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Author Topic: Converting a 1975 K&B .35 to BB front end ???  (Read 737 times)

Offline frank mccune

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Converting a 1975 K&B .35 to BB front end ???
« on: April 30, 2023, 02:56:38 PM »
     Hi All:

     As the header states, how is this done? In the past, I have seen this conversion done by bolting on a front end from a K&B .40 from the seventies.  Series 75 it may have been called.   This was also done to the K&B .35 Torpedo.  What parts are need from the .40?  Is this a direct swap or does the crank and rod also need swapped?

      What if any advantage would I gain?

      Inquiring minds want to know.

      Frank
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Offline Air Ministry .

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #1 on: April 30, 2023, 07:58:34 PM »
cording to this .http://sceptreflight.com/Model%20Engine%20Tests/K&B%2040%20Series%2070F%20RC.html

and this http://sceptreflight.com/Model%20Engine%20Tests/K&B%2040%20Series%2070F%20RC.html

it might be .0376 m.m. bigger in the gas passage. but I doubt it . the STROKE issa da SAME .

The opening and closing offa da Intakes a liddle earlier , maybe 5 degrees .

Soit should ' FALL ON ' no ploblem . Butcha wont know untill ya tryit . As In Dont first belt it over . Touchy feelly fingetip turn it cautiously .

Technically it might run freer & tourqueier . As in swing say a 11 inch prop ( 11 x 5 ? ) more happilly .
But essentially youd have a Iron Piston de bored K&B 40 Torpedo .  :P

So , if ' the bits ' were doing nuthing , theres no harm trying it . And It'd save nosweight so it'd be lighter . ( :-X)

Torp 40'd pull more aeroplane . The .35'd still be a .35 .
« Last Edit: April 30, 2023, 11:55:19 PM by Air Ministry . »
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Offline Clint Ormosen

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #2 on: April 30, 2023, 08:55:41 PM »
Quote from: Air Ministry . on April 30, 2023, 07:58:34 PM

it might be .os76 mm bigger in the gas passage. but I doubt it . the STROKE issa da SAME .

The opening and closing offa da Intakes a liddle earlier , maybe 5 degrees .

Soit should ' FALL ON ' no ploblem . Butcha wont know untill ya tryit . As In Dont first belt it over . Touchy feelly fingetip turn it cautiously .

Technically it might run freer & tourqueier . As in swing say a 11 inch prop ( 11 x 5 ? ) more happilly .
But essentially youd have a Iron Piston de bored K&B 40 Torpedo .  :P

So , if ' the bits ' were doing nuthing , theres no harm trying it . And It'd save nosweight so it'd be lighter . ( :-X)

Torp 40'd pull more aeroplane . The .35'd still be a .35 .

Anyone want to translate that into readable English?
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Offline Dave Hull

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #3 on: April 30, 2023, 11:24:51 PM »
I agree with Air Miniseries--whatever it is he said!

So you end up with a custom conversation piece without the ring to go bad?

The Divot
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Offline Air Ministry .

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #4 on: April 30, 2023, 11:57:12 PM »
Yea , looks like it'd go straight on .
And you wouldnt even need a big hammer .

You wont know till you try it .

If its stuck , put it in a vice , tight. and use a Stillson . & take a video .  VD~
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Online C.T. Schaefer

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #5 on: May 01, 2023, 04:49:59 AM »
We did this back in the day. The series 75 .35 had a ring like the .40.  In an effort to see if it might be a decent racing engine we bolted the front and rear from a .40 RI on there.  We found not much difference and abandoned it.  TS
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Offline BillLee

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #6 on: May 01, 2023, 08:45:24 AM »
Quote from: C.T. Schaefer on May 01, 2023, 04:49:59 AM
We did this back in the day. The series 75 .35 had a ring like the .40.  In an effort to see if it might be a decent racing engine we bolted the front and rear from a .40 RI on there.  We found not much difference and abandoned it.  TS
Same experience exactly.

Bill
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Offline Steve Helmick

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #7 on: May 01, 2023, 04:33:40 PM »
The 1975 K&B .35 is an engine I've never had, but I've had two K&B Series 61 .35's and various K&B .40 front intakes. My experience with them wasn't good, and the crankshaft was the main problem. Not sure if the 1975 .35 would have had the 'stuffer' type crankshaft, but some folks had the ring come adrift on them and cause havoc.

Mine usually snapped the crank off behind the front bearing (these were the ones with the prop driver held on with a set screw and later also pinned to the crank), but a few times the pressed-in crankpin came out and gouged into the backplate. The last type of K&B .40 (#4055) appeared to have fixed all that, but is about an ounce heavier. By memory, about 10.5 oz, which is just too much, and less stunt power than a .46LA. The best thing about the K&B #4055 is that the mounting bolt pattern is the same as a .46LA.  H^^ Steve
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Online Ken Culbertson

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #8 on: May 01, 2023, 09:03:42 PM »
Quote from: Clint Ormosen on April 30, 2023, 08:55:41 PM
Anyone want to translate that into readable English?
That was English, you need it translated into American. LL~

Ken
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Offline Air Ministry .

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #9 on: May 01, 2023, 09:16:04 PM »


Anyone tried the later one for SPEED or RAT .
Seems the bigger shaft should feed better ?

So it'd depend which front end He used . 60's or 80's



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Offline frank mccune

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Re: Converting a 1975 K&B .35 to BB front end ???
« Reply #10 on: May 02, 2023, 09:03:58 AM »
     Hello All:

     Thanks for all of the prompt replies!

     I have a great starting 1975 K&B .35 that I have started to break in for Sport use.  Just because can do it, does not imply that it may produce better results.

     Stay healthy,

     Frank
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