Hobbsy

My Feedback: (102)

A friend gave this K&B .40 to me for Diesel conversion, as you can see that is a no go. Check the back plate, it is really worn because the rear bearing was about 1/16th" from being seated. I used wood blocks and seated it with my big vise. Maybe some of you K&B officianados could comment on this odd combination of a loop scavenged engine with a Dykes ring. Then again maybe this was a common engine. Have at it.

earlwb

K&B .40 engines were very common many years ago. It sometimes seemed that almost everyone was using them. They are pretty good engines.
It used to be the mandatory engine for the Quickie 500 pylon racing class for many years, up until K&B quit manufacturing engines.
MECOA still sells them too. MECOA bought up the old K&B factory, tooling and parts and make new engines still.

As for yours, the best way to remove and install bearings is to heat up the crankcase and then pop them out or in while the crankcase is heated up and expanded slightly. If the bearings feel rough, noisy or loose then it is time for new ones. Boca-Bearings or rc-bearings for new bearings or even from MECOA.
You can get a new ring from MECOA or from Frank Bowman [email protected] Frank makes arguably the best piston rings around too.
The Dykes ring tends to wear out a little faster than regular rings. But it is easy enough to replace it though.

Some variants were Perry Directional porting and the pumper version with a built in fuel pump and a slightly larger bore carb. They also had a marine version for boats too.

The basic reason for the Dykes ring was to reduce ring flutter at higher RPMS over 15,000 RPMs or therabouts. Also the Dykes ring tended to make the engine feel like it didn't have much compression as the ring worked by having combustion chamber gasses pressing it out against the cylinder wall. The K&B .40 was sort of at the pinnacle of engine develpment for crossflow scavenged piston engines (baffle on piston) in that era. Later Clarence Lee developed the PerryDirectional Porting (PDP) for these types of engines, and that sort of made the engines a hybrid of being crossflow scavenged and Schnuerle ported at the same time. The PDP ported engines tend to run almost as good as a Schuerle ported engine, with not much difference in performance.

MECOAK&B website http://www.kbmfg.com/
and the K&B 40 webpage. You can view the owner's manual from there too http://www.mecoa.com/kb/40/4011.htm

djlyon

Loop scavenge dykes ringed K & Bs in the 29 to 40 range were very common in the 60s and very early 70s and were the power houses of choice for rat race, proto speed and early pylon. Also favored on B, C free flight .

Denis

coriolan

The marine version of the K&B .40 was also used in Sport-40/Div-I by NAMBA&IMPBA until the 90's. Good performer in these 36" hydroplane hulls which was restricted to loop scavanged engines (Div-II was for .45 no restrictions), at that time only HB and Webra still had LS .40 size engines but they were rare here!

downunder

It's not really all that odd. All of the square crankcase Testors McCoys (19, 29,35,40) were like that as was the model 6002 Enya 40 and certainly there would be others too.

turbo.gst

My Feedback: (8)

I still have a K&B .40 pumper. It thinks its a .45! I have always liked the engine as it has very good power and is very lightweight. It has a Dykes ring and loop porting ( no PDP). It does burn lots more fuel with the big carb.

Hobbsy

My Feedback: (102)

Thanks all, I am now K&B informed, at least more so. My friend has two more so I'll give this one back and see if he has one with a flat topped piston.
I am currently dealing with a messed up shoulder. I tore my left bicep muscle completely away from my shoulder. It's hard to work on engines with one arm. It is being repaired on Mar. 12, then six weeks with the arm lashed to my body, then no mowing, no tilling or Harley ridin until June 1. If I can get some help I may be able to fly a little.

earlwb

In this engine line they all have a baffle on the piston. You have to go with a K&B .40 rear or side exhaust Schnuerle engine to get a flat topped piston on them.  But K&B primarily made those for ducted fan use (albeit they made great outboard marine engines too).  The K&B .40 baffled piston engine with PDP, a pump and pump carb runs as good as most any of the Schnuerle .40 engines do with the flat topped pistons.

MrMotor

Dave
If your friend has a K&B 4050 ABC engine they look the same, but have a flat top piston and porting like the old Super Tigre G-21 series engines from the .29 through the .35 combat engines.

djlyon

The picture is of a Series 74 K&B intended for Formula 1 pylon racing. It is probably the last of the dykes ringed baffle piston competition engines by K&B. I believe the first was the series 64 then 67 and 71. After the 74 came a new design the 6.5 schnuerle engines. Then came the 5.9 and 6.6 and maybe more. The series 6x and 7x came in both front and rear rotor and were mostly intended for competition. From the basic design a sport engine also evolved which I believe continued on as a dykes ring loop scavenge until it was hanged to a flat top and ported as mr. motor says

Hobbsy

My Feedback: (102)

Thanks again all, good stuff.

Jim Thomerson

I ran a K&B 4011 on diesel fuel. I kept the glowplug heated for about 20 seconds after it started. Once warm it ran well and turned an 11 x 5 APC exactly the same RPM as glow, but with the Needle in 1.5 turns. The Schnurle K&B 6.5 should dieselize nicely.