Freeing piston rings

I'm sure this must have been mentioned before, so apologies if I have forgotten previously published solutions.

Last weekend I managed to remove the piston that has been long seized into the cylinder of the Lister CS 5/1 that I rescued a couple of years ago. The rings are solid with carbon and can't even see the gaps at present.

What's the best way to get rid of the carbon so that the condition of the rings can be assessed?

I saw a letter in Model Engineer recently concerning removal of carbon from inside the vapouriser coil of old paraffin bowlamps - heat to red and blow oxygen through to convert the solid carbon to CO2 - would this work for a piston, or is there too much risk of damage?


Reply to
John Ambler
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John, Why not check with David Harris to see if he's got suitable rings and if so break the b*ggers out. He supplied me with some diesel type rings for a Lister B, on which I broke (not deliberately) a ring. I haven't got his number to hand, but he's in SEM in the helpline.

Welcome back!

Reply to
Arthur Griffin

Health and Safety WARNING, this can be dangerous! Don't smoke or have a naked flame close by. If it was me, I'd heat the piston in the workshop and dunk it outdoors. Whatever you decide to do, it's your responsibility to ensure your safety and that of others.

Not mine ;o))

Heat the inside of the piston with a blowlamp. Don't get it too hot or the rings will loose their temper.

When hot, plunge into paraffin. If it catches fire, you've got it too hot, so do it outside and go steady!

If you've got it about right, there will be a slow cloud of white paraffin vapour driven off the bath.

Repeated heatings and dunkings will release the rings, soften the carbon and the expansion and contraction of the piston will also release the grip of the lands on the rings. You may need to tease them out mechanically after the spring tension has released them initially. Take your time, don't rush it.


Kim Siddorn

Bacon is a friend in the salad bowl of life

Reply to
J K Siddorn


In message , John Ambler writes

Soak in a bucket of diesel for a month - maybe two.

Methinks red might be a bit hot... The rings would almost certainly lose their temper.

I have been trying to free rings on a CS 6/1 piston for a couple of months now. The diesel soak was doing the job, slowly. I was springing the rings off slowly, using beer can shim stock to take up the slack and leave a bit of tension on them during the soak. I found the ring gaps using a cheap freebie Hayes modem screwdriver with a Philips bit one end and a straight bit the other - the straight end was just right for digging the crud out of the ring gap and levering the end of the ring up.

All was going fine until I bust the bottom (oil control) ring :-( It snapped like a rotten carrot.

A local plant hire firm managed to get me a brand new five piece ring set in original, modern, Lister-Petter packaging. I'm not sure I have the correct set, though - there were different rings depending on whether the bore was cast iron or 'Listard' chromed. I know the 'later' engines were chromed, but how do you tell them apart and when did they change from cast to chrome? An acquaintance of mine sez that if you run a cylinder hone down a chrome bore, 'it won't touch it'. I've yet to try. The upshot of this is that I may well have a set of standard (4.500") rings for a five-ring piston for a chrome bore to sell or exchange :-)



Reply to
Peter Scales

A lot of modern engines use a chrome plated top ring, and if you try and run one of these in a chrome plated bore, you've got trouble! The Lister chrome bore looks , well, sort of chrome plated, and there should be a Listard plate on the cylinder somewhere. Happy hunting!


Philip T-E

Reply to

In message , ClaraNET writes

I agree with Philip, the shine on a Listard cylinder is definitely brighter than a cast cylinder which can be bright but not shiny. I'm not sure 50's engines had a Listard plate - I now have 3 6/1's from 53, 55 and 57 and there's not a Listard plate to be seen, though the "use distillate fuel" and serial number plates have all survived.

Looks like I'm set for a summer season of dunking. As soon as I got the engine home, I filled the top end with diesel, and was surprised to see after almost 2 years that when the cylinder was finally persuaded out of the cylinder that the sides of the piston were dry - penetration had been minimal.

Reply to
John Ambler

In message , John Ambler writes

This particular engine dates from the end of 1950. I was taking a look at the bore again last night - I think it must be chromed. Wear is negligible, the rust streaks just rub away with gentle finger pressure, and it looks shiny and, well, chromed :-) No 'Listard' plate, though - all other plates present. This probably means my rings will be OK.

Mine had been left outside with the exhaust valve on the decompressor and the inlet open. There was half an inch of water/rust on top of the piston when I finally got it apart. The piston was seized in the bore and I had to persuade it out with a 4 x 4 and a lump hammer... All rings were solid with carbon/rust and the piston walls were dry. I finally got the oil out of the sump last week - no apparent water in there either.

Reply to
Peter Scales

On Tue, 8 Jul 2003 08:40:07 +0100, Peter Scales wrote:es have all survived.

I don't think all cylinders had the plate, only the early engines from the start of the chromed cylinders when they had to differentiate from the ordinary types already in service.

Kind regards,


Peter Forbes Prepair Ltd Luton, UK email: home:

Reply to
Prepair Ltd

In message , J K Siddorn writes

There *is* a step - must be at least a quarter thou...

Reply to
Peter Scales

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