Blue smoke from exhaust at high rpm

[K Simmonds]

Thanks for uploading such a good photo. I've just blown that right up on my laptop and can see the top edge of the piston appears to be slightly damaged, though that could be a visual distortion.

And yes, while that score itself might not be the sole cause of your oil burning it is indicative of damage caused by bore washing.

You need get the pistons out next to see how badly they are damaged (if indeed they are), you could be lucky and it's just damaged the rings but I'd be expecting to see damage to the skirts at the very least.

The block will have to be re-bored to sort out that scratch, it looks far to deep to hone out unfortunately.

Is only one bore scratched like that?

[K Simmonds]

I've just looked at that photo again in great detail, that bore is covered in small vertical scores, non of which should be there, I bet every bore is the same given the wet compression test result. That one just happens to be the worst.

[Bowie69]

Possibly, you sure that's not a crack? Looks jagged towards the bottom.

Either way, that bore looks well worn with many light scores, it needs a hone at the very least, probably a rebore, or a sleeve if that is a crack.

[K Simmonds]

You know what.... I've just looked again as closely as I can and that could be a crack, though these block's are pretty robust so I doubt it. I'd say it's more likely to be a nasty fresh scratch and suspect it gets worse bellow the top of the piston, it's likely to deepest where it bottoms out or very slightly above that point.

I'm very interested to see what state the pistons are in.

Feel sorry for the owner though, it's going to need a re-bore at the very least, so new pistons as well rings even if the pistons aren't knackered, which I suspect they will be.

If it's cracked I'd write the block off, be cheaper to get another one and start from scratch.

[Mikemul]

All pistons out. Nothing to see on it, pistonrings looks new. But the gap between the ends are a little big and not straight. There are two cilinders with a scratch inside the wall it is no crack

[K Simmonds]

Well you must have caught it in good time for the pistons to look absolutely fine still, the unfortunate thing is they are now useless to you as your going to have to go to first oversize of re-bore to get rid of those deep scratches.

At least you can sell your old pistons.

I've just blown the image of the piston up on my lap-top, right where your thumb is there are vertical scratches on the wall of the piston, they certainly shouldn't be there. Those pistons might be okay still, it's really hard to tell from a photo.

[steve briance]

I looked at oversize pistons for my 7A a few years back and found a Wiesco set.

They were around £900 and the block would have needed boring out to suit. I got a 3B block which was bored out to suit my standard pistons and a new set of rings. 14.7bar compression on each cylinder and all at less cost than going 7A oversize.

[K Simmonds]

That's good thinking Steve, though unfortunately gone are the days of cheap 3B blocks, he could get lucky though and pick a damaged one that already needs a re-bore.

[steve briance]

Well, as long as it costs less than a set of oversize pistons its still winning!

Only thing needed to do was replace turbo coolant feed core plug with a standard one and make a blanking plate to close off turbo oil feed return line. 7A standard size pistons are pennies to buy as there is no market for them so picking up a better set than is currently in it won't be too hard.

[K Simmonds]

Fair point point mate, I'm sure one can pick up a serviceable 3B block for 500 Euro's tops on the continent, so as you say even if those pistons are knackered, which I simply can't tell from the photo, he would still be winning. Changing a core plug is no hassle at all along with making a blanking plate!

Or of course one could simply buy a good replacement 7A bottom end or even a complete engine, getting a complete motor would probably be better as the head's now go for good money.