Tail kicking / metallic bearing noise?- Dampers!

[Aviation addict]

Hi Guys,

I’ve had a good 5 month hassle free flying with the Stratus, but the last few times I’ve taken it out, its made a real racket when I’ve been cranking it over during starting. In flight the heli had a slight metallic sound too. As the engine (YS91ST4) wasn’t as quiet as it used to be I replaced the bearings over the weekend and hoped all would be well afterwards.

I nipped out to the field today and found that there was still a pretty awful noise when cranking the starter, and even once running there was still a metallic type noise. The engine itself sounded good though.

Besides the metallic noise, what prompted me to replace the engine bearings was that, last week, on the second or third flight of the day the tail started kicking a bit at all headspeeds [at which point I landed and packed up by the way!]

Unfortunately I found today that the tail was still kicking despite new bearings in the engine.

I dialled the fan to less than 1 thou by the way, and I do also have the appropriate gap between the clutch driver and fan.

Any ideas what might be wrong? Would whatever it is cause the tail to kick? Bearing in Clutch bell unit gone? :dontknow

[Aviation addict]

Anyone out there ever had their 'Clutch bell' unit or 'Clutch Assembly' unit bearings fail before? As they both come pre-assembled I guess it might be hard to replace them or even check them. Could be anything though.

Weird that the heli was fine for months then starts sounding a little different and the tail starts kicking. :arggg: Anyone had anything similar happen?

Due to the metallic tone, I'm thinking mechanical rather than electrical at the moment.

[Peter]

Check your clutch driver dampner rubbers 0546-16 .....

[Aviation addict]

Thanks Peter. They are about 6 months old and looked ok at a brief glance when I had the engine out, although I don't know how you tell when they are shot. May be worth replacing anyway....

I wasn't going to mention it, but the metallic type noise almost sounds like it's the fan, although I am 100% sure that the fan is clear of the fan shroud, governer sensor etc.

Can I check anything else while I've got the the machine in bits?

[DavidH]

My guess it is the dampeners in the fan. Just because there is still rubber left in the slots does not mean they are not bad. The dampeners need to look like just have been put in new. When dampeners are bad, it sounds just like a bell that is being rang constantly.

You should be able to inspect and spin the clutch and clutch bell when you have it out. And tell if there is any bad bearings in those assemblys.

David

[Aviation addict]

Thanks Gentlemen. Have just placed an order for the dampeners and will check the clutch / bell assemblys too. Being new to MA it hadn't occured to me that the rubbers would degrade so quickly, but I suppose they get a fair bit of hammer.

Will try to come back with the result soon. Ta.

[DavidH]

John,
The dampeners will last a long time. But they can also go bad quickly. If the engine and clutch driver are not square to each other. The gap between clutch driver and fan is too great. Or the engine is running rough constantly.

Gap between the fan hub and clutch driver. Needs to be in the .030 down to .015 range. That is in inches. Also the gap needs to be the same when checked every 90 degs without turning the fan or clutch.


David

[Aviation addict]

I've taken everything apart now and the bearings all feel smooth. No gritty feel. I'll be sure to take my time getting the clutch gap just right when the new dampers arrive. Thanks for the advice. Didn't know any of this.

[Aviation addict]

Peter & David Thanks. I changed out the dampers this morning then spent ages trying to get the fan/clutch gap as good as possible through each 90 degree point. I had 0.019 all the way around in the end. Found initially that the left side of the heli was 0.018 but 0.019 on the right. I didn't know what the correct thing to do was in this situation, but I loosened off the 8 bolts on the top of the A frame and tried to persuade it to sit square then tightened them up again.

Test flew her just now (between the rain showers) and all was good. No metallic noise, no tail kicks. There was a slight ripple on the fuel tank at 1850 rpm, but no mixing or foaming. The starter related noise was still there when starting, but I noticed that if I lifted the starter higher up the starter shaft the noise disappeared. Maybe my starter shaft has worn a bit where the roller bearings grip? Thanks :thumbup:

[Peter]

Awesome !! Theres nothing quite like a great running Stratus.............. :noteworthy :noteworthy