Low compression on 2 cylinders but good cylinder leak down test

[Lake]

I recently aquired a 92 Legacy with a 2.2 engine (130k miles). The
compression on the 2 & 4 cylinders is 155, while 1 & 3 come in at 75
each. The engine passed a cylinder leak down test* administered by the
Subaru shop after they installed a new timing belt. The old one was
off by one notch. The owner pulled out at $400, figuring that they
were never able to get the car running smoothly again at a reasonable
cost. She had it towed away for donation. The removed parts were
placed in the trunk.

I bought the car for a song. It has a cherry body and interior , and
it was advertised as having a possible "bent valve". I have owned a 91
Legacy for 16 years, and I know this is a "non interference" engine.
That is, a slipped timing belt will not bend a valve. At worst, I
could put the engine from my 91 into this car. I reinstalled the
parts, and I have been driving it, albeit with a rough idle and lousy
gas mileage (75 miles on a half tank).

I would really like to see if I can solve this mystery.

The car was towed into Subaru after a failed start on a -10 degree
night. The owner "heard a clunk", and that was that. Before this
episode, the car reportedly ran well and seemed to be well maintained.
I interviewed the mechanic, and found that there were two siezed valve
lifters on the 1 & 3 side. I replaced these.

So far, I have replaced the fuel, changed the oil and added one quart
of Rizlone oil detergent. I've also changed the plugs. The 1 and 3
were carbon fouled, probably due to low compression.

My reasoning tells me that there could be a fracture between the 1 and
3 cylinders. This would have to be low enough to allow at least a 50%
buildup in compression and still pass the leakdown test. I could
probably test for this by removing the rocker train (to close all the
valves), moving the piston to the bottom-dead-center position and
applying air. I don't know what this crack could look like because the
block casting is probably sleeved. Then, the question: what to do
about it, short of ditching the engine.

Here are my questions to the group: has anyone out there overhauled a
2.2 in the 90-94 series? What is between the adjoining cylinders?
Coolant passage? Has anyone tried a product like thermagasket? (This
is a $100 treatment via the water system to cure head gasket problems
and block cracks).

It helps to write this stuff down. As I think about this, I am not
convinced that the "klunk" was the timing belt slipping. I've had
timing belts that were off by a notch, and the car was still
driveable. I would be interested in any other opinions. Thanks.



*Cylinder leak down is measured by pressurizing each cylinder in turn
with its piston in tdc position. This tests leakage thru valves,
gaskets, and rings.

 

[bgd]

If leakdown passed, cylinders are tight. Cracks to lose compression would
be very very obvious at runtime.
If valvetrain parts failed already, target the cams and timing. I have found
a Subaru with it wrong from day one at the cam (just one).
Fire out too soon would seize the valve train parts. ... and give some
compression on tight cylinders, but delayed intake to reduce it giving the
numbers you have. Theres my guess. 1 tooth off is indeed dramatic for a long
run.
-Barry

 

[Lake]

Subaru put in a new timing belt, and I checked the timing for each cam
shaft to make sure they got each side correct. I'm suspicious of the
leakdown test because it apparently is done with each piston at tdc.
How can this test reveal what happens when the piston is at the bottom
of it's stroke?

 

[Porgy Tirebiter]

Pull the heads and Magnaflux them..you will find the crack.....