Is this a sign of worn rings?

[zeiss150]

the pistons look like they have been "flycut" . Does anyone know if they Fylcut 70 and 71 240's. It would make sence with the E31 head being only 42cc . I just thought that the E31 was still had enough valve clearence. Maybe not:ermm: Sorry I dont have any Idea about the piston edge being clean. If Flycut pistons arn't "standard" then I would wonder who and why they did that to the pistons? Did they shave the head? Or do you really have a loose timming chain? If that were the case I would expect to find vavle damage. more questions than answers. Sorry for messing up your post!

Keep us posted, Matt-

[LanceM]

I would say that the clean areas are from oil wash. I wonder though how worn the rings really are. From the pic the little bit you can see of the second cylinder looks highly glazed. How do the cylinder walls look? if you wipe them dry of oil do they look highly polished like a steel mirror or say look like they have clear coating on them? On a well broken in and used engine the cylinder walls should have a dull used look to them.

If the walls are glazed the rings are not sealing hardly at all. If this happened during breakin the rings may have never seated and because of the small amount of friction may be worn little if at all.

This can happen during breakin and even after if the engine is used for short trips that never allow it to come up to full temp, with light loads. Once the cylinders glaze the engine turns into an oil pump since the rings can no longer do their job.

The first time I saw this was on a 41 Farmall A tractor. When I bought it from this old guy he had said that the engine had been rebuilt 20 years ago and used around the yard by his neighbor, he bought it from the estate and used it to pull grandkids around in a wagon. I get it home and running and it is one smoking SOB. I pull the engine down and find that the cylinders are glazed to mirror perfection. The big suprise was that the cylinders were 0nly .002 over spec and the ring end gap was on the minumum side of the spec. I honed the cylinders and put the old rings back in, broke it in right and have used it since with no smoke and a lot more power!

[240ZMan]

The picture is typical of all 6 pistons/cylinders. This is a 73 L24 and all the pistons are fly cut. The walls are very shiny and glazed. The block is original and to my knowledge, the pistons and rings have never been out. Mileage is 200k+. The last compression test I ran resulted in:

1: 155 psi

2: 155

3: 165

4: 160

5: 165

6: 170

The head was replaced with the E31 head and I was told by the PO that it had been recently refreshed with steel valve seats. So my assumption was that the rings were worn.

BTW, most of the "un carbon" portions are on the portion of the piston next to the sides of the block, not the front/rear. I think this would support the idea that the rings were worn and the pistons had too much clearance, at least side to side, in the bores.

Anyway, that block is now out of the car and my "new" L28 is in. Not sure yet what I'm going to do with the L24.

[SteveK]

240ZMan

In your first post you said that the compression was low on all cylinders and then on your last post you give figures between 170 (max) and 155 (min)

Why do you consider these reading low ?

I have only recently put a rebuilt engine in my car - run it in and am getting 160 -165 across all pots, which I am perfectly happy with.

[240ZMan]

SteveK, in my case I was also burning a quart of oil every 500 miles, even worse when I drove it hard. If my engine had not been using oil and had lower miles, then I wouldn't have been concerned about the lower readings. It was the combination that lead me to believe my rings were worn.

[SteveK]

OK -- all clear now, I'll go back to sleep