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Low Compression Before Break-in

Generation III Internal Engine 1997-2006 LS1 | LS6

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Low Compression Before Break-in

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Old

Jan 24, 2015 | 01:04 AM

#1

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Staging Lane

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Low Compression Before Break-in

I have a LQ4, new block, rods, pistons, and rings. I took my time and made sure everything was oriented correctly, while assembling the shortblock. I just got my head gaskets in so I put those on. I then decide to put a spark plug in each cylinder and give it a couple turns. So I turn the crank maybe a 1/4 turn when I started to feel some resistance, and then pssst!!! Air is leaking passed the rings, it scared me at first, but I figured it was because the rings haven't seated. I tried another cylinder same thing happened. I don't have a gauge so I just went by feel. Is this normal?

Last edited by Lethalwx69; Jan 24, 2015 at 02:04 AM.

Old

Jan 24, 2015 | 06:56 AM

#2

Teching In

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The piston rings do not create an airtight seal. At rpm the pressure does not have as much time to leak down. Normal operation

Old

Jan 24, 2015 | 07:31 AM

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If the system is primed up with oil then remove the plugs and install a comp checker. Jump power to the starter and check the comp the correct way. Report back what the readings are.

Old

Jan 24, 2015 | 08:43 AM

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Who knows what pre break in compression should be on his setup?

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Jan 24, 2015 | 02:35 PM

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Any engine will have that psst sound when you turn the motor over by hand with plugs in it.

Old

Jan 24, 2015 | 02:37 PM

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Combustion forces the compression ring out to seal

Old

Jan 24, 2015 | 03:35 PM

#7

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Its normal, all engines leak down about 10%.

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Old

Jan 24, 2015 | 04:22 PM

#8

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Staging Lane

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Thanks for all the info.

Quote:

Originally Posted by JRENIGAR

If the system is primed up with oil then remove the plugs and install a comp checker. Jump power to the starter and check the comp the correct way. Report back what the readings are.

I'll do that for sure when I get the engine back in.

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Old

Jan 24, 2015 | 04:52 PM

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Agreed it sounds normal, my last post was more a challenge for those say to do a test

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