k&b 6.5 quickie runs terrible
10-12-2004, 09:52 PM
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k&b 6.5 quickie runs terrible
HI to all
I have a lee custom k&b 6.5 and I'm having trouble with it.This is my first k&b so any help will really great.
Its runs but i spraying fuel everywhere.I looks to be coming out of the front bearing.I'm guessing that the front bearing is bad
and its leaking which is causing it to run bad.
I have a lee custom k&b 6.5 and I'm having trouble with it.This is my first k&b so any help will really great.
Its runs but i spraying fuel everywhere.I looks to be coming out of the front bearing.I'm guessing that the front bearing is bad
and its leaking which is causing it to run bad.
10-13-2004, 04:44 AM
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RE: k&b 6.5 quickie runs terrible
Fred,
Please tell us some more information about the engine.
How old is it?
Is it new, or are you preparing to do the break-in?
Has it been flown/crashed?
K&B engines, of the type that you have, are no different in behavior and require the same technique as other ball-bearing engines.
If I am correct, this 6.5 cc engine originated in the beginning of the 80s and excelled in power, but the MAN review done on it, by Peter Chinn, I believe, found the rear bearing was so loosely held in the crankcase, that it spun.
A noticeable leak through the front bearing, usually says there is a leak between the crankshaft and the crankcase, at the front port.
If your front bearing doesn't grind, or screech, it doesn't have to be replaced.
Please tell us some more information about the engine.
How old is it?
Is it new, or are you preparing to do the break-in?
Has it been flown/crashed?
K&B engines, of the type that you have, are no different in behavior and require the same technique as other ball-bearing engines.
If I am correct, this 6.5 cc engine originated in the beginning of the 80s and excelled in power, but the MAN review done on it, by Peter Chinn, I believe, found the rear bearing was so loosely held in the crankcase, that it spun.
A noticeable leak through the front bearing, usually says there is a leak between the crankshaft and the crankcase, at the front port.
If your front bearing doesn't grind, or screech, it doesn't have to be replaced.
10-13-2004, 09:13 AM
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RE: k&b 6.5 quickie runs terrible
Is this one of the newer RearExhaust 6.5 "q-500" engines (1990s), or an original 6.5cc Lee engine from back in the 1970's-80's ??
What exhaust system do you have installed ?? Pipe? Mini-pipe? Cross muffler ?
Which carb is installed (if it is an older version) ?
What prop are you attempting to run? Is it installed on a test stand or in an aircraft ?
What is the aircraft application ?
A few things to keep in mind in any case.....
The engines are tuned for high rpm. You have to prop them to run in the 15.5K to 16K rpm range (and above... they will run higher). If it is the newer version with the mini-pipe or an older one with a tuned exhaust, this is particularly the case. If its not turning up, its not going to be happy. Prop selection is key here.
A slight leak out of the front bearing is ok. The engines were set up with spiral lubrication paths leading from the carb location to direct fuel to that front bearing. The engine is suppose to "suck" most that fuel back into the crankcase as it runs. When the engine is new, with a ring trying to become seated... or if a ring is very worn out, there will be some positive pressure in the case during the power stroke, and some fuel can be blown out of the bearing. My experience was that even broken in and running well, it still shot some fuel out of the bearing. It is just an indication that the front bearing is being lubricated properly. There is nothing wrong with this. Sheilded bearings limit this, but they are not meant as a fluid and pressure seal... the shield is to keep particles out, not really to keep the fuel in.
When you have a chance, provide some of the additional information, and I maybe able to help you further.
Bob
What exhaust system do you have installed ?? Pipe? Mini-pipe? Cross muffler ?
Which carb is installed (if it is an older version) ?
What prop are you attempting to run? Is it installed on a test stand or in an aircraft ?
What is the aircraft application ?
A few things to keep in mind in any case.....
The engines are tuned for high rpm. You have to prop them to run in the 15.5K to 16K rpm range (and above... they will run higher). If it is the newer version with the mini-pipe or an older one with a tuned exhaust, this is particularly the case. If its not turning up, its not going to be happy. Prop selection is key here.
A slight leak out of the front bearing is ok. The engines were set up with spiral lubrication paths leading from the carb location to direct fuel to that front bearing. The engine is suppose to "suck" most that fuel back into the crankcase as it runs. When the engine is new, with a ring trying to become seated... or if a ring is very worn out, there will be some positive pressure in the case during the power stroke, and some fuel can be blown out of the bearing. My experience was that even broken in and running well, it still shot some fuel out of the bearing. It is just an indication that the front bearing is being lubricated properly. There is nothing wrong with this. Sheilded bearings limit this, but they are not meant as a fluid and pressure seal... the shield is to keep particles out, not really to keep the fuel in.
When you have a chance, provide some of the additional information, and I maybe able to help you further.
Bob
10-13-2004, 03:55 PM
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RE: k&b 6.5 quickie runs terrible
Its a original lee custom.It has the black carb,full length tuned pipe.looks to be new looking at the piston.I have it installed on a diamond dust turning a 8x8.It will start and run well at high rpm but has very little transition from idle to high.I figured it would not run like a os 40 but i cant even get it to idle at a high rpm.It will idle for 5-6 sec then it seems like it leans out then it may idle again or go so rich it quits.I noticed the excessive fuel everywhere and it looks to be coming out the front bearing and thought maybe that had something to do with it.The bearings are very smooth and do not feel bad.
10-13-2004, 04:25 PM
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RE: k&b 6.5 quickie runs terrible
Fred,
Does that black carburettor had an idle mixture needle, or disk?
Some high performance engines (Jetts, Bob?) are offered with no idle mixture control, to gain a few hundred RPM on top.
If this engine has been set up by engine guru Clarence Lee, I believe the crankshaft was originally built with the right clearance.
But who knows, maybe this engine 'ate' some grit, causing the leak.
I still don't think it is a bearing problem.
If there is a control for the idle mixture, it could be set up wrong. Try to make adjustments there. See if it improves.
It obviously cannot be both lean and rich at the same time...
Does that black carburettor had an idle mixture needle, or disk?
Some high performance engines (Jetts, Bob?) are offered with no idle mixture control, to gain a few hundred RPM on top.
If this engine has been set up by engine guru Clarence Lee, I believe the crankshaft was originally built with the right clearance.
But who knows, maybe this engine 'ate' some grit, causing the leak.
I still don't think it is a bearing problem.
If there is a control for the idle mixture, it could be set up wrong. Try to make adjustments there. See if it improves.
It obviously cannot be both lean and rich at the same time...
10-13-2004, 05:01 PM
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RE: k&b 6.5 quickie runs terrible
Its got the clarence lee custom stamp on the mounting tab.It has no idle mix screw.I have a jett 40 like that but it will idle high ok.Im new to these high rpm motors.It cant run lean and rich at the same time but it seems like it goes lean then all of a sudden goes rich slows down and quits really iratic..I just bought another 6.5 and as soon as it gets here i will try that one.
10-13-2004, 11:30 PM
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RE: k&b 6.5 quickie runs terrible
Used to run the K & B 6.5's in racing hydroplanes - the porting is timed strictly for high RPM (over 20,000 in a marine application), and we found that they were basically a 2 speed engine - "full bore" and "off". The pylon guys used to run the K & B's 6.5's with great success years ago - no carb, just a straight venturi with a fuel shutoff, and a straight pipe off the exhaust.
When you slow the engine down much past half throttle, considerable fuel spits out the carb especially if the engine has the K & B single needle carb with the air bleed hole in front. If you can find a twin needle carb to fit ( even a Perry if you can find one), that may give you more of a mid-range, but because of this engine's very high timing, achieving the low idle and good throttle transition most sport engines offer may prove difficult.
When you slow the engine down much past half throttle, considerable fuel spits out the carb especially if the engine has the K & B single needle carb with the air bleed hole in front. If you can find a twin needle carb to fit ( even a Perry if you can find one), that may give you more of a mid-range, but because of this engine's very high timing, achieving the low idle and good throttle transition most sport engines offer may prove difficult.
10-14-2004, 05:54 AM
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RE: k&b 6.5 quickie runs terrible
Thanks for the info.I think perry carbs still make a carb for this eng.I will fly it and see how it goes,If i cant stand it i will buy a twin needle carb and try that
