Mini-500 Final Setup Runup Rigging and Track & Balance

[bryancobb]

Timing belts

Timing belts

Remember, this all does not start happening at all until I have hovered for several minutes
And this is the thing that SHOULD make it easier to isolate, coz it appears its temp related.
Just watchn your tensioner wheel, could the cog belt be stretchn under heat.
The tensioner looks to be gradualy pushed put ( as the belt climbs up the teeth) then drops back in ( as the teeth realine again, maken the circunferance smaller)
I know its a long shot, a f****n long shot.

These types of belts are called `timing` belts because they, by design, cannot stretch or change length. It is not very old. It Line has 36 Kevlar strands in it and is stronger than steel.

The idler pulley is spring-loaded and as the engine bounces up and creates slack, the idler/spring moves in to keep it tight.

My current thinking is that the upper strut rubbers at the MRGB are just tooo softy! The hard ones are on their way!

 

[Jincamty]

Does the belt tensioner have any sort of dampener?
2x video speed, and I tend to agree with Birdy.
It looks like the belt is trying to climb a tooth.
There is definitely something resonant going on there.

Cheers Cam

 

[gyro]

Well, after watching the video and seeing that tensioner bounce I would have to say its to loose or the belt is climbing on a guide and jumping teeth. The engine may be pulling up and changing the angle of the pulley causing it to ride to one side and climbing on the belt guides you added.

 

[bryancobb]

Standard Tension

Standard Tension

Well, after watching the video and seeing that tensioner bounce I would have to say its to loose or the belt is climbing on a guide and jumping teeth.

Low Serial Numbered Mini-500`s did not have a spring tensioner on the belt, the MRGB was hard-mounted to the frame, and only the engine and muffler was mounted in rubber. The tensioner had a jack-bolt that tightened the belt to a fish-scale tension amount and a jam-nut kept it there.

The new spring-loaded arrangement like mine, was introduced on the Bravo model to allow the MRGB to be mounted in rubber too. Belt tension is held to `nominal` even though the engine, muffler, and gearbox move around a bit.

When the idler is bouncing, it is doing its job. The belt is not riding up and down the teeth or jumping teeth. The engine is what`s doing the bouncing. The pulley is just reacting.

Many Mini-500`s flew with this spring-tensioner with practically no problems if you adjust the belt tracking correctly.

 

[Stan V]

.

When the idler is bouncing, it is doing its job..

To keep a constant tension on the drive train is one thing but something in the belt drive is causing the tensioner to go nuts. If there were no idler (tensioner) pulley as in the pre bravo units, or if there were no spring associated with the idler pulley, I don't believe you would be having this issue.
The film clip you took bryan tells the story.

 

[bryancobb]

...something in the belt drive is causing the tensioner to go nuts...

If there were no idler (tensioner) pulley as in the pre bravo units, or if there were no spring associated with the idler pulley, I don't believe you would be having this issue...

I feel the engine is the culprit that is making the idler go crazy. When the engine moves, the idler moves twice as much.

 

[bryancobb]

Here`s the Pre-Bravo way it was done.

Here`s the MUCH-IMPROVED Bravo setup. The tension created by the double springs is per Gates` engineering information.

 

[birdy]

Buggered if i know Brian, i know high HZ vibes can distort vid images, but i see a tensioner dancen about, with no visable virtical movement of the drive pully.

Is that engine restricted from movement lateraly along the crank axis?

 

[bryancobb]

...Is that engine restricted from movement lateraly along the crank axis?...

NO. It can move in every direction, limited only by the eight rubbers at the mount and the two on the struts at the MRGB. The gearbox can twist slightly about the mast, under load, and it can rise & sink slightly along the mast as lift varies. The muff is soft mounted at the rear, and the gearbox is soft mounted to the frame. This setup has worked WELL on every Mini-500 except mine .

I just cannot see how any of the small changes I made could cause the problem I am having. The engine itself or the old rubbers HAS to be the cause???

 

[bryancobb]

Dennis Fetters

Dennis Fetters

Remember, this all does not start happening at all until I have hovered for several minutes
And this is the thing that SHOULD make it easier to isolate, coz it appears its temp related.
Just watchn your tensioner wheel, could the cog belt be stretchn under heat.
The tensioner looks to be gradualy pushed put ( as the belt climbs up the teeth) then drops back in ( as the teeth realine again, maken the circunferance smaller)
I know its a long shot, a f****n long shot.

Dennis,
Chime in please. Do you think a stiffer tensioner spring would be a mistake? I could be putting more torque in because of the bluehead and creating the same engine movement that caused the BAD Helicycle problem that caused Eagle R&D to have to redesign their mounting and tensioning system?

 

[Stan V]

I feel the engine is the culprit that is making the idler go crazy. When the engine moves, the idler moves twice as much.

You could be right bryan, but you have to ask yourself what's causing the excessive engine movement? I believe its from an out of round/balanced belt. If you can temporarly eliminate the tensioner spring, by ether replacing it with a stiff rubber sleeve (chunk of garden maybe) or locking the idler down tight, leaving a little slack in the belt. Your pulleys will grow with heat and your belt won't. If you try locking it down, be sure to leave some slack in the belt.

 

[wolfy]

Remember that torque available is just that... available.
It may not be getting used, it takes the same torque to hover/fly no matter how much is on tap.
It would have to be a big coincidence that your mtow is the heaviest (most torque required) bravo that has flown. Not like it only happens pulling max pitch
Is it possible to try another belt, even an old one.

wolfy

 

[bryancobb]

Stan and Wolfy...

I think you have convinced me to buy a new belt. They are only $85 and that is a lot cheaper than what I was about to do...send my engine to Lockwood for a rebuild including new crank, new pistons, new rotary valve shaft.

I would have argued that the belt could not cause this but ... I learned better from initially trying to run the 17 year old brand new belt that came in my kit and it WOULD NOT WORK! It had been in the dark crate on a vacuum card for all that time but it had turned to garbage due to age and being folded all that time.

 

[DennisFetters]

Dennis,
Chime in please. Do you think a stiffer tensioner spring would be a mistake? I could be putting more torque in because of the bluehead and creating the same engine movement that caused the BAD Helicycle problem that caused Eagle R&D to have to redesign their mounting and tensioning system?

I wish I had the magic answer. I'm not there with my hands-on the situation to look over all the details. I can't count the times a customer with a problem tried and tried to explain it over the phone insisting that he did everything according to the instructions. Then, after he finally would bring the aircraft to our factory or to a fly-in we would be at, we located the problem, and it was always something he did different and failed to tell us over the phone, thinking that change would not have mattered.

I have not seen your problem before. I have no good guesses on what it could be other than what I have already recommended to you. I'm sure it's something to do with a change you made, or something simple that anyone would have unforeseen.

However, I wish you the best of luck.

 

[tomb2b]

Bryan its not belt or the tensioner its the engine starving for fuel at that rpm...have a look at oil pump line where it goes in the oil pump see if it has air pockets at full rpm that will be the tell tell if you had a choke u could just pull it a little to see if it needs more fuel ...had the same some what problem with my old mini i replaced the manual fuel pump and also added a eletricte one .....

 

[tomb2b]

fuel

fuel

How i found my problem i got 2 old float bowls drill 3 1/4 holes vertical with gap 1/16 apart glued glass on inside and watch the fuel run on the real low side at full rpm its a real easy check ..........

 

[bryancobb]

How i found my problem i got 2 old float bowls drill 3 1/4 holes vertical with gap 1/16 apart glued glass on inside and watch the fuel run on the real low side at full rpm its a real easy check ..........

That sounds like a plan ! I will replace the Mikuni Pressure Pump and install my ``enrichener cables.`` The neoprene diaphragm was 17 years old too.

 

[J.C.Casabuono]

Starving for fuel should be noted on the EGT indication, I think ...

Did you check the clutch ?

 

[gyro]

If starving for fuel was an issue then why the change with the rubber grommets and before it did not start till after 12min of runtime??

 

[tomb2b]

His problem is the engine for sure watch the video very closely.... the engine paulsates at the rpm that he needs.. soon as the throttle is reduced slightly its smooth as glass its running like a.... power band on a dirt bike at full rpm.. egt might not show up.... its going to be fuel related