prerotator woes

[robertstodaro]

My prerotator belt was sticking so I replaced it. It was coned.

I'm having a very difficult time getting the new one to break-in.

I've adjusted the sheave alignment, the engagment wheel throw, and the pumpshaft to driveshaft distance. I even polished the driveshaft sheave.

It's still sticking and caking the drive wheel with a solid coat of rubber, not powder.

Any Ideas or tricks?

Or even wiseass remarks,, feel free.

Thanks

[GyroRon]

What brand belt are you now using? Did you try some corn starch on the belt?

[robertstodaro]

I'm using a a BANDO just like the original I'll try the corn starch.

What kind of belts are you using?

thanks for the reply, I wasted another day today and got 3minutes of air time.

[GyroRon]

If it is leaving black streaks on the pulleys It may be ruined.

I also use a Bando belt on mine - it is what came with it - but have used Gates belt and had good success with it. Also used a Browning belt and it worked great too.

The corn starch seems to help in some cases. Mine just worked fine right out of the box, no starch or break in needed. No black streaks on the pulley either. Just luck I guess!

[robertstodaro]

Can you get me part numbers and vendors for the Browning and Gates belts

thanks

[Doug Riley]

Make sure you're not getting oil or fuel on the belt. These substances soften the rubber and can cause the belt to stick or grab. Check the location of your gearbox breather -- re-route it if the oily vapors can blow back onto the belt.

Also look for oil leaks from the gearbox itself and from the engine block. Some Rotax cases will leak oil. Obviously look for fuel system leaks. Air cleaners will sometimes accumulate oil and drip. The vent hoses on Bing carbs can ooze fuel-oil mix on occasion.

Check your hydraulic fittings and hoses for fluid leaks.

Keeping the belt dry and having enough belt guards so that it doesn't drag when disengaged seem to be the keys to good service from this gadget.

[robertstodaro]

Explain belt guard please, Thanks

[Doug Riley]

The belt will assume a round shape when it's relaxed. In the case of a Dom. prerotator, that shape makes the belt drag on the bottom of the large (prop hub) pulley. The belt gets hot and sticky from the friction, and can start grabbing in flight, even though you're not squeezing the lever. This can become exciting, as the Bendix clatters into and out of gear every second or two. The softening of the belt can also leave the rubber deposits you're experiencing.

You need one or more guides (not guards -- bad choice of words) on the side of the belt OPPOSITE the tensioner wheel. These should be positioned so that the belt can't "balloon" out to the side when it's relaxed. The guide can be as simple as a bolt with a sleeve, proturuding straight back out of the pump mounting plate and crossing the belt on its outside (non-grooved) surface. Its should be placed so that, when the belt relaxes, it still lies in a roughly straight line tangent to the edges of both the pump pulley and the prop-hub pulley.

I believe that newer models of Ernie's prerotator come with this guide. Mine is several years old and didn't. I had endless problems until I made and installed one. The problems went away instantly.

[Aussie_Paul]

.......does it. A couple of pics to show how Magni run thier belt drive to their excellent flexible shaft pre rotator.

Aussie Paul. :)

[robertstodaro]

WOW !!! GREAT responses guys, anymore pics out there.

Thanks a million

[Doug Riley]

The guide I put on my Dominator is just about identical to the one you see in the first picture of the Magni.

[robertstodaro]

Thanks for all the help guys.

Here's a pix of my fix.

It's a #8 bolt, 2 sleeves, 1 washer, a missle nut and some locktite. piece0cake.

[Brian Jackson]

Please accept my apology in advance for my ignorance on this subject. I understand the centrifugal "ballooning" effect, and the inherent need for a belt guide opposite the tentioner wheel (which works like a take-up wheel in old reel-to-reel tape recorders). But I'm having trouble understanding the use of a non-moving guide over, say, a spring-loaded sheave. Wouldn't the stationary guide (bolt or otherwise) be a source of friction and super-heat itself? I'm assuming the belt should only make intermittent contact with the guide when "relaxed" beyond a certain threshold, which tends to maintain its physical contact with the driving and driven pulleys.

Sorry if that was long-winded.

My other question regarding belt-driven prerotators is during flight: Besides a significant loss of friction when disengaged, do the sheaves spin against the belt, or is there a clutch I'm not aware of that disengages the prerotator flex-shaft.

Thanks for any feedback. I've been following this thread with interest.

Respectfully,
Brian Jackson

[robertstodaro]

I'll try to answer, with my machine.

I don't worry about ballooning during engagment (that's not what it's for).

When the prerotator is not engaged, the belt does not turn and there is no
need for the guides to have rollers. When the prerotator is engaged the belt does not touch the guides

With the engine off, and the tension wheel engaged there is an air gap between the belt guard pin and the belt.(belt to pin rig)

With the tension wheel relaxed and tension held on the other side there is an air gap between the tension wheel and the belt.(tension wheel to belt rig)

I was getting inflight engagment because the belt was dragging on the bottom of the propshaft sheave. That's the ballooning that the new pin cures. (the belt finding it's original shape,,round)

With the belt held between the tension wheel (relaxed) and the guard pin there is slack under the crankshaft sheave.(that's what the new pin does)

The belt is the only clutch in the system.
There is a bendix in the rotor head end of the system.

The prop shaft sheave does touch the belt on the sides slightly,(tension wheel not engaged) but does not seem to cause it to drag (so far) a little corn starch on the belt did't hurt either.

How's that, clear as mud and longer than kite string?


Anybody else feel free to chime in here. thanks

(((( I make no claims that this is the proper way to rig Dominator. It's just the way I did mine yesterday.))))

[Doug Riley]

Robert's got it right, both in his installation and his explanation. The one point I'd add is that the "ballooning" is not caused by centrifugal force -- for the simple reason, as Robert said, that the belt doesn't turn when the unit is disengaged. The "ballooning" is caused by the belt's attempt to return to its natural shape, which is circular.

[Brian Jackson]

Thanks Robert and Doug for those explanations. I'd neglected to account for the belt's natural shape when slack.

Respectfully,
Brian Jackson

[Kevin_Aurandt]

Try a GOOD YEAR brand belt. I got one from Ernie about a year ago and it has worked great. Its impervious to oil or any thing else that has managed to get on it.


Kevin A.

[GyroRon]

Hey Kevin! where ya been???

Ron Awad

[Kevin_Aurandt]

Hey ron,
I'm still here in Punta Gorda. I have had a few setbacks due to hurricane charlie etc.. Most people around here lost thier hangars and thier aircraft.
I'm flying again and hope to have the bird tweeked out by BD's. Hope to see ya there..

Kevin A.

[GyroRon]

I will be there with my machine. did your gyro get messed up by the storm? Still keep it at the Doc's place?

[Kevin_Aurandt]

smashed pod, bent strut, bent blades. I'm back at Larry's now since my hangar got leveled. I was quite fortunate to have such little damage.



Kevin

[GyroRon]

I am sorry to hear that Kevin. So now it is a open machine or did you replace the pod?

[robertstodaro]

I still had trouble after all that.

I went on-line to the Gates web site (dealer locator) and ordered a pair of belts for 22 bucks each.

They worked from the first spin-up and left no residue.

I put one on the the drive wheels and tywraped the other around the gear box.

If the primary belt fails I can cut the tywraps and slip the back-up belt in place without removing the prop.

Ernie B. tells me that's an old airboater trick

Now my electronics are on the fritz, caused by a loose power lead. naturally.

UPDATE--I called Grand Rapids Tech from the copter and their tech support walked me thur the rebooting recalibration process, it works fine now,

thanks a million GRT

had a perfect flight with zero glitches, love it

[Caribean_gyro]

nEED help on pre rotator fly wheel. I am going to change the 6061 aluminum to 2024-t3. This way my brake pad will not eat up the aluminum too soon.

My question is I dont see any rivet or insert. SO I have to think this is heat mounted? Does any one have done this mounitng and repair on theires? I am trying to see the easy way not to destroy the plate and damage the ring gear if there is a correct dismantling methode. Please advice
ChuckP