RAF Sprocket

willisbr

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Maule MT7-235; RAF 2000 (sold)
I have some back and forth play in the prop that i originally thought was a worn jackshaft. After closer look at the belt sprocket, it seems that the sprocket may be faulty. The bearing on the mounting plate side can be pushed in and out by hand. Wasn't like this before. I pressed it out last time when I changed the bearings but now that one is very lose. Wiggles in place. On one bearing side, the inside is still anodized and the bearing requires a press to set but on the problem side it looks and feels lathed. It's shiny and smooth with a lip at that the top. Please watch video to see. What are your thoughts? *Is this normal? *If not how could this have happened? *What can I do to fix? *Possible to hone and fit a new bearing? *Thanks

Always great to find such an issue so close to Bensen Days.

Check out this video on YouTube:

YouTube - RAF 2000 Drive Sprocket
 

Brian

Brian Hebden
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Springville NY
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bearing should not be loose I would replace the sprocket, jack shaft, and bearings I am not shure how it is asembled but there should be no wear on the jackshaft or where the bearing seats but hopfuly some experts will comment brian
 

brett s

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Looks like it's time for a new sprocket, bearing, and jackshaft.
 

ggfirestar

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Section Al
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Have flown lot's of different ultralights 3 different Gyro,s Bensen,Dominator,Air Command
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over 1000 hours
Could you take it to a machine shop have the hole machine out a little larger and press and lock tite a sleeve in then replace the bearing.
 

Riff Raf

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Brian
How did you notice this?
Was there a vibration of some sort?

I've read that most put in a steel sleeve.

Ask Larry Boyer about it, he may know.
 

willisbr

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A slight play in the prop when blade is tapped front and back. Also when I Am at a cold low idle like 900 or below and at shut down I got a rattle. Like a ringing. I idle at 1000 or higher but just to give you an idea, real low rpm would ring the sprocket.

Just dropped off at the machine shop. Having a steel sleeve pressed in. He will check the tolerance on the other side as well. He felt that a steel sleeve is best anyway rather a bearing set in an aluminum sleeve or bore.
 

asmuzsr

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Clearwater, Florida
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It may have come from the belt being to tight. Should only have 1 1/2 belt width of movement when you push on the belt with your knuckle.
 

AirHorse1

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Kinderhook, NY
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RAF 2000 w/ lowered keel mod & HS
I agree with your machinist. The steel sleeve is the best way to go.

There is already an upgrade for the lower sprocket with this type problem which also involves fitting a steel sleeve in the sprocket so the bearing don't gaul out the aluminum. I just re-commented on it a few days ago. The lower sprocket is more important because if this type of thing happens it will take out your crankshaft.

http://www.rotaryforum.com/forum/showthread.php?t=4517&highlight=Butler
 

willisbr

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Tony, my belt tension has been good. I'm hangared with Dofin and he looks at my gyro often.

Air, thanks for this reference. I will consider this. Pretty similar to the monologe I got from the machinist today.
 

Riff Raf

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Brian
How many hours on your RAF?
 

LARRYEBOYER

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another solution would be to buy an oversized bearing. Take it to the machinist. He should know how much to machine out so the bearing could be pressed in.
 

Friendly

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Is the bearing you show in the video the same bearing that came out of it? If so are there any score marks on the out side of the bearing. I looks like the bearing spun in the sprocket. Alum. expands faster than steel when heat up is how it can happen. Installing a bearing cocked to one side can remove material on the sides or even just a mistake in machining by a few .0001


Thanks for posting, I am interested in the gates belt drive.
 
Last edited:

willisbr

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Ok here is a video of the latest and greatest. For those that don't have video capability, I'll provide a narrative. Both sides of the sprocket will have steel sleeves pressed in. On the "funnel cake" side, there will be a steel collar on the outside for reinforcement.

In the photos below, you can see one sleeve that has already been pressed in. It has not been bored to spec yet. In the photo of the "funnel cake" side, you can see some wear in the bearing bore. This will be sleeved as well. A collar will be pressed on the outside since this area is thin.

YouTube - Sprocket jackshaft and bearings
 

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willisbr

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Forgot to mention the machinist wants to knurl the jackshaft and then shave it down to tight fit on bearing.
 

Sheldon

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Knurling the jack-shaft is a very temporary solution, it can compress under load.

A new shaft and re machining with steel inserts or over sized bearings are your most cost effective solution.

The big question that needs to answered is why did this happen in the first place, and how do you keep it from happening again.
 

willisbr

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My current jackshaft pulled right out of the bearings when I first started this project. The entire length of the shaft is same diameter so nothing "happened". It apparently has always been this way. Looking at getting another shaft that is intended for the bearings RAF says to use. Not going with oversized bearings at this time because the sprocket is not designed for larger on one side. Getting the shaft right is the direction for now. Can I get some feedback from other RAF owners also? What are you guys finding with your jackshafts and bearing fits?
 

All_In

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This has turned into a great instructional thread Brian, way to help others!
 

Steve Osborne

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My current jackshaft pulled right out of the bearings when I first started this project. The entire length of the shaft is same diameter so nothing "happened". It apparently has always been this way. Looking at getting another shaft that is intended for the bearings RAF says to use. Not going with oversized bearings at this time because the sprocket is not designed for larger on one side. Getting the shaft right is the direction for now. Can I get some feedback from other RAF owners also? What are you guys finding with your jackshafts and bearing fits?

I had to replace the lower sproket bearings at around 500 hrs, but I am still using the upper sproket original shaft and bearing with 1000 hrs on it. I checked it the other day and still no wear so I am going keep running it. I do know if the jackshaft nut is not tight enough it will cause wear.
 
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