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MG MGA - Starting with new pistons and rings

Broken scraper ring and damaged piston so all four cylinders have new. The engine turns freely on the starter motor but not yet run up. It's an age since I rebuilt a petrol I.C.E. and I have a vague memory of injecting some upper cylinder lubricant before starting. Does anyone have any tips ? It's a 1500 bored out to 1588 - a very tight fit (no rim to speak of)with standard rings.
Roger Walker

I would just squirt some engine oil in each plug hole for first start. No high revs for a while.
What do you mean by a tight fit?
Art Pearse

Art - thanks; yes, I wondered if it should be engine oil.
Tight fit leaves very little room for further ring compression but leaves the pistons free to move.
Roger Walker

Did you measure your ring gap by placing rings in the cylinder before installing on pistons?
Mike Ellsmore

Mike - simple answer "Yes". The gap though was very small.
Roger Walker

According to the Workshop Manual, the Fitted Gap for the piston rings should be .008 to .013 in.

Jim
JL Cheatham

Jim - useful detail - with a torch I could see through the gap - just.
Anyway she runs ! Only four small bolts to go in the front edge of the sump - then it's done
Roger Walker

If thr ring gap is too small, upon heating up and thr ring(s) expanding, you likely can or will break a ring.....usually the top compression ring. It sounds like you did not actually measure them. Maybe should check but sounds like engine may already be assembled? Your choice, but I would do it. I have found guessing is not conductve to good engine assembly.

Regards,
Brian W.
ZBMan

As Brian says, the gap will close. The piston runs hotter than the cylinder. If too close you could seize up and need a rebore etc.
Art Pearse

Don't worry Roger

Although it's normal practice to measure ring gaps during assembly, most commercial ring sets now come pregapped to suit the bore size they are ordered for--rarely do they need adjusting and most likely because it's a used bore they will be up on spec a bit anyway---It's usually only custom ring sets that are ordered ungapped that need adjusting to size----There are piles of opinions on what size to gap rings at but mostly for a roady around .003"/inch of bore is the go, so around .009"+

just drive it like you stole it for the first lap round the block and she'll be fine--

willy
William Revit

Many thanks for all the advice. I shall follow Willy and drive her gently for a few weeks and then do a compression test. The results will be seen here.
Roger
Roger Walker

This thread was discussed between 24/10/2021 and 26/10/2021

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