Compression test and leak down

[jmfoust]

Sorry for the cross post if you're on the vanagon list.

’83.5 1.9L westy.


ompression check reads 120 lbs. on all cylinders. I tried to do a leak down test, but I’m not sure I was doing it correctly. I ended up pulling the rocker assembly and the intake manifold off of #1 & #2 cylinders. Filled with 100 lbs. of air, but had a constant leak from both cylinders. I placed my fingers inside of the intake ports touching the back side of the intake valves, but was unable to feel any air. I’m guessing for some reason my exhaust valves aren’t closed, or I have a cracked head. Is there a better way to do a leak down test? Every time I filled the cylinder with air, it forced the piston to bdc. Am I supposed to test at tdc or bdc?



I also made a pressure cap to test my coolant system. It seems to have a slow leak, but I was unable to locate a visible source. I made the cap by drilling a hole in the center of the cap and removing the guts. I pulled a standard wheel rim rubber fill valve through the hole, and filled the overflow port with a screw and jb weld. Worked great.



Thanks.



jamie

[Cat and Walter]

i have always used a leak down checker. TDC and having the engine roll over can be trying but doable.

[jmfoust]

[r39o]

There is a test gizmo. Some where on the internet, I am sure you can find how to make one and how it works. Most of us buy it. It measures leatkage in terms of percentage. More that 10 percent is not too good, I think. I forget, though.

Put the cylinder on TDC, screw the device pressure probe into the cylinder via the spark plug hole, apply air, calibrate and read.

You can keep a wrench on to help keep it from moving, too. Sometmes they flip, but the wrench helps. Or find some other way to keep things from moving.
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[jmfoust]

I've got the tool. I just didn't know if it had to be tdc or not. I'll try it again tonight at tdc w/ the motor locked.

jamie

[tencentlife]

If you have the rocker gear off it doesn't matter where the piston is. Both valves are closed and the rings should seal well thru the whole stroke range.

3 or 4% leakdown with a calibrated tester is an excellent engine. If it's over 10%, as Walt said, it's pretty bad. If you ascertain that most of the leakage is at the valves, then a valve job is in order. If it's mostly rings (lots of air escaping the crankcase breather, little at the valves), then you may be looking at a teardown. The ring sealing on these engines is usually good for high miles, so if they're bad it indicates a high level of wear overall. Sure, it could just be rings/cylinders, but unless you know of something wrong with that interface (i.e. poor quality replacement parts; incorrect installation), do you want to take a chance?

[Captain Pike]

Try to find a used engine__rebuild it_plug it in__keep yours for peace of mind.
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[jmfoust]

I ran the leak down test last night. #3 cylinder has a blown head gasket. Coolant came puking out in a hurry. Since all cylinders checked out w/ good compression, I'm going to yank the motor and do both heads and a clean up. I'll inspect the pistons, heads, and cylinders, maybe do a re-ring and hone, but I'm happy with the compression results, maybe I should leave them alone. Heads are both AMC, so I'm guessing they have been replaced - oem should have been VW. Both drain plugs in the heads were clean and came out easily, so it doesn't seem that the heads have seen a lot of time on the road.

jamie