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)
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.
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".
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.
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
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.
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)
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.
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.
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.
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