Hi all,
Yesterday was a very disheartening day...

I've been having some noticeable issues with the way my engine is running, and decided to do a compression test.

The results made me sick.

1 - 115
2 - 130
3 - 130
4 - 124
5 - 112
6 - 125

I put oil in each of the cylinders and repeated the test:

1 - 133
2 - 171
3 - 148
4 - 160
5 - 135
6 - 160

All of them raised between 15 to 30 psi with oil, which leads me to believe that all of my rings have failed.
For the record, this is the compression I took in May of 2017, after I broke in the engine:

1 - 175
2 - 172
3 - 176
4 - 173
5 - 175
6 - 173

Any idea what would cause this? I've done regular oil changes, and even use a high lubrication zinc additive to help protect my cam. The engine only has about maybe 15,000 miles on it in the last 2 1/2 years.
Did I just get a bad batch of rings?

Thoughts?

 

Very sorry to hear that, i watched your build and you were very thorough with it. Machine work possibly?

 

Maybe do a leak-down test?

 

Has any of the testing variables changed? For instance, a different compression gauge? Just thinking out loud. Technically the engine should be warmed up as indicated by oil temperature when making the test. Battery in good shape and fully charged. Throttle & Choke blocked wide open. I know you know this stuff.

More WAG: This isn't a solid lifter engine is it? Valves need to be adjusted properly. How about head bolts, maybe a torque check, any possibility they are loose? I agree a leak down test. Those numbers aren't "bad" bad, but it is strange to see a big drop.

 

Thanks for the responses.

The engine was fully warmed up from a 30 minute drive home from work. All 6 plugs were out and the TPS on my Sniper unit reading 99% (throttle fully open).
Battery is fully charged and the engine was spinning freely.

Same method I've used every time I've done a compression test previously.

The engine uses hydraulic lifters. I don't think it's a valve issue as the compression raised significantly in all cylinders with the addition of oil (some almost to the point they were at when I first broke it in).

I have ARP head studs, so there's plenty of clamping force. If something like that was loose, wouldn't I blow a head gasket or something? Resulting in low compression in just a few (most likely neighboring) cylinders?

And while I agree the numbers aren't bad, as in loss of compression, but they're still not good at all, and what you'd expect from an engine with some 200,000 - 300,000 miles on it.

Not sure what a leak down test would tell me at this point, as this seems pretty conclusive that the rings are just shot. I could do one though. It'll take some time as I don't have a tester or a compressor, so I'll need to track both down.

 

"Interesting" problem. Cast iron rings? Moly? Might be useful to take a peek at the cylinder walls, have they glazed over somehow?

It isn't burning oil is it? Sure seems like something else is going on, as in "these aren't valid numbers" but I don't know what it would be. You haven't installed a new cam or timing set in the interim?

 

If I recall, they're moly rings, but I can't remember exactly. It's been about 3 years since they were installed.
I have a scope / camera that I can put in through the spark plug hole and take a look.

It isn't burning oil, but it does seem to have a bit of blowby. I've noticed my crank case breather blowing more and more "steam" and my valve cover has a coating of oil all over it. I wipe it off and it comes back quickly.

No, I haven't touched any of the internals on the engine since I got it running, aside from swapping out the stamped rockers for roller rockers at some point.

 

Modern rings seat easily, so I'm told. Isn't it chrome moly rings that sometimes have trouble? Using synthetic oil? All I've ever used is cast iron rings. Maybe you can try the "Bon-Ami" trick. You probably don't want to know what that is.

 

Yeah, as you can see with my compression test numbers back in 2017, they did seat easily. I had ~175 compression in all six cylinders. It was tight.

Yes, I'm using synthetic

Heh, I looked up the Bon Ami trick. Not a bad trick for an old engine with lots of glazing that you want to get a few more miles out of, but I bet it wrecks havoc on the bearings too.

 

They had an actual service part # for it at Caterpiller or somesuch, not worn engines, brand new ones. Maybe somebody else, I can't remember the exact details. They had a real problem with chrome or moly rings that wouldn't seat, and that was the fix. It had to be Bon-Ami, not that Ajax or Comet stuff, no siree. Cleans without Scratching! Yeah, I figured you'd get a kick out of that. Aren't I helpful? 😇

 

Maybe have another machine shop take a look at it and get a second opinion.

 

Hi Welder,
The engine's already been broken down and rebuilt.
It was definitely detonation, and was evident once opened up. Needed to be bored out and new pistons and rings, as well as all the valve guides knocked out of true (which invariably knocked all the seats out too). Fun stuff.

 

Ya I read your build thread all the way through and I am definitely routing for you to get it all worked out. I definitely admire your persistence anyone else would’ve probably given up after spending all that time and money on an engine. I definitely like the idea of EFI and definitely have a lot of questions. I just started my engine rebuild journey. I have my engine torn down and started hand porting it and still have to make a trip to my local machine shop wish me luck lol.