Hi

Some repairs are underway, as with all work a journey of discovery where I find a little bit more is needed. Anyway, while the block is off and the piston is revealed I've been discussing the work with a mate, via email and photos. He's an experienced engineer and has lots of background in car engines, including racing engines. His comment on the piston, an NOS item was get "a more modern 3 piece oil ring (the bottom one) those old one piece cast oil rings are crap really, they stopped using them in the 50’s."

That reminded me of Cords Rings which were employed when you engine was generating too much smoke, back in the day.

Using the wonders of the internet to understand the operation a little better than just the 1 is compression, 2 is scraper/compression and 3 is oil control then I can see the logic of a 3-part ring because it leaves a gap for oil to return, and I can see the sense in keeping oil away from the upper rings.

The bore size seems to appear in rings catalogues, so there may be one available to fit the groove size of my NOS M20 piston. But would it be worthwhile?

Does anyone have any experience with a 'modern' oil control ring in an M20?

Any comments will be helpful in distracting me from finding more things to fix rather than actually getting her back together for the run in a few weeks....

Cheers

Richard

email (option): dickie.bobbie@hotmail.co.uk

You will often get such comments from people more familiar with modern engines who think everything old is rubbish...

I bought an M21 from someone many years back that was owned by the chap from new and had 104,000 miles on it..It had never had a rebore though the rings had been replaced once in that time....

So, the original rings can provide very long service with totally acceptable oil consumption...

I have used three piece oil scrapers many times in BSA engines...In fact my own oversize M21 is currently fitted with rings of that type...However, that was only because they were fitted to the (new) forged piston that I used...

One thing I have noticed with American ring sets which I am never entirely comfortable with, is that they run very high ring to bore pressures when fitted initially...I modified the 'spring' element of the ringset I used to reduce this somewhat. It was actually impossible to turn the engine over by hand on the bench with the head off...
The engine has run reliably ever since. I have fitted numerous examples of this type during engine rebuilds over the years.....

Another thing to beware of is the tendency for people more familiar with modern engines to recommend a reduction in tolerances to make them closer to those of a modern engine...DON'T DO THIS without first determining what is possible...Some tolerances can be 'tightened' and I have experimented over the years to determine what is possible and what is best avoided...However,it is probably best to stick to the original specs. unless you want to go down that route and have access to a fully competent engine shop to carry out the work...

In conclusion I would recommend fitting the original rings that you have, making sure that they are 'gapped' correctly prior to fitting...

I wouldn't regard the fitting of a 3 piece scraper ring as an 'essential' modification at all....(assuming you're not racing your M20.. )..Ian

email (option): ian@wright52.plus.com

If you are concerned about oil consumption and want to reduce this, you may want to machine a shallow recess just below the oil ring, about 0.020" deep and about 0.150" high. Then drill a few holes radially through to the inside of the piston. Oil scraped from the bottom of the oil ring then has somewhere to go. I have done this to a number of pistons on old machinery.

email (option): pvlietstra at gmail.com

There are allready holes in the piston behind the oil ring

John

email (option): john.kater@chello.nl