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HomeTurbineAircraftHelicopterTurbine Helicopters › Auto rotation hub
08-24-2014 05:15 PM  3 years agoPost 1
Richard

rrVeteran

Scottish Borders, U.K.

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Hi,

I have been trying to replace the main mast on my PHT3 Powercat by following Peter Wales instructions but I cant get the mast to slide out? I am going to fit a Vario 4 blade head.

When I tried to remove the pin at the bottom of the mast, it fell out in 3 pieces I can get the mast to slide up and down approx 10mm but I cant get it to slide al the way out. Could there be a fault with the auto rotation hub

Oh **** ! this is going to be expensive?

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08-24-2014 10:32 PM  3 years agoPost 2
heliayto

rrNovice

solihull, uk

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Just carried out the same mod. If the pin came out in three pieces then I expect there is still a piece stuck within the main shaft which is preventing the shaft from sliding out. Get a bright torch and have a look. The mod. is a little fiddly but persevere.

Hope this helps.

Regards

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08-24-2014 10:38 PM  3 years agoPost 3
Richard

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Scottish Borders, U.K.

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Hi,

I can actually see the hole in the shaft and slide a screw driver through it. If I pull the shaft upwards then down again the inside of the auto hub comes out enough to hold it and turn the shaft. This leads me to believe there is something inside the auto hub stopping the shaft sliding out.

Do you know if the pin was rounded at each end as the pieces of pin I recovered only had one end rounded.

Oh **** ! this is going to be expensive?

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08-24-2014 11:09 PM  3 years agoPost 4
mookie

rrApprentice

UK

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HI there, I have just made a new mast for for my PHT3. The drive dog that the pin locks into IMO would stop any foreign objects getting into the one way bearing. But it's worth getting the three pieces and checking the length to make sure you do have all the bits, if the pin has flared the hole slightly on the main shaft that would cause the problem you are having, it's a very tight tolerance. If you can, then rub some fine wet and dry over the hole on the main shaft to clean off any high spots. You might have to lower the bottom bearing to do this.
I'll ask Nigel to measure the length of the pin.

Malc

valve boy!

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08-25-2014 06:53 AM  3 years agoPost 5
PETER ROB

rrElite Veteran

Devon UK

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Reason for strip down?
Richard, what was the reason for the strip down?
If the shaft moves 10mm, I doubt it is the auto hub
Follow Mookie's advice and make sure the old shaft is polished smooth
If the reason is for a bent shaft, then chop off the old shaft as close as you can, and again make sure it is smooth before extracting it, it may be you will have to strip a side frame off to access it
We did a strip down yesterday to replace a split clutch locking collar, looks a bit of a mess but took 4 hours from start to finish
That pin should have been rounded at both ends, measure the length of the slot it has to fit into, allow a little clearance, I have used silver steel for a replacement, I have heard of the replacement cut from a 3mm drill bit, but I would think this would be too brittle
Peter R

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08-25-2014 10:07 AM  3 years agoPost 6
Richard

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Scottish Borders, U.K.

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Hi,

I will try and rub the shaft with fine emery paper to see if that helps.

The reason for changing the main mast is to fit a Vario Bendix 4 blade head. The Powercat pod and boom requires the main mast to be shortened. The hole in the mast for the head bolt is only approx. 3mm from the top. The new 4 blade head wont fit unless the mast is replaced.

Oh **** ! this is going to be expensive?

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08-25-2014 10:10 AM  3 years agoPost 7
modtron

rrKey Veteran

Oxford. UK

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Hi Richard,

Just doing you a reply pm

Are you using the old Bendix Head or the normal 2 bolt type ?

modtron
Oxford UK

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08-25-2014 11:34 AM  3 years agoPost 8
mookie

rrApprentice

UK

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This is the one i made for my 4 blade head which Nigel (modtron) Supplied, even this i had to polish on the lathe to get a good fit. I have a load of 10mm silver steel left over, unless yours is the 12mm shaft.

malc

valve boy!

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08-25-2014 12:31 PM  3 years agoPost 9
Richard

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Scottish Borders, U.K.

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Hi,

I followed your instructions Peter along with Malc's and got the shaft out by gentle tapping with a soft head hammer. I just now need to get a new pin and I can fit the replacement main shaft.

I will update this post when finished the work

Oh **** ! this is going to be expensive?

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08-25-2014 03:43 PM  3 years agoPost 10
mookie

rrApprentice

UK

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Hi Richard, glad you got it sorted out, did you remove a side frame to do this?

valve boy!

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08-25-2014 07:18 PM  3 years agoPost 11
Richard

rrVeteran

Scottish Borders, U.K.

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Hi Malky,

Yes, I had to partially remove one side, just enough bolts undone to spring the frame and let the gear out, I then used a soft head mallet to tap the mast out. The new mast just slipped in without a problem. Peter is going to send me a new pin.

Thanks again for your help.

Richard

Oh **** ! this is going to be expensive?

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08-27-2014 11:02 PM  3 years agoPost 12
Richard

rrVeteran

Scottish Borders, U.K.

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Thanks to modtron, Mookie and especially Peter for making me replacement pins.

Hope to finish the rebuild in time for the weekend.

Oh **** ! this is going to be expensive?

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