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wise(at)txc.net.au
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Posted: Thu Jul 14, 2011 2:37 pm Post subject: Undercarriage

G’Day All,

 

We have removed the mains from our 18T to replace a leaking seal in the left oleo. So decided to pull down both, clean, inspect and replace the seals.

What is the best way to refill. We have the charging tool. Is it really that beneficial to charge with nitrogen, or can we use clean dry dive bottle air?

What lubrication should we add?

 

Thanks and cheers,

Chris.

  [quote][b]

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Vic

Joined: 12 Aug 2008
Posts: 115
Location: Southern Bavaria

Posted: Fri Jul 15, 2011 4:37 pm Post subject: Re: Undercarriage

Hi Chris,



what is dive bottle air, 80 percent nitrogen and 20 percent oxygen ? How much water can be in a refill of very few litres of air from a dive bottle provided the bottle was filled in controlled conditions ? So we decided it was not worthwhile to go for pure nitrogen. 

  Basically silicone grease is a great lubricant for rubber or plastics and I use it in some places in the actuating cylinders . Or otherwise a heavy lithium grease for the bronce bushes in the landing gear and the ball locks in the actuators. We did a complete landing gear overhaul last winter and found that excessive wear in the bronce bushes showed in the scuffed anodised aluminium bushes. The original felt "seals" cannot keep the dirt out and the grease in the strut so I replaced them by seals used in hydraulic systems. A wiper seal keeps dirt out and an o-ring keeps the grease inside. I´d strongly suggest to do this mod but this may be too late in your case. The action of the landing gear on the ground is a bit stiff still, could be the grease and new bushes. But the unpressurized strut moved smoothly so I suspect with 20 bar in the system the o-rings produce a lot of friction. 

  The original damper valve has no springs so this creates a lot of backlash and knocking noise on rough airfields, so I did another mod to cure this. But this year still no real test on rough ground done to report. 



Cheers

Vic

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tigeryak18t

Joined: 26 Sep 2009
Posts: 233
Location: PARIS FRANCE

Posted: Sat Jul 16, 2011 11:25 am Post subject: Undercarriage

Hello vic



This is two interesting mods

Could you take a little time and take pictures or is it too late?



Anyway how difficult was it to do it. Did you need special tools ? Or skills?

Where can you have these new seals?



Thanks for any advice



Regards



Didier Blouzard

+33 6 2424 3672



Le 16 juil. 2011 à 02:37, "Vic" <vicmolnar(at)aol.com> a écrit :



 	  Quote: 	
		   

 

 Hi Chris,

 

 what is dive bottle air, 80 percent nitrogen and 20 percent oxygen ? How much water can be in a refill of very few litres of air from a dive bottle provided the bottle was filled in controlled conditions ? So we decided it was not worthwhile to go for pure nitrogen. 

  Basically silicone grease is a great lubricant for rubber or plastics and I use it in some places in the actuating cylinders . Or otherwise a heavy lithium grease for the bronce bushes in the landing gear and the ball locks in the actuators. We did a complete landing gear overhaul last winter and found that excessive wear in the bronce bushes showed in the scuffed anodised aluminium bushes. The original felt "seals" cannot keep the dirt out and the grease in the strut so I replaced them by seals used in hydraulic systems. A wiper seal keeps dirt out and an o-ring keeps the grease inside. IÂ´d strongly suggest to do this mod but this may be too late in your case. The action of the landing gear on the ground is a bit stiff still, could be the grease and new bushes. But the unpressurized strut moved smoothly so I suspect with 20 bar in the system the o-rings produce a lot of friction. 

  The original damper valve has no springs so this creates a lot of backlash and knocking noise on rough airfields, so I did another mod to cure this. But this year still no real test on rough ground done to report. 

 

 Cheers

 Vic

 

 

 

 

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 http://forums.matronics.com/viewtopic.php?p=346609#346609

 

 

 

 

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_________________
Didier Tiger YAK18T
Member of Commemorative Air Force
French Wing

wise(at)txc.net.au
Guest

Posted: Sat Jul 16, 2011 3:38 pm Post subject: Undercarriage

G'Day Vic,



Thanks for that.

Makes a lot of sense and we have one oleo stripped and I see no problem in

fitting a suitable seal.

I shall keep you informed.



Cheers,

Chris.



-

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Vic

Joined: 12 Aug 2008
Posts: 115
Location: Southern Bavaria

Posted: Sat Jul 16, 2011 4:47 pm Post subject: Re: Undercarriage

Hi Didier, Chris,



for dismantling the struts you may need two special spanners, as you see in the photo above. Didier, you can have them for a while - winter, I think, would be ideal for the job. Maybe we meet in Eggenfelden some day for you to pick them up. Also I made up some sort of shoe horn to help the piston ring over the shoulder in the strut. This is a pipe with 65mm o.d. and 62mm i.d. and ~200mm long cut in two halves. The nose wheel is different by few mms, I can check sizes later. The seals can be found in hydraulics industry supplies for piston rods with 52mm and 50mm dia. as dust wipers. And next to these I put o-rings in to keep the grease inside the strut. You need adapter rings for the seals to position them in the milled nut where the felt was before. 

The photo below shows the spring loaded damper valve with no backlash to get rid of the knocking on rough airstrips. Still not yet tested on real rough stuff but I am confident ...



Cheers

Vic

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wise(at)txc.net.au
Guest

Posted: Sat Jul 16, 2011 5:42 pm Post subject: Undercarriage

G'Day Vic,



Thank for the photos.

I have printed them and will check it out later today.

Do you have any info on the seals that you bought such as manufacturer and

numbers?



Cheers,

Chris.



--

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