Killer Bee crankshaft

Thanks, Roddie,

I tried and the problem persists with other drive plates as well. I am also puzzled as one would believe that the splined end, before the splining is added, is centered when made on lathes and grinding machines i.e. rotating machinery..

On the other hand the excentricity of the drive plate is so visible and big that the splined end would have probably snapped before reaching the excentrivcity by bending so much in e.g. a forced nose-dive landing - that I do not remember having suffered.

Well, every surface of the crankshaft is machined somehow, and that means it has been removed from and re-attached to the lathe or whatever at least once during the machining process. Actually it has to be attached three separate times, as the crank pin is most likely machined so that the shaft is mounted eccentrically, and the crank pin is in the rotation center. And probably the final finish of the bearing surfaces is done in yet another phase.

A mistake (like an itty bitty metal shaving in a the wrong place) in any of these phases would mean that the next machining would be off center. How does the counterweight end look? Any eccentricity there? Is the prop stud hole in the center of the shaft's main axis or in the center of the splined part?

In any case it looks like it's a manufacturing error.

I agree Kari..I think the stud hole is located coaxial with the splined end. I noticed severe engine vibration but the prop balance test proved negative. The Counterweight end looks good,so I also believe this is a rare production error.

The other issue I noticed with the anodized aftermarket crank-cases is the radial gap betwen the nose bore and the shaft is  more than on old stock engines.. this is also felt if you try to move the prop shaft radially and you feel the "play"..moreover, if you suck on the crank nose at the splined end (with the crankshaft placed in the case), even if there is oil captured inside the crank nose and on the bearings, there is a sensible leakage of air...even though the black anodized surface inside the nose is intact i.e. not worn because of the unbalanced run of the propeller on the excentric splined end. One may assume the lose fit is to reduce shaft friction and boost performance, but the gap will just grow further when the engine is hot (aluminum expands with temperature rise more than steel) and also compromises the sealing towards the crankcase.

Sic transit gloria mundi...aftermarket is not always up to the old-stock quality and fitting..

.. A KB crank is an expensive part to shelve. Have you only tested it in that one crankcase? Maybe try another "stock" crank in that case.. to see if it runs true. Alternately; try the KB crank in a different (older..) case, which still has good tight clearances. I know that it's laborious to pull-off and press-on drive-plates.. but you might be surprised with what you find.

Yes!!!!

It's happened to me several times, makes the engine run like crap. Doesn't matter what drive plate you use or how straight the bolt is. There was a bad run of those for a while maybe you have one of those?

I had the same problem also . Ended up throwing the two I had in the garbage . Wish I could get a couple of the original Killer bee cranks .

Mike1484

The first run of the after market KB cranks did have tolerance issues. I remember there being a close out on them 3 or 4 years ago. These have a hole in the center of the crank web. The later runs of these cranks were better and do not have a hole in the center of the crankshaft web.

Thanks to all for your answers and unfortunately similar experience. Roddie I will give it a try in another crankcase and see before I dump it

Jason_WI wrote:The first run of the after market KB cranks did have tolerance issues. I remember there being a close out on them 3 or 4 years ago. These have a hole in the center of the crank web. The later runs of these cranks were better and do not have a hole in the center of the crankshaft web.

Bingo Jason...the problem shaft really has a hole in the middle of the web....I checked the other that runs fine and it does not. Just wondering how I did not notice the difference when I bought the 2 together...thanks anyway. The next time I buy one I will ask the seller not to pick one with the hole in the middle of the Web.

I had one of the wobblers a few years ago. I think the seller replaced it and I threw the bad one away.

I got a new case and two bad crankshafts (i will have to ck. and see if the web has a hole ) didnt know this , I just gave up on it without buying the shaft and case together , and then Low and Be hole i got a golden bee case that has one in it feels good to , the engine has a muffler on it ? !

I had bought one of the LH TeeDee cranks off e-bay and it too as not concentric... pretty pricey item, so I sent the seller a note that started an argument

I mailed the problem shaft to him and he did a side by side with others he had and sent me a new one with no other comment

Mine was bad enough to be visibly evident

I had read, on another forum, a note written from a guy who worked at Cox and he related a lot of the Cox success was the very well trained ladies that did a good job of culling out the bad parts--- AND once many were detected--- the whole Barrel of that part was put to the side to be examined and the error corrected back up the production line...In the later years the new owners were not so prone to trash an entire LOT of suspect parts

fredvon4 wrote:........I had read, on another forum, a note written from a guy who worked at Cox and he related a lot of the Cox success was the very well trained ladies that did a good job of culling out the bad parts--- AND once many were detected--- the whole Barrel of that part was put to the side to be examined and the error corrected back up the production line...In the later years the new owners were not so prone to trash an entire LOT of suspect parts

I have no feel of how much  purchase value the price,  i.e. less than 4 bucks in the mid 70-s, of  a COX Babe Bee had, but still wonder how that high quality work and precision that 4 USD could pay for, let alone the profit that COX obviously also included...

Assuming a 10-times inflation rate of the US currency since the mid 70-s (it may have been quite different than my assumption) , it would still be hard to understand how a COX Babe Bee that would sell accordingly at 40 bucks today, could be produced today at such cost of less than 40 dollars - to allow for some profit as well...

So the cost coverage for the quality that a COX engine represents to me remains an unresolved puzzle....

In answer to questions posed in this thread:

1) Some years ago we had a bad run of KB cranks. We salvaged the good ones and recall bulk-auctioning the not-so-good ones. At the time, anyone who got a bad one from us and let us know would have received a replacement; the caveat being that they were purchased directly from us and bought as "good".

2) We, nor anyone else besides Cox, have ever manufactured a crankcase. Everything out there in the marketplace is OEM Cox production.

3) We, nor anyone else besides Cox, have ever manufactured a complete engine. We did manufacture tanks, backplates, etc; in short everything past the end of the crankcase. The reason that we can offer a Babe Bee for $45 is because we purchased 35,000 Surestart engines from Cox at fire-sale pricing.

Thanks for the clarification Bernie, I guess we all agree that no offense was meant with this thread, but simply a discussion on the similar experience of some of us with the faulty run of KB crank shafts. I personally do not even remember if I bought my wobbler shafts from you or from others, but I do remember I bought 2 good KB shafts from you that I have built in my TeeDee Reedie engines and already use one with satisfaction.

What still puzzles me and this may have been already discussed here before is why the anodized crankcase seemingly has a bit larger bore diamater in the nose than non-anodized ones? I clearly feel the radial play and can suck air through the crank while I cannot suck air through a non-anodized one, nor feel the radial play. Maybe COX assumed anodizing will add a few microns in material thickness and the bores were drilled a bit loser for anodized cranks than for non-anodized?

Absolutely no offence taken Andras

If anything, anodizing adds an extra layer, more-or-less depending on colour, so anodized versions should, in theory at least, have less play.

Cox did not make any different for anodizing. However, we derive our crankcases from the 35,000 complete engines we purchased and they are from a variety of different production runs, each seemingly with different tolerances. In Cox's latter years, tolerances were more "relaxed" to keep costs down.

Andras,

1. You pose a most interesting question.  I believe you somehow ended up with a poorly machined crank is the bottom line. I've found that it tends to be "Russian Roulette" whether or not one actually receives the best parts (or engine) that they hope for. One needs accurate machinist quality tools to measure such things in order to pronounce them good or bad, usable or unusable. I suppose this is why I prefer (whenever possible) to obtain new old stock original Cox parts for the best "hope" of consistency. I've previously proven in competition that standard parts from Cox International have been excellent. I've also had new "bad parts" that I've had to return... This is no different than when Cox produced originals in California.(They had bins of returned engines, many which were not even faulty)
Since I don't have access to factory drawings, my selection process is simply to swap various parts onto a "known" good running engine. If they perform "below par" (or vibrate excessively), then I have my answer & those offending parts are quarantined...(or scrapped). Fortunately, the relatively lower cost or Cox parts compared to other engines makes scrapping parts much less traumatic.

2. Fit of the crank to the c/case: Again I do not know the factory spec for this clearance, but I do know that (for high performance mouse racing) it is CRITICAL to .0005". (one half of a thou) So much so, some racers have added a bronze bushing that they precisely hone for the "ideal fit". The late Joe Klause of K/K fame used to offer these bushed c/cases. HOWEVER after obtaining some, I note with dismay that they can run 1,000 RPM slower than my stock plain anodized c/case!! So therefore I've concluded that if the crank to c/case clearance is either too little or too much, both are bad for high performance running. I will grant you that the bronze bushed c/cases will have a much longer service life than stock. My very best running Cox's just use the original stock hard anodized c/cases ( Killer Bee, Venom, Black Widow). On occasion, my inspections have revealed the anodizing has rubbed completely off at the front end. if the performance has dropped off, these c/cases are then relegated to "sport status" or scrapped.

No doubt you've come across tiny metal pieces, dirt, or even baked on oil that have virtually welded themselves to the steel crankshaft. In such cases these "bumps" must be gently removed on the lathe (or drill press) with fine sandpaper to prevent such cranks from damaging a newly fitted c/case. The use of Crocus cloth is useful to restore the final finish to the crank.

It would indeed be fascinating to be guaranteed an engine where all these things are "blueprinted to spec". Unfortunately that raises the price to way beyond what most people feel  "a Cox 049 is worth".  In the meantime us tuners will continue to "play"... & have FUN!

There used to be more people to ask about such things, but sadly most of them have passed on. I hope this helps, Andras.

Cheers, Paul ( aka Mr. Mouse)



" this thread, but simply a discussion on the similar experience of some of us with the faulty run of KB crank shafts. I personally do not even remember if I bought my wobbler shafts from you or from others, but I do remember I bought  2 good KB shafts from you that I have built in my TeeDee Reedie engines and already use one with satisfaction.

What still puzzles me and this may have been already discussed here before is why the anodized crankcase seemingly has a bit larger bore diameter in the nose than non-anodized ones? I clearly feel the radial play and can suck air through the crank while I cannot suck air through a non-anodized one, nor feel the radial play. Maybe COX assumed anodizing will add a few microns in material thickness and the bores were drilled a bit looser for anodized cranks than for non-anodized?"

[/quote]

Thanks Paul this is a really comprehensive answer and I appreciate the details.

(I am a bit embarrassed because while I truly love COX engines I seem to be one of the most scrupulous owners when it comes to judging their quality that COX in my eyes is a champion for, and the occassional quality issues on these critters  are annoying me even more so...)

The radial gap I experienced on the anodized crankcases was not the consequence of excessive wear or metal grits stuck to the shaft...they showed this gap from the time the postman shipped them.

In my opinion the excessive radial gap will not only end up in poor sealing of the crankcase, but sooner or later - like any journal bearing of these symptoms - will get worn even more by the shaft that is floating radially and hammering the crankcase. I guess engine longevity and right (not too tight, not too lose) fitting walk hand in hand: the approx. 300 hours runtime on one of my TD051-s born in the 1970-s would not have been reached before I retired it in a still workable condition, had this engine had the lose fits in the cylinder and crank that later engines sometimes showed. Yes it is true that COX parts are available at a relatively low price, but I want to keep the genuine components running till the engine falls apart...


I tend to accept that later - though genuine - COX parts may have been subjected to less stringent quality control, and my anodized ctrankcases may come from that population.

Notwithstanding the above, I keep loving them...

Well Andras.. that does shed some light on the subject. We all learn from these postings.. and the experience/knowledge shared from others. It helps us understand what we're dealing with.

I "think" I've gathered one valuable thing from this conversation. Old Cox engines are probably worth buying.. for their attention to parts-fitting during the early years. There's thousands of old engines out there... that were fitted by people who cared about what they were doing. Your TD 051 was one of those engines my friend!

While I'm at it, I find it useful to have a look at the surface finish of the crank pin. Some crankpins are surprisingly rough!
(especially when viewed under a 10X magnifying glass ). If the roughness is not too bad, then I find the crankpin finish can
be restored with 400-600 sandpaper & oil followed by crocus cloth (with no oil) for the final polish. Afterwhich, the assembly
is cleaned in solvent with a toothbrush. Using a 5-40 prop stud for a mandrel, I mount the crank in the lathe for ease of handling
while I work on it.

As you know, super clean, polished crankshafts tend to spin easier in a given crankcase...

Cheers,

Paul G. (aka Mr. Mouse)