Performance coatings on pistons

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rx1jim

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Does anybody have experience with the use of performance coatings on pistons? I bought new OEM pistons for an 00 SRX 700 engine I am rebuilding as a spare. I had the pistons skirts and dome coated by Swain Coatings. They put a low friction coating on the skirts and a ceramic heat sheild coating on the domes. I have read good reports about the use of these coatings in performance engines so I decided to give them a try. Swain advertises the use of the Poly-Moly piston skirt coating to build up the diameter on pistons which are slightly undersize. For about $28 per piston, they claim they can bring the dia. back into spec.. Thanks!

Jim
 
The coatings work great on the high build up, youll only gain about .004" back and have to hand sand to get your clearance with wet dry paper but it does work well! Have used that on several engines before to help the customer from buying new pistons if his were just under the min spec.

All of my own engine have coated pistons, the pc9 on the skirt works great! with some oil on them they are slippery!

I dont personally do the domes anymore as it makes them very hard to read as the carbon doesnt like to stick to them after coating.
 
Hello Don,
Interesting that you say the carbon does not adhere to the coated piston domes. This might be a technique to keep the power valves cleaner longer: have the valves coated with the piston dome coating. There is plenty of clearance between the valves and the pocket inthe cylinder for the coating. This would be worth a test but I suspect the coating will not help keep the valves cleaner since they operate at a lower temp, the entire valve does not get exposed tothe combustion temperatures. I'll find out if Swain will coat a set of power valves for me. Then all I need is more snow to test them.

How have you been checking the piston to cylinder clearances: micrometer and cylinder bore gauge or feller gauge between the piston and cylinder?

What is your opinion on having the cylinder domes coated?

I had the domes coated with the thought they would have be more resistant to damage from detonation. Next season I will use a dose of octane boosted on every fill up of 93 octane gas.

Jim
 
I have not had any dealings with Swain, but I can verify after 3 years on a race engine that it does work. If you do the piston dome coating though make sure they do the coating to the first ring land on a high compression engine. Burned to the first ring one time on the exhaust side (detonation) the first time I had some done. But I was really pushing the limits lol. After that, no issues. Coating the domes on the heads are a good idea too in my opinion.
 
I did the heavy build up that mr viper mentions above in lieu of buying new pistons. I haven't torn it apart to check it out yet but I have 1,000 miles on them with no known issues.

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In addition I wouldn't use feeler gages.You need to keep the pistons round/symmetrical, with feeler gages your bound to have low spots or to much from one side .Its a matter of matching each piston to each cylinder.It takes time and patience .001 to much and your back to where you started... with pistons that are to small.


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