New guy here.  I picked up a lightly used C/L K&B .40 off the Bay, and would like to know more about it.  It is a ball bearing engine, and appears to have 3 piston rings.  I've got a Brodak Thunderbird next in line to be built, and am hoping this will be a good engine for it.  Are there any bad habits with this engine, or things that need to be modified?

I have other engines, but there's something about this one...

I appreciate any help! 

Jeff - a friend of mine had a K&B CL 40 and mentioned that it would tend to run away. He wanted more of a classic stunt run.

He sent me the head and I made a small modification. I created a hemispherical combustion chamber with a .45 inch radius while narrowing the squish band to .040 inch.

He stated that the mod tamed the engine and gave it the exact type of run he wanted.

Keep in mind that although the mod worked well for him, I can't be positive that you have the exact same version - there may have been a few different ones.

I suggest that you remove the head and and see how the chamber is configured - then you can decide what to do.

I've attached before and after pictures of an OS 60 head that I modified.

Bob Z.
 

Jeff - the one I did was a 4011 also but there are, I believe, different versions of that one also.

The one I did had a flat-top piston.

Bob Z.

They sure like 3 separate rings to me.  They're a different color from the piston material.  Three separate lines on the piston, all equally spaced.  How thick would a ring for one these be anyway?

It may be a late model ABC K&B 40 and those rings are actually oil grooves. Look closely. 

Hi, Jeff - at this point, a test is worth 1000 expert opinions!

Try it in the T'bird and see how you like it. If it runs away, first try extra head shims and if that does not work, do the "hemi-head" trick.

I would avoid cutting the sleeve since messing with a chrome/brass interface could result in the plating peeling.

Bob Z.

Well, you can be pretty certain that the T-bird will NOT be tailheavy. I ran a K&B #4055 (the CL version of yours) in a Humongus, and it wasn't enough suds. The .46LA worked MUCH better and it's lighter.  Steve

Well, I managed to run about 24 ounces of fuel through the engine today, and I was quite pleased with the way it ran.  I used some 12% fuel with a 50/50 oil mix in it, and used a 10X6 Master Airscrew, I ran it right around the 2/4 break for most of the time, and got as high as 11,500 rpm for short bursts.  The break-in run was done in about 5 stages, with full cool-down in between.  This thing runs great!

I also broke-in a new O.S. FP40 on the same prop and fuel, and it got up to 12,000 in short bursts.  It seemed happier to be running in a lean condition, and didn't have much of a 2/4  break like the K&B did.  It also ran half again longer on a tank of fuel...

Windy used that K&B 40 in the prototype profile Cardinal.  Ran well, after he putzed with mufflers and props
for a while. Ended up using, as I recall, a very wide blade wood prop, like a 11x6 wide cut down to 10" or so.
Did the job adequately, not a powerhouse, but not bad at all.  Dave Z. has good set-up info, follow his
guidelines.   

Hi Bill,

Those ABC "Stunt" engines were made for Brodak as you know.  His first entry into the "engine arena".  IIRC, the Stunt ABC was set up by the boys from Norfolk: John Tate, Willis Swindell, Mike Garmon.

Stan Powell used to build engines for Les McDonald WC Stiletto, and Dave Hemstraught's PT 19, plus his own Dove.  When they first came out, Stan said they were "OK", but could use a touch of work, PaPa Dave H. had one in his PT .19 and seemed to work well, but I don't know if Stan breathed on it.  I did set up one of the ringed engines per Stan's specs, but haven't run it yet.......

We have a NIB ABC one that I bought for Aaron when they first hit the market, gonna eventually use it!

Bill