Cold Compression Numbers

JD3020 · Mar 5, 2013

Gonna be pulling my engine soon, so i'm trying to determine whether or not my engine is worth putting money into(re-sealing), or if i should track down a good long block to swap in. Reason i'm cautious is my truck has never ran smooth, hazes after a long idle, and has a little more blow-by than i like. Always starts fine, but blue smokes a lot. Never really sounded right either. But it passes a contribution test every time with flying colors, except for the one time it randomly showed #8 at fault. Stopped today and got the HF tester, and made my adapter.

Anyways the truck hasn't ran in over a week, and has been sitting in the shop. Just got a fire going a little bit ago, so the shop is just starting to heat up some. EOT right now is 36*. So far i've tested #1 and #3, with 330 and 320 respectively. Stopping after the 4th "hit". Working on testing all 6 others as well.

IMO those numbers are low, but is this because the engine is cold or because i do have compression issues? BTW, the truck has 205-206k miles.

JD3020 · Mar 5, 2013

Got the rest of the numbers now.

#1-320
#2-320
#3-310
#4-340
#5-315
#6-300
#7-310
#8-285

CSIPSD · Mar 5, 2013

The motor I just blew up had numbers just like that... It went 80k before popping a hole in a cylinder... The 285 is WAY low, the 320-325 numbers is what I had. I would suspect the #8 hole has an issue with a valve or rings.

JLDickmon · Mar 5, 2013

CSIPSD said:
The motor I just blew up had numbers just like that... It went 80k before popping a hole in a cylinder... The 285 is WAY low, the 320-325 numbers is what I had. I would suspect the #8 hole has an issue with a valve or rings.

the difference between that one and the 340 is too large..
squirt a little bit of 30w motor oil down the hole, if it comes up, it's rings.. if not, it's valves..

JD3020 · Mar 5, 2013

CSIPSD said:
The motor I just blew up had numbers just like that... It went 80k before popping a hole in a cylinder... The 285 is WAY low, the 320-325 numbers is what I had. I would suspect the #8 hole has an issue with a valve or rings.

Thats what i'm thinking as well. Visually the valves appear to be moving fine, but that doesn't tell me much. And it doesn't really have me super worried, i imagine its been like this for the 30k miles i've owned the truck. It has no signs that its gonna let go on me, just not happy with how its running.

But its thrown a wrench into my plans big time. Truck is down because of an oil leak. Plan was to yank the engine, fix manifolds/up-pipes leak, oil cooler leak, this new oil leak, and then run it. But I can't bring myself to do that to an engine with a weak cylinder, nor do i wanna spend the money to buy a good LB unless i find an awesome deal somewhere. :shrug:

JLDickmon · Mar 5, 2013

JD3020 said:
Thats what i'm thinking as well. Visually the valves appear to be moving fine, but that doesn't tell me much. And it doesn't really have me super worried, i imagine its been like this for the 30k miles i've owned the truck. It has no signs that its gonna let go on me, just not happy with how its running.

But its thrown a wrench into my plans big time. Truck is down because of an oil leak. Plan was to yank the engine, fix manifolds/up-pipes leak, oil cooler leak, this new oil leak, and then run it. But I can't bring myself to do that to an engine with a weak cylinder, nor do i wanna spend the money to buy a good LB unless i find an awesome deal somewhere. :shrug:

well, do like I suggested and put a couple squirts of oil down the hole and see if it comes up.. if it does, yank da' heads and do summa dat valve grindy chit..

lincolnlocker · Mar 5, 2013

hone it, ring it, valve it, run it. or find a long block with good compression.. me, i opted for a complete rebuild.

JD3020 · Mar 5, 2013

JLDickmon said:
well, do like I suggested and put a couple squirts of oil down the hole and see if it comes up.. if it does, yank da' heads and do summa dat valve grindy chit..

I saw Harbor Freight had an awesome angle grinder on sale for $10. Should get the job done!!! LOL

Planning on squirting some oil in tomorrow and seeing what happens.

lincolnlocker said:
hone it, ring it, valve it, run it. or find a long block with good compression.. me, i opted for a complete rebuild.

I'd like a re-build, but thats out of the budget right now unless i could get by with a hone/re-ring, which i doubt.

May have a couple leads on decent long-blocks that i'm gonna check out tomorrow. Kinda wishing i still had the one i sold last winter.

ghohouston · Mar 5, 2013

oscs hooked dentexpowerstroke up on here, he found him an e99 engine for way cheap, i mean i think like $600 cheap, we swapped it in, compression tested, and all cylinders were near 500 psi, thats a bad ass deal! you never know what you may find

CSIPSD · Mar 6, 2013

You can pick up motors cheap all day every day...

More so where you live...

I will be in this motor about $1000 bucks when its all said, maybe less. Bought the whole truck for $2750 and parted it out from there.

JD3020 · Mar 6, 2013

I used to have a hook-up through a friend with a guy that scrapped busses, so i could pick up complete IH 7.3's for $1k.

But i did find a complete 200k mile 95 engine for $950 earlier, gonna call about it shortly. Although i don't feel like driving 4 hours to compression test an engine, and find it to be the same as mine. LOL

golfer · Mar 6, 2013

JLDickmon said:
the difference between that one and the 340 is too large..
squirt a little bit of 30w motor oil down the hole, if it comes up, it's rings.. if not, it's valves..

how does the oil not just sit in the bowl in the piston? I assume you intended the oil to run to the perimeter of the piston like a flat/domed top gas engine piston?

JD3020 · Mar 6, 2013

golfer said:
how does the oil not just sit in the bowl in the piston? I assume you intended the oil to run to the perimeter of the piston like a flat/domed top gas engine piston?

I was thinking about that earlier.

Either way its getting a new engine. Found a complete, low mileage 7.3 for $800 i'm hoping to get. Should be able to get my money back out of everything, if not make money which will be nice.

Marty · Mar 7, 2013

ghohouston said:
oscs hooked dentexpowerstroke up on here, he found him an e99 engine for way cheap, i mean i think like $600 cheap, we swapped it in, compression tested, and all cylinders were near 500 psi, thats a bad ass deal! you never know what you may find

500 psi?

SICKS LITER · Mar 7, 2013

yeah those numbers are really low. i just did a comp test on a customers 00 7.3L, 363,000 on it and it had 425 in every hole, i was impressed!

JLDickmon · Mar 7, 2013

golfer said:
how does the oil not just sit in the bowl in the piston? I assume you intended the oil to run to the perimeter of the piston like a flat/domed top gas engine piston?

yeah, yer right, I forgot about that..

Jeez I wouldn't want him to bend a rod if it had something as simple as a smoked exh valve

ghohouston · Mar 7, 2013

Marty said:
500 psi?

Swear to you, and I have compression tested my fair share of powerstrokes. The gauge is used weekly, at least what I remember. Hell I guess gauge could be faulty

JD3020 · Mar 7, 2013

Trying to work out a deal for this low mileage 7.3. And all i can say is, its a blast dealing with people on CL. LOL I asked him today if he has a way to move it, and he's like, "welllll, i've got a cherry picker that will barely pick it up. But i doubt it'll get it into a truck." Then he asked me if i had a way to load it, and i told him i'm not driving 2 hours with a tractor in tow on a hope that this engine is actually a 120k mile 7.3. Guess he's gonna try to get his neighbor to move it for him now.

I just hope it is what he says it is.

JD3020 · Mar 10, 2013

New engine is home. Hoping it turns out good though. Couldn't do a compression a test as theres no trans adapter/flywheel, but we drove 2+ hours, and the price was right so i bought it. Its a complete, late 97 engine.

Its odd though, as i was told it only has 120k miles, but i'm still not sure who's truck it came out of. There is no rust on the oil pan, most of the block still has the factory paint on it, oil cooler is dry and looks good, and most of the parts on it appear to be the factory parts. Overall its just a very clean looking motor, which is nice.

Now the really odd thing is the exhaust manifolds. They were off the engine when i bought it, but he isn't sure why. Its been sitting in his garage for 2 months, and he hasn't touched it. But the manifolds look new, just some surface rust on em. You can clearly read the casting numbers.

I"m just hoping that when we do do a compression test, it checks out with 400psi.