[68WarDog]

After about 12 years of service I decided to refresh my 455. To my surprise I discovered 2 scuffed piston skirts. What could have caused this.? There were no unusual engine noise, or decrease in engine power. New shop is saying improper boring.

[NeighborsComplaint]

Are the pins tight or do they rotate freely? Partially seized pins will do that as will too much piston side clearance allowing the pistons to rock in the bores.

[68WarDog]

Originally Posted by NeighborsComplaint

Are the pins tight or do they rotate freely? Partially seized pins will do that as will too much piston side clearance allowing the pistons to rock in the bores.

I run floater, we didn't notice any excessive pin clearance. Pistons rocking in the bores ? Would that be audible " piston slap"?

[hurryinhoosier62]

Originally Posted by 68WarDog

I run floater, we didn't notice any excessive pin clearance. Pistons rocking in the bores ? Would that be audible " piston slap"?

Could have happened on initial start up. You don’t normally hear piston slap until there is significant cylinder bore wear. What was the tolerance on your piston pin in the pin boss and the rod end? I like to see .001-.0015.

[NeighborsComplaint]

Piston slap sounds like Diesel engine clatter on cold start.

[77 TRASHCAN]

Originally Posted by hurryinhoosier62

Could have happened on initial start up. You don’t normally hear piston slap until there is significant cylinder bore wear. What was the tolerance on your piston pin in the pin boss and the rod end? I like to see .001-.0015.

I'm thinking lack of lubrication on initial start up...also.

[steve25]

Is the top ring Moly?
How does that face look, worn away in spots?
If so then it could have been from a rich condition washing away the needed wall lube.

[lust4speed]

I'll go with your machine shop on a couple of tight bores. Only two pistons out of eight should rule out lack of lubrication or a rich condition.

["QUICK-SILVER"]

Which cylinders did those two pistons come out of?

Could be normal wear and tear for #1 and #2. Oil pressure drops at every leak point as it moves forward through the block. #1 main/#2 rod get the least amount. That makes for less splash lube and cool on the front cylinders. Less lube equates to piston scuff. Less oil cooling pistons makes for more piston swell that can cause piston scuff.

Gets worse when you have oil pressure loss from engine getting over heated.

Clay

[geeteeohguy]

Originally Posted by lust4speed

I'll go with your machine shop on a couple of tight bores. Only two pistons out of eight should rule out lack of lubrication or a rich condition.

I agree. This can be verified by measuring the bores and comparing them.

[Vid]

Good call on the refresh. You might have saved yourself from bigger problems and heartache later on!


Sent from my iPhone using Tapatalk

[77 TRASHCAN]

I wonder about how much material was lost in the scuffed areas??? Wondering if they look worse than they measure???

[Elarson]

Boss Bird pistons looked like that (and worse) till we loosened the piston to wall clearance. On start-up, the pistons grow faster than the block and tend to tighten up. After everything is warm, the interference goes away. I'd be inclined to go with the theory of a couple of tight bores or a couple of bigger pistons. Easy enough to measure. If you want to reuse those pistons, check them very carefully for cracks in the skirts and ring lands.

FWIW,
Eric

[Mike Davis]

Originally Posted by "QUICK-SILVER"

Which cylinders did those two pistons come out of?

Could be normal wear and tear for #1 and #2. Oil pressure drops at every leak point as it moves forward through the block. #1 main/#2 rod get the least amount. That makes for less splash lube and cool on the front cylinders. Less lube equates to piston scuff. Less oil cooling pistons makes for more piston swell that can cause piston scuff.

Gets worse when you have oil pressure loss from engine getting over heated.

Clay

Add to this the front 2 cylinders run the coolest since they are right next to the water pump. Pistons will expand faster than the bores. Curious as to which 2 cylinders.

[68WarDog]

Originally Posted by Mike Davis

Add to this the front 2 cylinders run the coolest since they are right next to the water pump. Pistons will expand faster than the bores. Curious as to which 2 cylinders.

Cylinders with the scuffed pistons were 4 and 7. We won't be reusing any of the old pistons . I don't believe it was caused by a rich condition, pistons had little to no carbon build up for 12 years old. And I trust the new shop's assessment ( Joey Arrington Racing). But a lot of good suggestions.