Additional Cooling for the Vespa PX engine

 My friend Bill installed Stella Auto cowls on his 2 stroke Stella shifty.  These are vented cowls that maintain a tasteful original look.  The Auto version of the Stella was only imported in small numbers in the United States (300 I believe) and parts are not readily available.  The claim was that additional engine cooling helped pull fresh cool air into the engine compartment to be available for the fan.  The engine does run cooler with no cowl at all, so any advantage is a plus.  Bill was seeing 15 to 20 degrees cooler cylinder head temperature.  That is an advantage I could use!

 I don't have the means to cut louvers or vents into the original cowl and make them look have decent.  The original cowl on my bike was damaged in a crash before I bought it.  The body filler and stickers make it look presentable today.  I do have a square sheet metal punch that is slightly smaller dimension than the checker tape on the lower part of the cowl.  This gave me an idea that I thought was pretty brilliant.  If I cut square holes in the center of a few of the black squares of checker tape, the holes wouldn't really be noticeable.  The additional airflow should be exactly what is needed to give the additional cooling.

The final carburetor settings after all the modifications DR177 kit, SITO+ exhaust, UNI foam air filter come out to be:

Stock 20/20 carb
40/120 idle
160 air
BE3 atomizer
106 main jet

I take the same road over Reesers Summit every Wednesday to meet up with the Three Mile Island Scooter Club.  This road run is the temperature test bed to prove if I knocked holes in the cowls for any good reason.

CHT without holes = 315 °F

CHT with holes = 306 °F

If you wanna run cool ...

... add surface area

For those of us that live in a warmer climate than the Sunbeam was designed to run in, additional cooling is desirable.  I've seen folks add an extended sump.  Well, that's more oil to circulate, but when its all hot you are back to the situation of the standard sump, it doesn't help the engine run any cooler.  It just allows you to run farther between topping up the oil.  Fiddler Fred went to extremes and added an oil cooler and an oil powered grip warmer.  I was looking for a quick solution that doesn't disturb my original machine too much, but just enhances its range and tolerance to warm ambients.

So I was thinking.  If I add some more fins to the engine, I can make it cool better.  The sump pan is already pretty low, so I can't add much, but its the most logical place.  Its a nice flat area where I can strap a heat sink.  The trick was how to attach it.  I drilled hole at the back of the heat sink to locate the rear center sump stud.  This keeps the heat sink from moving around.  Then I made two clips to pull the heat sink to the sump securely.  This locates the heat sink left and right, as well as keeping it secure.  Thermal Mastic compound (a.k.a. "monkey shit") is a must!

It's a fairly inconspicuous modification and easily reversible.  I'll have to take it out on a hot day and see if it helps.  Any little bit of energy rejection has to help.  The heat sink is rated for four Solid State "hockey puck" Relays, which handle 10 amperes a piece.  It will handle more watts of energy in this application, but it will also be running at a higher temperature differential.

From the side

The ground clearance is only reduced by about 1.1".  And no one will really notice the mod unless I point it out.