Coated Piston

paulb

paulb

New member
Joined
Jul 14, 2006
Messages
1,673
There was some interest in the past about how well piston top coatings hold up. Here is a picture of a piston out of my 05, after about 28,000 miles and about 350 1/4 mile passes. Most of the passes were low 11's high 10's. It dyno'd 1015hp corrected and 1040hp uncorrected.

http://i30.photobucket.com/albums/c305/NowWereSmokin/05UsedPiston.jpg

The clean areas is where the injector spray hit. The coating is Swains Gold coat. There isn't any sign of the coating wearing off.

Paul
 
Impressive...

You're obviously still at stock compression ratio? Those aren't cut..
 
Damnit you treed me. That looks awesome btw!
 
Last edited:
Nice!! Good to see an aftermarket product hold up to it's claims! What EGT did it run at?
 
I like the way the Swain stuff looks. I went with Polydyn because they could cut the valve reliefs and then coat. They did a poor job on both. Their coating process is sloppy and uneven when you hold them up next to pistons coated by swain.
 
Good to know. I've often wondered how the coating holds up, I also have the GoldCoat on the crowns and PC-9 on the skirts.

Granted I'm nowhere near the power you are, but atleast I know it's not likely peeling off
 
joefarmer said:
Nice!! Good to see an aftermarket product hold up to it's claims! What EGT did it run at?
Click to expand...

It usually peaked at 1550 during a 1/4 pass. It would peg the gauge at 1600 during a dyno pull.

Paul
 
did you have to add any clearance to the cylinder bore due to the coated skirts?
 
chris lang said:
did you have to add any clearance to the cylinder bore due to the coated skirts?
Click to expand...

Not a simple answer for this...

The main reason I had the tops of the pistons coated was to help control the amount of heat that the piston absorbed. I do not believe that the coating would stop a piston from being melted. If an injector were to hang open, to much timing, etc. the piston would still melt. IMO. What I wanted was to reduce how much heat was transfered to the engine oil and to control the expansion of the piston. At high horse power levels everyone ends up using more piston to cylinder wall clearances to keep from scoring pistons and cylinders. The Cummins piston uses a keystone ring as the top ring. The keystone ring works very well in diesel engines because it is "self cleaning", and isn't as prone to sticking. A problem with it though is as piston to cylinder wall clearances increase the amount of leakage (especially at TDC and BDC) greatly increases. The reason is that the keystone ring is tapered and the farther out of the ring land the more axial clearance it has.

My goal was to be able to reduce piston to cylinder wall clearance, to help ring seal, and not have scuffing. The clearance in this engine was .0035, and in the 28,000 miles there wasn't any abnormal scuffing. Without coated pistons in the past I was running as much as .0075, and still getting some scuffing.

Paul
 
paulb said:
Not a simple answer for this...

The main reason I had the tops of the pistons coated was to help control the amount of heat that the piston absorbed. I do not believe that the coating would stop a piston from being melted. If an injector were to hang open, to much timing, etc. the piston would still melt. IMO. What I wanted was to reduce how much heat was transfered to the engine oil and to control the expansion of the piston. At high horse power levels everyone ends up using more piston to cylinder wall clearances to keep from scoring pistons and cylinders. The Cummins piston uses a keystone ring as the top ring. The keystone ring works very well in diesel engines because it is "self cleaning", and isn't as prone to sticking. A problem with it though is as piston to cylinder wall clearances increase the amount of leakage (especially at TDC and BDC) greatly increases. The reason is that the keystone ring is tapered and the farther out of the ring land the more axial clearance it has.

My goal was to be able to reduce piston to cylinder wall clearance, to help ring seal, and not have scuffing. The clearance in this engine was .0035, and in the 28,000 miles there wasn't any abnormal scuffing. Without coated pistons in the past I was running as much as .0075, and still getting some scuffing.

Paul
Click to expand...


DAMN!! Thanks for sharing. I'm running 5 thou with the steel pistons as they swell next to nothing.......LOL I need to tighten that chit up.....

MIND you, in a drag racing application your not into the heat nearly as long.

What ring gap did you get away with?
 
Joesixpack said:
DAMN!! Thanks for sharing. I'm running 5 thou with the steel pistons as they swell next to nothing.......LOL I need to tighten that chit up.....

MIND you, in a drag racing application your not into the heat nearly as long.

What ring gap did you get away with?
Click to expand...

I set the top to .022. I'm going to go with .020 this time. Hard to tell when it's to tight until you get it to tight. :) .022 seemed to be plenty.

One other thing is that I had cracks in two intake valves. It's going back together with exhaust valves in both the intake and exhaust sides. Possibly from the extra cylinder heat with the coatings?

Paul
 
What did you set the second ring to? I'm still baffled why I stuck pistons with .035 top and .022 second ring gaps. I've been told that my oil film may have broken down because of the hard to spool combination I was running.
 
paulb said:
One other thing is that I had cracks in two intake valves. It's going back together with exhaust valves in both the intake and exhaust sides. Possibly from the extra cylinder heat with the coatings?
Paul
Click to expand...

I think that's a good idea Paul. If I remember correctly, the exhaust valves are 100% inconel and can handle the heat better. Just remember to cut the correct angle. Intake is 30* and exhaust is 45*
 
joefarmer said:
What did you set the second ring to? I'm still baffled why I stuck pistons with .035 top and .022 second ring gaps. I've been told that my oil film may have broken down because of the hard to spool combination I was running.
Click to expand...


Don't think a keystone would like those gaps at all. It does not want to see any kind of equilibrium pressure on the backside at all.

Min gap would be no more than equal than top ring maybe a touch more as the expansion rate of the material is more.

I'm on 20 thou top ~30 thou second. However these pistons do put the top ring a little deeper.



On the valves the cracks are a little disturbing alright......I switched to inconel on the intakes as well and cut them to 30 degrees which at that time at least seemed to flow the best.
 
Last edited:
You must log in or register to reply here.
Back
Top