Piston and cylinder scoring.

[sharpeyie]

Hi all.

Had the head off Z1B recently and noticed some marking inside cylinder #1 which was re-sleeved about 500 miles ago. Also some scoring on rear of pistons 1 & 4. Wonder if anyone has any idea what is going on here? Given it is so few miles since the sleeve at least was renewed I am concerned about it.

Thanks.

Stewart

[zed1015]

A tricky one as skirt scuffing like that is not uncommon with contaminants in the oil and normal wear etc and i would have suggested that maybe the clearances were done a little tight on the resleeved one but #4 looks worse unless it's the pic angle.
Were all the bores bored or honed and if so were they washed down with soapy water or solvent before assembly ?

[sharpeyie]

A tricky one as skirt scuffing like that is not uncommon with contaminants in the oil and normal wear etc and i would have suggested that maybe the clearances were done a little tight on the resleeved one but #4 looks worse unless it's the pic angle.
Were all the bores bored or honed and if so were they washed down with soapy water or solvent before assembly ?

I know what you mean wbout #4 looking worse. None were rebored all were honed. Were they ‘washed' down is subjective.... they were cleaned but possibly not adequately. The rings were replaced according too ‘old’ instructions and subsequently have been identified as an issue (notched one upside down - smokin’ like hell.) That’s why the head is off as they’re being replaced - correctly this time. Just didn’t want to ‘entomb’ a known/existing problem - which is why I was most concerned about the scoring on the new sleeve. The other sleeves are relatively unmarked.

Tell me this, is there anything here you’d be worried about?

[zed1015]

I'd suspect that the bores weren't washed with warm soapy water which lifts and carries away trapped grit as opposed to solvent that just degreases the surface and leaves dry microscopic abrasive particles from the honing process in the resulting crosshatching which then scuffs the pistons.
I'd say any damage is already done so it is what it is and shouldn't get worse..
If new rings are going in it's pot luck whether they will seal correctly ( or take much much longer to bed in ) without another "light" hone which would be the correct thing to do if it doesn't push the clearances too far .
Either way a proper wash of the bores with soapy water and wipe clean with a white lint free rag until no discolouration of the material is achieved will ensure the bores are clean especially in the unswept lower area of the bore where the rings haven't scraped the bores clean .

[sharpeyie]

That's much appreciated. I was planning to re-hone again before the new rings. I'll make sure they get the soapy wash (which I know they didn't last time.)

Hopefully the little damage that has been done this time is what it is and not too tragic.

Thanks again.

Stewart

[Gray17]

Hi just noticed your post, as you will see i ended up stripping my full engine down to enable vapour blasting, when i look at my pistons after some 20+ thousand miles they also had very light scoring on the skirts but not as pronounced as yours, of course I've no idea if the engine has been refreshed in its 40+ years assume yes, although its still using original ART pistons and on standard size.
I used very fine wet and dry, then polished with solvol and washed all there was no other wear in bores or pistons so there going back as is, the head however is a diff matter see my other post.
Its always difficult to know how far to go and what to and what not to replace in these situations, guess it comes down to size of your wallet! Hope all goes well with your rebuild, of course mine didnt smoke before i stripped it so yours has diff priorities to mine.

[sharpeyie]

Hi just noticed your post, as you will see i ended up stripping my full engine down to enable vapour blasting, when i look at my pistons after some 20+ thousand miles they also had very light scoring on the skirts but not as pronounced as yours, of course I've no idea if the engine has been refreshed in its 40+ years assume yes, although its still using original ART pistons and on standard size.
I used very fine wet and dry, then polished with solvol and washed all there was no other wear in bores or pistons so there going back as is, the head however is a diff matter see my other post.
Its always difficult to know how far to go and what to and what not to replace in these situations, guess it comes down to size of your wallet! Hope all goes well with your rebuild, of course mine didnt smoke before i stripped it so yours has diff priorities to mine.

Thanks for that. I came on the forum this afetrnoon to ask if I should go at the pistons with some wet n dry..... so there we go.

Presumably the cylinder ‘seal' is created by the top ring and the top of the piston and therefore the lower part really plays little part in that aspect - have I missed anything with that statement??

What I did spot was that the scoring/wear shown in the barrel in my photo posted yesterday, aligned perfectly with a little nick in the bottom of the piston (see new photo.) My assessment is that when onnthe table and the head was off but pistons still in place, that the crankshaft was turned and the piston moved down and basically snagged off the top of the crankcases causing this little nick (there are similar ones on other pistons. I’ll put money on the nick having flared the alloy out creating a minute protrusion which has caused that line in the barrel.

[Gray17]

To be fair all rings play their part, the top ring does indeed form the initial compression seal, however the 2nd ring then takes care of any of the compression that leaks past the 1st ring.hence reason ring gaps are staggered 180 apart. The oil control obv controls the oil preventing excess entering the bores.
The skirt should be smooth to avoid creating excess wear without any high spots hence why i use very fine wet and dry to smooth off any wear marks. Obv dont go roo far with this as long as its smooth, you dont want to go at it with a file and weaken it.
Also pay close notice of any cracks or large gouges which would then need replacement.
Thats my take, others may advise different, but as sods law states we pays your money and takes your choice.
Good luck

[sharpeyie]

To be fair all rings play their part, the top ring does indeed form the initial compression seal, however the 2nd ring then takes care of any of the compression that leaks past the 1st ring.hence reason ring gaps are staggered 180 apart. The oil control obv controls the oil preventing excess entering the bores.
The skirt should be smooth to avoid creating excess wear without any high spots hence why i use very fine wet and dry to smooth off any wear marks. Obv dont go roo far with this as long as its smooth, you dont want to go at it with a file and weaken it.
Also pay close notice of any cracks or large gouges which would then need replacement.
Thats my take, others may advise different, but as sods law states we pays your money and takes your choice.
Good luck

All noted. Thanks.

Stewart.