Piston Polishing

[MikeH]

Hi All, I'm in the process of rebuilding my TR4 engine, and while waiting for the machine shop to grind the crank for a new rear seal conversion and balancing all components, things keep creeping into my head. Somewhere I read or heard that polishing the piston skirts lessens friction and possible breakage, if piston slap occurs. Am I correct or is this an old wife's tale. Apologies to any ladies out there. Am also having the head shaved, can I do some of the required reshaping on the combustion chamber myself, following Kas Kastner's competition handbook? What would I need in the way of tools? Thanks, Mike

63 TR4 Surrey Top

 

[Adrio]

I don't know about the polishing but I can comment on the head reshaping. I did the head reshaping myself on my TR4A. All it took was an air powered die grinder and a long neck carbide bit. You may as well port the intake and exhaust while you are there with the grinder. The process was not that hard, just make sure you read all about it and know where the water chambers are so that you don't get too close to them. Also I would do this before you send the head in to the machine shop (you would hate to slip and hit a freshly machined surface).

 

[Alan_Myers]

Hi Mike,

I think the key benefit of polishing the pistons (pretty much all over, not just the skirts) is that carbon will have a harder time building up, helping the engine stay clean and run more efficiently.

There might be some piston-slap benefit, too, but not very likely with stock or most standard aftermarket piston. It's more likely to see slap with forged racing pistons (expensive). So, unless those are what you are running in the motor, there shouldn't be much (or any) slap, so polishing can't effect it.

Cheers!

Alan Myers
San Jose, Calif.
'62 TR4 CT17602L

 

[Dave Russell]

[ QUOTE ]
Hi Mike,

I think the key benefit of polishing the pistons (pretty much all over, not just the skirts) is that carbon will have a harder time building up, helping the engine stay clean and run more efficiently.
Cheers!

Alan Myers
San Jose, Calif.
'62 TR4 CT17602L

[/ QUOTE ]
Hi Alan,
Just something to ponder. Engines do not obtain full thermal efficiency until a layer of carbon has built up on the pistons & chambers. Heat that could be doing useful work is escaping into the cooling & lubrication systems.

Builders of Diesel engines & high output gas engines, regularly apply a ceramic thermal barrier coating to piston tops & combustion chamber surfaces.

The light carbon buildup acts in the same way. It has been demonstrated on dynos that an engine has more power & efficiency with a light carbon build up on these parts. Maybe carbon build up is better than shiney clean. A properly setup engine will only build a minimal carbon coating after which any further build up is burned off.
D

 

[CraigFL]

[ QUOTE ]

Hi Alan,
Just something to ponder. Engines do not obtain full thermal efficiency until a layer of carbon has built up on the pistons & chambers. Heat that could be doing useful work is escaping into the cooling & lubrication systems.

Builders of Diesel engines & high output gas engines, regularly apply a ceramic thermal barrier coating to piston tops & combustion chamber surfaces.

The light carbon buildup acts in the same way. It has been demonstrated on dynos that an engine has more power & efficiency with a light carbon build up on these parts. Maybe carbon build up is better than shiney clean. A properly setup engine will only build a minimal carbon coating after which any further build up is burned off.
D

[/ QUOTE ]

I'm curious... do you know if that study was comparing a regular surface to a carbon buildup or comparing to a mirror finish? I would expect that the mirror finish would reflect heat better and actually run cooler. The problem being that the finish wouldn't stay mirror for too long because of the severe environment.

Craig