Dominator hyd pre-rotator belt won’t slip.

Kurtacrandell

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Nov 14, 2018
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I recently purchased my 2 place Dominator. It has the Viking 110hp engine. The pre-rotator is a serpentine belt driven pump. The old owner put grease on the belt so it would drag (not turn) when not in use. My instructor did not think this was a good idea. I cleaned the belt and the pulley the best I could. I tried using a silicone spray but it still grabs. The belt is as loose as I can make it. What do others use? Help please.

Kurt
 

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GyroPaul

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Mar 3, 2009
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Ramsey, MN
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Fisher Celebrity (Biplane) Single seat Dominator
I recently purchased my 2 place Dominator. It has the Viking 110hp engine. The pre-rotator is a serpentine belt driven pump. The old owner put grease on the belt so it would drag (not turn) when not in use. My instructor did not think this was a good idea. I cleaned the belt and the pulley the best I could. I tried using a silicone spray but it still grabs. The belt is as loose as I can make it. What do others use? Help please.

Kurt
Looks like you don't have any room left to adjust the drive pully. Maybe an inch longer belt would give you room to adjust tension so it would be less likely to grab.
 

mark treidel

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Ernie told me years ago to rub corn starch on the inside of the belt.
It acts like talcum powder and allows smooth slippage upon engagement
of the clutch drive. Also keeps the belt from engaging when released
(provided it has the proper slack). Corn starch will not harm or deteriorate
the rubber of the belt like grease (or the aluminum pulley) and is not messy...apply too much and a
simple 'puff' clears excess away.
The important factor here to remember about starting a belt driven pre-rotator
is to use slippage to your advantage by starting smoothly and increasing pressure
as RRPM increases along with throttle. If it grabs abruptly, this will cause a sudden
and unwanted amount of torque twist and 'shuttering' on the mast increasing the chance of unseen
premature metal fatigue.
I had a Viking 110 on my old Sport copter and never had an issue using the above technique.
I've used corn starch on all my machines with complete success and apply it religiously
during each post flight clean up so it's ready to go next flight. Additionally, part of my post flight
process here involves using denatured alcohol to clean the contact surface of the large pulley wheel.
This prevents rubber build up which can precipitate grabbing.
After looking at your photos, I tend to agree with post 2 above that the belt may be too tight.
If it is engaging when running released, it needs adjustment. If it will not adjust any more to
the loose side, a slightly larger belt (1") is called for. Try lowering the adjustment plate on the
top wheel (4 bolts) a bit if there is room under the bolts to drop it down just a hair... doesn't take much
although the photo appears to show it at it's lowest limit.
Do NOT fly with it if it is always engaged on its own. The belt will swell and squeal and
eventually overheat the bearing and freeze up the pully unit causing damage and a possible engine out.
Good luck.
PS, Ron was correct below, I thought about it after I went to bed. Now corrected to corn starch. (apologies)
 
Last edited:

GyroRon

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Sometimes, once a belt becomes " grabby " no amount of powders or sprays will fix it. You may find that you just need to buy a new belt. Certain brand belts worked better than others, can't remember the name of the brand that worked best, but I believe it was made in France!

And its not baking soda that Ernie suggested, it was Corn Starch powder. You would want to shake out some of that powder onto the inside of the belt, and you couldn't use too much if you know what I mean. You would have to reapply fairly often.
 

Abid

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Buy a new belt. When setup incorrectly at start or if he did pre-rotation incorrectly the belt can overheat and actually shrinks up. Then it will grab no matter what you do.
 

Gyro28866

David McCutchen
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First, based on the picture. It doesn't appear to have any more ability to create slack in the belt. Get a belt which is 1" longer. you can adjust a too slack belt by loosening the 4 mounting bolts and raising the pump/mount. baby powder is what I use (per Ernie). You can't use too much. A very liberal amount BETWEEN the belt and Prop pulley. I generally, rotate it until the entire belt grooved side has a slight coating on it. You will have to adjust a little to find the sweet spot.
Now, you ain't gonna like changing the belt. It requires removing the Propeller. Not a big deal, 6 bolts. Just be sure to use a good quality torque wrench when reinstalling it.
When you get the new belt. Turn it inside out and grind/sand the majority of the grooves off. Make sure the grooves are fairly uniform and not wavy. Turn it back from inside out and put it in a deep pot of water and BOIL the snot out of it for 30 minutes.
Now you are ready to reinstall.
 

GyroRon

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First, based on the picture. It doesn't appear to have any more ability to create slack in the belt. Get a belt which is 1" longer. you can adjust a too slack belt by loosening the 4 mounting bolts and raising the pump/mount. baby powder is what I use (per Ernie). You can't use too much. A very liberal amount BETWEEN the belt and Prop pulley. I generally, rotate it until the entire belt grooved side has a slight coating on it. You will have to adjust a little to find the sweet spot.
Now, you ain't gonna like changing the belt. It requires removing the Propeller. Not a big deal, 6 bolts. Just be sure to use a good quality torque wrench when reinstalling it.
When you get the new belt. Turn it inside out and grind/sand the majority of the grooves off. Make sure the grooves are fairly uniform and not wavy. Turn it back from inside out and put it in a deep pot of water and BOIL the snot out of it for 30 minutes.
Now you are ready to reinstall.
I never had to sand the inside of a belt or boil it to make it work good.

Usually just a good new belt, with some corn starch added once in a while was all I ever needed.

You do have to remove the prop to install a new belt, that does kind of suck... If this belt issue becomes too much of a pain in the butt, let me know, I will buy the gyro off ya!
 

Gyro28866

David McCutchen
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I never had to sand the inside of a belt or boil it to make it work good.

Usually just a good new belt, with some corn starch added once in a while was all I ever needed.

You do have to remove the prop to install a new belt, that does kind of suck... If this belt issue becomes too much of a pain in the butt, let me know, I will buy the gyro off ya!
I just followed Ernie's recommendations
 

Doug Riley

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I had persistent problems with my hyd. prerotator belt at first. Sanding, ointments, cornstarch, a new belt and other quirky remedies didn't help a bit. Having the Bendix popping up in flight was unnerving.

A tractor mechanic provided an easy answer. The belt tries to revert to a circular profile when you release tension. This makes the bottom portion rise and grab at the large pulley on the prop hub. The fix: add one or more fixed guides to keep the belt in its A-shaped profile; I added mine on the side of the belt opposite the tensioner wheel. That's the right side of the gyro in the picture.

As Dave McC. says, your belt looks as if it may not have enough available slack. As already recommended, try a slightly longer belt -- and add a guide on the non-tensioner side to keep the belt from ballooning out to the side. While you're at it, you can shape the guide so that it also helps keep the belt from sliding back toward the prop.
 

Kurtacrandell

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Nov 14, 2018
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Charlotte, Michigan
Thank you everyone for the advice. I will try the corn starch first and if that doesn’t work I’ll look into getting a new belt. I will post back here with my results.

Also Thank you GyroRon on the offer to purchase. Lol I hope it does not come to that.
 

GyroRon

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Something no one is pointed out yet, is you can not only adjust for belt tension by moving the hydro pump up and down in the slotted holes, the tensioner pulley is adjustable as well. You may have that pulley adjusted too far inwards, making the belt too tight. You can play with that adjustment to see if it helps...

In my opinion though, once the belt was greased and sprayed with oils, its probably shot. Some belts get " sticky " once exposed to oils, and you don't want a sticky belt. You might could remove it and clean it good with some brake cleaner or degreaser, but probably will still be sticky. New belt isn't too much, just order a new one and corn starch it and I bet you will be okay.
 

Kurtacrandell

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Charlotte, Michigan
Something no one is pointed out yet, is you can not only adjust for belt tension by moving the hydro pump up and down in the slotted holes, the tensioner pulley is adjustable as well. You may have that pulley adjusted too far inwards, making the belt too tight. You can play with that adjustment to see if it helps...

In my opinion though, once the belt was greased and sprayed with oils, its probably shot. Some belts get " sticky " once exposed to oils, and you don't want a sticky belt. You might could remove it and clean it good with some brake cleaner or degreaser, but probably will still be sticky. New belt isn't too much, just order a new one and corn starch it and I bet you will be okay.
The corn starch did the trick. I had already cleaned the belt with brake cleaner and wiped it down to the point my rag was pretty clean. I used the alcohol on the pulleys and belt. As I was applying the corn starch before I was finished she was sliding around the main pulley with no sticking at all. I took her out and everything worked great.
Thanks for all the advice. Looks like I won’t have to sell her after all.

Kurt
 

GyroRon

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awesome! Yeah, if all is well, you won't have to corn starch it too often, maybe once every 20 hours or so.
 

MikeBoyette

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I never had to sand the inside of a belt or boil it to make it work good.

Usually just a good new belt, with some corn starch added once in a while was all I ever needed.

You do have to remove the prop to install a new belt, that does kind of suck... If this belt issue becomes too much of a pain in the butt, let me know, I will buy the gyro off ya!
Something He got from a Greg at Magni. Boiling it makes it shrink a little and takes less time to break in. It also takes very little corn starch doing it this way. The grinding takes the sharp edges off the groves of the belt and provides just a little more grip. Give it more surface area. The boiling and grinding makes just about any brand belt work good. Never put oil or grease on it.
 
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