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View Full Version : Wet compression test=Sad



T-spoon
06-21-2010, 06:41 PM
Ok well, I thought I had done a wet compression way back when the problem first surfaced on the 7m, but then it sat for a couple years and I couldn't remember. I just went and did one and the results sound bad. #3 is at ~60 dry and 175 wet. The others are 150 dry. Is there really anything else that could be than blown rings on #3, and if no, that pretty much means a whole bottom end rebuild since the cylinder would then need re-honing?

If that's the case, then it sounds like my options are to just retire the 7m and go 2j, or rebuild the 7m (which would still be less reliable at equivalent power levels than the 2j). I am definitely not a 7m hater per se, but maybe enough is enough.

90blacktrac
06-21-2010, 07:13 PM
A compression test on a cold un-primed engine is(edit: could be) inconclussive, my roomate just got a low miles b20 for his civic and when he ran the comp. test cold un-primed and then primed it came up very simalar to your results, and 10k miles later it's still goin strong. Can you get the engine warmed up and try again?

Also no 1j love? They are cheaper and never mentioned in certain movies about stealing dvd players.

T-spoon
06-21-2010, 08:28 PM
I'm not going to do all the work for a swap and have a 1j under the hood. Yuck. The 2J is almost identical amount of work and simply better.

Also about a cold test being inconclusive.. in what way? Are you saying that after warming up cylinder 3 won't have low compression? The dry test is identical results to the one I did two years ago except that #3 is even worse now after sitting while the others are the same. The engine is definitely not running right, so I'm not really sure what that civic story has to do with anything?

Sure I'll try warming it up first and doing it again, but I really don't expect different results.

90blacktrac
06-21-2010, 09:01 PM
Just trying to help, also you could do a sort of leak down test by detatching the gauge from the compression tester and removing the valve core from the threaded end, then move the piston in question to tdc of the compression stroke and hook an air compressor the the nipple where the pressure gauge was. Compare the amount of air coming out of the pcv or oil fill to the other cylinders. Not the most scientific test but it will reveal cracked ring broken ring lands or excessively worn cylinder walls.

T-spoon
06-21-2010, 11:43 PM
For the sake of being thorough I just warmed the car up (farkin smelly/smokey operation. It was FTL.) and tested again. Previous test confirmed. Obviously not the exact same numbers wet, but it was still around 60 dry and came up to 160 or so wet.

My question was more.. is there any chance that's not the rings/piston/block or is that pretty definitive?

KoreanJoey
06-22-2010, 01:59 AM
Sounds pretty definitive to me...

andy
06-22-2010, 02:40 AM
the 1jz is less work it bolts in, you have to beat or cut the firewall to run the stock turbos from a 2jz on a ma70 supra.

90blacktrac
06-22-2010, 04:35 AM
My afore mentioned hillbilly air compressor test would show a warped valve or bad head gasket as well but low compression and oil smoke is most likely a ring related problem or small chance of a bent valve.

T-spoon
06-22-2010, 06:31 AM
the 1jz is less work it bolts in, you have to beat or cut the firewall to run the stock turbos from a 2jz on a ma70 supra.

Good thing I already have an awesome single on the 7m. I've done the research. The 2j is not much if any more difficult to put in. It would be a little more expensive.. BUT.. that is made up for with how rock solid a platform the 2j is. 1j is just simply meh in comparison. Other than cost, it really has no advantages over the 2j.


My afore mentioned hillbilly air compressor test would show a warped valve or bad head gasket as well but low compression and oil smoke is most likely a ring related problem or small chance of a bent valve.

It's actually hard to tell how much oil is in the exhaust due to all the fuel from how rich it is. I don't have an air compressor anyway. Doesn't show any signs of headgasket (and I'd hope not, had done it recently before all this with ARPs and checked their torque a few times). I was hoping maybe valve (although I had recently had those out for new seals too) but it doesn't sound like these results leave that possibility on the table.

85gtsblackman
06-22-2010, 08:31 AM
id vote build a nasty but relible 7m, or swap a 1uzfe. it can be done, and it can make about the same of not more power than a jz. oh and ive ridden in a 600+ whp 7m, it was insane and the same long block has done fine since a rebild 5 years or so ago.

T-spoon
06-22-2010, 06:10 PM
Yeah.. I had the supporting mods for 600ish just didn't get a chance to turn up the boost. The problem is, I'm not sure what would have caused the current failure. The only thing that happened to it around the time the problem appeared was the massive oil overfill that blew the front main. I wouldn't have thought that would kill rings though and on just the one cylinder.. it's strange. It just makes me wary of messing with the 7m more :wacko:

Mafix
06-22-2010, 06:43 PM
you own a 7m. was there ever a doubt that this would happen?
i would double check the head bolt torque if they were never re-torqued.

T-spoon
06-22-2010, 08:23 PM
you own a 7m. was there ever a doubt that this would happen?
i would double check the head bolt torque if they were never re-torqued.

re-torqued at like 250-500-1000 miles or so after I put the new head gasket in. But.. looks like I'll be taking things apart, so I'll probably check anyway even though nothing else is pointing at head gasket right now.

It never had a blown headgasket btw, I just had to take the head off to have a spot on the head repaired where a friend tried to drill out a broken stud and got a little sideways with the drill.

Mafix
06-23-2010, 05:11 PM
yeah it sucks when stuff goes a-stray like this but i always use it for an excuse to build bigger and better.

T-spoon
06-28-2010, 11:17 PM
I just rechecked the torque on the head studs for kicks. There were 1 or 2 that were maybe a couple ft/lbs low (did them all to 75 which is the commonly accepted thing to do with 7Ms, factory is like 45.. lol). Interestingly none of the very slightly low ones were around cylinder 3. I checked compression again and consistantly #3 now hits 110. The others are still 150. This strikes me as peculiar. Is this somehow indicating that it could in fact be the HG in such a way that doesn't mix the oil and coolant and has compression go up with a wet test? I just find it really odd that very minor changes in the head torque would gain dry compression, but I didn't change anything else.

rizin
06-29-2010, 01:52 AM
My buddys evo had a crack running the center of the piston and is tested the same as what you are showing. Supposibly this is something common on stock pistons for them. So I guess you never know untill you are in there.