Tips needed for Comp Check and leak down
Tips needed for Comp Check and leak down Before I make any major repairs to my motor I want to make sure the bottom end is in good shape. What are the proper procedures to perform these tests?
Should the Car be warm? Which should I do first? If I have good compression do I have to do the Leak down.
Should the Car be warm? Which should I do first? If I have good compression do I have to do the Leak down.
TECH Resident
Joined: Apr 2003
Posts: 791
Likes: 0
From: Tulsa, Ok
i would just do the leakdown. it will tell you a lot more.
to do the leakdown test:
1.warm up car
2.pull all spark plugs
3.loosen the rockers (gotta have the valves shut)
4.hook up leakdown guage to air compressor
5.screw air hose into a cylinder
6.connect guage to air hose in motor (make sure you have the motor locked up and the e-brake on)
7.check PSI on both guages and find the percentage leakage
8.move on to the next cylinder
if one of the cylinders is losing a lot of pressure, you'll be able to hear where it is escaping. into the intake is a bad seal with the intake valve (maybe bent), into the exhaust is a bad exhaust valve seal (maybe bent), or into the crankcase is a bad ring or piston.
good luck to you
to do the leakdown test:
1.warm up car
2.pull all spark plugs
3.loosen the rockers (gotta have the valves shut)
4.hook up leakdown guage to air compressor
5.screw air hose into a cylinder
6.connect guage to air hose in motor (make sure you have the motor locked up and the e-brake on)
7.check PSI on both guages and find the percentage leakage
8.move on to the next cylinder
if one of the cylinders is losing a lot of pressure, you'll be able to hear where it is escaping. into the intake is a bad seal with the intake valve (maybe bent), into the exhaust is a bad exhaust valve seal (maybe bent), or into the crankcase is a bad ring or piston.
good luck to you
this might be a stupid question but how do you work on a hot car? Won't you get different readings as the car cools. It is going to take a while to get the car up in the air, remove valve cover, Ign, starter, and plugs. How will my motor hold the heat that long?
TECH Resident
Joined: Apr 2003
Posts: 791
Likes: 0
From: Tulsa, Ok
it won't be "hot" but it will still be warm. i just did a leakdown on my motor this past weekend and it took about 2 hours. the motor was still warm when i finished and the readings i got were the the same from the time i started to the time i finished (i redid the first cylinder just for that reason, i wanted to see if it showed anything different after the 2 hours of cooling). i think the main idea is to not be working on a cold engine.
TECH Fanatic
Joined: Nov 2001
Posts: 1,248
Likes: 0
From: Kansas City, MO
I did a leakdown on a 427 this weekend that ended up with an 18% leak on a warm motor. We checked 3 cylinders and then said the hell with it, the engine is junk. No use putting more effort into it.
8 out of 8 plugs had a dark band on the ceramic, 6 out of 8 had burnt through the ceramic in the same band. Nothing like an engine that burns 3 quarts of oil/1000 miles.
8 out of 8 plugs had a dark band on the ceramic, 6 out of 8 had burnt through the ceramic in the same band. Nothing like an engine that burns 3 quarts of oil/1000 miles.
thanks for the replys what's the maxium % leak down? my motor has about 72,000 miles on it. My heads are fairly new but who knows what shape their in I got them from JPR. So I might have any number of problems.
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