Pre Rotator Problem

TJMay

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After getting my muffler problem sorted out and after several full stops and nut tightening, I was ready to go fly around some.

When I got out to the end of the runway and lined up, I started my pre-rotation. Almost immediately after starting, I felt and heard something funny and immediately noticed that the rrpm was not climbing but falling.

Stopped the process, locked the rotor down and taxied back to the hanger. After climbing up a ladder to look at the pre-rotator, the problem was immediately evident.

The top bearing plate of the pre-rotator was loose and flopping around. I'm fortunate that it did not fall out (and through the prop) and that it was not lost. Apparently, this plate is simply pressed in rather than secured in some way. I guess I can driill, tap and put a retaining screw to hold it in.

Anyone else have a problem with this?

Tommy
 

Harry_S.

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Yep, sure did, Tommy.

I wrote it up, with pics, of what happened and what repairs I did. I had bought the newer Bendix housing some time ago so it didnt take me long to get airborne again.

I don't have time right now to look up where I posted that info. It may be in this thread. I'll check later today for its location. You may find the postings before then.

This has happened a number of times to different folks, that's why RAF redesigned the Bendix housing.


Cheers :)
 

Harry_S.

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Thanks Jeff for finding that post, but that's not the one I was after.

After two hours of checking different threads, I got smart and lucky by doing a search on "BENDIX" and found what I was looking for.

Here it is Tommy...start at post #180 and read on.

http://www.rotaryforum.com/forum/showthread.php?t=9678&page=12&highlight=Bendix

The safetying of the old cap was covered in a PN from RAF Mkt.

Evan after I did safety the cap. it failed. You may want to try RAF Canada, to see if they still have the new Bendix housing on the shelf.


Cheers :)
 

TJMay

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More Problems

More Problems

Got my bearing cap back on today. After installing and checking that all looked OK, I manually rotated the clutch plate and saw that the Bendix was rotating within the Bendix housing above.

I pre-flighted, got in and taxied to the end of the runway to begin my pre-rotation. Nothing. No noise, no vibration but no rotation either.

I taxied back to the hanger, pulled a ladder up to inspect further and tried the manual rotation again with the same results. The Bendix rotated with the clutch plate.

So, I removed the pre-rotator cable sheath top and bottom and then the Bendix itself. I found that the four welds that connect the square collar to the Bendix shaft had sheared allowing the collar to rotate freely around the shaft but with just enough grip to turn the Bendix with the clutch plate.

The fix seems to be to simply grind the four welds down, drill the four holes out and reweld. Anything else I should be aware of?

I also noticed a roll pin through the main Bendix shaft performing the same function as the welds. Any reason I should not consider drilling through the collar and shaft while in place and using a smaller roll pin?

Thanks for your help.

Tommy




I
 

Harry_S.

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Tommy,

I'm assuming you're refering to the 1/4" rollpin. This pin is the only means of attaching the shaft to the Bendix. I wouldn't mess with that rollpin other than driving it out with a 1/4" punch, so as to facilitate rewelding the square tube to the shaft. After a good weld, insert the shaft and then drive the pin in again. A caution here...after driving the pin home, make sure the Bendix rotates freely with no interference.

May I reiterate about the stress takin' place up there when starting to turn those 100 lb. 30 footers. ;)


Cheers :)
 

Resasi

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My instructor always cautions about low RPM when clutching in or throttling up due the stresses of the blades on the pre-rotaror.

Had problems with it not dis-engageing, but dissasembling and greasing seemed to sort that.
 
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