Odd Compression Test Results

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Feb 20, 2019 | 04:35 AM

#21

treimche

Thread Starter

Joined: Apr 2006

Posts: 566

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From: Fort Myers, FL

Quote:

Originally Posted by Billman250

The classic #4 cylinder liner failure will result in high compression in number 4.

Check the cylinder with a scope, with piston at BDC. Liner failure will look like a wide black stripe.

Do not pull the full pump fuse for a compression test. Fuel will still spray into the cylinders and skew the readings. It is also unhealthy for the engine.

Disconnect the injectors instead.

I will do a little searching, but do you have more info on this cylinder 4 liner failing?

Feb 20, 2019 | 05:03 AM

#22

Billman250

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From: Long Island, New York

Just bore scope it, it is easy to spot.

Feb 20, 2019 | 05:06 AM

#23

Billman250

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From: Long Island, New York

Quote:

Originally Posted by fatjoe10

What's the mechanical/scientific reason behind having high compression with damage to the liner? interesting.

Liner damage allows excess oil to flood the compression rings, raising the compression.

Feb 20, 2019 | 05:54 AM

#24

flanders

Joined: Aug 2013

Posts: 4,151

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From: Sweden

Quote:

Originally Posted by treimche

Let me explain a little better. With the leak down tester in cylinder 1, I can hear air escaping through cylinder 2 and 3 spark plug holes. It wasn't leaking through the spark plug hole where the tester was.

Thanks that makes perfect sense.

Feb 20, 2019 | 06:18 AM

#25

treimche

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Joined: Apr 2006

Posts: 566

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From: Fort Myers, FL

Quote:

Originally Posted by Billman250

Liner damage allows excess oil to flood the compression rings, raising the compression.

That makes sense. Any idea what causes this to happen? Something ring related that scores the cylinder liner?

Feb 20, 2019 | 07:48 AM

#26

Deckoz

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Joined: Jun 2018

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40% leakdown? what the **** lol. my 220k motor has 6-8% across all 4 and all read 210psi with 5 cranks.

Something sounds wrong lol.

Feb 20, 2019 | 08:42 AM

#27

treimche

Thread Starter

Joined: Apr 2006

Posts: 566

Likes: 29

From: Fort Myers, FL

Quote:

Originally Posted by Deckoz

40% leakdown? what the **** lol. my 220k motor has 6-8% across all 4 and all read 210psi with 5 cranks.

Something sounds wrong lol.

Yeah tell me about it. This really sucks. This is the pic I took of the gauges when checking cylinder #2. Maybe I did the math wrong.

Feb 20, 2019 | 12:07 PM

#28

rpg51

Joined: Jun 2016

Posts: 3,296

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From: Vermont

Do I understand correctly that the engine runs fine?

Feb 20, 2019 | 12:44 PM

#29

BrewDay09

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Joined: Feb 2019

Posts: 141

Likes: 35

Your results seem pretty high for an engine that actually runs. I notice you didn't have the cylinder head cover off during the leakdown test. How did you confirm each cylinder was at TDC during the test? Perhaps you had some valves that were not completely closed?