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Help deciphering compression results


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18 replies to this topic

#1 simbey1982

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Posted 23 September 2006 - 06:32 PM

Hey all,

I just ran a compression test on a 2.5l SOHC Phase II engine. Engine was cold. I tested each cylinder cranking 10 seconds on each (engine doesnt start).

Here are my results

Cyl 1 100psi
Cyl 2 80psi
Cyl 3 70psi
Cyl 4 70psi

Tested in order of 2,4,1,3

Im not sure what these results are telling me about my valves, can anyone help?

Thanks

Cory

#2 porcupine73

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Posted 23 September 2006 - 06:39 PM

Hm..those seem pretty low I think, never done the test but I think you should be getting like 175 psi peaks. Let me check the book... the procedure is engine warm, battery fully charged, all spark plugs removed, throttle fully open. Then you should see 176psi peaks, or at least 137psi, and no more than 7psi difference between cylinders.

I'd say either the test wasn't done correctly, the gauge is inaccurate, the timing is off by a few teeth, or maybe you have bent valves as you say, which you might be able to tell with a cylinder leakdown test.

#3 simbey1982

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Posted 23 September 2006 - 06:43 PM

Yeah my options are limited because i cant start the engine, so throttle wide open and warm engine are not possible....leak down test?? how would i do this?

#4 porcupine73

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Posted 23 September 2006 - 06:51 PM

Ah ok, well I would at least hold the throttle fully open while doing the compression test. I usually do this by pulling the throttle wide open in the engine compartment and loosely clamping small vise grips onto the area near where the throttle cable attaches to the throttle body there. If you didn't have the throttle wide open I'd say that could cause your readings to be low. That'd be the first thing I'd try would be do it at WOT after charging the battery for a while if it's low at all; supposed to be turning 350 rpm per the procedure.

If you're getting any readings at all then I guess your timing belt can't be busted. Did you replace it recently or anything? When did this thing start not starting?

Cylinder leakdown test is a pressure gauge with a port or connector to inject compressed air, then you get the cylinder under test to a position where both the intake and exhaust valves are closed and inject like 80psi or whatever and then see how fast it leaks out.

#5 gbrand

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Posted 24 September 2006 - 11:58 AM

make sure throttle is blocked open, and retest. I ould crank about 20 secoonds or so and let guagfe climb unitil it dooesnt get any higer. would make sure battery has full charge.

If readings are really that low then shoot a little (10-20cc) oil in each cylinder and retest-if compression comes up then rings are shot. If not then HG or valves, or is there any possiblity timng belt is jumped?

You say engive wont start-was it running and quit, or is there any more history?

let us know

#6 simbey1982

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Posted 24 September 2006 - 03:16 PM

Ok i will retest under those circumstances.

As for timing belt, i replaced it a month ago (this is an ongoing project) as i thought the timing was off. Timing belt was correctly reinstalled and ready to go. It MUST have been off before because when i replaced it the cranking sounded way diffrent and the car stopped "Coughing" when cranking. So i wanted to check and see if valves might have been bent.

The reason it wont start is a secondary electrical issue that is making half the ignition coil not spark and the other half spark weakly.

Cory

#7 OB99W

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Posted 24 September 2006 - 03:48 PM

It's likely that the problems are related, and that you have not correctly installed the timing belt. See:
http://www.ultimates...ead.php?t=64923

#8 grossgary

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Posted 24 September 2006 - 05:25 PM

more details on why the belts were replaced and what was wrong with it when you got it would help. i'd guess the timing belt has issues. either the cams or crank aren't lined correctly or the tensioner in the timing belt is bad, making the belt artificially off all the time or under load.

on the older subaru motors you can look down the spark plug holes and see some of the valves and the piston head. might have a flashlight handy and take a peak down the holes. maybe you can tell if the valves are bent, pistons have marks in the heads or any coolant in the combustion chamber (head gasket leak).

#9 simbey1982

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Posted 25 September 2006 - 05:42 PM

This is a motor i picked up for a transplant into my impreza after my 2.2 died. (along with wiring, and ecu) It was taken off of a 1999 forester, It came with a timing belt that i didnt make sure was lined up.

When i would try to start it with the old timing belt...it would crank funny and "COUGH" every 4 or 5 cranks.

Decided that timing belt could be an issue so i replaced it and installed CORRECTLY

When i try to start with the new timing belt...the crank sounds more normal and the "COUGH" has dissapearred. (which prompted me to look for valve damage)

My only measurable symptom at this time is that i have no spark on half of the coil and weak spark on the other half (I have tested the coil and even tested it with a new coil, also i have tested new Crank Angle, and Cam position sensors.

So i guess my question is could it have jumped teeth? the tensioner looked to be working fine when i took it out..?? how would i tell without just taking the whole thing off again?

Thanks for the help

#10 OB99W

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Posted 25 September 2006 - 07:03 PM

[...]Decided that timing belt could be an issue so i replaced it and installed CORRECTLY

I apologize for suggesting that you may not have installed the t-belt correctly. However, the symptoms you described do fit those of an incorrectly timed engine.


When i try to start with the new timing belt...the crank sounds more normal and the "COUGH" has dissapearred. (which prompted me to look for valve damage)

Perhaps I'm alone in this, but "cough" implies to me that there is ignition of the mixture at least sometimes. A no-start condition and not even a "cough" suggests no ignition of mixture at all. That can be due to lack of spark, lack of air/fuel, lack of compression, or things not properly coinciding in time and space (otherwise known as engine timing problems).



My only measurable symptom at this time is that i have no spark on half of the coil and weak spark on the other half (I have tested the coil and even tested it with a new coil, also i have tested new Crank Angle, and Cam position sensors.[...]

If this is not due to incorrect timing, then that could leave things like a bad ECU or wiring problems, damaged reluctor(s), etc.

#11 porcupine73

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Posted 25 September 2006 - 07:18 PM

Sorry if I missed it but did you put in the ECU that came with the engine you're swapping in? Seems like I read something like this in another thread with a weird no spark/weak spark thing on an engine swap and it went away when the engine's actual ECU was installed.

#12 keltik

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Posted 25 September 2006 - 08:34 PM

Was this *COUGH* one of the cylinders actually firing? When i snapped the timing belt on my old prelude it made a nice cough knock kind of noise every 2 revolutions, which of course was the piston smacking into some valves. If you had serious valve damage i would expect one or two cylinders to be drastically lower than the others.

#13 ShawnW

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Posted 25 September 2006 - 09:40 PM

Bent valves would register ZERO compression.

Timing is definately off if its coughing.

You said you put a 2.5 in place of the 2.2. The easiest way to do this is to install the 2.2 intake manifold and all its sensors, gears, and wiring onto the 2.5L motor. Thats assuming your 2.2 has the cyl heads and front timing belt plastic that is identical in appearance to your 2.5.

You must put the same configuration of cam and crank angle gears on your 2.5 as was on the 2.2. The crank gear will have 42 teeth or so instead of 6 like the older engines have...and the cam gear on the drivers side of the engine will have 6 teeth pointers on the back that talk to the cam angle sensor instead of 2.

You need to keep virtually everything from your original engine and transfer it to the longblock 2.5 to even have a chance of it running.

Also:
Its going to be a lot easier to compare all the parts and swap stuff over with the engine out so pull the 2.5 back out of the car and while you have it out adjust the valve clearances. .008 and .010 are intake and exhaust for this engine give or take a little bit...like .002 at the most. You want this thing to run good so this will help insure that it will and if you need to do a compression test on the engine you need to know that the valves are opening all the way and closing all the way.

These numbers could even be that low from a weak battery. Make sure its real well charged before doing any compression tests.

#14 nipper

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Posted 26 September 2006 - 12:03 AM

Numbers to be that low, the iming is off. People have come in here to say the timing is perfect, but when double or triple checking they have found out its off. Timing being off is the only thing that can give you number across the board that low. The number should be 150psi or higher. If you still insist the timing is ok, then you have a very tired engine.
You need to do a wet test, as a dry test doesnt really tell us anything except you have low numbers. If the numbers dont come up on a dry test, then its a valve train issue, meaning timing. Bent valves would give you zeros. Burned valves zero. Go back and check the timing belt again

nipper

#15 simbey1982

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Posted 26 September 2006 - 06:40 PM

Hey guys, didnt mean to sound like i dont think it is the timing. Cuz its the only thing i can wrap my brain around that makes sense. And just because i think i installed it correctly, doesnt mean i did =0)

To answer some questions.

Originally i had the wrong ECU but purchased the correct one later.

As for the swap, it is a COMPLETE swap. I have an ECU, Wiring and a complete motor that i have spliced in.

I too thought it was a wiring issue or other, but i have verified that the injectors are pulsing, and that the correct signal is getting to the coil. Then only thing i can possibly think of is that the timing is off...but when i redid the timing and it still didnt work, i was going nuts!

The cough did not sound like a fire at all...it sounded just like a cough like it was aspirating

If the consensus is timing i am all for looking at it again. I do have a question though, whats the best way to check it, short of taking the belt off and re installing it?

Thanks again for all of your help

#16 grossgary

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Posted 27 September 2006 - 08:48 AM

if you pull the covers off you can verify the timing belt alignment without actually reinstalling it. just verify all your marks are dead on.

there's no chance of the wrong pulley, sprocket or tensioner being on this engine is it...thereby artificially throwing the timing off?

#17 simbey1982

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Posted 27 September 2006 - 04:57 PM

i would say no, but i guess anything is possible at this point, any way to verify those?

Also, arent the marks on the belt off unless it goes around x number of revolutions? or should the belt marks line up every time the sprocket and Camshaft gears are strait up? or should i just verify that all the sprocket gears are strait up?? I need some specifics on this

Thanks a million to everyone

#18 porcupine73

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Posted 27 September 2006 - 05:15 PM

You need to make sure all the marks line up. It should still start if you're only one or maybe even two teeth off but more than that who knows. You need to verify what marks you're looking at, i.e. _not_ the arrows on the cam sprockets but rather the hash marks, etc. The marks on the belt will not line up on every revolution.

#19 Wayne Boncyk

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Posted 27 September 2006 - 05:51 PM

i would say no, but i guess anything is possible at this point, any way to verify those?

Also, arent the marks on the belt off unless it goes around x number of revolutions? or should the belt marks line up every time the sprocket and Camshaft gears are strait up? or should i just verify that all the sprocket gears are strait up?? I need some specifics on this

Thanks a million to everyone


Make sure that every mark on cams, crank, etc. are lined up with their references, and then you can install the belt using only the guide marks. Still better to double check by counting belt teeth. The cams, et al, do NOT line up in exactly the same places with each revolution; the marks will definitley be off after just a single rev of the crank.




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