Piston rings?

[rio678]

Hi everyone

My head gasket blew the other day back from the shops, managed to nurse it home for 2 miles (started to pink quite badly under load)

It had blown between 1 & 2, managed to sort that all out, since putting it back together it has started puffing blue smoke When started the engine idles cleanly, when revved it smokes then clears if you hold the revs then soon as you idle and rev again it smokes.

Taken the head off once again, replaced the stem seals. I did turn over the engine by hand a few times and noticed a small amount of oil collects at the top of the cylinders. Also the pistons can be moved left to right slightly in the bores. I am assuming it might be the rings that have gone?

If that's the case how on earth do I tell if they are standard or oversized, it's a 1098cc engine.

Thank you in advance

[chrisryder]

if you clean up the top face of one of the pistons you should be able to see if it says '010' or '020'. oddly i did have an engine that said '0.508' which transpired to be a metric value equivalent to 20 thou. if it says STD it's standard, or if there is no mention of 010 or 020 etc then it suggests it's standard too. you would find a bit of movement in pistons in the bore, but i'm not sure how much is permissible.

hindsight is a wonderfull thing, but it could have been worthwhile to do a compression test before removing the head to see which bore it could be. are all the plugs the same colour?

[rio678]

Yep plugs are all the same colour... All were very very slightly oily

I know should have done a comp test , don't wish to put it all back together only to find I will have to replace the piston rings

[Chris Edgar]

Use a piece of plastic or similar to scrape off the carbon. Don't use metal or you will damage the piston faces & may destroy the indented stamping which tells you the size.

[rio678]

Okay I have the following on the pistons

M2007

M25 one says M26

3 with a v underneath it (same on the face of the block) and MOWOG

[bmcecosse]

Just measure the bores. May not be worthwhile fitting new rings - complete new pistons don't cost that much more - so a rebore may be the best way forward. You should NOT have driven the car 2 miles with the blown gasket - it may have scoured the block and/or head where it was blasting through the gap...........

[rio678]

Well it was hardly easy for me to tell what had happened at the time unfortunately

There is no scoring or damage that I can see to the block or head.

[rio678]

60mm on each bore, I am guessing this is standard for a 1098?

[bmcecosse]

Errrr - No! 2.543" is the standard bore size = 64.58mm.

[rio678]

hmmm perhaps I am measuring it wrong

[MarkyB]

Probably, "Just measure the bores" makes it sound easy, which it isn't as you are looking for thousandths of an inch.

[bmcecosse]

Aye - but 4.58mm diffrence is not just a few thou! A digital caliper will easily tell the size near enough to decide if it's been overbored.

[rio678]

I have now honed out the bores ready for the pistons to go back in, what method of cleaning does anyone recommend for cleaning the bores after honing?

[bmcecosse]

Wash with paraffin or diesel oil.

[rayofleamington]

What did you find witht he pistons out?
Also did you measure the ring gaps on the old rings and how bad were they?

[rio678]

rings were worn, bores were surprisingly in good nick, a hone and it was nice and smooth. Measured ring gaps in cylinders and all were within tolerance

All back together now and running once again!