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Piston rings too thick

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Andrew Phillips 406/02/2019 19:08:37
12 forum posts

Hi All, I frequent autojumbles, looking for stuff for my '50s AMC singles. A while ago I picked up a +60 piston, sans rings, always useful to have in reserve. I recently found a set of +60 rings for a fiver, but although the 2 compression rings fit, the oil control ring is a couple of thou too deep top to bottom. I have a book from the 30s that describes how to make piston rings on a lathe, but it is a lot of hassle. I thought a simpler way would be to put the ring on a surface grinder and take a thou or so off top and bottom faces. I might be able to do this at the local tech college, or pay an engineering firm. Any thoughts? Cheers, Andrew

Emgee06/02/2019 19:24:16
1442 forum posts
212 photos

Andrew, taking 2 thou off the ring thicknesswill not damage it at all, just need to make sure it can compress enough to get below piston diameter.


John Rudd06/02/2019 19:50:09
1367 forum posts
62 photos

Cant you make the ring groove slightly wider? Chuck the piston in the lathe and use a 'parting' style blade?

Or have I misinterpreted the dilemma?

Andrew Phillips 406/02/2019 20:54:34
12 forum posts

Hi John, I had thought of that but making a mandrel and some sort of drawbar to fasten to the gudgeon pin seems a bit tricky. Worth a thought, though. Andrew

martin perman06/02/2019 21:45:49
1808 forum posts
78 photos

Thick piece of glass with fine emery cloth laid on it then put some water on the cloth and carfully rub back and forth checking for size every other pass.

Martin P

Phil Whitley06/02/2019 21:45:56
1145 forum posts
142 photos

You could use a surface plate, or a sheet of plate(not float) glass with sone fine abrasive paper, and flat it on both sides, done it a few times, not as hard as it sounds, as long as you know the clearance you are aiming for!


Phil Whitley06/02/2019 21:47:11
1145 forum posts
142 photos

you beat me by seconds Martin!!

not done it yet06/02/2019 23:42:12
4477 forum posts
16 photos

I increased the width of ring grooves on an engine where the rings were very flimsy. Can’t remember whether I had to do one or both compression ring groves. Engine ran OK afterwards and is likely still going as it was a diesel. Oil control ring was left original. I dare not try to thin the new rings on that one.

A long time ago (over 30 years) one ring on a 4 3/4 inch bore would not seat at the bottom of the groove (piston crown had been hammered by a valve dropping into the engine until the engine seized) so I filed the inner corners of the ring. Engine is still running well, but I was expecting the honed bore to wear out the rings on that piston as the hone seemed to hardly have any effect, I thought.

Neil Wyatt07/02/2019 13:11:20
17703 forum posts
697 photos
77 articles

One way is to make a wooden disc with a short boss to fit the inside of the ring.

This makes it very easy to work the ring evenly on a sheet of abrasive, probably laid on a surface plate/sheet of glass.


Andrew Phillips 410/02/2019 21:46:18
12 forum posts

Thanks for your replies; thinning the ring using emery on a surface plate is the way to go. I have a suitable piece of engineering plastic to make a holder, as Neil suggested. Cheers, Andrew

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