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Old 10-13-2004, 11:44 AM
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Unhappy Compression Test Results....Rings or Valves ?

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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Old 10-13-2004, 12:14 PM
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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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Old 10-13-2004, 01:13 PM
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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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Old 10-13-2004, 01:28 PM
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Still a fairly new motor then with only 500miles or so on it. Was it rebuilt with Chrome moly rings?
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Old 10-13-2004, 01:37 PM
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I agree with brainsboy, drive it a little more then do a leak down test next.
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Old 10-13-2004, 02:27 PM
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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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Old 10-13-2004, 03:57 PM
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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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Old 10-13-2004, 03:57 PM
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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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Old 10-14-2004, 12:50 AM
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Did you ever run any block sealer or radiator sealant after the rebuild like your supposed too?
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Old 10-14-2004, 07:39 AM
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?????
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Old 10-14-2004, 07:58 AM
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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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Old 07-03-2014, 09:19 AM
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What is meant by a leakdown test.
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Old 07-03-2014, 09:30 AM
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You picked a 10 year old thread to ask?? LOL
It checks for cylinder and or valve leakage.
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Old 07-03-2014, 09:39 AM
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Cmon cut me some slack. I'm working on my first real hotrod and I'm trying to learn as much as possible.
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Old 07-03-2014, 11:38 AM
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Quote:
Originally Posted by lilikeaguirre View Post
What is meant by a leakdown test.
It's a way of putting a number on the condition of the motor. It can tell you if your motor is 95% or 90% or 85% or 80% or whatever.
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