The Stovebolt Site Forums The Shop Area Engine Shop Which piston rings are better?

Good Morning all

I am about to start an engine rebuild on the 58 vintage 261 in my 54 Chevrolet pickup. It is a used engine which has 130lbs compression that I decided to runs as I got it. It still has great compression and nice power but blows blue smoke out of the tail pipe (added content -->) during acceleration.

My question
I was always told that chrome-moly rings were better than cast iron rings because that were designed for racing. My question which is REALLY more durable and makes for a longer lasting engine? Cast iron or chrome? Is there another option out there now? I am currently using my classic pickup to get to class with. I need an engine that will last a while under normal driving.


Before the question can be asked: I don't romp and stomp and tear around in my pickup. Its just too much fun putting around and seeing the looks of admiration on peoples faces.

Walt Williams
La Verkin, UT
(I suppose you could say I am gaining a little wisdom in my middle age in that I am questioning what I thought I knew.)

Racing engines are designed to run a very short time...compared to street engines. Not exactly what your looking for.

If your just looking to 'clean up' your tail pipe emissions have you determined it's actually the rings that are the problem? Could just as easily be valve guides... What compression and leak down tests have been done?

You would have far better luck using cast iron rings. I wouldn't go so far as to say chrome plated rings are for "racing" engines but they will require a much longer time to seat and therefore iron will seal better and faster for oil consumption. Chromes advantage is that they wear slower and therefore last longer. You will often see iron compression rings and chrone rails on oil rings. One piece oil rings are often chrome too for HD applications. So each has it's place but the application is the key to longevity. It could well be valve guides, seals or other things causing your smoker.
Its' iron for your intended use.

With clean oil and air, and some sort of attempt to do a PCV system the cast iron rings should go 150,000 or more miles.

I would use the cast iron rings. There has been some mention here about what may be causing the smoke. In general, I would say that if it smokes while pulling away after idling at a stoplight, that would indicate there is a problem with valve seals, and or guides.

Hello Walt, I have to agree with everyone else. I've rebuilt several engines over the years, and cast is the way to go, they seat very quickly and with normal oil change maintenance they will have a long life. I used chrome rings in one engine I rebuilt, and they took a very long time to seal, also I believe the chrome being very hard, they are harder on the cylinder walls. Go with cast, you won't regret it. Just my two cents, Ken.

You might consider moly faced rings. Chrome seems to be a relic from the past, they even used to chrome the cylinder walls. However I would as mentioned check the valves. These don't really have the sort of seal that wears out, they are either there or they aren't. Unless of course someone had installed wiper type seals at some point in the past. Which by all rights should work just fine, but I had them installed on my engine when I rebuilt it and within 300 miles I had to pull the head due to all the exhaust valves being galled and sticking. I still don't know if it was the seals or the fella didn't give enough clearance. Either way I still have them on the intakes, and not on the exhaust.

I am looking for an engine that will last a GOOD LONG while.

I had not realized that chrome was hard on the cylinder walls. I have decided to go with cast iron.

Thanks for all the input.

Walt Williams
La Verkin, UT
(The Gateway to Zion National Park)

"I had not realized that chrome was hard on the cylinder walls."

You should not take away from the discussion here that chrome rings are hard on the engine block. That isn't true. It is simply a harder material and wears at a slower rate and has less friction but let's not qwibble over such a minute point. It just lasts longer but doesn't actually seal better. A very misunderstood part.

If you have 130 compression, leave the rings lone. All of the hard rings such as chrome are made for a rebore and will not seat by simply honing the cylinders. Besides that, if your oil rings were worn out, it would smoke during deceleration. You might have worn out valve guides and seals. But there again, high vacuum such as deceleration is what sucks oil into the chamber. Did you recently change the exhaust system? Quite often the exhaust smokes blue until you burn the oil out of the system.

I have now torn down the engine. I found that this engine had a "Farmer John" overhaul done on it. (Nothing personal to farmers) A Farmer John overhaul is fine for a lightly worn engine by not for one this worn. Here is what I found.

The person responsible cut the ridge off the top and honed the crap out of the cylinders and put new rings in it. Nothing more. The STD sized cylinders had .008 to .009 taper. The pistons had a .030+ fit. The severely worn out rod bearings were re-used. Several of the rod bearings had copper showing. Also, you could actually look down the side of the piston and clearly see the top compression ring.

The engine parts are now at the machine shop. The block will very likely be pocked out to .030 over to clean it up. The crank rod journals will need to be ground to .030 under to remove the scoring caused by the work out bearings; the mains will be ground to .020 under. I am also having the non-261 (235) cylinder head in being worked over to include reconfiguring it to be a 261 cylinder head -- drilling the steam vents.

Leaving the rings along with this kind of piston fit and taper would have been devastating to this 261 engine block.

Thanks for all the comments
Walt Williams
La Verkin, UT

the best choice would be moly rings, they pretty much seat immediately, there is no chrome-moly rings as far as I know. The Moly is porous and holds oil, and has high resistance to scuffing. It is just an overlay on a standard cast iron ring usually, although there is ductile iron, and steel rings as well.