the HEADSMESS thread :o

[Fabian]

i might try a skyhawk piston, the one in mine is domed. but then ive heard the heights are different.

Not only are piston heights different between different manufacturers but also the cylinder heights.

When using the CR Machine Manufacturing billet cylinder head with the CR Machine Manufacturing custom remanufactured piston incorporating piston ramps, i needed to use 4 head gaskets to prevent piston to cylinder head contact.
Compared to the OEM pistons used in all of my other engines, the CR Machine Manufacturing piston sits approx 2mm taller and it includes a more pronounced piston dome.

I am sure that if i purchased a matching cylinder from CR Machine Manufacturing, the deck height would have worked out to be correct.

 

[HeadSmess]

so, let me get this clear. your piston stands proud of your cylinder?

so you have four head gaskets that form "a cylinder" so to speak?

with a hi comp head bolted on top of that?

and any so called "squish band" is negated by having sections of the piston crown removed or "ramped" for timing changes??


inch: inch:

im ashamed to say my real initials are CR.

i stated how i will do (havent done but will do) a cylinder and a head as a matched set, and hopefully explained exactly why such a thing is necessary.

so if available, buy the matching cylinder

i will never modify a piston crown as a permanent fixture. its a trial test ONLY before changing ports.

someone SOLD it to you? inch:

i wont sell anything until i myself am satisfied.

and im fussy. i take offense at people that will sell something... half done.

hobby versus making money, huh?

why dont you use a stock piston, and use base gaskets,or even an alloy base spacer, raising the cylinder, to clear the head?

improves squish band. increases ex and tran without degrading piston integrity in the area it recieves the most abuse!

then intake timing changes but the piston can be filed for that side. that modification i approve of.





hmmmmssss


still got that chamfer on the top edge of your cylinder? and just where abouts does the top ring come too?

 

[Fabian]

and use base gaskets,or even an alloy base spacer, raising the cylinder, to clear the head?

I am also using 3 base gaskets to raise the cylinder to help utilise all of the port window. In standard configuaration with a single base gasket the piston only uncovers half of the transfer ports.

Having said that, my bike made the most power using the 3 hole (low compression) CR Machine Manufacturing billet cylinder head with piston reliefs cut out of the piston for alteration of the transfer and exhaust port timing.

In fact i have all 5 of Cr Machine Manufacturing billet cylinder heads: the three hole low compression version. The two hole low compression version. The conventional low compression version. The medium compression version and the high compression version, plus i have the Rock Solid Engines high compression (toroidal combustion chamber) billet cylinder head.

Do a Google search for:

"Twin Spark Plug Cylinder Head for 80cc Happy Time Engine"

 

[Fabian]

The top ring still sits in the cylinder bore, by the skin of it's teeth.

 

[Fabian]

so, let me get this clear. your piston stands proud of your cylinder?

so you have four head gaskets that form "a cylinder" so to speak?

with a hi comp head bolted on top of that?

and any so called "squish band" is negated by having sections of the piston crown removed or "ramped" for timing changes??

Yes that is correct, but with a "low compression cylinder head" with three spark plugs installed to further lower the compression), and that is the configuration which made the most power; when firing the air/fuel mixture from the rear most spark plug and towards the exhaust port.

When spinning the three hole low compression cylinder head around 180 degrees (firing the mixture from the now front spark plug towards the intake port) it makes the least power and firing either spark plug from the side makes an intermediate amount of power.
That was the biggest surprise - spark plug angle and location and it's effect on power, when conventional theory says that a centrally located spark plug gives greatest power.
I have tried using the billet low compression cylinder head (which has higher compression than the three hole low compression cylinder head) with a single centrally located spark plug and it makes less power than the 3 hole low compression cylinder head firing the mixture from the rear most location.

Dividing numbers into numbers, i.e. max speed going up my benchmark "dyno hill", the 3 hole low compression billet cylinder head with 3 base gaskets and 4 cylinder head gaskets gave 15% more speed than any other configuration i've tested.

My experience has been that high compression cylinder heads are not necessarily a good thing, being that the lowest compression cylinder head (at the maximum spark advance from the Jaguar CDI) gave the greatest power.
The highest compression cylinder head detonated like crazy on 98 pump fuel, even using the lowest (Jaguar CDI) spark advance curve. The medium compression cylinder head needed the lowest advance curve, yet made less power than the lowest compression cylinder head.

Another point is that the higher compression cylinder heads made the engine less willing to rev, which matches what Honda was doing back in the days when they were racing in the 500c Grand Prix era. They lowered compression to improve the engine's ability to rev more quickly.