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Clarence Lee K&B .61 vibration issue

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Clarence Lee K&B .61 vibration issue

Old 01-12-2016, 11:57 AM
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carlgrover
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Default Clarence Lee K&B .61 vibration issue

I've got a new Clarence Lee K&B .61 I've been running in my Kwik Fli for about a year and this has got to be the worst vibrating engine I have ever owned. I've balanced the prop and even checked it again after multiple flights thinking it's the problem but I'm sure it isn't. I balance it on a magnetic prop balancer.

I have cowl screws loosening after nearly every flight with this engine. Seems like it wants to vibrate the whole plane apart. Anyone else experience this with a .61? No other glow engine I've ever had vibrates anywhere near this much and I've run them for nearly 30 years. I'm running an 11-7 prop.


carl
Old 01-12-2016, 12:40 PM
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AwwNaww
 
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I have two of the CL .61 and cannot say there is excessive vibration. I would give him an opportunity to comment on this.
Old 01-12-2016, 12:51 PM
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blw
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Tell us more about your prop. What other props have you tried?
Old 01-12-2016, 01:02 PM
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1QwkSport2.5r
 
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More importantly - what exact balancer are you using? I've fought with a LOT of props and their respective imbalance. Turns out the balanced I was using was total rubbish. Top Flite magnetic balancers are junk. Got three sets of new cones and a new balancer shaft from Hobby services and every which way you set it up (different cones, different shafts) gave a different balance. I went to the Dubro balancer and have had MUCH better luck.
Old 01-12-2016, 03:10 PM
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Not sure exactly what the .61 is like, but the cast iron piston old style stuff did shake a lot if you rev them high. ABC pistons are much lighter and easier to balance the motor internally. I have had my hand tingle when letting them go at full throttle.
Old 01-12-2016, 03:21 PM
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1QwkSport2.5r
 
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I have an HB .61 which is basically a German K&B .61 and it literally runs butter smooth with a well balanced prop. They shouldn't shake any more than any other typical .61.

I'm a bit over the top with most of what I do, so I balance the blades first and balance the hub after. I use mostly APC props which usually have pretty well balanced blades, but the hub is often off a bit.
Old 01-12-2016, 06:41 PM
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CLBetten
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Mine is very smooth, as good as I would ever expect. I'd say you do in fact have a problem. Prop, spinner, engine damage, etc.
Old 01-12-2016, 10:33 PM
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Very rare, but I've seen shafts draw. Check the "run out"?
Old 01-13-2016, 04:23 AM
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carlgrover
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I don't think I have any engine damage. It runs and idles great, just so much vibration. I'm running a Top Flight 11-7 wood prop and use the Top Flight magnetic balancer. I haven't tried any other props yet. I've got a Robart High point balancer I could check it against but every prop I've ever balanced for many years has been on that magnetic one.

The next time I fly it I'll try an APC prop without the spinner and see if it makes any difference.

At this point I'm happy to know that the engine isn't a vibrator by design so I'll keep working on it.


Carl
Old 01-13-2016, 05:25 AM
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1QwkSport2.5r
 
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I used the Top Flite for years and always had vibration problems. Maybe one in a hundred works properly, mine wasn't one of them. Worth a look: http://youtu.be/h5PgZ-UePZo

I'm a cheapskate so I hate spending money... But the Dubro balancer is worth the money IMO. I've not used the high point balancer so I can't comment on it.

Last edited by 1QwkSport2.5r; 01-13-2016 at 07:42 AM. Reason: Fixed typo
Old 01-13-2016, 07:08 AM
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Sport_Pilot
 
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That engine has an aluminum piston and runs real smooth. However it is a more powerful engine than the Kwick Fli was designed for and you may have a resonate frequency issue as well. I would try running it on the stand and also look for any cracks in the wood around the firewall and front of the fuselage. If it runs smooth then add some foam or even reinforce the area around the firewall with balsa or soft spruce. Anything that could dampen or change the resonant frequency.
Old 01-13-2016, 07:49 AM
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pkoury
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Have you balanced the spinner?
Old 01-13-2016, 08:45 AM
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CESSNA 421
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I use a high point balancer, I don't think it is available any longer. It has two wheels on each side which provides a frictionless balance point. I use paint to balance my props and have not had an issue. I also clock my props to accommodate hand starting since I never have had the desire to use an electric starter or chicken stick. This clocking may offset some of the natural imbalance of the engine. I use REV-UP props which are also no longer available but in my opinion are far superior to any prop on the market today. There is also pitch balance, that is if the pitch from one blade to the other is not the same due to improper machining of the prop this could also cause an out of balance type issue.

Last edited by CESSNA 421; 01-13-2016 at 08:54 AM.
Old 01-13-2016, 12:10 PM
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blw
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I use a DuBro and my spinners are the Great Planes plastic spinners with aluminum backplates. I balance those with the prop, and either scratch or mark the assembly so they line up together when reassembling.

I also check the run out.
Old 01-13-2016, 02:30 PM
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i know these engings well
They have the power of a good 46 ,by todays standards
They are RPM engines , and will not turn large diameter props
You have to much prop and the wrong brand , on it in my opinion
Stay with 10/6 or 11/5 apc
Run the engine in the recommended RPM range , use a tach
The K & B is a bushed bearing engine ,not ball bearings
The engine has been around for decades ,and an Os 46 or a ST 51 ,would be more power ,and turn more prop than your 61 K & B
Just a heads up , hope it helps
Enjoy
Old 01-13-2016, 02:41 PM
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The bushed engines SB run on 20% oil , in your glo fuel
Some castor oil is always recommended by me ,in every two cycle glo engine
A glo engine that is handled by a experienced person ,will run and last for a very long time
I service all my glo engines ,and i am very often pleasently surprised by the condition of the internals when i have a need to go inside
My engines require very little maintenance and many have a lot of run time on them ,years
Make a point to never run them lean ( get them overheated ) and always run all fuel out of the crankcase at the end of a day at the field
Old 01-13-2016, 02:53 PM
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Sport_Pilot
 
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This is not a bushed engine and has more power than a .46. The 11-7 prop should be OK but an 11-6 may be better.
Old 01-13-2016, 04:00 PM
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It is possible the crankshaft is bent slightly. You should check the runout on it. it does happen when manufacturing the engines. Someone may have missed it somehow. The other possibility is a touch too much compression and it is getting some pre-ignition effects. Worst would be if the crankshaft somehow was not balanced much of any at the factory. They tend to balance one or two cranks, and then copy that for the rest of the ones being made. So it could have been a screw up of sorts at the factory if that happened.

I would expect it to like higher pitch propellers such as a 11x8, 11x7.5, 11x7.75 sizes more. But a 11x7 should be fine though.

One other thought is that the firewall in the plane may be weak or the fuselage sides surrounding the fuel tank up front to the firewall. I have seen firewalls come unglued before on one side and that can really allow a lot of engine vibration to get through to the plane then. A flimsy motor mount is another issue too.
Old 01-13-2016, 05:37 PM
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He advertises in Model Aviation magazine, call him. D.H.
Old 01-13-2016, 07:48 PM
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The High Point balancer was manufactured and sold by Denis Belick about 30 years ago. Denis sold the design to DuBro, which made slightly cheaper product. The High Point is all metal (aluminum and steel) and much of the aluminum is gold anodized. The DuBro has a lot of plastic parts. The design of both balancers is based on proven concept common in machine shops. Denis marketed a short stand version for boat propellers. Spinners can be balanced on these devices too. Occasionally High Point balencers show up at swap meets, and should be picked up if not damaged. There has been a lot of prop suggestions in this thread. My suggestions would be an 11/6 or 11/7. If you can't find the source of the vibration, send it back to Clarence Lee. Good luck, and if you find the problem let us know what it is.
Old 01-13-2016, 07:51 PM
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Fantastic information, Greg. Thanks for posting that.
Old 01-14-2016, 04:28 AM
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carlgrover
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Thanks for all the good information.

As far as the plane is concerned, it's brand new and has only been flown a dozen or so times. There are no weakness issues at the firewall or anywhere else. I built it myself from plans. The motor mount is an aluminum Sig mount.

I may get out Sunday if the weather holds. I'll let you all know what happens. By the way, the letter in the box with the engine suggested an 11-7 or 11 7 1/2 prop. It was signed by Clarence Lee himself.



Carl
Old 01-14-2016, 04:47 AM
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Originally Posted by carlgrover
Thanks for all the good information.

As far as the plane is concerned, it's brand new and has only been flown a dozen or so times. There are no weakness issues at the firewall or anywhere else. I built it myself from plans. The motor mount is an aluminum Sig mount.

I may get out Sunday if the weather holds. I'll let you all know what happens. By the way, the letter in the box with the engine suggested an 11-7 or 11 7 1/2 prop. It was signed by Clarence Lee himself.



Carl
The plans were from the 60's when engines were less powerful. Also I mentioned resonate frequency, that has little to do with strength but the frequency that the air frame will vibrate in resonance with the engine frequiency. BTW metal mounts are more likely to cause resonate frequency issues so suggest removing that and put at lease 3/16" thick sheet rubber between the mount and the firewall.
Old 01-14-2016, 06:38 AM
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1QwkSport2.5r
 
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What about a Glass filled nylon engine mount? Any better for resonance?
Old 01-14-2016, 07:07 AM
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Originally Posted by 1QwkSport2.5r
What about a Glass filled nylon engine mount? Any better for resonance?
Yes, but still possible. I raises the frequency which hopefully is above the highest frequency the engine can muster. So it is still possible.

https://en.wikipedia.org/wiki/Resonance

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