Confusing compression test results - a good mystery (1 Viewer)

[kenavt]

Oh great MUD hive mind, I need your help and advice.

I picked up a used 2F for my FJ60 (build thread), and have been trying to run compression tests on it and have been getting weird results. The story on the engine is that I bought it off a guy who took it out of a FJ60 with 140k miles; the engine had been rebuilt in 2016 (have a receipt) and had about 30k miles on it. (he now has a sweet EROD installed, it's a beaut). I had a video of it running, and bought it on that faith. Met the guy and picked up the engine and drove it home, didn't have suspicions. But then noticed the crankshaft was only going through 2/3rds of its rotation... was able to seemingly break it free and wear it in (over a few revolutions it became easier until it was pretty easy), and then installed it in my truck. Before going farther I borrowed two testers from O'Reillys (first one was broken) and got some... odd results.

I want to trust the engine previous owner that it was in great shape when I received it, and it should be in great shape (got a lot of verbal reassurance). He did leave it outside for ~6 weeks (when the back of the carb and a couple of other surface things rusted), and I suppose I could have done something bad to it when I was loading/unloading, bolting on a belt housing, and installing under the hood. But I should have really run compression tests on it when I went to buy it... definitely learned a lesson there.

These tests are with the engine in the truck, all plugs out, carb bolted in (but no air cleaner), no downpipe mounted to the exhaust manifold. I did Round 1 on Saturday, first time ever doing compression tests, and got not great results across the board.

Round 1
Cylinder 1 - 80
Cylinder 2 - 30
Cylinder 3 - 62
Cylinder 4 - 43
Cylinder 5 - 65
Cylinder 6 - 80

Round 2 I did on Monday, and unlike the previous time, I tried to hand-tighten the hose as much as I could into the spark plug hole. It had been difficult to thread it in for some of the cylinders, and this time I was unafraid to put some strength into it. I was really wrenching on it (but only by hand), and scores improved quite a bit. But other then Cylinder 1 I really don't want to put this in my truck.

Round 2
Cylinder 1 - 150 (+70)
Cylinder 2 - 30 (-)
Cylinder 3 - 100 (+40)
Cylinder 4 - 70 (+27)
Cylinder 5 - 85 (+20)
Cylinder 6 - 100 (+20)

Round 3 I did right after Round 2. I tried cleaning out the spark plug holes (I noticed the spark plugs' threads were dirty and so was the hose, I could wipe it off with a rag), and also had my roommate hold the throttle wide open on the carb.

Round 3
Cylinder 1 - skipped
Cylinder 2 - 30 (-)
Cylinder 3 - 105 (+5)
Cylinder 4 - 67 (-3)
Cylinder 5 - 93 (+8)
Cylinder 6 - 130 (+30)

I really don't know what to make of these results. I've heard that you can have bad compression for four reasons... none of which (or all)? seem to be at play here. These are all dry; I haven't done them wet (with oil) yet since I figure I can't go back from that.

1 - bad seal against the spark plug holes. hopefully not a problem since I really hand tightened them for later rounds.
2 - bad valve timing, would probably show across all cylinders. the engine previous owner did tell me the engine needed valve lash adjustment and I could hear valve tick in the running video, but it didn't seem that bad. I figure for really bad valve timing to affect compression, things have to be awful. And cylinder 1 seems good (and maybe 6).
3 - bad head gasket. which would probably show as individual cylinder issues.
4 - bad piston seals - could confirm with wet tests, would probably be individual cylinders as well.

I'm reluctant to just pull the engine apart and start digging into it until I have a better idea of what I'm going for. Anyone have any suggestions or insight?

 

[Godwin]

Adjusting valves is easy enough. Do that and rerun the compression test, you will at least have ruled out valves out of adjustment.

 

[NeverGiveUpYota]

Wow all terrible. Do as ^^^ said then... Leak down would be the next appropriate step. ***, edited... I didn’t read fully and see it was rebuilt. Ignore most of this - Rebuild or engine swap. Most likely broken landings on the pistons and rings. I had two broken pistons and one piston w/ broken rings. All rebuilt now.

 

[Zjohnsonua]

Dang. Tough to see given all that you've done.

Valve lash, wet test, then leak down... by the end of that you'll have a solid prognosis.

 

[2mbb]

The compression tester I have has an o-ring that seals where the washer on the spark plug would seal, I think. I've never had to any more than snug it down, mostly by twisting the end with the gauge on it. Also, to get the "best" results you need to have a proper charge on your battery and each cylinder should go through about the same number of rotations. After you've done all the adjustments mentioned above, you might want to spend some $ on a compression tester. You shouldn't need one with all the adapters for the 2F, unless you want to use it on other vehicles you may have.

 

[Randy88FJ62]

My numbers are trash and my 3FE still chugs along without a care. Is it the fastest pig? No but it cruises at 80 on the highway if I wanted to (assuming flat ground).

 

[vipergrhd]

I would rent a different tester and go at it. Good advice on check valve clearance,make sure battery is fully charge.

 

[Miloslavich]

Yea, thats all over the place. as mentioned adjust valves, and see about following the aforementioned instructions (proper test procedures, good battery charge, throttle 100% open, no plugs in other cyl's, etc)

 

[OSS]

The compression values given in the manual are only relevant to an engine that has been running and is up to temperature, then shut down and tested.
Since you're testing it incorrectly (cold and dry) and the compression gauge is an unknown, the values you're getting are only curious at best. I don't think a compression test is valid the way you're doing it

 

[Zjohnsonua]

Dry tests on healthy, cold engines should give reasonable numbers, albeit slightly lower than warm and dry.

As a plus to the OP, I've seen broken rings, badly scuffed cylinders, and burned pistons turn in better than 30 psi (all tested cold) so something up top is likely screwing with #2.

#4 and #5 are the suspicious ones to me.

 

[SteveH]

I had a compression test go sour when bits of carbon crusties fell off the spark plug and held a valve open, but your numbers are shaky across the board. I would also inspect the o-ring on the compression tester hose and be sure that it's not grossly distorting when you hand-tighten the hose in the spark plug holes.

If there's any way you can test run the engine on a stand (or in the truck) even without a cooling system and exhaust system, and blow out some of the crap, and then re-test it, warm, and both wet and dry, you'd learn a lot more. I wouldn't toss the engine just yet, but you need better and more consistent numbers.

 

[kenavt]

Thanks everyone for all the advice, this is awesome This is making me feel better and giving me more to go on

The compression tester I have has an o-ring that seals where the washer on the spark plug would seal, I think. I've never had to any more than snug it down, mostly by twisting the end with the gauge on it. Also, to get the "best" results you need to have a proper charge on your battery and each cylinder should go through about the same number of rotations. After you've done all the adjustments mentioned above, you might want to spend some $ on a compression tester. You shouldn't need one with all the adapters for the 2F, unless you want to use it on other vehicles you may have.

I had a compression test go sour when bits of carbon crusties fell off the spark plug and held a valve open, but your numbers are shaky across the board. I would also inspect the o-ring on the compression tester hose and be sure that it's not grossly distorting when you hand-tighten the hose in the spark plug holes.

If there's any way you can test run the engine on a stand (or in the truck) even without a cooling system and exhaust system, and blow out some of the crap, and then re-test it, warm, and both wet and dry, you'd learn a lot more. I wouldn't toss the engine just yet, but you need better and more consistent numbers.

Yea, thats all over the place. as mentioned adjust valves, and see about following the aforementioned instructions (proper test procedures, good battery charge, throttle 100% open, no plugs in other cyl's, etc)

The battery was charged (for round 1 it was at 12.6V, after round 3 it was at 12.3V) but I'll charge it up before my next round. There were no plugs in other cylinders, and throttle was 100% open for round 3. On other advice for rounds 2 and 3 I really held the starter for a few revolutions... round 1 was like 5-6 (based on just me being arbitrary), round 2-3 were like 10+ (when the gauge seemed to stop moving up).

Its hard for me to see the o-ring on the compression tester hose and what sort of shape it's in... it's really in there. I would feel a lot more confident if I could tell how that seal was.

Dry tests on healthy, cold engines should give reasonable numbers, albeit slightly lower than warm and dry.

As a plus to the OP, I've seen broken rings, badly scuffed cylinders, and burned pistons turn in better than 30 psi (all tested cold) so something up top is likely screwing with #2.

#4 and #5 are the suspicious ones to me.

It's also suspicious to me that they aren't all within 10 psi of each other. Cylinder 1 definitely seems good, but I feel cautious saying cylinder 6 and 3 are good either.

I had a compression test go sour when bits of carbon crusties fell off the spark plug and held a valve open, but your numbers are shaky across the board. I would also inspect the o-ring on the compression tester hose and be sure that it's not grossly distorting when you hand-tighten the hose in the spark plug holes.

If there's any way you can test run the engine on a stand (or in the truck) even without a cooling system and exhaust system, and blow out some of the crap, and then re-test it, warm, and both wet and dry, you'd learn a lot more. I wouldn't toss the engine just yet, but you need better and more consistent numbers.

The engine is in the truck without a cooling or exhaust system - it's just bolted up to the trans and I'm running the starter. Unless you're saying straight-up run the engine with fuel for a while to warm it up? If it was able to do that, then I wouldn't worry about these compression tests at all but I haven't tried.

These are going to be my next steps, and re-test after each one. Might take me some time since I'm going to be traveling for the next while.

• Charge battery up some more off a different car
• Adjust valve lash (lash I'm assuming is just normal valve adjustment?). I know from the PO that the cam was modified
• Leak down (this hadn't occurred to me, need to see if I can get a tester).
• Wet test
• Cry, maybe salty water would help

I might try a different tester as well, but since I got a 150 on cylinder one I feel confident the tester isn't the problem.

Below is the picture I got from the engine PO with details on the custom cam grind... I believe this means I should set the valve adjustment to be 0.014" on both intake and exhaust valves (versus normal stock 0.008" and 0.014" per my FSM).

 

[NeverGiveUpYota]

Dry tests on healthy, cold engines should give reasonable numbers, albeit slightly lower than warm and dry.

As a plus to the OP, I've seen broken rings, badly scuffed cylinders, and burned pistons turn in better than 30 psi (all tested cold) so something up top is likely screwing with #2.

#4 and #5 are the suspicious ones to me.

True even w/ mine being the way they were the lowest readings I got were 125 if I recall right. My leak down readings were something like 10-15%.

 

[SteveH]

Unless you're saying straight-up run the engine with fuel for a while to warm it up?

yes - I have run a number of engines for a couple minutes with no cooling system. Watch the head temps and don't be stupid about it - see how it feels at 90 seconds and go from there. If it has been parked for a long time, I try to dump some antifreeze into the water pump (for the sake of the bearings) or just pull the fan belts so the pump doesn't spin. By starting the engine and getting it somewhat warm, you might get a more valid compression test if you do one right after shutdown. If you have any carbon bits floating around from spark plug removal, this will take care of that, too.

 

[Dallas Cruiser]

I suspect that there might have been some rust in one or more cylinders since you couldn't turn the engine a full revolution at first. The rings in that or those cylinders are probably stuck and or not sealing properly.

 

[ArizonaFJ]

I would finish the installation, check the valve clearances and timing and fire it up. If it runs well, change the oil and drive it. Don't do another compression check unless you have a specific reason to. Compression testers are useful diagnostic tools but doing a compression test for fun often leads to seemingly random numbers, much consternation and too many "rebuilt" engines that had many good miles left in them.

 

[Spook50]

I would honestly 86 the compression testing and buy (and study up on using) a leakdown tester. Leakdown testing will tell you much more than just a compression test will, and will also tell you exactly where and how bad the problem is.

 

[Dallas Cruiser]

I have an OTC brand leak down tester that I use at work. I got it off amazon a few years ago.

 

[kenavt]

Due to personal business I won't be able to do this until next week, but I really appreciate all the support and help from everyone on here

I see leak-down testers are at Harbor Freight, I'll consider swinging by and picking one up. Need to do more research on those.

I would finish the installation, check the valve clearances and timing and fire it up. If it runs well, change the oil and drive it. Don't do another compression check unless you have a specific reason to. Compression testers are useful diagnostic tools but doing a compression test for fun often leads to seemingly random numbers, much consternation and too many "rebuilt" engines that had many good miles left in them.

Are you saying don't do another compression check for the sake of consternation, or because I could risk actual damage?

 

[OSS]

Doing a compression check will only damage your peace of mind - it won't hurt the engine