know what kind of rings were used. A couple observations I do have are

1) the spark plugs have a wet black look on the outer ring
2) After any high RPM my oil dipstick is pushed up a bit.

I assume that this means that oil is still getting by the rings and splashing on the spark plugs a bit and pressurizing the crankcase?

I guess I am currious if the rings will seat better and tighten up the combustion chamber. I find it hard to believe that they all didn't set properly.

Greg.
 

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The Smell of Nitro in the morn
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The dip stick pushed up is excessive crank case pressure.
The black is a rich carb.
A leakdown is always good to do. It will tell what valves are bad, intake or exhaust or ring blowby.
A leakdown is the very first thing we do after a race to check the valves before pulling the heads, and tell how bad the rings are.
I would suggest a good tune-up and a long drive and then start to check over the motor again, adjust the valves to be safe after the ride.
 

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Race it, Don't rice it!
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Could there be water sitting ontop the piston and reducing the chamber size? It would only take 8cc or less to make 50 pound difference on a small chambered head.
 

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Discussion Starter #11
ok...I agree. Because of the rebuild it is a little early to tell. So, I will lean the engine out a bit and put some good easy miles on it and then do a new compression test with the engine "warm". (This compression test was on a cold engine, but I wanted to find the cylinder with the coolant in it, which I think I did, I didn't want it to burn off)

Also, I don't know of anyone that does a leakdown test. I'll have to call around but that sounds like a good next step. I want it to be anything but the rings!!!

Thanks, Greg.
 

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Hello,

Well my motor was rebuilt 2 summers ago and I have probably put 500-1000 miles on the engine but because of a possible blown head gasket (engine is pressurizing the cooling system) I did a compression test and now I am wondering about the results.

Basically most of the cylinders were 145-155 on a dry test and one was 135 except for the cylinder that I think the coolant is leaking into. That one is 175, bang, right on the first dry test. So, that's why I suspect that cylinder has coolant sitting in it.

My main problem is that when I squirted oil in the rest of the cylinders, only the one beside the 175 shot up to 170-175. The reast seemed to max out at 155.

So why are only 2 of my cylinder up to 175 on a wet test? Is this telling me that my rings still haven't set yet or are the valves leaking 20% of my engine compression?

Are the rings still seating?

Just looking for your thoughts....thanks, Greg.:(
Greg if that thing is pressurizing the coolant forget about finding which cylinder it is by test, just get the heads off and fix it. The thing you should worry about is coolant in the oil, it is very distructive to the bottom end components.

At this point compression testing is not important, the longer you mess with this the worse the damage.

Bogie
 

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In the future instead of resurrecting old posts, create a new thread in the hotrodding basics forum for questions like this.

The engine forum is for actual engine building questions.;)
 
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