Mainshaft vertical play and Main gear lash

[Steve Graham]

OK I got my new pinion and a few other wear item parts.  I'm having a couple concerns.

The mainshaft has what I would consider excessive vertical play.  In the past I had used as many as two shims and just taken the slop out with the shaft collar that rides on the upper bearing.  This time I'm measuring just under two mm's of vertical play.  I would need around 6 of the .3mm shims to fully take up this play.  I think other synergies may have had lower bearing blocks that could be moved up or down to take out this play?  I suppose bent bearing blocks could cause this but mine are flat and true as far as I can tell.  I'm tempted to just crank down on the upper shaft collar and fly it but if that slips I'll have issues with flight controls at least.  Without the shims the lower bearing could also float up out of place. 

The second issue I'm having is with excessive main gear lash.  I grabbed a new pinion as my old one was clearly worn out but I'm still seeing about the same amount of backlash with the new gear.  Without pushing the clutch starter shaft out of alignment there is no way to tighten lash unless I'm missing something.

Looking for suggestions from the experts here.

[Matt Botos]

Hey Steve,

Make sure the middle bearing block is not upside down. 1-2 shims is normal, 6 shims, there is something bent or installed incorrectly. The bottom bearing block is susceptible to bending if you’ve had a hard crash inverted.

The main gear lash is set by either using or not using the engine shims. The lash does not have to be tight with the cnc helical gears, a little more lash than usual is okay.

Hope that helps!

Thanks,

Matt

[Steve Graham]

Thanks Matt,  I didn't want to pull the bearing blocks cause I'm kinda lazy but I suspected that was where the issue lay.  Yep, middle bearing block slightly tweaked and bad bearing so I'm replacing all three bearings and the middle block.  I've definitely bent a couple lowers in the past, one clear into a U LOL.  That one does appear to be straight at least until I crash it again

[Steve Graham]

I put 3 new bearing blocks and bearings in today.  It probably only needed one but I replaced all 3 for cause.  While I had the heli stripped down I went ahead and replaced both rear frames which again probably didn't need it but they were getting a little tattered from 4 years of abuse.  After buttoning it all up the vertical play was all but gone.  I did put one shim on top of the lower bearing but it honestly probably didn't need it.

The gear lash does seem to be a little better.  Since I had the frames apart I made sure that they were true per the 90 degree check in the manual.

I also attempted to do the balancing of the clutch/fan and bell assemblies per Matt's recent video.  I have the same Dubro balancer he used but I honestly didn't feel there was enough imbalance anywhere to reliably read or warrant shaving any weight.  I may see if there's a local machine shop that could do a spin/dynamic balance on these parts next time I have them apart.  I've never been able to get the MSH brain FBL to rescue reliably with this heli so had given up even trying awhile back.  I think we are still at the state of the art with rescue we were in the beginning with FBL where the units are just really sensitive to vibrations.  I don't really miss the rescue since I never flew with it prior to late last year.

I also replaced the fuel tank rubber edging which had gotten pretty hard with age.  I should have done the fuel tank while it was out as it is showing signs of wear along the lines where it comes in contact with the edging.  The tank is intact for now however.

[Grimmy]

I also attempted to do the balancing of the clutch/fan and bell assemblies per Matt's recent video.  I have the same Dubro balancer he used but I honestly didn't feel there was enough imbalance anywhere to reliably read or warrant shaving any weight.

If you can see any imbalance using a balancer, even minute, will be a lot more when it's 15k rpm or higher.  The pickier you are with this, the better things will be in the long run.

Had a crankshaft balancing machine where I used to work.  It had a great operators manual that explained things really well.  I don't remember the numbers they used, but it was something like if you were out of balance by 1 oz on a crankshaft, and spin it so many rpms, it was like 100 pounds of force pulling outward on it, which is hard on bearings and many other things.

From what I've read the MSH rescue has never worked well with Nitro.  Just too many vibrations to get it to be reliable.  I would think that would be the same for any rescue system, as they pretty much use the same technology (accelerators).

[Steve Graham]

Totally agree with you Grimmy,

I just don't think the static balancer is sensitive enough to really balance very well when talking the kind of RPM's we're dealing with.  I may try and find a local machine shop that can spin balance something like this.  When I flew it with the new bearing blocks and bearings the vibration logs did show much less vibration than I recall seeing in the past.  It did self level, sort of.  It was off by about 30 degrees.  IME that's about as good as I've seen on my N7.

[Gabriel Sandoval]

That's why I use the unit from Top Flight which uses magnets to float the bar. Only part I couldn't float was the clutch shoe with the X-Tra large clutch. Too heavy to float, but the rest of the parts were no problem. I get a better tolerance this way but I am balancing all the parts individually then setting runout with the dial indicator when attaching the clutch shoe to the engine.

[ktmdiesel]

I have ikon on my n7 and 600n. The rescue works almost flawless on the 600n. As for the n7 i had a constant low noise vibration that caused rescue to take off to the left. I took it all apart and balanced the clutch assembly better. Only problem is I have to wait until spring to try rescue again.

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