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Piston Ring Wear: is this Normal?

577 Views 16 Replies 6 Participants Last post by  eutu1960
I am refreshing my 383 sbc tpi with 54000 miles on her she has been getting low on power, I dissembled the engine
and the top rings all have the same wear witch seems excessive to me, the rings were ductile iron and the pistons were Hypereutectic,
is this normal. Thanks for opinions. Also 2 of the rings were broken.
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I looked at the picture, the wear and damage is typical to insufficient end gap, the ring is being pinched in its groove. That’s the side or face wear you see at the butt ends.

I’m assuming by “ductile iron” you mean they are uncoated with either chrome or moly?

Hypereutectic pistons run hotter than lower silicon alloys whether cast or forged. Therefore the clearances need to be a bit wider both vertical and back side of the ring groove and the end gap. The circumfrencial raised edge is a sign that either the ring is being pinched at the ends or is fluttering in its groove due to excess vertical or insufficient back side clearance. Or is being slightly detonated. When I see the gap ends the out side surface that rides the bore wall is polished, this indicates the ring has run out of gap and is distorting into the cylinder wall.

Another sign is the busted rings this again is typical of insufficient gap also an indicator of detonation. I also see what looks like metal flakes here and there on the rings, this is another potential sign of detonation. Either or both of these problems will eventually fail the top groove.

It’s a fair bet at this point the pistons are junk. In the old days the ring groove would be salvaged with a widening tool then a special ring set used that includes a spacer that puts things back to the vertical groove clearance. But this process similar to the use of plain cast iron rings harkens back to the days of 45 mph speed limits common before the 1950’s. By the mid fifties rings were being hard chromed for the upper, phosphate treated second ring and 3 piece stainless oil ring replaced a cast oil ring. All of this to get piston rings to live with higher loads as power levels came up and higher speeds as road speed came up along with higher operating temperatures. Eventually the hard chrome on the upper ring was replaced with a moly coating or fill depending on the manufacturer. The upper ring especially is in a brutal environment of high heat and often less than no lubrication so to live in this environment coatings of chrome or moly are self lubricating and sufficiently different in molecular make up from that of the cast iron cylinder wall that under these operating conditions these materials don’t micro weld to the cast iron cylinder wall

Another approach to this problem is Nickasil which essentially is a chrome carbide coating applied to the bore walls. A rather expensive process that is used in high end engines, finds expensive use in aircraft piston engines as well.

Bogie
 
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