The Stovebolt Site Forums The Shop Area Engine Shop Engine compression problems how to fix?

Hey, I have a 54 chevy 3800 with a 1957 235 engine in it. I tested it for compression and had at a maximum of 90 psi. The other three cylinders were pretty bad at 45,40,75psi. I put oil in the problem cylinders and the compression shot up to 100 psi. Does this mean I have bad piston rings? If so would I have to rebuild the engine or get it machined. I'd rather not spend 1000's at a machine shop if I can help it.

Let me know what you think.

I would say most likely bad rings but that might not be all thats going on. Could be some head & valve problems. If you decide to tear it down to replace the ring I would go ahead and overall the engine or find a suitable replacement. If I remember correctly the 235 compression should like 120-130's psi.

you could look for a nice used 235 to drop in. they are available here at the swap section, on eBay, and Craigslist. depending on condition they are generally way less than $1K.

Searching "chevy 235 engine" on eBay brings up a running motor in a Bel Air for $750.

ask to do a compression check on any engine before you buy. paint up the motor and swap it out - no more work than removing/reinstalling your existing motor. you might even get a little back for your worn motor as a rebuildable core ($100-$200).

since you have a '57 engine in your '54 truck, you aren't concerned with a numbers-matching situation - all the more reason to just go with a used motor swap.

my $0.02. good luck!

If you can find a motor in your local area and check it as suggested above then fine. Buying it from 'out of town' and you might be getting a 'pig in a poke' with the same or even more problems than you already have. Plus shipping.
I'd find a good local rebuilder and get a price baseline of what you have, and what it will cost to correct its problems. This will give you a good idea of what kind of dollars you can spend on a replacement.

Is this a running engine that you run regularly or is it one that has been left to sit up for a longtime and you're just now starting to mess with it? If it's been sitting a longtime, the compression may improve after you run it some. If it's one that's been running recently then I'd say it's worn out. You'll have to tear it down to see just how bad. You can also perform a leakdown test, but I'd say that effort would be a waste of time.

To answer the question, yes. If oil in the cylinder brings up compression, then you have a ring sealing issue. Now WHY they're not sealing is another matter! You didn't say whether or not this engine had been running for the last several years. If it has NOT been running for 5 years or better, then the chances are that the rings are just stuck in the lands. There are several products that you can use to leave it set and soak. My personal choice is Marvel Mystery Oil. I'd also give it the full Monte. SLOWLY pour it down the carb while running, (or you can hydro lock it and bend rods and stuff. It ain't pretty...) Usually hold the engine at about 2000 rpm while pouring until it stalls the engine. (Don't MAINTAIN 2000. Just start there) Once it stalls, pull your plugs and give it a good healthy amount in each cylinder. I know it's hard to leave it set, but leave it alone for a week. After a week, crank it over with the plugs still out. Install your plugs and start! Don't start revving the snot out of it! Just keep it running until it will idle on its own. Once it comes up to operating temperature, take it out on the road. Don't hammer it in first gear. Wait until second. Hammer it, but don't wind it tight. In third, hammer it and wind it tight. Make sure you watch the mirror when you do! Slow down while still in third and hammer it again. When it stops blowing smoke when you wind it up in third, you're down. Most likely. you'll have to drop the idle when you're done.

If it HAS been running, you can try this anyway. You have nothing to lose but the cost of the MMO and some time!

If the engine will start and run, try this: fill the crankcase with non-detergent 30 weight oil and add 2-3 quarts of kerosene or Diesel fuel, enough so the crankshaft and connecting rods will dip down into the mixture and splash it around vigorously. Run the engine at a fast idle (1500 RPM or so) for 20-30 minutes with NO LOAD on the engine- - - -do not drive the vehicle at all. Idle down to normal speed, shut down and drain the oil while it's hot. If the rings are stuck in the ring grooves, this procedure usually unsticks them. Be aware it will also find any places where oil can leak, such as loose sheet metal parts and possibly front and rear crankshaft oil seals. Sludge makes a pretty good sealer, and sometimes that's all that's keeping an engine from being a serious leaker.
Jerry

I've done this many, many times. It does work well. Something I did discover over the years though is that it's usually also a good idea to disconnect any crankcase breathing equipment (PCV, etc)

I've just recently started to mess with it. It hasn't ran in 25 years. It was sitting in the neighbors grove for that time

Has not run in 25 years is critical piece of info...........likely rust and pitting on the cylinders walls and stuck rings and maybe partially stuck valves and rusty valve seats.

It is some want amazing the engine turns over and was not stuck from sitting.

No loss is trying the flush trick but chances of success might be low.

Low budget, you could disassemble, clean things up, replace the rings and the other bare minimums to get it back on the road. Not the best solution but these engines can be forgiving with get by specs. As mentioned used engine might have the same or worse problems. Obviously Best used engines come from running vehicles that are being converted to modern drive trains.

I had a '52 truck with a 216 sitting in the driveway for 18 years without ever turning the engine over. As soon as I got gas to the carb, that baby fired right up and idled as smooth as when I shut her down 18 years prior. Those inline six engines want to run. It is up to you to give them what they require to do so.
Don't be so quick to give up on yours.
Compression numbers mean very little on a cold engine.
Carl

Provide that engine with some clean gas and a hot spark, and it will almost surely start and run. Once it's running, you can work on making it smoother and more reliable. I've seen engines wake up and run surprisingly well after longer dormant periods than yours many times. They're simple and rugged, even when they haven't been pampered.
Jerry

It will interesting to see how this engine come out.........but..........engines that are not stuck after sitting for years often ( not always) are not stuck because when they were running they were consuming large amounts of oil. The excessive oil helps present the rust. So when they do run after very long time sitting they make really good mosquito foggers.

Assume during your Initial testing and observations you tried to determine if the cooling system was ok.........no external cracked blocks, head or missing or damaged freeze plugs, water pumps turns like is should.

Good luck keep us updated.

Here's a video of an old International Harvester that I resurrected one time. Not the original engine in the chassis, but it was also stuck, just not as bad as the original one was.



I used Coca Cola to free them up.

Would the engine run with poor compression like that so I can try and see if the compression could get better or should I just tear it down and redo rings right away.
Thanks

Yep. As long as at least one cylinder has compression you should be able to get it to start and run. I'd recommend pulling the valve cover off and oiling the valve stems good first. I also like a take a small hammer and tap the valves from the top to make sure they're all free. If you find a sticky one you'll know, it'll sound different. You can work them with a hammer and some pb blaster and free them up before you attempt the start.

I will say it again...
Compression numbers on a cold engine mean next to nothing.
You have been given recommendations including, give up and buy another engine, give up and have this engine completely rebuilt, and try to get this engine to run.
Now it is time to reread all of these posts and make a decision.

Thanks for the help. I will keep you posted

You might as well try and start it, nothing to lose. If you go with a used engine, be careful with what you buy and from who. There are a lot of people trying to pass off some real junk, like cracked heads and blocks. By the time you get done repairing another engine, you might be better off rebuilding what you have.