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Torque454 02-18-2013 08:15 PM

Piston ring choices - Iron Vs Moly Vs Chrome
 
I am working on overhauling my engine and I see three choices of piston rings. Standard Iron rings, Moly rings, and Chrome rings.

What are the pros and cons of each? The way I understand it is that the iron rings will seat faster than moly rings, but wont last as long. I dont know anything about the chrome rings.

What are the cons of it taking longer for the moly rings to seat?

I don't know if it matters or not but the engine is a (currently) stock Ford 302 in an 87 F150. It will not exactly be a race/high performance engine but i want increased torque for pulling a trailer, and longevity. The engine uses a speed density EFI system so it will probably not see excessive changes, unless i convert to mass air.

I do plan to use a Comp Cams 31-255-5 cam and lifter kit, possibly gt40 heads (maybe even shaved some for a little extra compression), and a set of headers. Everything else will be stock (intake, pistons, bearings, oil pump, timing set, pushrods, rocker arms, rods, crank, etc)

BOBCRMAN@aol.com 02-18-2013 10:46 PM

Used bore with minimal wear, graze breaker or berry bush hone= cast rings.

Fresh straight bore properly honed for moly rings= instant break in.

Straight bore with proper finish= Chrome rings. For heavy duty, constant heat/load. Take longer to break in. Will last longer under the right conditions. No tolerance for dirty air/oil.

Mr. P-Body 02-19-2013 07:46 AM

Along the same lines as previously said, "used bore" gets iron rings. Fresh bore gets moly.

We don't use "chrome" rings anymore, except in rare cases where heavy equipment NEEDS them, usually diesels operating in relatively clean environements. Not uncommon to see an oil-bath air cleaner on engines designed for chrome rings. No machine shop I know of will put a warranty on a street or race engine using chrome rings, against rings "seating".

Jim

ap72 02-19-2013 09:12 AM

high heat or RPM you can use chome faced rings- very common on turbo builds.

BTW, moly and chrome are both a type of facing material that is put on a cast, ductile, steel, or other ring set. The cheap sets are on cast rings, then ductile, then steel. Steel rings are usually the best you can find in wide applications and there are many other coatings that can be used to fit your needs.

There really is a BIG difference between a $400 set of rings and a $40 set of rings.

hcompton 02-19-2013 12:18 PM

I use hastings cheap cast/ moly rings. Most rings packages have more than one type of ring usally the top and bottom compression rings are different.

Now 87 ford may have low tension piston rings from the factory. If stock bore is being used it would be best to use ford factory rings.

prumora1 02-19-2013 05:13 PM

I ve done many small fords for moderate stock builds always use ductile iron, cast rings can be brittle due to heat and wear, iron ductile is great for ring seat and great wear and many applications

oldbogie 02-20-2013 11:12 AM

Quote:

Originally Posted by Torque454 (Post 1647870)
I am working on overhauling my engine and I see three choices of piston rings. Standard Iron rings, Moly rings, and Chrome rings.

What are the pros and cons of each? The way I understand it is that the iron rings will seat faster than moly rings, but wont last as long. I dont know anything about the chrome rings.

What are the cons of it taking longer for the moly rings to seat?

I don't know if it matters or not but the engine is a (currently) stock Ford 302 in an 87 F150. It will not exactly be a race/high performance engine but i want increased torque for pulling a trailer, and longevity. The engine uses a speed density EFI system so it will probably not see excessive changes, unless i convert to mass air.

I do plan to use a Comp Cams 31-255-5 cam and lifter kit, possibly gt40 heads (maybe even shaved some for a little extra compression), and a set of headers. Everything else will be stock (intake, pistons, bearings, oil pump, timing set, pushrods, rocker arms, rods, crank, etc)

Ring material depends a lot on machining accuracy and oiling of the engine. The simple cast gray iron ring harkens back to a day when machining was pretty loose both in axis accuracy, straightness and finish. This was also a period where bottom end oiling was excessive by design where often, if not always, the rod was drilled to put an indexed pressure oil stream onto the cylinder wall and bottom of the piston to prevent upper cylinder wear and reduce operating temperature of the piston and ring pack. At that engine life was not long espeically by todays standards. The chrome plated ring came along in the 1960's which needed much less upper cylinder lubrication but also required better machining the latter possible by the OEMs but usually not the corner auto repair shop. In this period the OEMs also eliminated pressure oiling of the cylinder wall and piston bottom, drying up the bottom end somewhat because the chrome ring did not requre near so much lubrication and cooling as simple gray cast iron. The problem with chrome rings occur mostly in rebuilds where the cylinder walls were not aligned well enough with the crankshaft while the bore was not concentric enough in roundness nor straight enough in the lenght of the bore top to bottom while the free hand of the finish hone added to these errors plus often had a finish that was too smooth so the rings had a hard, if not impossible, time seating into the wall. Bon Amy anyone? High oil consumption and blow by was the result.

Moly coatings, filled or plasma spray, provided much the same benefit of chrome in that they live with very little upper end lubrication while not micro-welding to the cylinder wall. This greatly reduces the wear rate so the engine holds better compression for a longer time. They fit well into the scheme of modern low emissions engines by allowing even less lubrication of the cylinder walls and piston bottoms and are tolerant of high operating temperatures. They are not as wall finish sensitive as the chrome ring which makes them very effective for rebuilds that come from shops with older machining equipment and/or questionable capabilities of the machinests.

The base material of the ring has changed a lot; the old cast gray iron ring with or without coatings of chrome or moly are better suited to less well machined and finished cylinder walls with pistons of softer alloys (low silicon) as the softer gray iron doesn't pound on the soft ring lands of these piston types with such intensity as ductile iron or steel rings will do. Ductile iron whether coated with chrome or moly is better suited to modern high silicon cast pistons like the hypereutectic or forged pistons whether low silicon 2618 or the high silicon 4032 alloys as forgings are harder and can tolerate the better ring alloys beating on the ring lands with every direction change of the strokes.

Bogie

Torque454 02-20-2013 10:22 PM

Quote:

Originally Posted by oldbogie (Post 1648409)
Ring material depends a lot on machining accuracy and oiling of the engine. The simple cast gray iron ring harkens back to a day when machining was pretty loose both in axis accuracy, straightness and finish. This was also a period where bottom end oiling was excessive by design where often, if not always, the rod was drilled to put an indexed pressure oil stream onto the cylinder wall and bottom of the piston to prevent upper cylinder wear and reduce operating temperature of the piston and ring pack. At that engine life was not long espeically by todays standards. The chrome plated ring came along in the 1960's which needed much less upper cylinder lubrication but also required better machining the latter possible by the OEMs but usually not the corner auto repair shop. In this period the OEMs also eliminated pressure oiling of the cylinder wall and piston bottom, drying up the bottom end somewhat because the chrome ring did not requre near so much lubrication and cooling as simple gray cast iron. The problem with chrome rings occur mostly in rebuilds where the cylinder walls were not aligned well enough with the crankshaft while the bore was not concentric enough in roundness nor straight enough in the lenght of the bore top to bottom while the free hand of the finish hone added to these errors plus often had a finish that was too smooth so the rings had a hard, if not impossible, time seating into the wall. Bon Amy anyone? High oil consumption and blow by was the result.

Moly coatings, filled or plasma spray, provided much the same benefit of chrome in that they live with very little upper end lubrication while not micro-welding to the cylinder wall. This greatly reduces the wear rate so the engine holds better compression for a longer time. They fit well into the scheme of modern low emissions engines by allowing even less lubrication of the cylinder walls and piston bottoms and are tolerant of high operating temperatures. They are not as wall finish sensitive as the chrome ring which makes them very effective for rebuilds that come from shops with older machining equipment and/or questionable capabilities of the machinests.

The base material of the ring has changed a lot; the old cast gray iron ring with or without coatings of chrome or moly are better suited to less well machined and finished cylinder walls with pistons of softer alloys (low silicon) as the softer gray iron doesn't pound on the soft ring lands of these piston types with such intensity as ductile iron or steel rings will do. Ductile iron whether coated with chrome or moly is better suited to modern high silicon cast pistons like the hypereutectic or forged pistons whether low silicon 2618 or the high silicon 4032 alloys as forgings are harder and can tolerate the better ring alloys beating on the ring lands with every direction change of the strokes.

Bogie

So what would you recommend for a Std OEM bore with Std OEM pistons and little wear on both? There is no ridge in the cylinder wall but there is some minor scratches that you cant feel with your fingernail.

I'm gathering from all the posts that I should use either Iron or Moly, but not sure exactly which. I may decide to just leave the rings alone as good as the cylinders are (no ridge, no smoke, plugs are light brown in color, compression was 165-175psi across the board)

Thanks for the info!

64nailhead 02-21-2013 11:40 AM

Quote:

Originally Posted by Torque454 (Post 1648733)
So what would you recommend for a Std OEM bore with Std OEM pistons and little wear on both? There is no ridge in the cylinder wall but there is some minor scratches that you cant feel with your fingernail.

I'm gathering from all the posts that I should use either Iron or Moly, but not sure exactly which. I may decide to just leave the rings alone as good as the cylinders are (no ridge, no smoke, plugs are light brown in color, compression was 165-175psi across the board)

Thanks for the info!

If you are replacing the pistons, then do not consider reusing the rings. If you are going 'glaze bust' the cylinder, then do not consider reusing the rings and I would say to use iron rings if you are not reboring - IMO.

hcompton 02-21-2013 02:46 PM

Quote:

Originally Posted by Torque454 (Post 1648733)
So what would you recommend for a Std OEM bore with Std OEM pistons and little wear on both? There is no ridge in the cylinder wall but there is some minor scratches that you cant feel with your fingernail.

I'm gathering from all the posts that I should use either Iron or Moly, but not sure exactly which. I may decide to just leave the rings alone as good as the cylinders are (no ridge, no smoke, plugs are light brown in color, compression was 165-175psi across the board)

Thanks for the info!

If you take apart a good running with miles on it and put it back together it will smoke every time. The rings never seat back in well the second time around. It at least needs rings. Why not just order oem replacement rings. These will be the correct rings for your unbored engine. If you find out the rings are about 300 bucks from all mfgr then you can bet they are low tension steel rings. And your stock bore has been prepared for those types of rings. Best to go with oem when your not sure.

Do the scratches go from top to bottom or cross each other at an angle. Scratches from top to bottom that can be seen is the reason cylinders a bored. I would bet your going to need to have it bored to make it right.

Torque454 02-21-2013 08:11 PM

Quote:

Originally Posted by hcompton (Post 1648986)
If you take apart a good running with miles on it and put it back together it will smoke every time. The rings never seat back in well the second time around. It at least needs rings. Why not just order oem replacement rings. These will be the correct rings for your unbored engine. If you find out the rings are about 300 bucks from all mfgr then you can bet they are low tension steel rings. And your stock bore has been prepared for those types of rings. Best to go with oem when your not sure.

Do the scratches go from top to bottom or cross each other at an angle. Scratches from top to bottom that can be seen is the reason cylinders a bored. I would bet your going to need to have it bored to make it right.

So far the pistons and rings haven't been removed from the block. So they should be ok. And yes the scratches are up and down in the cylinder. Odd that there is no ridge tho. I may just leave it alone. I really only wanted to take it apart to have the block cleaned up and put in new cam bearings. I can replace the main and rod bearings with the rods and pistons in place.

64nailhead 02-22-2013 12:20 AM

In you original post, you said you're looking for some more torque and longevity. If you have vertical scratches and you do not bore, then you are dramatically cutting into the longevity.

You said you're looking at swapping the heads and cam. I think it would be crazy spending the amount of money you're planning on spending without doing the job completely. I'm quite confident (not guaranteeing) that if you don't bore it now, then you'll be either pulling it back apart later or adding oil often.

I'm sure many of the guys here have been burnt by not doing the job right the 1st time - ME INCLUDED. The 1st engine I rebuilt was my wife's daily driver. I did it 3 months after I changed the timing belt. I replaced the timing belt because it was in poor condition and past the recommeded replacement interval. Also, the service manual recommeded rebuilding the oil pump at the same time - I said the heck with messing with the oil pump. 3 months later the pressure reilief plunger spring in the oil pump broke and, I mentioned this was my wife's car, she tried to make it home with the 'oil' light on. You can figure out the rest.

I was in my early 20's at the time, it was an 85 Park Ave with a 3.8, and I was trying to save a few dollars. Well, I did for a few months. I lived, I learned. I wish there were forums like this around back then to set me straight. Maybe some others can chime in and agree or disagree with me, but I'm saying find a machine shop you trust and do it right the 1st time.

Good luck;)

ap72 02-22-2013 06:27 AM

Quote:

Originally Posted by 64nailhead (Post 1649162)
In you original post, you said you're looking for some more torque and longevity. If you have vertical scratches and you do not bore, then you are dramatically cutting into the longevity.

Not just longevity but torque as well, without good ring seal your power will be going out the crank case breather, and the oil consumption will mess with your burn.

A well sealed cylinder is like the foundation of a house- without that the rest is for nothing.

cliff tate 02-22-2013 06:46 AM

piston rings
 
molley(plasma sprayed ) ar the best. a example i have is when i was s.maneger cat dealer,they inther wisdom went to chrome top ring, in stead of molley in lower output engines. this resulted in maney failures of new and rebuilt 34 12 3408 engines.they did not make dealers aware of the change.the 3406 inline engine which made more hp per cyl had no failures.we fialy twiged to cats change.re rung all with molley rings end of problem. I in retiement do a few engines per year,i will only use molley rings,tho 1 must use the corect hone for the supper fine cyl wall finish.all 3208 cats with 2 ring pistons used molley rings,jobers tryed chrome,poor life and failure in high load use.

oldbogie 02-22-2013 10:45 AM

Quote:

Originally Posted by Torque454 (Post 1648733)
So what would you recommend for a Std OEM bore with Std OEM pistons and little wear on both? There is no ridge in the cylinder wall but there is some minor scratches that you cant feel with your fingernail.

I'm gathering from all the posts that I should use either Iron or Moly, but not sure exactly which. I may decide to just leave the rings alone as good as the cylinders are (no ridge, no smoke, plugs are light brown in color, compression was 165-175psi across the board)

Thanks for the info!

I would do a very light hone although not to the point of a final bore finish that comes following a rebore which usually removes about .005; just enough put some tooth on the wall for new rings to seat into. Any ring new or old will have trouble getting a bite on a wear smoothed wall. Keep in mind that honing will increase the piston to wall clearance similar to what happens when the bore wears. This isn't quite that bad in that the bore is round and not tapered as happens with wear. But the pistons may be a bit noisy till the engine warms up. You want to use an abrasive ball brush hone with about a 320 grit pass it through the bore about 5 to 8 times, use plenty of light oil do not ever let it go dry. Keep moving be careful not to dwell at the ends or middle of the stroke or the wall will develop tapers, or dips these cause the rings to flex in and out of their lands as they track the wall which will result in lost compression to blow by and increased oil consumption. If youíre not sure of your abilities take the block to a pro, this is very easy to screw up and the only recovery is to rebore with new pistons. For the average guy this job has a high risk of failure combined with a lot of expense to repair. If using a coarse grit or a diamond hone it is necessary to go back with a finer hone of 400 to maybe 600 grit to smooth the rough cut that coarse grits produce and especially any diamond cutter will make. Moly and straight cast iron rings need a better finish than does chrome. The wrong finish will kill moly or uncoated iron almost instantly. When the honing is done wash the bores first with solvent then with hot water and detergent when you think they're clean wash 'em again. Dry the bores and the block with compressed air and apply WD40 on the cylinder and bearing bores, spray into the oil passages and onto the gasket surfaces.

I'd use a moly ring, they last much longer than simple cast iron, they bed in quickly and since they are hard but porous they reduce wall wear by carrying an oil film way up the contact portion of the cylinder wall. Wall wear that's seen as taper and ridge at the top of the bore is largely the result of cylinder pressure behind the ring pushing it into the wall with little to no lubrication. The lack of lubrication causes similar metals to micro weld themselves together. The motion of the piston forces these welds to fracture tearing out microscopic pieces of ring and wall, which of course now circulate with the lubricating oil becoming an abrasive between every other moving part. Moly and chrome are very hard materials that innately do not form micro welds with the iron cylinder wall. This greatly improves both ring and wall life by preventing the formation of all that micro-wreckage (some not so micro) that circulates with the oil. Moly, and to a lesser extent chrome, have pores and channels that trap oil which then carries a lubrication into the upper bore area where itís really hot, the forces are high and the lubrication is thin at best, if at all. In this context chrome is probably more the brute force solution being very resistant to wear because of its harness but not as well lubricated by the oil as moly. Chrome unless treated chemically or physically actually sheds oil not unlike water beading on a plastic surface. The wear characteristics of the ring material is really important with modern engines where the oil circulation is much reduced compared to engines of 50 years ago, which may still have been the same casting as today like the SBC Gen I and II, SBF W and C, and the SBCh. The OEMs changed from plain iron rings to chrome in the 1960s and moly in the 1970's. Given their cost consciousness I'd take those changes as really big technical message.

Bogie


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