K&B Drum Rotor 7.5 Motor, Info needed on power, et

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crrcboatz

Well-Known Member
Joined
Oct 18, 2002
Messages
403
Can you all give me info on the Drum rotor 7.5 K&B. Reliability, power, mods necessary to help, etc. I have an almost new one I traded for and would like to put it in an aeromarine scorpion 37 inch hull. It has the higher timed exhaust cylinder as the notch at the top of the exhaust port indicates. Drum appears to be well made, ie good bronze bushing for the rotor. Carb is quite large in venturi diameter and has remote needle.

Also is there a water cooled exhaust made for it. I have a prather exhaust throttle I could freeze the throttle open with red locktite but would prefer something lighter.

I realize they are not of the output caliber of the Mac and Cmbs but hope with a good setup and the scorpion hull which I really like could be made to be competitive.

Pipe settings would be helpful also. Plan to run 40% nitro.

Regards Curt
 
:blink: Well, been @ 10 years away from running Ka ~ Booms but here you go.

The liner porting is fine, but if wanting the most bang? level out the EX port to the higher level accross the entire port. ;) Make the roof slighty arched so the middle is highest and the sides slightly lower.

:unsure: This way the piston gets tucked in at time of ex port closing not snagging the top edge.

:rolleyes: Intake rotor timing ( Get a degree wheel ) Open at @ 32 degrees ABDC and close at @ 65 to 68 degrees ATDC.

;) ;) ;) If you can be ACCURATE !! ........... Open up the transfer passages on both transfer runners of case, remove 3/4 of the boost ports bridge on case and sharpen the bridge area thats left.

Then all the typical blueprint tricks matching up all the edges for best flow and removing some of the piston skirt that is at the rear to uncover the boost ports at BDC.

Get an RPM ROD !!!!!!!!!!!!!!!!!!! The stocker is GARBAGE and hold up worth a damm.

Replace the MR6901 rear and R6 stock bearings with BOCA's or WTB's , and use the TH9 retainer type .. Kind of a hi tech nylon composite.

On 40% fuel ( What I ran too ) Head clearance was @ .014 + /- .002"

:p Now ....... This will REALLY wake up the K&B and most likely cause it to break rather quickly :angry: :angry: :angry: :angry:

I chased Piccos in the early / mid 90's with them, beat them a lot too but had MAJOR failures all the time. Break the cranks pin right off the journals.

They were VERY VERY fast but to unreliable to race with.

******** Best pipe hands down !! a OPS .67 nitro pipe restingered to @ .370 I.D. and set at @ 10 3/4" to 10 5/8" ......... Second best pipe a MACs 10cc aircraft pipe at about the same lenths.

My Ka ~~ Booms were running at 26,000 / 26,500 when tested by a sonic tach running WOT in my Cal craft monos.

:D Good Luck.

Scott
 
Last edited by a moderator:
Scott, you sound like da man!

What can you tell me about my K&B .67 and .82? Both were purchased from ebay a yr or so ago. The .67 is new, never run and the .82 is used.

The .82's conrod is a skinny looking dogbone type of thing just waiting to break :rolleyes: ! The engine looked great like it had been barely used when I got it but it had low compression. I took it apart and it looks like someone had taken out the little used piston and sleeve and substituted a totally worn out pair. My first ebay ripoff :angry: .

Anyway, I'm not planning on racing but I'd like to know as much as possible to make them go as fast as possible. I'd like them to be reliable. Thanks, Scott.
 
Oh, I forgot to add that the only pipe I have is my muffled pipe that came with my OPS .65 that I purchased way back in 1979!

It's pretty quiet and I'd like to stick with muffled or quiet pipes even if I give up a little power but I'll take any recommendations you have. BTW, how are the Mac pipes? They make a bunch of different nitro and quiet pipes!
 


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