Tail bearings... again

[lainchy]

Hi forum,

Quick question... thought I'd found the answer to this one, but my HK450 belt heli keeps destroying it's tail box bearings! It's in a hughes 500 fuz, so bit annoying to keep getting the mechanics in and out.

I thought this was down to a slightly bend tail rotor shaft, which was replaced... but my issue is back.

So, I'm wondering two things now... Maybe a slightly off centre front belt drive unit... as in the notched pulley possibly being not centred?? This maybe tensioning the belt strangely during drive, or tail blades?? They are loose in the grips. How can I tighten them? I've seen blade grips sold in packets for mains and tails.

How likely is this going to be? The belt pulley... I can see this as the belt will be pulling tight and going loose very slightly of course... but enough to knacker the bearings???

Tail blade tightness?

My other HK450GT is fine... smooth and has had LOADS of flights.

Ta

[Roger Fowler]

I've seen this too. Changed two sets of bearings over a few flights. Had flown a long time before with no problem and have flown a fair while since. Poor quality bearings?

Roger

[macdad]

I don't know, just guesses here:

How tight do you tension the belt? Those tail shafts are pretty easy to bend. Not sure it is possible to bend on due to tensioning... A high tension will also put a pretty good side load on the radial bearings. They don't like that.

I also wonder if it is a tolerance issue in your tailbox. Maybe there is enough of a misalignment between the two bearings to cause the issues you are seeing?

I personally never had an issue with loose blades in the grips on a standard 450. You could crank it down some or put a shim in the grips if need be.

Again, just brainstorming here.

[lainchy]

Hi both, and thanks for the reply... apologies for the long delay.

I'm going through a complete rebuild on it at the moment, and going to change the tail unit out. It never seems to be tight when re-assembled, but I'm thinking misalignment or the like... looks straight though. I'm just at a loss. I double checked the belt tension on my good HK450GT, and it's about the same, so I don't think I'm over tensioning.

Over the past week, I've replaced both main bearings, main shaft, tail drive pulley gear and bearings, tail box, belt, and checked/oiled/refitted the motor.

I've spooled it up on the bench, with the blades off, and it all looks good at the moment. (Said that before lol)

I'm going to puck a couple of flight packs through it out of the fuz, and all being well, I'll refit.

Watch this space... I'll have it airbourne again, hopefully at the weekend, or early next week.

[lainchy]

Another bearing!

Tail rotor grips??

New tail box has been fitted and bearings throughout. Losing the will to live with this

[gimbleguy]

a tight belt can cause it, also check for binding.

[Ah Clem]

Did you lube the bearings?

[lainchy]

Yep, Lubed all bearings... in the tailbox, tail drive, OWB, Mains... all done. Luckily not fitted back in the Hughes fuz!

Just ordered new boom and tail rotor.

It has to be something silly, but I know it's not my building. Never had this issue before. I'll be sure to tell you when I do sort this, but I just have no idea at the moment.

[lainchy]

Looks ok? All seems well at the moment... 2 flights in.
Tail rotor blades are not quite pitch equal with this though. This is a new tail rotor too. HK quality no doubt! Could be the tail blades?? The first set were dirt cheap fibre glass ones... just for the yellow/black. Binned those, and put a standard pair of HK ones in.

It's the bearing by the fin that always fails.

450 se v2 belt tension & spool up (0 min 42 sec)

Many thanks for your help with this.

[sconel]

I went thru this some yrs ago....eventually found it was me damaging the bearings when installing them because the tailcase was somewhat tight. Had to pound them in and didn't know where to pound (pound is a strong word, but they were tight) If you have to beat on the bearing to get them in, maybe consider a new tailcase.

Only beat on the inner race if they need "persuasion". I use a nut driver the same size as the inner race. Better yet is to put the tailcase in the 400deg oven for 10 minutes if there is no plastic...and put the bearing in the freezer for the same time. It expands the tailcase and shrinks the bearing slightly. Generally, bearings will almost fall in if you do the assembly immediately after the freeze/heat treatment.

[lainchy]

Hi Sconel,

Not so in my case, the housing near the fin is a close snug fit, but the other side needs some retainer to hold it in place. No stressing at all with either tail box. Well worth noting though Cheers

[wrench567]

As a big truck mechanic I am inclined to think miss installation. But since getting into this hobby I am more inclined to think bad QC on the bearings manufacturer and HK. My HK 450 belt tail vibrated like all heck. I found that the bolt together spacers between the plates are three different lengths! I had to make shims out of brass shim stock to even the plates to the longest spacer. I probably could have filed the long ones shorter but I didn't want to squeeze too much or risk not having a square end on the tube.
I am considering this tail assembly from Tarot. http://tarot-rc-heli.com/Tarot_RC_He...l-Box-Gear-Red
It does come in different colors. Looks a lot more durable than the stock unit.
Some things to consider.
Pete

[lainchy]

To be honest, 4 flights later, and another one gone... I checked the next bearing carefully before fitting... Hmmmm, notch in that. And the next one. Found the best one in a pack of 4 and used that. Fingers crossed again lol

[gimbleguy]

ceramic bearings might be the next option, but they are pricey. It would be nice if all helis had ceramic bearings, especially in the motor.

Align trex 450 l dominator with new ceramic bearings (5 min 43 sec)

[lainchy]

Will bear that in mind Gimble Guy. Cheers. Fingers crossed though for sure... I've had this heli apart soooo many times. Short of the frame, I think I've got 2 other heli's now lol.

We'll see

[lainchy]

Solved! (I think)

5 flights on this now and no more issues.

Combination of three things in the end...

Iffy Tail Pitch Assembly - Somewhere the centre tube wasn't installed on the alloy unit square so the whole thing vibrated while spinning. Difficult to spot that one

One of the tail blades wasn't true. The pitch changed along it's length.

I also went through the packs of bearings and chucked 2 brand new ones away. Picked the one that had no notches, or seemed to be the better of the bunch.

Changed these out and so far, so good. Few more flights and it can go back in the fuz.

Thanks for the help all