Piston Rings

[moodyblue]

I recently purchased a set of piston rings for a new old stock engine block I'm rebuilding and I'm a bit confused as the two top ring look identical. There is no chrome compression ring and both look like dark grey cast iron and both have the TOP marking, which in the past meant the top side of the middle ring. Does anyone know if the top two are actually identical and why they decided to change to this type of rings. I haven't checked the the ring gaps in the bores as I'm assuming because the block and pistons are new all should be fine.

[Hasbeen]

You lucky boy.

Back in my day even F1 & F2 rings were cast iron only. They are much softer on the bore than chrome rings. Chrome rings were introduced to extend the life of the rings, at a cost of increasing the wear on the bores. This meant that by the time the rings were worn, the bores required a rebore to be useable.

With today's much better oils, & modern oil filters, bore wear should no problem whatever ring you use, & cast iron rings should also have an extremely long life. I expect a well built & maintained engine in a toy car, like our 7s, with the best available oil & filters, will outlast most owners & their kids.

Don't under any circumstances trust ring gaps will be suitable as supplied. Those lovely cast iron rings will snap very quickly if they have insufficient gap. I would expect the suppliers would be catering for standard engines, with a thou or 2 wear, & a honing, so the gaps should need increasing in a new stock bore.

Hasbeen

[moodyblue]

Thanks Hasbeen, good advice as always.

[nick]

If you measure them I believe one is slighly thicker. I just went through this exersise while installing the 9.5:1 pistons into my sprint conversion project.

[moodyblue]

Thanks for the info Nick. I didn't notice any difference, but I'll check tomorrow if I have time as I'm rebuilding the engine at work.

[moodyblue]

Well I checked today and the rings are the same width and thickness about 1.72mm. Anyway I now have a bigger issue to worry about, on inserting the rings in the bores I found that the ring gap is only 0.004", and they should be 0.015" - 0.025". I tried another good used rings (chrome) and it's 0.019", how on earth could they get it so wrong? Surely these should be manufactured to original specification, the buyer shouldn't have to start removing material just to get them to the correct size. It seems like one step forward and two back with this project, mostly down to poor quality parts from suppliers.

[Hasbeen]

Easy there Moodyblue, it is not a big deal, one advantage of those cast iron rings. They file very easily. We always used a points file back in the day, & just a few seconds each would remove the necessary few thou from the end of the ring. I don't know if you can still get points files over there, but even a diamond nail file will do it very quickly.

The main thing is to be careful, as they are very brittle. You don't have to stretch them very far for them to snap, hence the preference for a thin file. The same applies when fitting them to a piston.

As I said, ring suppliers have to cater to a range of bore sizes they may have to fit. To use the rings in a perfectly useable engine with a little wear requires replacement rings to be a bit too long in circumference than a new stock bore, but filing is quick & easy.

Just think, you are going to be a real expert after this.

Hasbeen

[moodyblue]

Yep, I think they must have decided that all the engines that these rings would be fitted on would have done over 60k so they gave us some extra material for free

[FI Spyder]

Yep, can't be too many never used blocks out there. You can always file a few thou off. A little harder to add it back on.

[moodyblue]

Given the choice, would you guys prefer to fit these new Grants cast rings or the very lightly used ones, unknown make but original spec. bought in the late 90's I think, with chrome top ring? Just thinking about saving myself some grief sorting gaps out and I like the idea of these original spec. rings. They're not as wide as the Grants for some reason but having compared them with a genuine old set they look identical which is encouraging.

[Hasbeen]

I would reckon I'd won the lottery if I found a set of new cast iron rings. 20 minutes spent filling the gap would be a joy, to have them.

Why are you rebuilding the engine if the rings are only lightly worn? Have they ever been overheated?

The only rings I have ever reused were the cast iron oil rings in my TR3 & Ford Cosworth engines. I used them to avoid the horrible chrome segmented things the manufacturers had gone to, in an attempt to make engines use no oil between changes. I never could see any reason for this in engines that used very little anyway.

Hasbeen

[sonscar]

Whichever rings you use it is important that not only do they fit the bore but also that they correctly fit the pistons and that the pistons themselves are also serviceable.but I guess that this goes unsaid?Steve..

[moodyblue]

I had no choice as I found a small crack in the original block so I bought a new one. About 5 years ago I bought a new set of original spec rings but I think that that cast rings are all that's available now.