Compression test - dead piston or head gasket issue?

[freeloader700]

Just did a compression test on my LB7. It was done cold and all look good besides #7. Think it is head gasket or piston/rings? I was about to get some injectors ordered but now I am not sure what I am going to do. See the mist/smoke while cranking, is that oil fume from crankcase pressure?

Source: https://youtu.be/32x85aVlRYY?feature=shared


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[LBZ]

140 psi. How’s the blowby when it’s running?

 

[freeloader700]

Blow by is very minimal. Upside cap stays on just fine. Upper radiator hose does not stay hard after cool down. Coolant system does not seem to be pressurized. There does not appear to be any water nor fuel in the oil. I think I have checked all my bases. I got this a year ago and finally in a position to work on it. Originally was pretty certain it was injectors, lots of white smoke and decently hard knock from them.

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[jlawles2]

If you did not pull the bail connectors on top of the engine, you could be seeing fuel being ejected from the hole.

Try putting some oil down the glow plug hole and see if that brings the compression back up. If it does, then you may have a weak set of rings.

One other thing to check would be valve lash. If intake lash is way off, the valves are closing too early leading to low compression.

 

[ikeG]

What were the original concerns, the reason you're compression testing?

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[freeloader700]

If you did not pull the bail connectors on top of the engine, you could be seeing fuel being ejected from the hole.

Try putting some oil down the glow plug hole and see if that brings the compression back up. If it does, then you may have a weak set of rings.

One other thing to check would be valve lash. If intake lash is way off, the valves are closing too early leading to low compression.

I did not remove bail connections on the passenger side however I disconnected both large connectors on top of the motor feeding those circuits. Plus I removed fuses #1 EDU & #3 Fuel HT. If it were fuel coming out, wouldn't that effect all of the injectors? This was only happening on #7.

I will try the oil and see if that changes anything.

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[freeloader700]

What were the original concerns, the reason you're compression testing?

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White smoke a injector knock. Low power, all the typical injector symptoms while not having the head gasket symptoms. So for peace of mind I wanted to rule out the gasket before ordering the injectors and here we are now.

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[ikeG]

A leak down test would tell the story.

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[freeloader700]

Put some oil into the glow plug hole and no ZERO compression. Verified that the gauge is still working with another cylinder.

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[Ron Nielson]

Possibly valve stuck open/damaged

 

[ikeG]

Possibly valve stuck open/damaged

This is probably the case, in my experience. A bad piston will pretty much always read zero on the compression test and max out the balance rate(-15.00 mm3). Just had one here that made 150 psi, had all 4 valves bent from a piston chunk breaking off.

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[jlawles2]

The big connectors on top of the engine are the Bail connectors I was referring to.

This eliminates the fog being fuel.

You need to bore scope that cylinder to see what's going on. I agree with others, add oil and it got worse sounds like something other than HG issues.