Pre-loading Main Bearings

[lperagallo]

I learned something new today that I thought was interesting. I was speaking to an engineer at AST about bearings wanting to find a high precision bearings for the main shaft of my Turbine. As we were discussing the set up the engineer wanted to make sure that the pre-load was done correctly to keep the bearing from developing vibration or harmonics. While the Bergen has is collars on the top and bottom bearings to allow for a preload, I never thought of pre-loading the collars. He indicated that the proper procedure for bearings of this size (10X19X7) is to establish about 4 to 5 pounds of pre-load. This way the radial run out is taken out and the bearing will run true. This also helps keep the bearing well seated in the bearing block since it's a press fit.

I believe the proper procedure to do this is to lock the lower collar first, then holding the upper collar, suspend the frame and exert a 4 to 5 pound load while locking the collar. I'm sure the weight of the Turbine is in excess of the pre-load so don't go overboard. Also this is probably better done with two people as it would be hard to hold the collar, suspend the frame, and lock the set screw on the collar at the same time. I guess you could also find a way to wedge something between the collars and exert the proper load without suspending the frame. I think I'll try to find a way to do this before I fly again. It can't hurt.

Thought it would be a good practice for those of us who have a design that allows for preload.

Lou

[ErichF]

If you do the pre-load as you desribe, you will only be applying 2-2.5 pounds of preload to each bearing. Remember they split the tension of the collars on the shaft. So if you secure one collar, you need to then apply 8-10 pounds of pressure as you secure the second collar. Then you have 4-5 pounds of load on each bearing.

[v22chap]

And Lou ,,not to be a smart A$$ or anything ... but the manual tells you to do that preload thing ... maybe not to that many pounds ,,and it is a little fuzzy on what it is for too ,, but I believe it is there .

[lperagallo]

Larry,

I went back to the Turbine manual I downloaded, and while I agree the intent might be to get a preload, it just says to push up un the split collar. Here is what I found in page 19:

"Install one split collar on the shaft, under the elevator yoke. Note the ring on the bottom
of the collar goes against the bottom bearing face. Slide the other collar in place on the
main shaft, above the elevator yoke, again with the ring on the collar facing the upper
bearing. With the shaft in place, tighten the frame bolts and nuts holding the bearing
blocks in place. Now pull up on the main shaft, seating against the main gear and tighten
the bolt on the bottom split collar. Here is where the good set of hardened allen drivers is
most important. The heads of the bolts are turned down to fit the collars. If you use a
soft set of allen wrenches, you are very likely to strip the head of the bolt out. This is the
ONE area where we DO NOT suggest using loctite. It makes it even more difficult to get
the bolts loose when needed. Push the upper collar against the upper bearing and tighten
the bolt."

I would not have read into that to push up with some force to get a preload of 4 pounds. Since I didn't know that a bearing requires pre-load to track properly I thought the intent of the collars was to keep the shaft from moving up and down changing where the main gear would ride on the pinion. I thought I'd share the information I learned so others who missed it in the instructions could make sure they did it.

Lou

[v22chap]

Like I said it is very vague ,,and I didn't write the instructions ,,so not even sure of the intent ...and your right it doesn't say anything about how much ,,, and I too didn't realize that a bearing had to have that much to preload .Learn something new every day ....:)