First, kudos, nods and thanks to Larry Renger
for letting us know about his OK Cub
modifications.

Second, disclamer. Your results may vary.

   I've had a fun weekend playing with old
engines. I purchased a couple of Cubs from
a fellow club member for $15.00 each.
They're nothing fancy, just decent old Cubs.
I like them for Musciano.

   Months ago I bought a real clunker Cub for
$5.00 that someone had taken a pair of plyers too.
After reading Larry's post on setting
up Cubs, I thought I'd see what I could do to
the clunker. The only real mod was grinding the
"flywheel" to improve the counter balance.

After the mods, using a K&B idlebar plug and
a Thimble Drome 5x3 prop, the clunker turned
13,500 on SIG 35% + castor. (to 28%)

The clunker with exact same set up turned
12,500 on Omega 5% + castor (to 28%)

Here's the interesting part....

I mounted my recently aquired $15.00 Cub
and moved the plug, prop and fuel from the
clunker to the $15.00 Cub.
On Omega 5% it turned 9,800 rpm.

I then disassembled the $15.00 Cub and
did Larry's crankshaft mods. I didn't do much
else. I remounted it and installed the exact
same plug and prop and used the same Omega
5% fuel.
It turned 12,500 and surged to 13,200 for a
brief period.

Call me a liar if you want to but I'm convinced
Larry has a good idea about Cubs!

Cheers! - Keith Morgan

It is always "iffy" to give hop-up directions, as so much can be overdone, done wrong, screwed up completely (like my latest AP Wasp crankshaft, now residing in the trash).  I am glad to be of help.  In my opinion, fitting the crankshaft to the case and removing all obstructions to clean air flow are the key elements.  Balance would come 2nd.  But - whatever works for you!

Oh, the Wasp crank?  I broke off the drill I was using to drill out the crankpin, and ruined the pin trying to get it out.  Dang, the rest of the work to the crank had already been done, and was good. 

The crankshaft polishing thing seems to be a simple and very effective hop-up.  If the crankshaft/case fit is good, use 2000 grit paper to just smooth the surface.  If the crank and case, clean and dry, seem at all tight, use 600 grit until the fit is smooth, then the 2000 for a mirror polish.  Just as a reminder, you chuck the shaft into a drill, running at low speeds, and fold a piece of the abrasive paper with oil in a "U" around it.  Pinch the paper tight against the shaft and run it up and down the shaft.

One final trick, if the compression seal is really good, is to use some 600 grit paper to taper the top of the piston and the bottom of the cylinder bore.  just a lick and promise is all it takes!

Lots'o oil and a careful break-in.  Think Fox .35, not Cox .049

 

SSSH! We are working on a new line of kits for the Cox Surestart engines. These planes will stunt with the cox engine and I am sure that a OK Cub will also work on them. 
Top Secret
Larry
BHM