Puch head on the PK

mountain80 · #1 03-13-2010, 02:02 AM

First of all a BIG THANKS TO FOUREASY for sending me down this road by telling me what head he used and I ran with it from there.
Well as some of you have been following I have a Dellorto Phbg with a machined bushing to work with the stock manifold. I have finally got my Puch head welded and redrilled today. The combustion chamber was remachined by myself as i cc'd it and was at roughly 13:1 uncorrected versus my modified head at 8.2:1, to high to run even on premium fuel.I set the Puch head at 8.7:1 for now as it has 160 psi cranking pressure. Can always go back and remachine for higher compresion if need be. Spent alot of time doing the calculations but it came out well finally today. Had headgasket sealing issues as I drilled out the holes but the cyinder had a radius that came to close to the redrilled holes and leaked combustion pressure up through the studs so a reweld/ redrilling on a milling machine was in order. Also remachined the OD of the combustion chamber as it was smaller then the bore of the cylinder. Heres a few pics of the head hope to get it reinstalled and tested this weekend. The Puch head has roughly 50% more cooling area then a stock head and has a squishband instead of the stock PK hemispherical chamber. Note the sandblasted finish, this is a trick 2 stroke aircooled guys used years ago to increase the surface area for more cooling and also the set of 3 holes on each set of pependicular fins for more cooling.

K.i.p · #2 03-13-2010, 06:48 AM

I just wanted to comment that I respect your ingenuity and "do it in house" approach. Dropping names and quoting prices is great but this kind of stuff is where the real action is. I sand blasted my stock head as well, but only to bust off the crap silver paint job, now I have a high tech. explanation as to why I did it.

mountain80 · #3 03-13-2010, 05:58 PM

Well the Puch head is on and after 2 retorques on the head gasket all seems to be well. More midrange and top end just by the seat of the pants of feel but I am going to have to play with the needle, main jet combo and possibly my slide cutout now, it just doesn't want as much fuel anymore.
The head is definitely keeping the temps lower as i put the infrared temp gauge on it. Anways heres a few more pics installed.
Cheers.

K.i.p · #4 03-13-2010, 08:55 PM

Very cool, congrats!

Riding Rich · #5 03-13-2010, 09:23 PM

Looks pretty good.
What was the final compression ratio:

Corrected compression of course.

mountain80 · #6 03-13-2010, 10:09 PM

IF my numbers are correct as to the percentage of stroke after the exhaust port closes then the corrected compression ratio is 8.1:1 with my sparkplug shimmed and 8.8:1 without the shim. If anyone has this stroke percentage calculated correctly let me know and I will verify if my numbers are correct its been awhile, been busy on the machining side of it.

Update: pretty close: still 7.9:1 and 8.6:1 by riches stroke numbers