Piston Coating - Pro's and Cons

[4WheelDrifter]

I looked into piston coatings, but as you point out Mark, the expansion rates change, so clearances become an issue.

[mcandmar]

Interesting about the side coatings, not something i would have thought of. The top coating i was told is for heat, but that has me thinking now, with the coating deflecting heat would the piston expansion rate be less? And therefore do they run tighter piston to wall clearance?

[gnutz2]

Never thought about it like that

These 1.8t pistons i took out had worn the coating right down so you could see the machining marks on the skirt.

[Jamo]

Regarding skirt coating

I am sure that you have already thought of it, but remember when you measure pistons with skirt coating prior to block machining and bore sizing you will also be measuring the thickness of the coating in addition to the actual piston diameter.

This coating will wear after not too long and alter your piston to wall clearance if your machinist measures the pistons in this way, without taking account of the coating and its subsequant wear.

Shouldn't be a problem if the pistons are supplied with accurate dimensions on the job sheet and you work to these (I have found JE's to be very accurate), however I prefer to measure the pistons myself to be on the safe side, something that can't be accurately done with the skirt coating applied, even if you have a ballpark figure for the coating thickness.

Another option would be to order your pistons naked and measure and set up the machining before getting them coated.

I have actual experience of this coating wear causing the the pistons to slap like fook even when hot after only a few k miles. I still have these pistons and can take pictures that show this wear in the skirt coating well. Let me know if and I'll dig them out....

Mind you, having said all of that skirt coating cuts down on friction and that has to be good, if you have a good machinist who knows what he is doing you should not have any problems.

Now you say that Mark, I wonder if that what happened to the original stroker pistons?

It fits, it was bored by a machine shop the pistons when the pistons were coated and then after engine breakin period the gap was too big.

hmm thats serious food for thought.

[Mark Halligan]

Regarding skirt coating

I am sure that you have already thought of it, but remember when you measure pistons with skirt coating prior to block machining and bore sizing you will also be measuring the thickness of the coating in addition to the actual piston diameter.

This coating will wear after not too long and alter your piston to wall clearance if your machinist measures the pistons in this way, without taking account of the coating and its subsequant wear.

Shouldn't be a problem if the pistons are supplied with accurate dimensions on the job sheet and you work to these (I have found JE's to be very accurate), however I prefer to measure the pistons myself to be on the safe side, something that can't be accurately done with the skirt coating applied, even if you have a ballpark figure for the coating thickness.

Another option would be to order your pistons naked and measure and set up the machining before getting them coated.

I have actual experience of this coating wear causing the the pistons to slap like fook even when hot after only a few k miles. I still have these pistons and can take pictures that show this wear in the skirt coating well. Let me know if and I'll dig them out....

Mind you, having said all of that skirt coating cuts down on friction and that has to be good, if you have a good machinist who knows what he is doing you should not have any problems.

[gnutz2]

Apparently coating the skirt helps for better bedding in of the rings. I know for a fact that audi coat the skirts on the 1.8t 20v because mine were coated.

As far as coating the crowns is concerned it seems pointless to me. The theory is to keep the piston cooler but all the heat has to go somewhere ie, heating up the inlet charge (not good) and adding heat to the head.

Why not let the crown and top two rings do their job by transferring the heat into the cylinder walls.

A better use for ceramic as a thermal barrier would be to coat inside the exhaust ports and inside the exhaust manifold thereby reducing cylinder head temp and giving faster turbo spool.

[Jamo]

Well i'm going for coating it seems when I order been searching the net and I can't find a negative about it.

[terrybullwon]

care to explain L'enfant Terrib?

I was told by some one who used to work with cosworth that there pistions were made by another company under instruction of cosworth

But Jamo, has painted the tar on and thrown the feathers in the mix

Good game.....

[terrybullwon]

And i even gave him the bloody gun and loaded it

[Jamo]

I would be like to know who makes the pistons for cosworth as they dont make them

"Cosworth Pistons are manufactured entirely in house at our Northampton UK facility"

care to explain L'enfant Terrib?

[terrybullwon]

Cosworth coat all their piston skirts as standard AFAIK to try to prevent scuffing.
That would suggest to me it is worthwhile.

I really can't see the point in coating the crown though?

:Edited due to insuficant info:

[Jamo]

Thats headache material! Make sure you get some painkillers before reading that pdf Jamo!

I'm all out after moderating today

[s2_bo]

http://www.ae-plus.com/Journals/Soft...ton-piston.pdf

have fun

Thats headache material! Make sure you get some painkillers before reading that pdf Jamo!

[Error404]

http://www.ae-plus.com/Journals/Software%20-%20Computer%20simulation%20of%20piston-piston.pdf

have fun

[Error404]

Cosworth coat all their piston skirts as standard AFAIK to try to prevent scuffing.
That would suggest to me it is worthwhile.

I really can't see the point in coating the crown though?