Paul,

The earlier Series 75 8011 K&B .40 has the "small" front end. It uses a roll pin and a setscrew to attach the drive hub to the crank. That worked ok if not abused. (I abused several....)

The later 4011 K&B .40 has a larger front bearing and a one-piece crank setup. No roll pin or setscrew involved. I think all of the rest of the parts are interchangeable--we certainly have done so on the Quickie Rat engines.

I suspect that the idea behind the 8011 multi-piece crank setup was to make replacing dorked cranks less expensive. If the main part of the crank is still straight, you can just replace the threaded stud and aluminum hub. In practice....? There's a reason they switched to what is a standard construction for every other engine manufacturer....

There have been other variants in the series, such as the 4045, which is based off of the 4011. Their numbering system generally makes sense.

Sounds like your carb situation is most (all?) of the problem.

Dave

Paul,

The earlier Series 75 8011 K&B .40 has the "small" front end. It uses a roll pin and a setscrew to attach the drive hub to the crank. That worked ok if not abused. (I abused several....)

The later 4011 K&B .40 has a larger front bearing and a one-piece crank setup. No roll pin or setscrew involved. I think all of the rest of the parts are interchangeable--we certainly have done so on the Quickie Rat engines.

I suspect that the idea behind the 8011 multi-piece crank setup was to make replacing dorked cranks less expensive. If the main part of the crank is still straight, you can just replace the threaded stud and aluminum hub. In practice....? There's a reason they switched to what is a standard construction for every other engine manufacturer....

There have been other variants in the series, such as the 4045, which is based off of the 4011. Their numbering system generally makes sense.

Sounds like your carb situation is most (all?) of the problem.

Dave

I hope that's the case.  The Irvine carb manual recommended a MUCH richer initial low needle setting than what I had.  I'll give that a go before swapping engines.

Paul,are you sure it is the engine.  I have had several engines that worked great on the bench but not work on the plane.  I was using three line Roberts/Brodak.  Seems it needed a littlecleaning up the bell crank system and the handle.  The sharp edges were working against each other.

If its ABC its the 4055 r.c. or stunt ( no differances inside ) The big front ends got the same sizes as the SRII 20+000 rpm engines , and a real con rod . So shouldabe the fastest of the Torpedods ,
wotwere SPEED & Rat Race top line engines , in the 1960s .

https://outerzone.co.uk/plan_details.asp?ID=13862&pth=brwsplns

" Someone once said: it's what's up front that counts, and as far as the K&B .40 is concerned it has more power, right out of the box, than anyone has ever seen in this type of engine before. "

Brett,

While the overall concept of a replaceable stud might be the same, it sounds like the Jett has a more robust detailed design. The Kay Und Beast 8011 forward shaft is held on by a tiny roll pin and one setscrew thru the drive hub as shown in the picture. For ease of assembly, the hub is a slip fit to the shaft, not a press, so that adds instability to the joint as well. There are several ways that this scheme can come apart on you. The first is trying to use a spinner nut with the stud and the stud makes contact with the pin before the nut bottoms on the prop...and you're D-U-N done. The next is when the engine has been run hard and the setscrew (hardened steel) chews its way into the crank. Then it's good for one more run--maybe--and yer prop departs.

To solve the first failure mode, get rid of the stud and use a hexbolt instead. Make sure the bolt is short enough with the props you are using to never make contact with the roll pin. Or, use some red LocTite on the stud to keep it from creeping into the drive hub as you keep swapping props around during testing. To somewhat mitigate the second issue, grind the end of the setscrew flat and grind a flat on the crank after you have drilled the hub/shaft for the roll pin. You have to ensure alignment, else you are using up some of the material strength just on poor assembly work.

Once I got past these issues, I have run the 8011's for years in Quicky Rat. There is one obscure advantage to the 8011: since the drive hub has a shoulder on it, you have to counterbore all your props out to the molded ID of the APC prop. (7.8x7's are de rigueur). You therefore eliminate any grief from unbalanced props that came from the factory with the hole not centered. Silver lining!

Dave

PS--Air Miniseries showed the picture and plans for a Grmzpf, but he also had a Sprntr and maybe even a Grzula---all designs by one of our former club members here in the SoCal--Don Burke.

Brett,

While the overall concept of a replaceable stud might be the same, it sounds like the Jett has a more robust detailed design. The Kay Und Beast 8011 forward shaft is held on by a tiny roll pin and one setscrew thru the drive hub as shown in the picture. For ease of assembly, the hub is a slip fit to the shaft, not a press, so that adds instability to the joint as well. There are several ways that this scheme can come apart on you. The first is trying to use a spinner nut with the stud and the stud makes contact with the pin before the nut bottoms on the prop...and you're D-U-N done. The next is when the engine has been run hard and the setscrew (hardened steel) chews its way into the crank. Then it's good for one more run--maybe--and yer prop departs.

  Agreed, that is less-than optimal!  Dub knew enough not to put set screws into the side of the shaft. I am not sure why so many manufacturers took excessively "creative" ways to drive the prop, McCoy was using a taper arrangement in 1947, at least for the engines intended only for airplanes. Those intended for tethers cars had it set up proper for that, and a big mess for props that was clearly an afterthought.

    I will take one apart later but the Jetts are completely conventional, using a split-taper wedge arrangement (at a steeper angle than the ST and similar, so it is not so prone to jamming) and no threaded section. It's just drilled and tapped for a long 1/4-28 set screw, so you can whack it into the pavement at full speed and it doesn't hurt the crankshaft.

   Brett

The bench run went PERFECT.
With the Irvine carb set to factory default values it did exactly as forecast.

First flip hand start.
Running rich at 14,000 RPM.
Leaned out to 16,000 PRM (9-6 Master & 10% nitro)
Idled down to 4,000 RPM.
From low to high and back down smoothly.
Engine could not be stopped by a throttle jockeying.

Tomorrow is the air test.

I am familiar with the prop stud design of the #8011 and earlier K&B Series '61 etc., and I had at least one #4055 long ago. I am fairly sure that the #4055 also had a replaceable prop stud. I got some extra long replacements studs from K&B/MECOA to use on a RO-Jett to experiment with stacking props. I'm not sure why MECOA had them. Maybe so one could screw a spinner tip directly onto the prop stud? Otherwise, no idea.  Steve

It was just silly. The cranks of the Series '61 and possibly the 8011 had a ring around the crank disc, the crank pin was pressed in, the propdriver was held on with the setscrew, and the prop stud screwed into the propdriver. I've lost count of how many parts that totals up to, but it was dumb and caused me personally a lot of engine failures.

The crank would snap off at the rear side of the front bearing, a shaft run would ensue, the crankpin would work its way out, eating the backplate, which trashed the piston/cylinder fit, ate the glowplug, and in one case, blew the post out of the middle of the exhaust port in the cylinder. But K&B was very good about free repairs. Still a PITA.

Other than that, the engine would put out a lot of power, such as 105 mph on a Big Iron based combat model, 9-8 tornado nylon and K&B 100 fuel (10% nitro?). I never really got one through the break-in stage before the crank broke and barfed the rest of the engine. Leading me to changing to the unbreakable Super Tigre .35C, which would run 116 with a full 9-8 Tornado nylon on 50% Fox Blast sans streamer. The ST did NOT like crankcase pressure, but ran great with a Binky pacifier.    Steve