Clarence Lee K&B .61 vibration issue
#26
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I also have a K&B 61, one thing to check is the prop stud. Those engines had a screw in prop stud and if you don't have it screwed all the way in it can cause vibration. I have a Kwik Fly II that I fly with a Webra Speed. I guarantee you that the Webra vibrates a whole lot more than the K&B and it isn't a big problem, I do use a glass filled mount which dampens the vibrations.
#28
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Hi Carl, I am new to RCU and read the threads for amusement, but I am going to throw my two cent in on this one. I bought a K+B 61 in '77 and '89 both ran great, the standard prop was 11x7 or 7 1/2 for sport or pattern flying. Your Kwik Fli with a K+B 61, what a classic combination! You probably have done it by now, but I would first try a different prop and then if that did nothing, remove the prop stud (if it is removable) and roll it across a flat surface. All single cylinder engines, have vibration issues, that change depending on the RPM. Usually the mid-range is where the vibration is the most noticeable, usually aggravated by the mixture going a little rich. I am a life long wood worker and all wood is in constant movement usually due to atmospheric conditions, so I would be suspect of the wood prop, it may have taker a twist. It also could be a manufacturing defect, where the crankshaft wasn't drilled and tapped properly and causing the problem. I always liked sig mounts and never had a problem with them, besides you scratch built the plane and isn't going to fall apart like an arf from vibration! I also doubt given the RPM range of the K+B that any amount of fanatical prop balancing would be of any help. I hope this has been helpful, let us know when you find the problem, it should be interesting. Jim
#32
I think the iron piston comment was comparing the vibration of an iron piston to say ringed aluminum or ABC...
FWIW, the K&B .61s are ringed aluminum pistons in steel liners and have a twin ballraced crankshaft. I think the Carburetors they came with varied over the years though. Probably mostly Perry, eh? This is all AFAIK anyway. I'm kinda dum tho...
FWIW, the K&B .61s are ringed aluminum pistons in steel liners and have a twin ballraced crankshaft. I think the Carburetors they came with varied over the years though. Probably mostly Perry, eh? This is all AFAIK anyway. I'm kinda dum tho...
#35
My Feedback: (3)
I ordered a K&B carb and remote needle valve from C. Lee. He gave me a $5 because it was an engine he had modded. Normally, the carb looks like a block sitting there but these have the nice K&B badge and give the engine a great look. It's the only 2 stroke carb that I've thought improved the looks of the engine.
#36
I ordered a K&B carb and remote needle valve from C. Lee. He gave me a $5 because it was an engine he had modded. Normally, the carb looks like a block sitting there but these have the nice K&B badge and give the engine a great look. It's the only 2 stroke carb that I've thought improved the looks of the engine.
#39
Yup. That is the newest K&B carburetor with the remote needle assembly. I think they're really good Carburetors. All of my Sportsters have them and the K&B .40 I sold recently had one although the .40 had a remote needle version. They're a breeze to set.
#41
Thread Starter
Ok here's what I have so far.
I balanced an APC prop using my highpoint balancer, hub and all. I also compared that to my Top Flight balancer and they were the same. Checked the tracking too (fine). The prop stud was not quite screwed in all the way. I checked the runout just behind where the prop rests and the indicator barely moved. I checked it again at the end of the prop stud and it was all over the place, swinging maybe .030" or better each way. I took it out and rolled it on a level steel plate and it kind of had a lope in it. I tried to get a stud last night around town but couldn't find the right size so I ordered several from McMaster Carr. I will be replacing the spinner as well. The old one was pretty ragged.
Maybe my major issue is the stud. I'll have to wait another week to try running it.
Carl
I balanced an APC prop using my highpoint balancer, hub and all. I also compared that to my Top Flight balancer and they were the same. Checked the tracking too (fine). The prop stud was not quite screwed in all the way. I checked the runout just behind where the prop rests and the indicator barely moved. I checked it again at the end of the prop stud and it was all over the place, swinging maybe .030" or better each way. I took it out and rolled it on a level steel plate and it kind of had a lope in it. I tried to get a stud last night around town but couldn't find the right size so I ordered several from McMaster Carr. I will be replacing the spinner as well. The old one was pretty ragged.
Maybe my major issue is the stud. I'll have to wait another week to try running it.
Carl
#44
Thread Starter
So by some great stroke of luck the prop studs arrived real late Friday afternoon and I was able to button it all up and try it out today. The vibration appears to be pretty much gone. I'm going to attribute the majority of the vibrating to a bent prop stud and also to the fact that it may not have been screwed in all the way. My old spinner was pretty ratty so i replaced it with a nice metal CB associates one. If anyone needs prop studs for a K&B .61, Mcmaster Carr has them for $.95 each.
Thanks for all the help. I'm declaring victory on this issue.
carl
Thanks for all the help. I'm declaring victory on this issue.
carl
#46
Last I checked, you don't want the prop stud bottomed out. Screw it all the way in and back off a thread or so. This way when the prop gets tightened, the stud stays straight. If the stud is tight, it may not be straight in the crank.
#47
My Feedback: (287)
REPLY TO: Tony0707....
YOU ARE ABSOLUTELY WRONG ABOUT THEM BEING HIGH RPM ENGINES! K&B .61 engines, and also the .40 ring, will have crankshaft pin failure at high rpm (they are also double ball-bearing engines...don't confuse them with the bushed "Sportster series engines). The crankpin is a pressed-in fit and will fail if run over 13,000 continuously. I have been using the #6550 K&B .61 for over 30 years (I still run a K&B .61 regularly) and have had this failure.
However, you can buy the crankshaft from the .61 "Twister" engine, which is a one piece forging, then rpm won't matter. I do believe you need to replace the rod also.
The K&B .61 is, in reality, a torquer engine and will do great with the larger props at lower rpms.
YOU ARE ABSOLUTELY WRONG ABOUT THEM BEING HIGH RPM ENGINES! K&B .61 engines, and also the .40 ring, will have crankshaft pin failure at high rpm (they are also double ball-bearing engines...don't confuse them with the bushed "Sportster series engines). The crankpin is a pressed-in fit and will fail if run over 13,000 continuously. I have been using the #6550 K&B .61 for over 30 years (I still run a K&B .61 regularly) and have had this failure.
However, you can buy the crankshaft from the .61 "Twister" engine, which is a one piece forging, then rpm won't matter. I do believe you need to replace the rod also.
The K&B .61 is, in reality, a torquer engine and will do great with the larger props at lower rpms.
Last edited by Red Baron Mike; 02-19-2016 at 03:06 PM.
#49
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There is some degree of 'forum drift' and maybe some clarification is in order. The OP Carl, was working with a C. Lee engine and has successfully diagnosed his vibration problem. Some other commentary has been added. Red Baron Mike is absolutely correct in that the KnB crank pin and rod are not happy at mid to high rpm. C. Lee uses twister cranks and rods in his builds and bushes the rods due to the OEM clearance that he feels is excessive. The PDP porting will not equal Schnuerle designs but does provide for higher rpm capability. In this forum back in 2/08 is a more complete description of what Mr. Lee does and what he thinks that the engine is capable of. I like them a lot but the price has intruded on neuvo Rossi and so on so ymmv. It may be worth reading the old post on the CL KnB 61.
#50
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Mr/Lee is a gracious man. I would send the engine back and tell him your problems include the type fuel, prop used, RPM and anything else you can think about. I am sure he will look at the engine and do what is necessary to get right.