Think a weak cylinder will ever heal itself?

[TylerW]

Normally, I would say no.

However, my scenario is a bit different. I bought a '79 SWB Scottsdale a couple months back to use and eventually(maybe)restore).

I got this thing cheap because it barely ran. Compression sounded even when it spun over and it didn't make bad noises when it did run so I decided it had some potential.

The engine is a no-name reman 350 with an estimated 60,000 on it. I struggled to get it running right for quite a while. I checked cam lift, timing chain slop, both those passed. I finally realized that the timing pointer and balancer were a mismatch, so the timing was about 30 degrees retarded.

Now, the engine runs much better, idles on it's own, but it still has a slightly rough idle and much more pronounced when cold. I ran a compression test and got 120-125lbs across the board, except for #5 which came in at 90lbs.

I immediately did a wet test which brought that cylinder up to about 135lbs, so evidently there's a ring seal issue looks like.

Here's the backstory on that:

When I got this truck #5 plug was fouled out with gas. In fact, the oil smelled like gas also, which in retrospect was likely from the engine being so far out of tune. The other discovery was that all 4 drains in the heads were stopped up, so the valvetrain was being flooded with oil. I know because when I took off the driver side valve cover about 1/2 a quart dumped out.

So, based on the PO saying it was only used around his farm occasionally for the last several years, I'm surmising that #5 was ran dead a long time and had fuel wash.

Has experience proven that this can reverse itself with use, or has the damage been done? The engine is solid otherwise, no noises, the cam and chain looked great. No smoke at all now.

Thanks for any insight.

[Ziegelsteinfaust]

Damage done. Run it till oil consumption matches mpg.

[IIGW]

If it were me, and this is something you are planning on keeping for a while, and only at 60k, id pull the motor, run a ball hone through the cylinders and install a new ring set. This way with the ‘current’ rebuild, some new crank and rod bearings are cheap, and besides a used cam, you’d be well on the way to a ‘fresh’ motor. I mean with no labor, you’d be into it for less than $400 bucks and could have no worries and a fresh motor. For a few more dollars, small performance cam/lifter kit, and a new timing chain and now your entire lower half if at zero miles. And while the heads are off, you can lap them yourself to check the seats just in case, and lastly install the new valve stem seals that come in the new gasket kit and voila, your whole motor is at 0 miles… with peace of mind knowing you went through it, and not guessing if that one cylinder will heal itself one day.. (bad rings means fuel going into oil, so your oil will break down faster-it’s just not worth it to me)

[Corts60]

Mechanical damage is mechanical damage. It does not repair itself.

[Old Truck Man]

Ive run lots of engines that others gave up on. My 84 ford ranger had a broken valve spring. It was a state surplus vehicle, I bought it at auction for $150. It had a new rebuilt carb, new fuel pump and all new ignition plugs & wires. Ran like crap and smoked excessively. Thinking the cam was worn out I pulled the valve cover and the cam follower was laying there. put it back and revved the engine and it spit I out again. then I discovered the broken spring. Replaced the spring and number three still didn't hit to good. the exhaust valve was the one with the broken spring. The spring had enough tension to hold the valve closed but not enough to keep the follower in place. so number 3 was certainly washed down. I changed the oil and added 25% lucas oil treatment. the smoking stopped and it ran pretty good. Used it hard for three years. never changed the oil again just the filter every 6 months. Im of the opinion if its not broke don't fix it. Over the years I was of the opinion that if you used good oil you never needed to add anything to it. My expierence with additives like STP, engine honey ect was all they did was gum up your engine. However the Lucas actually works when used as recommended. I know of a diesel semi that has over one and a half million miles on the engine. Never so much as the valve covers removed. Ran shell rotellatt oil & 2 gallons of lucas . changed the oil & filtersevery 10,000 miles. and its still going strong. The gas has made the cyl run rather dry. That likely has removed the glaze from the cyl wall. that glaze will eventually return and heal the cly somewhat.

[Corts60]

Sorry, cylinder glazing is what causes smoke! Rings cannot seat properly with glazing in place. And cylinder glazing is mostly associated with diesels from engine temperatures not reaching a sufficient level to effectively burn the fuel, i.e.: lots of idling and no/low load situations.