Combustion chamber heat

[Shaun Brady]

>Is your motorcycle engine air cooled? If so, did you run into problems 
>with the larger expansion/contraction of air cooled's parts?

The motor is a Honda Hawk.  647 cc, Liquid cooled, aluminum, V-Twin, 3
Valves per cylinder.  I assembled the engine at a local shop that sponsers
me, and while it sat on the bench an old car oval track racer came in and
shared his experiences with coatings.  They were much more expensive in his
day, and not widely known.  They coated an aluminum headed small block
chevy's pistons and combustion chambers.  Initially they didn't see much of
an improvement on the dyno, but they couldn't get the oil or water
temperature into the normal range either.  After they had revised the
cooling systems and carb jetting, they saw a 35 hp improvement on a 500 hp
motor.  It startled me how close this comes to Vizards publications.  This
was a fully developed motor configuration they had been using for years.
The Hawk motor was good for 71 Hp from 40 cubes.  Stock was 42 Hp.  The
motor had 11.5:1 compression, a fairly radical cam, cleaned up ports, stock
valves, low restriction exhaust and intake systems.  The motor output is
limited by the valve sizes, a really poor combustion chamber design, and an
exhaust port with limitations similar to a Cleveland ford.  I selected a
piston manufactured from a material that allowed tighter piston-bore
clearances, coated it, and assembled the motor with clearances on the tight
side of recommended.

>Can you give more details of exactly what brand and type of coatings you 
>used? Were they Jet Hot, or ceramic, or what?

I used the Polydyn Coatings (713-694-3296), as mentioned in Vizards book.
It was a very thin baked on coating, probably ceramic, probably serving a
reflective rather than insulating function.  Summit (330-630-3030) sells 3
oz bottles for less than $30.  There are separate coatings for Aluminum and
Iron.  They are sprayed on and then baked at either 350 F (Al) or 450 F
(Fe).  Polydyn Coats Piston tops for $14, combustion chambers $28, valves $5
ea.  They will also do the backside of valves and exhaust ports.  I've seen
Harley pistons for sale precoated with the other coating system Vizard
mentions (Swain Technologies).  Friction reducing coatings are also popular
among motorcycle racers, but I've heard their useful life on piston skirts
is fairly short.  I spent more on the UPS than I did the coatings, and that
was for little motorcycle parts. I'd like to do a 460 ford boat motor I'm
building, but can't imagine the shipping costs this would involve, and will
probably give the Summit coatings a try.

I would think that everything you can do to keep the heat out of an air
cooled motor would be a good thing.  Vizard suggests that the secondary
modifications allowed by coatings would improve power further yet.  Things
like narrower valve seats.  Tighter piston clearances are another
posibility.  Do car guys use Nikasil bores yet?

I see reference after reference to proffesional engine builders using these
coatings, it is more than a fad.  If you can find someone who specializes in
your engine, and will sell you a set of coated pistons, assemble them to the
clearances they've developed.  Otherwise, your left with starting with the
tight side of recommended.

Good Luck

SBrady