Mini-500 Support Thread

[Blue Chips]

Did Auria suggest and staking or Loctite?
What fit did the recommend?

Ken

[bryancobb]

Originally Posted by Blue Chips

Did Auria suggest and staking or Loctite?
What fit did the recommend?

Ken

Ken,

That's a good question. I am not ready to do assembly stuff right now. I am just rounding up all the components I intend to assemble, and do any mods that's called for under the newest Revolution literature. I'm tweaking things as I deem logical on some things even though not called for by Revolution.

To answer your question, I will get very specific information on tightness of interference fit, for this use, from Aurora at the time I am ready to assemble the cheek plates and these bearings.

Pertaining to retention, I will be using LocTite #231 (according to LocTite Tech Rep, suitable substitute for 7331 specified in the assembly manual) just as the Revolution Assembly Manual instructs.

Staking is not possible, because the bearing bore in the cheek plate is exactly the same depth as the outer race of the bearing. It presses in flush. I feel the problems many had with this is because Revolution's fit was too tight and led to the outer race to moving around from the forces exerted on it by the inner sphere, which distorted the cheek plate material and caused it to loosen.

I guess we will see if mine get loose. These certified aviation bearings I now have are obviously monitored much more closely during their assembly process than the ones shipped with Mini-500 Kits. Their fits between sphere and race are tested and QC documents completed.

[bryancobb]

When I disassembled my centrifugal clutch for inspecting, lightening, and balancing, I focused my thinking on the bearing arrangement because the heat, vibration, and bearings spinning their outer races caused some problems, back in the day.

The two bearings it was equipped with were sealed on both sides with the black plastic-looking seals. They were very stiff to spin and my conclusion was 16 year old grease and no use in that period of time. I popped the seals out and found a nice light green grease inside that was not the slightest bit hard. It was similar in consistency with the AeroSHELL #14 helicopter grease. Very thin for grease and the bearings spun very free after removing the seals.

I cleaned all the grease out with MEK and let the bearings dry. They spin smoothly with just a whisper of air blowing on the outer races.

These bearings only spin when the engine is running and then, only until the rotor is engaged. Once spooled up to 3000 engine RPM, the clutch locks and the bearings no longer rotate. They stay like this until throttle is rolled off to below 3000, and then they only turn long enough for the belt and pulleys to coast to a stop or the same speed. The other one way clutch is overrunning at that point and the belt is not driving the rotor and the bearings are not under any load.

BY FAR THE MOST IMPORTANT THINGS THESE BEARINGS DO...is to keep all components of the clutch concentric so they don't get unbalanced, and to carry the load when the belt is driving the rotor and trying to force the engine PTO cog and MRGB input cog closer together.

I have analyzed it and decided that when I reassemble the clutch, I will leave off the inner seal on each bearing, and pack enough AeroSHELL 14 in the inside drum area of the PTO cog (shaded area where the two bearings reside) so that during the time after the clutch engages (entire time in flight), the grease will be slung to the outside limits of the drum and be forced into both bearings' balls by centrifugal force. Then every time the clutch is disengaged fresh grease will have been forced into the bearings before they are required to spin. Seems like a good idea.

This will cut the rolling resistance in half that the seals created. This MAY have contributed to the outer race spinning problem? It will also do a better job circulating grease around and making sure it hasn't stagnated in the ball retainer/spacer which doesn't lubricate a thing or do a BIT of good.

I also ordered some longer "low head" screws to attach the clutch bell to the cog. The OEM ones' threaded portion was only 1/2" long and has to pass through 0.147" of the clutch bell before grabbing threads !!IN THE ALUMINUM COG!!
0.353" of threads of a fastener that has 18 threads/in. means that only 6.3 threads was grabbing aluminum on each of the four. I can increase the thread-grip to 0.578" without contacting the bearing outer race. That means 10.4 threads per bolt, carrying the load. On such a critical location where those 4 bolts carry all the engine horsepower IN SHEAR, I like that extra meat.

[luckyluciano]

Good work Bryan!
I am going to make the holes in my clutch the same as yours but I will tilt the milling cutter to some degree, to create a pumping action to increase hot air displacement from the clutch and the crankshaft. I will name the mod (Bryan's tornado) . With your permission of course.

Regards
Luciano.

Originally Posted by bryancobb

I got the holes milled in the clutch bell and the front shoe keeper plate. I would guess this will help a lot with the heat issue during rotor engagement.
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[bryancobb]

Originally Posted by luckyluciano

...Good work Bryan!...I will name the mod (Bryan's tornado) . With your permission of course...

Thanks Buddy.

I'm really trying to preempt problems before they occur, while not really re-inventing the wheel. The idea of "scarfed" holes to draw the air is a great idea.
I considered that but I didn't want to go tilting the mill head. The shop foreman would be mad at me if they had to dial it in again before doing a "for revenue"
job.

LOL! The Tornado... fine as long as you don't call it the Hurricane! They are our arch-rival football team!