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Discussion Starter · #1 ·
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.
Material property Silver Jewellery Screw Close-up

Automotive tire Wood Asphalt Road surface Bumper
 

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Discussion Starter · #6 ·
Not enough end gap the ring ends are expanding when hot and butting together pushing the ring into the bore wall which might also be damaged.

Bogie
If you look at the pic's I am talking about the wear on the land area of the ring, the but ends look fine and the cylinder walls look pretty good and only have about .002 to .003 wear at the top of the cylinders.
 

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Those were Hasting rings that came with the pistons, they were moly ductile iron, 2nd ring and oil ring look fine, fitment was fine when new.
the rings in my failure experience were also Hastings. in my case the engine ran very well for 3k miles. I pulled it out and reringed it at my expenses to make the customer happy. Hastings had no interest in talking about the issue. #NeverHastings
 

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Mic the ring and you'll find it tapered. It's been smashed flat, because it rocked in the bore.
It rocked in the more from either the bore on the big side, and/or the piston lands are too big.
The smearing of the face is your biggest clue.
 

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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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The worn side of the ring....is that the upper side or the downward side??

How does the piston ring land look, on that side was against the worn ring side??
How does ring groove width compare to the ring thickness?

Engine run without an air cleaner??

Engine compression ratio and camshaft specs might be helpful info too.
 

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Discussion Starter · #11 ·
The worn side of the ring....is that the upper side or the downward side??

How does the piston ring land look, on that side was against the worn ring side??
How does ring groove width compare to the ring thickness?

Engine run without an air cleaner??

Engine compression ratio and camshaft specs might be helpful info too.
Worn side is the down side
Piston ring land looks good
engine was run with air cleaner
cam is .480 lift, 210 int./ 219 ext. 112 lsa
comp. 10.42
no signs of detonation on pistons that I see, I will take a pic
it's hard to tell ring fit in land with the ring worn, I will be replacing pistons.
here are some pics of piston with unbroken ring and pics of piston with broken ring,
 

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What brand pistons are they? I don't know about others, but K-B hypers place the top ring closer to the top of the piston, so they get hotter and require a larger gap. As I recall, K-B recommends .026" for a 4" bore (normally aspirated), instead of the more common .016". Some folks have been known to ignore this, for whatever reason, but they are flirting with disaster.:oops:
 

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Discussion Starter · #13 ·
What brand pistons are they? I don't know about others, but K-B hypers place the top ring closer to the top of the piston, so they get hotter and require a larger gap. As I recall, K-B recommends .026" for a 4" bore (normally aspirated), instead of the more common .016". Some folks have been known to ignore this, for whatever reason, but they are flirting with disaster.:oops:
Pistons were Sealed Power, If I remember the pre gap rings were more over .020, that was back in December of 2015 so I am really not sure.
 

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1st post says "383 TPI" so I"m assuming iron heads??
At 10.42:1 compression with relatively short cam and restricted intake it can lead to detonation.

what do the upper halves of the rod bearings look like??

Pistons just strike me as subjected to repeated levels of mild detonation....
What cylinders had broken rings??.
 

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Discussion Starter · #17 · (Edited)
1st post says "383 TPI" so I"m assuming iron heads??
At 10.42:1 compression with relatively short cam and restricted intake it can lead to detonation.

what do the upper halves of the rod bearings look like??

Pistons just strike me as subjected to repeated levels of mild detonation....
What cylinders had broken rings??.
L98 aluminum heads 113 castings, rod bearings look good, cylinders 3 and 5 if I remember correctly.
 
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