Piston rings rusted to bore
 

Hi So I'd taken the head out on my W115 240D to do a valve seat job, and it took some time, now when I went to turn the engine over by hand at the crank shaft pulley it seemed jammed and when I applied some force it came loose and the pistons started to move, it seemed the piston rings had rusted themselves onto the bore and now there's a little lip on the bore where it had rusted itself, so my question is can anything be done besides re-boring and slewing the engine? someone said it can be rubbed off with a very fine sand paper, is this true? also there is some surface rust at the bottom of the bore where I can reach but the piston ring rides obviously

Rusted rings
 

Make sure you have lots of lubricant on the pistons and bores and just turn the engine by hand, a lot. At first, wipe off the cyliner bores at the bottom of the downstroke and re-lube before each piston starts back up.

When the rag comes out with no more orangish-red rust color on it, after wiping down the cylinder wall, you should be ready for start up. (change the oil first!)

When I fished commercially in Alaska, every year there were boats that had stuck cylinders from sitting all winter. Those that pulled the head to free things up used this process.

Those that didn't pull the head just worked the crank back and forth until everything was broken loose and then hit the starter.

Try to feel for any rings dragging as you're rotating the engine; it should be a smooth and consistent turn.

Wouldn't the lip from the rusted on piston ring break off the piston ring once started up? I mean the engine can rev up to like 3600RPM *I think*, the lip feels pretty hard, I could easily remove some surface rust rubbing it off with some oil and a rag but this doesn't seem to come off, its as hard as welding kinda :confused:

But do NOT ! work the crank back and forth. Do a search on here and I believe it should only be turned in the direction of normal operating rotation.
Alan

If you have that much rust on left on the cylinder walls your rings may be shot. Try chipping it off with your fingernail or some plastic. I'd also think that some very fine steel wool would work, something that would just polish the cylinder wall and not actual remove much material. I wouldn't use sandpaper it may be to abrasive. Make sure to get all the dust and bits removed before rotating the engine.

If the timing chain is removed, I'm not sure that it is critical to only rotate the engine in the direction of normal rotation. The reasoning behind never rotating the engine backward is because you can cause slack in the chain and cause it to skip a tooth. But with no chain this is kind of a mute point. But it's always better to be safe than sorry.

I doubt that the rings have broken and deposited themselves on your bore. if the engine is out of the car i would hone and replace rings as a minimum. If not as a minimum I would hone one cylider at a time and reassemble. You may not have done any permanent damage.

If it were me i would ask my favorite machinist to come look at it and pronounce what is needed.

You have to have all cylinders freed up before you start it. The idea is to have any lip removed and clean and the engine rotating freely by hand; before you start it up.

Rotate the engine by hand, if the rings stick on something, figure out which cylinder it is and make it smooth.

A brass wire brush and petroleum jelly works good. You can soak the cylinders in oil. Don't scrape with anything harder than the cylinder walls and if you can't get it smooth, I think Honing is your next step.

Pictures would be helpful showing how much of a lip is present.

Also, how long has the head been off?

Answer
 

If you where able to break it loose by hand; Lubricate the cylinder bore, and ignore it = it will clean up from running.

Never use sand paper or steel wool on a cylinder wall, it leaves an uneven surface, breaks the glaze:

*Requires boring cylinders over size and replacing pistons to match.

*Requires honing cylinders (if within specification for standard rings) and replacing piston rings.

*Requires pressing in new cylinder sleeves and boring cylinders to match your pistons + new rings..

.

Hunter has this right, go slow and steady. I would change the oil after firing and operating for an hour, then follow up with another oil change at 500-1,000 miles. I had a gasser in the same condition, it ran great for a long time after freeing up the previously seized pistons -good luck!

I tried taking out out with my nails.... thats the first thing I did after I found it but its too hard, also the problem is that after you scrape some rust off it sort of falls in between the gap of the top of the piston and bore, the engine is in the car, a mechanic near by told us about the sand paper, but he hadn't seen the bore in person (although described to him over the phone by my father :rolleyes: so its bound to be wrong) so....... its not safe to trust his opinion. I don't want to have the rings break off or something after starting it and maybe have the engine run away! :eek: also if you were to sort of jiggle the crank pulley back and forth is it normal to have some play in the movement of the pistons?

The trick is to put grease around the gap between the piston & bore before you try & remove the rust. That way if any falls, it doesnt go down the gap. just wipe the rust & grease away. If you smear grease on the bore & turn the motor over it will leave most of the rust & crud at the top of the bore.
When I was a teenager we got many rusted up old motors going by just cleaning the bore & then running. Never had a broken ring as a result.

Hope that helps,

Good Luck.

This is off topic but why don't cars have 240V AC outlets? couldn't the alternator do that? so you could have the 240V available only when the engine is running... LOL I could bake a cake while driving or do the ironing :cool:

^ ^ hehe, the mother of all off-topic posts... :) and it's a serious post too... :)

but yeah, I'd like to know too. haha

I have 2 X 240 v outlets in my jeep !! If you want outlets, get yourself an inverter.

Ok so on a serious note, it looks like I could scrape off the rust with a piece of cloth and then rub it out, but when you turn the pulley back and forth there is a, I would say significant amount of play, is this ok? if it is I could get back to assembling the engine :D

Thanks J