Piston and Bore clearances

[elliotaw]

I'd appreciate any advice from the experienced engine builders amongst you lot.

I've just had my engine bores and pistons measured to check for wear etc.

Results are :-

Piston 1 - 3.446"
Bore 1 - 3.449" 0.003" clearance

Piston 2 - 3.4455"
Bore 2 - 3.4475" 0.002" clearance

Piston 3 - 3.446"
Bore 3 - 3.448" 0.002" clearance

Piston 4 - 3.4455"
Bore 4 - 3.4475" 0.002" clearance

Piston 5 - 3.445"
Bore 5 - 3.4475" 0.0025" clearance

Piston 6 - 3.4455"
Bore 6 - 3.4475" 0.002" clearance

Piston 7 - 3.446"
Bore 7 - 3.4475" 0.015" clearance

Piston 8 - 3.4455"
Bore 8 - 3.448" 0.0025" clearance


I think the clearances should be between 1 and 1.5 thou at their optimum.
My engine builder thinks I am nuts trying to improve on what I have, but as far as I'm concerned, if the manufacturer has recommended a dimension, I'd like to get as close to it as possible. He has suggested the cheapest option is to have the pistons ceramic coated (about $30 each) and he says that will increase the piston diameters of the skirt by about 0.001". That will obviously reduce the clearances by the same amount, thus bringing 7 of the 8 clearances into the recommended range with only number 1 being slightly out of range.

Is am concerned with the longevity of such a coating in a volatile situation like on a piston, but from what I've been told, some major performance engines are now doing this to their pistons to reduce noise, friction etc. Anyone had any experience with this ?

What are my other options? Can I buy new pistons from toyota which are oversize ? What are the standard dimensions for this engine? 1991 US spec LS400 ?

Anybody ?

Elliot

 

[slyalfa]

I would say you might need to have them bored to the same size you see to get then true.
if it is worn the size will not be the same in all directions.
also you will need to hone them so the new rings will seat.