Check The Runout

[SteveH]

Just wanted to caution everyone as I'm building my second Frenzy I found the fan hub where the clutch mounts with .006" runout. That much runout will cause unexceptable vibration levels and will result in the heli being shaken to pieces as well as possibly distroying electronics.

[BC]

Can you tell me or point me somewhere to learn how to do that properly? I have the tools to do so...

[SteveH]

All you need to do is install the fan, put the engine in a vise, and use a dial indicator to check the runout as you turn the engine over. It needs to be a maximum of .0015" where the clutch installs.

I was helping a friend checking the runout of his clutch after he had a crash, and we found the runout at almost 1/8". UNBELIEVABLE!

This shows that the metalurgy used in these helis is pretty poor.

[heartnspirit]

Is it the clutch you're finding with excessive runout or the fan? Most everything I've read and heard in other kits recommend anything within .002" as an acceptable amount. I know the Synergy N9 hubs were really hard to get below .003"

[SteveH]

It's the top of the fan where the clutch mounts. If it has excessive runout there, the clutch will have excessive runout. + or - .0015" will result in an overall runout of .003"

[crashagain]

Where do you get a tool for checking this???

[SteveH]

Got mine from Harbour Freight years ago...it's a cheapie. You really can't build a glow helicopter correctly without one.

You need the dial indicator, and the magnetic stand.

[heartnspirit]

Hi Steve,
Do you think the excessive runout is because of the fan not being bored dead center or the clutch mounting holes machined off center? I had a tough time getting my clutch to go down into the fan hub and it actually dug into one side of the fan hub. I'm wondering if my fan was not machined true. Do I have excessive vibrations? Kinda hard to tell with a reciprocating engine banging away at 18,000 rpm. Nothing visible in the tail fins, the fuel doesn't foam and the spartan has never complained. Guess I better get the dial indicator going tonight to be sure.

[SteveH]

It's definately the fan hub machining, or the fact that the aluminum is very soft. My clutches are not very accurately machined either, because with the fan hub having a few thousands runout, I can install the clutch one way and the runout is worse, then install it 180 degrees out, and the runout is better. My clutches have fit into the hub quite well, but my friend's was almost a press fit, and had to be turned down a hair.

I think we are just dealing with a very cheaply made helicopter, and we need to learn the deficiancies and learn to deal with them. But, they sure do fly good.

If you pick up the heli by the head to carry it out to the flight line and you feel the engine vibrating, I would bet the clutch had excessive runout.

[BC]

Steve, what did you do to fix yours? Your post on RR mentions every hub you tried was out. The Raptor one isnt long enough i understand.

[SteveH]

While turning it on the engine, I determined what direction it was out, and marked it. Then very carefully I sanded a very small amount of aluminum off the underside of the fan where it mates to the front engine bearing using a sanding block. Then reinstalled and rechecked runout. Basically, since I don't have a lathe, I very tediously hand fitted it. Lots of work, and lots of trial and error. Not something I recommend, but better than .006" runout and the helicopter distroying itself in the air from clutch vibrations.

[BC]

I found mine to be out .008 too, and when i removed the washer between the fan and engine, it was out .006.
Another thing i noticed was the black anodizing where the crank goes into the fan is rubbed of on 1 side, a sign of the crank galling it when tightened up.
I will try to get someone to turn it for me on a lathe, the sanding thing isnt my forte'.
Thanks for making the thread.
A Main are you listening??

[BC]

I ended up sanding mine and got it down to .0012. I used 400 grit to start and got it to .002 then used 600 to finish it. This is with the os washer removed, when i put it all back together I now have 1.5 mm of clutch shoe sticking out below the bell!! augh.... Hopefully I can get the same tolerance with the washer in.
FYI: i used wetted sandpaper on a sheet of glass to "mill" the said protrusion off the hub.
Back 2 the bench for another couple hours.

[crashagain]

Maybe they are getting better or I just got lucky...

After reading about this I decided to buy a dial indicator at harbor freight and check mine..
.002 is what I got... Woo Hoo, no sanding..

[SteveH]

Yes, I think they've had a bad run lately, as my first one was good, but my latest one was junk.

Also, if you crash it, check the runout again....was helping a friend after his crash and his fan was so far out at the clutch mounting that we just thru the fan away.

[SteveH]

An update on this topic....a friend brought a motor/fan/clutch assembly over for some help dial indicating it after a crash. We found it almost an 1/8" out, and this HAD to be a result of the crash. Thought the crank shaft might be bent, but after examination, we determined it was not. The aluminum in the fan is soft.

So, if the fan can bend that easily, I figured why not try bending the fan into alignment in the beginning. I now use the dial indicator to determine runout, and if it excessive, I use a small wooden hammer to tap against the high side, and actually bend the fan into alignment. I know, scof all you want, the procedure works, unlike ordering a new fan which may be just as far out of true.

[BC]

Holy crap that is soft!
No wonder this heli is so cheap, get what ya pay for! But I dont mind the tinkering.....its worth it for the flight performance.
Thanks Steve.

[Ghostfit]

That soft huh ???

I'm just wondering, would'nt it twist out of alignment if the motor/main rotor blades loading is high enough ?

[BC]

SteveH, how close can you get the runout with the hammer method? lol
Then do you use the sanding method to bring it to 002?

thnx

[SteveH]

With the "hammer method" I got mine from +,- .004" down to +,- .001". I used a rather light wooden hammer, and I was holding the engine/fan combo in my hand while smacked it.

I suppose if you used a metal hammer you could damage the fan easily, so don't think I would use a big heavy steel hammer.

I realize this is an unaccepted "method", but sometimes you gotta do what you gotta do.