Piston coatings?

[bulfin]

Hi,

Just opened up my TwinCam because of a head gasket failure. The pistons (well, 3 of 4) appear to have a black coating on them. A mild cleaning did not remove it. The piston without a coating was the one with water in it; it was shiny after I wiped it off. This coating looks too smooth and uniform to be crud, so I am wondering if it is some kind of heat shield coating. I have never seen pistons like this before, although I have very limited experience. I am attaching a couple of pictures. The skirt/sides are not coated, although the very top on the sides is.

Thanks for any help/insight you can give me.

Bob
69 Elan S4 DHC

[rgh0]

Yes looks like some sort of cwramic heat shield coating. Coatings are available for the tops of pistons for heat shielding and skirts for oil retention and wear and friction reduction. it would be unsual to do on a road car, more likely on a competition engine though the benefits for even a very highly developed twin cam are relatively small.

Strange to only have 3 coated, maybe the DPO had a blow up and only replaced the failed piston which he did not bother to get coated. Do you know the engines history at all

regards
Rohan

[bulfin]

Thanks for the reply. Some answers below.

Yes looks like some sort of cwramic heat shield coating. Coatings are available for the tops of pistons for heat shielding and skirts for oil retention and wear and friction reduction. it would be unsual to do on a road car, more likely on a competition engine though the benefits for even a very highly developed twin cam are relatively small.
Strange to only have 3 coated, maybe the DPO had a blow up and only replaced the failed piston which he did not bother to get coated. Do you know the engines history at all
regards
Rohan

I was told by the previous owner that the owner before him raced it and the engine was prepared by a NASCAR shop in North Carolina. I did not put much faith in that. The engine appears to be stock except for an electric fuel pump and electronic ignition.

I think the uncoated piston was coated; I can see some evidence around the edges. It was the one that had coolant leaking into it, so maybe it burned it off. There are a couple of places on the other pistons where the coating looks to be wearing off.

Assuming I reuse these pistons (haven't checked roundness of pistons or bores yet), should I coat the one, remove coating from all, or just have a mixed set?

Thanks again.

Bob
69 Elan S4 DHC

[rgh0]

I personally would like them all the same - either all coated or all not coated. You dont need the coatings for a road car so probably easier to remove it from the 3 pistons than to try to get one coated to the same specification or to redo all 4 pistons with new coatings.

regards
Rohan