Ceramic Piston Coating

[ek02]

I have had a set of 9.562 JE custom 9.5-1 forged stroker pistons for a 4.1 standard bore sitting around for a couple of years looking for another mint standard bore block, which does not seem to exist. They came out of my 269" 4.1 N/A on Nitrous that cracked from the center main bores to the cam bearing bores. I have a couple of standard blocks, but they would not clean up until I honed them to .007 piston to wall clearance. I heard about CP-9 ceramic piston coating that can add up to .004 to the piston diameter. I had TuffCoat on the JE's that wore off pretty fast. I sent the pistons to Swain Tech Coatings in New York and had the heavy coat CP-9 applied for $26.00 a piston. They took off the TuffCoat and applied the CP-9 to the skirts. It added .006 to the diameter of the skirt, and they all mike exactly the same, which they did before the coating was applied. I may not have enough clearance now when the block is finished being honed. Swain says the coating can be wet sanded carefully to get the desired clearance, but I will probably hone it to size. From what I have read on other forums, this stuff does not wear off like TuffCoat, and Swain says to set up the clearance with .0005 less than what JE recommends, which is .005. It will be a while until I can get a stroker crank, rods, and damper to build this spare iron head flat tappet engine and try it out. I will use all the parts from my spare 3.8. It will just be a backup engine if and when my girdled 274" needs a rebuild. Anyone tried this stuff? It seems too good to be true, but from the research I did, it seems to work well to take up clearance. They did a nice even job to get all the diameters the same. Here is a photo.

 

[dr_frankenstein]

That looks like good stuff! I have tried the tuff coat and i was unimpressed that it didnt last very well. Id be leary of leaving the bore to piston that tight if your under boost, but since your staying NA you might even be okay to tighten it up a hair more since the JEs have real tight expansion rate. Were you going to spray this engine?

 

[ek02]

I didn't plan to spray this engine. It's just an engine to drive around with if the girdled engine needs to come out. I had the pistons, but the rest of the parts may take some time to gather. I have some file fit rings that will work fine even after I hone it to size. I decided to hone to size and not sand the coating.

 

[dr_frankenstein]

what did the coating feel like after it was done? was it slightly bumpy or perfectly smooth? just curious to the coating itself.

 

[ek02]

The coating is smooth, with a flat finish. It seems about as hard as the aluminum the piston is made from. I tried to scratch it in the pin area with a small screwdriver, and it made a mark like a pencil lead would. The coating is supposed to be very slippery and reduce friction. They make a coating for the top of the piston too that is super hard. My piston heads are polished, so I passed on that.

 

[ek02]

I finished honing my block, but had to stop a little short of .004 piston to wall on 4 cylinders. My ring end gap was getting a little critical, even with .005 over file fit rings. I had to sand the coating .0005-.001. I started with 1200 and water, but it would not touch the coating. I went to 600 and water and it took awhile to get the coating down .0005 on each side. It's some pretty tough stuff. Washing the pistons in mineral spirits did not affect it. Brake cleaner also had no affect.

 

[Paul Lohr]

Did Swain Coatings provide instructions for sanding the coating?

 

[ek02]

All they said was that when a heavy coat is applied, they cannot keep the thickness consistant and hand polishing may be requiered. Mine were fairly consistant with 2 pistons .001 smaller than the rest. The normal coating thickness is .0008. They recommend 400 grit or finer to sand them. I tried to keep it as even as possible. Ideally, you would hone the cylinders to the correct clearance and not sand the coating, but I had a too large ring gap issue to consider. My pistons were already .002 over standard, so I was dealing with .008 over with standard bore .005 oversize file fit rings. If I was boring the block and buying new pistons, I would probably not use this coating on a street engine. The horsepower gains are small from what I have read. I have no real information on how long this coating will last mile wise either, except Swains information on their web site that says it extends engine life and cuts friction.