924Board.org

[Smoothie]

I'm actually checking out a salvage yard bought 4 cyl 2.5L Jeep engine, but the same would apply to a 924 engine, so it's not completely off topic. I'm wondering what other testing can be done and how nuts is the testing I've already done - or are some of these things more-or-less common practice...

I have the engine mounted to an engine stand. First day it got a cleaning and a quick check by turning the engine - I could feel compression at every 180 degrees, so that's normal and good.

Today I got the compression, leakdown, and oil pressure testers out.. Removed the spark plugs and the distributor. Oh yeh, first drained the oil to have a look at it. Looked ok, dark, but free of coolant and any visible metal particles. Put most of it back into the engine along with a quart of Gunk motor flush. Attached the oil pressure tester in place of the oil pressure sender (whoops this is one thing you can't do with the 924 motor) - I used a flat blade screwdriver with its' handle in a socket and that chucked to a drill, went in through the distributor opening and spun the oil pump via drill power. Good reading - it climbed gradually to almost 90 psi, then popped down to a steady 75-80 as the pressure relief opened. Very boring - ok next tried a dry compression test - got very low readings, but my technique wasn't developed yet, so I'll disregard those results and try the dry again tomorrow.
For the wet test, before testing each cyl, I squirted 10cc of oil into the cyl and gave the engine a few spins with a reasonably powerful 1/2" drill and socket on the crank pulley bolt, then did the wet compression test turning by hand with a wrench. (The drill isn't strong enough to turn the engine with the comp tester attached.) I got #1-131, #2-132, #3-127, #4-105 psi. (The lower reading on 4 makes sense because during leakdown testing later, I could hear air escaping through the exhaust while testing #4, so the exhaust valve on #4 isn't sealing well..) Of course those numbers would be higher if it could have been tested via a starter motor, but I was suprised to get the numbers I did while turning it by hand.

Subsequent leakdown testing gave dismal results, but it's actually supposed to be done on a recently run, warm engine, which isn't possible during "bench" testing - this is my main reason for posting this - I'm wondering if a leakdown test on a cold engine is of any use and if so, by how much should you adjust the numbers? The dry leakdown test averaged about 30% on all cylinders and the wet leakdown test improved to an average of 22.5%.

So, is bench compression and leakdown testing just nuts? Or is it of any diagnostic use? -And if applicable and if anyone happens to know...how much should you adjust the numbers by?
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Paul]

Yes it is of value.

I would return the motor, sounds as if it has a burnt exhaust valve.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[endwrench]

Can't say I have ever heard of cranking an engine by hand for a compression test! I would have not thought of even trying it. I'm impressed with the numbers you got with this method. If #4 were better I would call it good. You need to plan a teardown or return the engine.

Todd
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'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Smoothie]

Well I'm most concerned with the bottom end because that's what's unsalvageably messed-up on the engine that's in the vehicle now. Piston #1 had shattered on that one and left some deep gouges in the cylinder wall. (I had gapless piston rings in that engine by the way. How much they had to do with the piston coming apart, I don't know, but I'll be using normal rings in the future.)

If this new-used engine is good on the bottom as it seems to be, I'll keep it. I have no problems with having the head reworked. So far, compression looks very good, while the leakdown shows a need for new rings. I re-did the compression test by hand today without adding any oil to the cyls - just ran the oil pump for a while, then spun the engine with the drill a while, then ran the oil pump again while at the same time turning the engine by wrench to get the innerds well lubricated - then re-did the hand-operated comp test...
Today I got -
1- 135
2- 140
3- 137
4- 135
So #4 improved - presumably due to the exercise that the engine got over the last 2 days. -But it's still not 100% and still looks like the head will need reworking - I still hear some hissing through the exhaust while leakdown testing #4, though much less than yesterday.
On the dry leakdown test yesterday, #4 was lowest. Those first readings were -
1- 51
2- 56
3- 52
4- 48
(this is with the compressor supplying 90psi, and the left leakdown gauge set at and reading 75psi - the numbers above are from the right side gauge)
Then after adding 10cc of motor oil to each cyl for the wet test yesterday, I got -
1- 61
2- 62
3- 45
4- 61
So #4 with its' leaky exhaust valve was actually not the odd one out during the wet leakdown test yesterday.
Todays' leakdown test (without adding more oil to the cylinders) went like this -
1- 54
2- 56
3- 43
4- 61
So still, #3's the odd one out, but more oddly #4 looks best while still hissing some through the exhaust. Apparently #4 has the best-sealing rings and so much better than the others that it beats them even while leaking some past the exhaust valve.

Anyway, I'll most likely replace the rings in addition to having the head reworked - it's just too fun and easy with the engine out and mounted on a stand.

To try and answer my own question from yesterday, today I did leakdown and compression tests on the 931 while cold and again after it was warmed-up. I found that while the compression numbers improve by 15-20 psi on each cyl with the warm-up, it had no effect on the leakdown test. -So if I were able to start and warm-up this new-used Jeep engine, I might be getting compression test numbers in the 150-160psi range + whatever running it with the starter motor would add.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[endwrench]

Interesting info.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[PORSCHEV]

It's common for junkyard engines to have sticky valves...even when you first start them. I have seen engines that have sat for 3-4 years installed that smoke and skip, misfire. Add a little auto transmission fluid to the fuel and it lubricates the valves. I know it sounds strange....but it does work. It make engines that sounded terrible come right around.
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1976 924
5 lug conversion, 17'C2 wheels,custom body work,327 vette engine.

1978-#53 "D" track racer.