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Speed,Combat,Scale,Racing => Carrier => Topic started by: Jim Roselle on February 12, 2016, 11:53:48 AM
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I plan on eventually building a class 1 model and have a chance to pick this motor up for $40, would it be suitable? I'm intrigued with the idea of rotating the intake 90 degrees for reverse rotation.
Thank you,
Jim
(http://i.imgur.com/T8gv43M.jpg)
(http://i.imgur.com/U4QyUBB.jpg)
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Is 90 degrees exactly right? Will that give exactly the same timing in reverse? It seems too good to be true.
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Is 90 degrees exactly right? Will that give exactly the same timing in reverse? It seems too good to be true.
I know right? I've never done it but I've seen it discussed here.
Jim
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I have done it, but never used the motor in competition. It did seem to run well in reverse though.
PS as I recall it was right if you looked from the rear to the front.
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A CL I with this model K&B will not have the High Speed potential of a K&B 6.5 or Nelson .40 powered plane. Low Speed will be fine.
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K&B makes a reverse crank for this engine, if you can find one.
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If you rotate the front housing 90 degrees counterclockwise (as you look at it from in front of the plane), the timing will be correct for clockwise rotation ('Pusher' prop direction). The actual timing numbers (for the crankshaft) of the K&B .40 are open at 35 deg. after bottom dead center and close at 45 deg. after top dead center which is 190 deg. total. Rotating the front end, and measuring in the other direction, it opens 45 deg. after bottom dead center and close at 55 deg after top dead center. Represents a 10 degree shift, but still 190 degrees total. This was what I just measured on an older model K&B like the one in the OP. (I think that is the 8011 model).
Other makes of engines will have slightly different numbers, but they would still be close (enough to run, anyway).
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An OS 40 4BK carb fits some of those K&B 40's really nice. The K&B is not a Nelson or 5.8 but it will get you going.
Wayne
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Thanks for the input guys!
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An OS 40 4BK carb fits some of those K&B 40's really nice. The K&B is not a Nelson or 5.8 but it will get you going.
Wayne
Wayne,
Do you prefer the OS carb over the perry?
Thanks,
Jim
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If you are going to leave the pump on it, keep the Perry carb. If you won't be using the pump, then the Perry will have too large a throat and you should switch to something which will run on suction.
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I have never had any success with Perry Carbs. Gary Hull turned me on to the 4 BK when I flew a Class 1 Guardian several years back. I had a K&B 40 with the large throat and was fitting the Perry carb. So I tried the OS 4 BK and wa-la ran just great. So when I started out using the Irvine .36 in my PC which came with a Perry I ditched it quick and put the 4 BK in. Once I got it set it was really steady and provided what I needed. I like them. Good steady performance.
Wayne
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I have used perry carbs and never had any problems, but os carbs are easier to adjust in my view. I would think the os 4 d would be good for the K&B.
One point on perry or any carb. If they have sat around and we're not put away clean they can have junk inside. The perry carb is particularly sensitive to this. By the way some K&B 40's came with perry carb and some with a K&B carb which is very good also.
John
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I have used Perry's without incident also - though they are a little more sensitive on the low speed adjustment. But that Perry carb will have a much larger throat diameter than a suction carb - and if one wants to run the pump, it will add power to use the Perry pump carb. If you are going to switch to something smaller (like a 4bk or a 4d), there is no point to running the pump. And an already 'sport' engine will get even 'sportier'.
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Another plus with the K&B is that, if you want 'more' (which we all do eventually) any number of engines will fit the mount holes. Ie. OS SR series, K&B 'S' and 6.5 etc. TS
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Perry does or at least did make a suction carb that fit the K&B sport 40. As I recall it was fairly common on RC models. No I won't say why I know about RC.
John.
PS here is a link of a review that may be helpful
http://sceptreflight.net/Model%20Engine%20Tests/K&B%2040%20Series%2070F%20RC.html