compression test on motor that can't start
Thread Starter
thing knower
Joined: Mar 2017
Posts: 3,404
Likes: 942
From: wpb
compression test on motor that can't start
hey all, I want to do a compression test before I pull my motor, but I got no coolant so I can't warm her up...
squirt some oil in the plug holes and test like that sound good?
I figure I'll follow the same method once overhauled so I can compare against the base test
drew
squirt some oil in the plug holes and test like that sound good?
I figure I'll follow the same method once overhauled so I can compare against the base test
drew
Le Mans Master
Joined: Apr 2013
Posts: 5,376
Likes: 1,118
I think it would be ideal to check at normal operating temps, but you have no way of doing that, correct? I suppose you can then use that as a baseline l to compare to ring seal with the engine cold after the rebuild.
Why are you even bothering to check it if you’re rebuilding it though?
And, obviously, when you rebuild, you’ll want to get the rings broken in and seated properly before you do a leak down test to see if the leakdown rate is acceptable.
Team Owner
Joined: Sep 2014
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Safety Car
Joined: Jun 2017
Posts: 4,786
Likes: 425
From: North Georgia, USA
Sort of.
You'll get a fair indication of relative cylinder wall condition with a "wet test" with a bit of motor oil in every cylinder. Rings don't seal very well cold, so "dry" compression test results will be low. That could be actual ring issues, or it could be just normal cold conditions.
A flush with hot water is a way back to raise temps. Start by hooking the hose to hot water tap. You can boil 3 to 5 gallons of water in a turkey frier and pour that through for even more heat in the block.
It's better to start the engine. If you're going to steam clean or hot tank the block, just run straight water in it. If the radiator isn't available, put a corrugated hose from the upper hose fitting to the lower hose inlet. Just watch the coolant temp,either with a gauge, obd-ii scan tool, or with a point and shoot IR thermometer to watch the temp of the hose at the upper hose outlet.
You'll get a fair indication of relative cylinder wall condition with a "wet test" with a bit of motor oil in every cylinder. Rings don't seal very well cold, so "dry" compression test results will be low. That could be actual ring issues, or it could be just normal cold conditions.
A flush with hot water is a way back to raise temps. Start by hooking the hose to hot water tap. You can boil 3 to 5 gallons of water in a turkey frier and pour that through for even more heat in the block.
It's better to start the engine. If you're going to steam clean or hot tank the block, just run straight water in it. If the radiator isn't available, put a corrugated hose from the upper hose fitting to the lower hose inlet. Just watch the coolant temp,either with a gauge, obd-ii scan tool, or with a point and shoot IR thermometer to watch the temp of the hose at the upper hose outlet.
Thread Starter
thing knower
Joined: Mar 2017
Posts: 3,404
Likes: 942
From: wpb
ahh well the bottom end is going to remain stock, not touching pistons/rings/mains... i just want to know what it is now, and if its close to after new heads/cam/clutch/etc...
looks like i got a cracked end tank on the rad, i suppose i could fill it back up with water, but i'd really rather not run it up to temp without doing a coolant purge/vac...
the motor runs fine, did a strong dyno pull recently.... i'm pretty sure the short block is fine, i just want to make sure i dont run in to any problems with push rods being too long or something that will make the compression numbers wacky....
looks like i got a cracked end tank on the rad, i suppose i could fill it back up with water, but i'd really rather not run it up to temp without doing a coolant purge/vac...
the motor runs fine, did a strong dyno pull recently.... i'm pretty sure the short block is fine, i just want to make sure i dont run in to any problems with push rods being too long or something that will make the compression numbers wacky....
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