gbgastowers

I know I'm gonna get ripped for this but it never hurts too bad to ask. If you have identical 4.7 Euro S blocks(90k M28/11 and M28/12) with identical tolerance pistons can you switch the good rings,rods and pistons to the block with the bad rings(low compression 30-60 in all 8)? I think the answer is new rings on the bad blocks pistons but I want to verify since my extra pistons w/ rings "look" good. Gunar

GlenL

Pistons: yes.

Rings: no.

Check for tolerance groups. These are the 0, 1 and 2 stamped on the pistons and the holes. As the blocks get worn you may be able to use a larger number in a formerly smaller hole. 0 is smallest.

Roy928tt

Rings have a measurable wear indicator, remove a top ring and fit it into a bore that you intend using it in, push it down the bore with the piston you just removed it from till it is at the most worn part of the bore (the height of the piston crown down the bore, you will see where it should be.) now the ring is sitting in the bore as it would under use. You need to measure the end gap, the gap between the ends of the ring, using a set of feeler gauges.

Unfortunately I can not for the life of me remember what the rule of thumb is for that gap, xx thou per inch of bore diameter.

I guess, also fit one of your Bad rings and see what gap that has, presuming that those rings are worn out that gives you an upper limit, work it out from there.

I once built an entire Mini engine from second hand parts which was then turbocharged and drag raced, it eventually knocked out one of the second hand big end bearings. but not before before laying down a respectable time and providing hours of entertainment. There is something quite satisfying about turning worthless pieces of engine into something that works, with your own hands.

Good Luck

Cheers Roy

dcrasta

U can definitely reuse pistons that are mechanically sound, but rings are wear items and should be replaced. I think this is a situation where it would be pennywise and pound foolish to reuse old rings..

YMMV.

mark kibort

yep, always replace the rings. they are expensive, but you should be able to find some deals on them.

we pulled the BMW 5 liter engine apart and the rings were gaping about .017', new rings were in the .012" range. they also were a little different, almost .2mm thicker width. thickness was the same. so, who knows. his rings were $1200 per set from the dealer. (dealer item) he also has the same type of AluSil block as us with coated pistons.

mark kibort

those are pretty clean, for very old pistons. not much carbon, but lots of gunk on the side. they need to be cleaned professionally. there is not much side coating left, so whoever cleans them should be careful. not so much on the tops, but the ring lands need to be really cleaned. re-ring and go.

what did the bores look like?

karl ruiter

I think the WSM has a procedure for measuring the end gap and testing the wear limit. But when I pulled apart my last motor the old oil rings were super brittle and just shattered. So there is something that can go wrong with them other than wear. I suspect they had been too hot, but I can't really say and I don't know how you would test for it. In my case there is no way the oil rings would have ever come off the pistons intact.

Landseer

Gunar, FWIW I'll make the run south to help you attack this thing.

gbgastowers

Thanks- I'll let you know. My wife has me doing some other things first but I'm still sneaking out some. I have the CIS off and was going to do some flow testing on it off the car. If your coming anyway for your folks, by all means stop by. Gunar

928mac

So now that you know what you should do.

I had a 69 nova.
one night on a booze run to a bar in ontario at a maintained speed of 140 mph down a secondary road for 15 mins Bang.
lost a cylinder, but continued on.
After the bar closed drove him home. Drove home 1/2 hr the next day and pulled plug wires and then the plug of the dead cyl.
plug end smashed.
removed the one side intake and then removed that head.
A chunk the size of a dime broke off the piston from the ring land.
I pulled the pan and slid the piston out.
Slid one in from a junker 350 block sitting outside after I cleaned it with some carb cleaner.
I put new rod bearings in while i was there.
There was a nice/bad scratch on the bore.
It burned oil for 2 weeks but cleared up.

Its called mop and glow and away we go.

It was a $800 car and a beater for work.

Should you do that to yours .... your choice.

Normally only done on a demolition derby car.

gbgastowers

The bores off the 1st engine that had the metal piece stuck in the ring. This is where my extra pistons/rings/rods/rod bearings might come from.

WICruiser

Unless there are no other options always use new rings. Old rings have been worn in relationship to the bore they came out of and even though they should rotate they never seal the same once they have been run, regardless of the end gap, or the bore they are put back into.

As was stated above the pistons should be fine (using the right select fit number) provided tha tthey are cleaned and still have their suface coating.

There is a lot of action going on in a small space between the piston and the bore. High pressure, high temperature, etc. so it doesn't take much to screw things up. The bores are what they are because you do not want to do any thing to them. The means the pistons need to fit correctly, and the rings need to have the right clearances on the edges and the right tension against the bore to do what they are designed to do.

Mrmerlin

to clean the pistons soak them in simple green full strength then use a tooth brush to scrub them thats all you do ,
dont use any other type of abrasive as you will wear off the chrome finish,

the finish is a dull green color,
rinse them off with hot water then spray with WD 40

namasgt

Simple green eats Aluminum, I wouldn't use it. I would use this stuff from berry man, http://berrymanproducts.com/Default.aspx?tabid=146

I would use the first one, Part #0901 NET 1 Gallon. If your pistons are reasonably clean it should only take 15 to 20 minutes for the piston to look like new and it will not damage the coating. only use a tooth brush to clean the carbon off the piston tops and ring lands. Let the piston sit in the solution for 15 minutes then take it out and use the brush. If it still has some carbon left you can put it back in the solution for another 10 minutes and try again. When your done rinse them off in a parts cleaner or just use break cleaner to get the chemicals off. Autozone only carries the second one on that page, but its not strong enough and you have to spend a longer time cleaning the engine parts. Car quest is the only place that I have been able to buy the first one. It should only take you 2 to 3 hours to get all the pistons clean.

dr bob

The ring lands in the piston are critical. When rings stick in the lands it's often the death of the piston. Lands need to be intact and able to support the rings, holding them perfectly square with the bore. The grooves can't be so worn that the rings move/flutter in them as the piston moves, else there will be oil left on the bores and the pistons will quickly look like the ones you show.

The rings themselves need to have enough tension to stay tight enough to maintain a seal in the bore, yet not so tight that they have too much friction in the bore. It's a delicate balance. Old rings lose that spring, especially if they've been abused by overheating or detonation. Excess oil left on the walls will cause a lot of detonation, so you can imagine that it's a slippery slope after just a little oil passing.