How to unstick stuck piston rings: cheap and easy fix?

I'm running an unusual race car: Mercedes 190E with the 2.3L 16-valve engine. Paid a small fortune to have the engine built with cams and everything. The builder delivered a paperweight: no compression on 2 cylinders; shims missing; parts missing. Basically, I got scammed.

Now I don't have the time or money to have the race engine rebuilt properly. I was offered a parts car with a Bekkers 2.5L stroker engine... but it had been sitting for 8-9 years. This "new" engine runs, but is low on compression across all cylinders. We did a valve adjustment on the head. The head seals well, looks like the compression loss is on the bottom end.

My mechanic says the rings are stuck because it had been sitting so long. The more we run it, the better the compression seems to get. He says that if I just drive the piss out of it for a while, the rings might eventually pop back out and start sealing reasonably well.

Meanwhile, is there anything else I can do to help move things along? I've read about putting Marvel Mystery Oil or ATF into the plug holes and letting it soak. Is that really a thing? Can anything be done short of pulling the engine out for new rings & bearings? I don't have the time or budget to get into another engine build right now. Looking for a quick fix just to. get me through the couple if races I have planned for this summer.

Saturns used to gum up rings pretty badly. The trick was to pour some seafoam into the cylinders and let it soak overnight.

Change the oil and fire it up the next day. Your neighbours will think you're fogging for mosquitoes.

Seemed to work on my friends old crappy DD Saturn.

Marvel works too.

We mix Marvel Mystery Oil and ATF and pump the cylinders full. Freed up seized engines in this manner.

Basically anything that is a light weight high detergent oil will work. The already mentioned Marvel and ATF are just that but a small amount of diesel also works well.

Here's how I personally do it; Pour enough selected oil down spark plug holes until your're confident that the entire piston is covered. Let oil sit for 24-48 hours while occasionally turning engine slightly by hand. The oil will usually drain into the crank case over the 48 hours. If after 48 hours there is still oil on top of the piston leave the spark plugs out and crank the engine over with the starter to clear the oil. Put plugs back in and see what you got.

I had a Miata with this problem. Actually, it was much worse. The 'yata had a stuck engine- as in, would not turn. I drained the oil and filled the engine with a combination of diesel fuel, PBlaster (you can buy by the gallon), and ATF, in about a 1:1:1 ratio. And when I say filled, i mean I filled it so the level of the fluid was up over the tops of the pistons.

Then I let it sit for a few days, and every day I'd go out and gradually turn the engine a bit with a breaker bar. Once it rotated freely, I drained all that crap out, refilled with cheap 5W-30 and got the engine to fire. It smoked profusely, which I assume was the rings not being free.

After letting the engine warm up fully, I drove it around, more and more spiritedly, eventually redlining it on shifts. The smoke gradually cleared up, and eventually went away. Changed the oil again, and never had any more trouble with the engine.

There would be no harm in soaking things in some light oil. But without taking it apart, there is no way of really knowing what is wrong. Do the rings have some rust, or just carbon build up? Really either way soaking it might make it better. The best stuff for rust would be Kroil, but other stuff could work if you can't find that. Since it does run, you could warm it up, then take the plugs out and pour stuff in with it warm, leave it for a few days and then drain it all out. Drain the oil, and spin it with the plugs out. No real harm in running a old motor at the track, provided it still has good oil pressure. Keep a eye on the oil pressure, if it drops at all, shut it off. It might be a little low on power and it might use oil but it will run. How long are your events? Have you run 20/50 oil before? I had a track motor that had terrible blow by, catch tank had to be drained after every session, but it ran great.

Kerosene will work also.

LanEvo wrote: My mechanic says the rings are stuck because it had been sitting so long. The more we run it, the better the compression seems to get.

This.

My old track Miata went from burning 1qt per day to nearly nothing after a few track days.

Just keep beating on it.

Just to put things in perspective, the 2.5 stoker engine should make about 13 +/-1 bar (about 190 psi) per cylinder and the lower limit of normal is listed as 10.5 bar (about 150 psi)

My engine is now measuring around 95-100 psi per cylinder.

It runs and makes ok power. Not nearly as strong as it should be, but it can pull all the way to redline and moves the car well enough.

TED_fiestaHP wrote: No real harm in running a old motor at the track, provided it still has good oil pressure. Keep a eye on the oil pressure, if it drops at all, shut it off. It might be a little low on power and it might use oil but it will run.

It looks like the more we run the engine, the higher the pressure readings have been getting. It's a little smokey, but not full mosquito fogger status. Can't judge oil consumption yet because we've only run it a few min at a time.

TED_fiestaHP wrote: How long are your events? Have you run 20/50 oil before?

It's BMW CCA Club Racing and VARAC vintage racing. Qualifying and sprint races are generally 30 minutes. Enduros are 1 hour (with mandatory 5 min pit-stop), but they're not done at all events; usually just sprints.

I used to run Brad Penn 20w-50 in my old E30. Sometimes even added a bottle of Lucas Oil Stabilizer. Kept oil pressure high and consumption close to zero on a very tired M20B25 engine with uneven compression numbers. That's what I was planning to do with this one as well.

TED_fiestaHP wrote: I had a track motor that had terrible blow by, catch tank had to be drained after every session, but it ran great.

I did install a catch can (well, a Gatorade bottle with a hole in the lid...but still). Again, I haven't really run the engine long enough to monitor blow-by.

z31maniac wrote: My old track Miata went from burning 1qt per day to nearly nothing after a few track days.

So that really works? I was worried that maybe it was just wishful thinking on my part...and a mechanic who just wants to get my car off his lift LOL

I'd do the Seafoam or MMO soak and then get it good and warm and drive it HARD (lots of mid-rpm heavy throttle and high rpm closed throttle to get the rings moving). See what it does after that.

I'd pull out a piston and look. I have not had the same luck with pouring random things into the engine to stop smoke You're not really rebuilding, you're just popping off the head and oil pan.

I've done the MMO treatment to several "frozen" engines that sat as long as 20 years. I take my time figuring a week. MMO through plug holes followed a day later by the slow rock using a breaker bar, then turn over with the bar over slowly for a few days eventually hooking up battery to turn them over. Once started change oil & start running longer and to higher RPM each time.

Is there a "best practices" guide for soaking rings? Specifically:

(1) what's the best stuff to use? I imagine penetrating lubes like Break-Free CLP or PB Blaster would be best. I guess MMO is the classic choice. I've read that a 1:1 mix of acetone and ATF might actually outperform everything. What does the hive say?

(2) what's the best procedure? Get the engine hot, pour it in each plug hole until full, wait 1-2 days, suck it out with a hose on a syringe, change the oil, and go?

Keith Tanner wrote: I'd pull out a piston and look. I have not had the same luck with pouring random things into the engine to stop smoke You're not really rebuilding, you're just popping off the head and oil pan.

That would be great. But I don't have the time or budget for that.

For better or worse, the "new" engine is in. My mechanic wants the car off the lift and out of his shop (can't blame him for that). I don't have the space, skill, tools, or time to do it myself.

I'm going to go after the "race engine builder" who turned a rare Cosworth engine and pile of expensive (and hard to source) race parts into a giant door stop. Until then, I have to make do.

My budget is blown. Just trying to salvage my upcoming race season with a functional car. If I get in too deep, I'll miss another season of racing.

LanEvo wrote: Is there a "best practices" guide for soaking rings? Specifically: (1) what's the best stuff to use? I imagine penetrating lubes like Break-Free CLP or PB Blaster would be best. I guess MMO is the classic choice. I've read that a 1:1 mix of acetone and ATF might actually outperform everything. What does the hive say? (2) what's the best procedure? Get the engine hot, pour it in each plug hole until full, wait 1-2 days, suck it out with a hose on a syringe, change the oil, and go?

Our mix is 1:1:1 of acetone, ATF, and MMO. Pour it in until the cylinder is full to the bottom of the sparkplug holes (usually cold, because we are freeing up seized engines), let it sit for a few days (or until it drains past the rings), pour more in, let it sit a few more days and then drain everything and fill with fresh oil.

Depending on what is really wrong, running it will make it better or worse. Running fairly short events, just make sure the oil is topped off, and check it after each session. Can't hurt to give it a good soaking then run it some. Provided the bearings are OK and it holds good oil pressure, run it. I am sure taking this thing apart is no small task, so run the one you have, until you can sort out the bad one. Wonder what is wrong the other motor, something wrong with the rings, or did they get the bore wrong, so many little things can go wrong. The rings might have rust or carbon, either condition might improve with a good oil soak. Or they are just worn, and a oil soak won't make that any better or any worse.

I did have a race motor that was always a little low on oil pressure, that thing ran great. Then one day the pressure was just slightly lower, still wish I had shut that thing off at that point. That made a big mess. When a bearing seizes onto the crank at race RPM, there won't be much left.

seafoam in the crankcase, and a seafoam ,Italian tune up.

works wonders

LanEvo wrote:

Keith Tanner wrote: I'd pull out a piston and look. I have not had the same luck with pouring random things into the engine to stop smoke You're not really rebuilding, you're just popping off the head and oil pan.

That would be great. But I don't have the time or budget for that. For better or worse, the "new" engine is in. My mechanic wants the car off the lift and out of his shop (can't blame him for that). I don't have the space, skill, tools, or time to do it myself. I'm going to go after the "race engine builder" who turned a rare Cosworth engine and pile of expensive (and hard to source) race parts into a giant door stop. Until then, I have to make do. My budget is blown. Just trying to salvage my upcoming race season with a functional car. If I get in too deep, I'll miss another season of racing.

The budget is just a head gasket and an oil pan gasket. It's about as complicated as a shock change, you're just opening a box and looking at the parts inside. Heck, you may not even have to pull the engine. I'm looking at the crank for my Cadillac right now, and I could drive it to lunch today if I had the oil pan gasket. If the parts are expensive and hard to source, this is the safe solution. But sometimes you just have to cross your fingers and go for it, I understand. Just usually not before the season starts!

Scammer engine builders are the worst. We've had to be the bearer of bad news a few times when we've opened up a "high end built engine" and found junkyard parts. It always turns into a he said, she said situation.

I think any of the above suggestions for soaking the rings would be good. I'd probably go with MMO. I've had some amazing results with that, but it's way slower to work than others. I once freed up a porthole (more "window like" than porthole, but functioned more "porthole" than window) on a ship with MMO. Steel bulkhead and brass frame met at the hinge pin. In a salt water environment, they had welded themselves together. A little MMO every day and a slight wiggle and in a couple weeks, it was moving like butter.

Also, drive the piss out of it. My 22R rebuild was less than completely successful. I had a machine shop assemble the block for me because I was short on time. I usually do that myself. Anyway, not sure exactly why, but I used a quart of oil every 300 miles when I first got it back together. Best it ever did was about 1 per 500 miles. Rings not seating. Finally, I put the cheapest oil I could find in it, didn't change it at all and drove the piss out of it, rev limit shifts, etc. and in about 10K miles, consumption went down to a quart per 1K or better. Then I started changing it again and back to full synthetic. Last quart lasted me 1800 miles.

So, I suggest: Soak it with whatever makes you happy, then drive the piss out of it.

Drain the engine oil, replace with ATF, drive the snot out of it.

Spraying a can or two of carb cleaner in the engine with it running helps too. Hold it up to a high idle and try to stall it with cleaner.

FYI I have not seen a very strong correlation between compression numbers and horsepower. Often, compression will be way down after a season of racing and yet power will be pretty close. Run it!

Knurled wrote: Drain the engine oil, replace with ATF, drive the snot out of it.

No no no no no! Unless that engine would be happy being run flat out with cheap 5W-20 in the crankcase, this is a quick ticket to bearing damage IMO. Plus, modern ATF isn't any better at cleaning than modern engine oil, it just happens to be a fairly thin oil which can be useful for cleaning.

tuna55 wrote: FYI I have not seen a very strong correlation between compression numbers and horsepower. Often, compression will be way down after a season of racing and yet power will be pretty close. Run it!

I'd expect to see a significant drop in low rpm power with the difference getting smaller at higher rpm. Things get more leaky as they wear, but there's less time in a cycle for leakage to occur at high rpm, so the pressure loss (and power loss) is much less at higher rpm.

I've seen an engine with a slightly dinged valve show 70 psi on a compression tester in 1 cylinder (others were 180-ish). It had an almost dead miss on that cylinder at idle, but got smoother / better as revs increased. At high rpm, it wasn't even noticeably down on power.