Tony

At what point do piston / cylinder scratches need to be addressed.

How are they "fixed"..if at all?

Funny thing is, the worse of the marks(1st pic below) is on a piston that came out of a cylinder with one of the best leakdowns!

Is it common to see a number of marks/scratches along he skirts?


nasty huh! I have no idea how this was created?


others....

Lagavulin

It's better that the piston has the scratch on it's skirt versus being on the cylinder wall. That way, the compression rings are above the scratch on the piston, and they can do their intended job and seal 'perfectly' against the un-marred cylinder wall, thus the reason you have good leakdown/compression result.

UKKid35

Do you have any pics of the cylinder walls? I know mine have lots of scratches and I'm beginning to wonder whether I've made them myself since taking the heads off.

tresamore

I doesn't take much to get a scratch. Something gets in the oil. A little vac leak sucks up some junk. You can go crazy looking at these motors after they're apart. You just have to make some judgement calls and put it all back together or spend a small fortune and redo everything as it came from the factory. I was going nuts after I had my 87 apart, but after a few phone calls, some trips to the machine shop and quite a few posts here as well (and quite a few $$). I was on the return end of the project and hopefully will finish it someday soon.

atb

I've got a whole slew of stockers in excellent shape if you're interested Tony. I'm keeping a couple for experimentation, but I'd let the remaining ones go pretty cheap.

Jim bailey - 928 International

I often think that what you do not know can be better . Small scratches may have little or no real effect on compression or blow by , oil consumption and such engines may run great . But when pulled and inspected like doing a valve job or changing bearings the tendency is going to be wanting to make it "perfect" . This is when a $4,000 valve job becomes a $10,000 rebuild . The scratches on the cylinders can only be fixed by boring / honing to oversized and buying new pistons or the block can be nikasiled (plated ) then honed for the standard size piston . Given the "experimental " nature of this engine and the fact that you are not paying for labor ......probably run it as it is . Besides we all know eventually you are going to stroke it any way !!!!!!!

WallyP

Scratches on a piston skirt are not very serious.
In fact, one or two scratches on a cylinder wall have virtually no impact on performance.

Lagavulin

Hey Wally that's good to know. When I changed my head gaskets, I noticed that 3 of my cylinders have a singular scratch running down them. I wasn't too happy about it at the time.

Jim bailey - 928 International

Most of the engines we pull apart will have small visible scratches in the bores . It only needs a small loose piece of debris to get lodged on a piston for a bit to leave such a "mark" .

Tony

Thanks a bunch guys.

I thinks Jims philosophy is right on. As much as i would like to make it "perfect" it ain't gonna happen. Kinda goes against the grain in the way i think but i know it would be a steep slippery expensive slope to make it "perfect" The whole idea is to keep things as cheap as possible, as stock as possible and as reliable as possible in this little rebuild/SC motor, keeping variables to a minimum. That in itself can be a juggling act. . My experience in this 928 engine building process is Very limited so im drawing on all of your knowledge and opinions as well. The manuals as you know are vague and what you see in them cant all ways be interpreted from a written description.

After machining, ceramic top and new rings/bearings, they are going back in to their stock matched bores..


thanks