Compression readings... ?? help with interpretation of results please :)

[Vombil]

Hey Guys n Gals

I did a compression test on one of 308's (HX) by myself the other day. Results were taken after cold engine had been idling for a couple minutes. Late afternoon and about 18 degrees. Open throttle and 7-8 cranks.

I got the following results

150, 130, 135, 142, 135, 128, 132, 132

Ive read that the variance between the figures is important. I just want to know if its close to death or should still have a few good skids left in her

Cheers

[adam perth]

Hey Guys n Gals

I did a compression test on one of 308's (HX) by myself the other day. Results were taken after cold engine had been idling for a couple minutes. Late afternoon and about 18 degrees. Open throttle and 7-8 cranks.

I got the following results

150, 130, 135, 142, 135, 128, 132, 132

Ive read that the variance between the figures is important. I just want to know if its close to death or should still have a few good skids left in her

Cheers

they are supposed to be done @ engine running temp, sounds like you had it warmed up a bit.
-/+ 5% is the rule for a very good motor, +/- 10% for a good motor.

that motor looks fair to good.

also did you use the threaded compression gauge or the push and hold in type (not as good)?

[ozbox]

i would disagree with adams fair to good...i would put that as excellent..
the majority i see are around the 125 to 140 range...if it doesnt make a knocking noise and its not blowing smoke then its a good motor..
cams and lifters are the biggest killer and generally most people rebuild the whole motor when it only needs a cam.:Chin:

[Vombil]

they are supposed to be done @ engine running temp, sounds like you had it warmed up a bit.
-/+ 5% is the rule for a very good motor, +/- 10% for a good motor.

that motor looks fair to good.

also did you use the threaded compression gauge or the push and hold in type (not as good)?

I used a threaded setup. I was bit of a homo when it came to sinching it right up because i couldnt get my fingers around it to undo if it was super tight... mind you if its not tight enough you can hear the air leak out on compression.

motor had idled for about a minute or two

[adam perth]

i would disagree with adams fair to good...i would put that as excellent..
the majority i see are around the 125 to 140 range...if it doesnt make a knocking noise and its not blowing smoke then its a good motor..
cams and lifters are the biggest killer and generally most people rebuild the whole motor when it only needs a cam.:Chin:

fair enough.
i have always used 165 as the standard as thats what a new 308 "crate" motor would get, and anything less than 120 means there is a problem - usually just needs valve relap.
totally agree on the cams, they are only good for 150000 km in my opinion - this goes for the v8 chev stuff too..

[wbute]

Put a squirt of oil down the bores and re-do the compression test, if the compression comes up its worn rings and if it stays the same its valves.

[ozbox]

fair enough.
i have always used 165 as the standard as thats what a new 308 "crate" motor would get, and anything less than 120 means there is a problem - usually just needs valve relap.
totally agree on the cams, they are only good for 150000 km in my opinion - this goes for the v8 chev stuff too..

if its 150 across the board thats a real good motor...even 125 across is still good..
i find with major differences its crap around the valves so i just give them a wrecking yard tune up...hold it at 4k for 5 minutes plus with a few valve bouncing revs in between and if its not blowing smoke by the end of that its a good useable motor...this also usually cleans crap out of the valve seats and will even up the compressions......

[Vombil]

just did comp test on my HX Mandarin

180,180,180,178,180,190,180,180

its done 40,000kms since rebuild according to the previous owner. results like these prove it! STOKED!!!!!

ive got a 253 that is meant to be fresh too... apparently was built with brand spankin new block (wouldnt of thought you could buy a new block) post readings soon

[Kiwivan]

Like ozbox said even if they are all 120's I would be happy,Ours is in the 165-175 range,But that may vary depending on who does it and how,Our Brock is up to 200 and that scares me just a little(all 195 to 198)That motor is just 4000ks old and the van is 2000200ks on her so I recon she is good.And not a tick from the motor.

Cheers Kiwivan

[adam perth]

its all about the variance in numbers, not the number itself.