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Following an unfortunate lift home courtesy of the AA, I have now investigated the problem. Broken piston rings. In the absence of any in stock at Mdina, where is a good place to order some? I'm thinking of full sets for front and rear and according to my measurements they are standard 62mm.

1980 Strada.

King of Pistons Italy - if they still will deliver to the UK?

https://www.thekingofpiston.com/collect ... morini-350

How are the pistons themselves? If they aren’t great then Mdina do have complete 62mm piston, pin and ring sets for what I would say a very reasonable £100. They also have 64mm so a good excuse for a few more cubes

Pistons don't look too bad, although could do with a brush off.

64mm hmmm, tempting but will need to rebore the cylinder....

I'll have a look at King of Pistons, thanks.

The King of Pistons rings are 62.4mm, so would probably need new pistons anyway.

Have you checked the bore itself to see if it is within tolerance? No good replacing rings if the bore is worn.

It is a hard decision, but one that needs all the components to be in good condition.

I sent mine to SEP at Kegworth who measured up the bore and looked at the pistons, all I needed were new rings, which NLM supplied, and a hone.

I kept my old and slightly scored pistons and rings, well they might be all there is one day.
I do know someone who got a better fit by centre punching around the edge of the crowns, on a lorry engine.
Best not to think about that.

MickeyMoto wrote: ↑17 Apr 2022 12:29 The King of Pistons rings are 62.4mm, so would probably need new pistons anyway.

Have you checked the bore itself to see if it is within tolerance? No good replacing rings if the bore is worn.

It is a hard decision, but one that needs all the components to be in good condition.

I sent mine to SEP at Kegworth who measured up the bore and looked at the pistons, all I needed were new rings, which NLM supplied, and a hone.

Good Point. They also seem to list individual piston rings in various diameters and thickness if you browse their site.

i've had excellent service from these guys
https://www.thn.nl/en/
Just make sure you know exactly what you want, and they can provide the rings.
usually cheaper than OEM too.
i have a couple of oddball engines where spares dried out decades ago, they have been able to provide what is needed so far.

just dont start a email conversation about a single oil control ring costing a couple of euro, they have a business to run.

If you can only get the 62.4 rings then you could simply 'gap' them to your worn bore diameter, gapping should be done with the rings at the bottom of the bore. Even with correct sized rings gapping would still need to be carried out, no gap results either in very quickly worn bore or broken rings.

gapping should be done with the rings at the bottom of the bore

I have a question about this. Looking at my 3 1/2 Sport barrels, and the wear marks on the bore, I can see the rings do not travel all the way down. They stop about 4cm shy of the bottom of the bore. So, should measuring be done at the bottom of the bore (where there is going to be no wear), or 4cm from the bottom?

One other thing, I believe the bore is tapered.

It makes no difference whether the bore is machined with a taper or not. As you would expect on ANY engine the bore will always wear tapered, so if gapping on a used bore then gap at the least used part of the cylinder the bottom. You only gap rings at the top if it is a new bore, but it won't make much difference if you think about it. I would suggest Morini only employed a tapered bore to quieten the engine by reducing piston slap. Having fitted Omega pistons to a couple of Morinis of mine the bores were always bored parallel which made no difference to mechanical noise always quiet.

Im surprised no-one's mentioned Cox & Turner in Yeovil. Amazing old-fashioned service. They make piston rings, often send them out pre-payment on trust, virtually next day, providing you have some rings they can match, not dear either
They cant supply for Nikasil bores (but then as I discovered after 4 engine removals and top-end rebuilds on my 501 engine, investigating harsh running and oil-burning on a new engine, nor could North Leicester Motorcycles, until I fitted OEM rings from Italy)

That is a very useful engineers, I had forgotten about them. I have some standard Strada pistons and barrels on my shelf but they do not have rings, and some oversize Sport pistons with rings but one is scored and I think the other has a crack near the pin.
John

You could try https://www.tremezzo.de/impressum.html