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HomeTurbineAircraftHelicopterTurbine Helicopters › Long Life JetCat starter O-ring
04-21-2009 02:41 AM  9 years agoPost 1
seattle_helo

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Seattle, WA USA

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Has anyone managed to find an O-ring replacement for their PHT3 that lasts longer than the stock JetCat parts? I've read several posts about different durometers but don't really understand it. Is it the relative hardness of the rubber compound in the O-ring? Is higher durometer better for our needs?

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04-21-2009 06:57 AM  9 years agoPost 2
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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I think the harder it is the more pressure you will require to get the starter nut to stick to the o ring , so it's a compromise between the correct working of the bendix , to the wear of the o ring.
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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04-21-2009 07:04 AM  9 years agoPost 3
PETER ROB

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Devon UK

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"O" rings
Nick, There used to be 2 types of "O" ring soft and hard, how it is measured I do not know
The soft was on the PHT3, which had a smooth end to the turbine main shaft
The hard was on the SPH5, which has a knurled end to the turbine main shaft
Now when you order "O"rings they seem to be the same
To get the longest life out of your "O" ring it is important to get the starter to turbine mainshaft alignment spot on, it can take a little time until you are proficient, but if the alignment is the slightest bit out then the rubber grinds it'self away,
To check if the alignment is correct, after running the starter in test mode (push ignition button on GSU)and wipe around the starter rubber/ turbine main shaft area with a piece of white cloth if there is any black rubber on the cloth the alignment is incorrect,
Regular checks with the cloth after a run and cool down, is a good idea, there will always be some black it is a matter of checking to see if is excessive
Peter R

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04-21-2009 05:20 PM  9 years agoPost 4
chopper jockey

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uk

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To check if the alignment is correct, after running the starter in test mode (push ignition button on GSU)and wipe around the starter rubber/ turbine main shaft area with a piece of white cloth if there is any black rubber on the cloth the alignment is incorrect,
Peter,
how do you adjust the alignment if it's wrong?

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04-21-2009 06:15 PM  9 years agoPost 5
PETER ROB

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Devon UK

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Adjusting alignment
On the PHT3 (seattlehelo)the starter is held with 4 bolts, Do I need to explain more?
If you are asking about the SPH5, it was originally designed to self align, as it is held in a semi flexible holder, this can be,(in the wrong hands) bent out of alignment
Peter R

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04-21-2009 07:10 PM  9 years agoPost 6
seattle_helo

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Seattle, WA USA

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Hmmm... Maybe misalignment is my problem. It seems like the original, factory installed O-ring on the engine lasted forever. But it did eventually wear out and after changing it last summer it seems to be wearing out faster now. On this next replacement I'll be sure to pay close attention to alignment. Also interesting, on my PHT3 the rounded main shaft section where the ring engages is knurled.

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04-21-2009 07:38 PM  9 years agoPost 7
PETER ROB

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Devon UK

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PHT3 end of shaft knurled
Nick, that is probabley why all the "O" rings are now hard, most of my PHT3's the end are smooth
Another thing Nick did you alter the position of the bendix, when you changed the "O" ring
If the bendix is to close to the end of the shaft the bendix does not get enough travel to work correctly
Conversly if the bendix is too far back up the shaft then it tends to slip
My way was to make sure the turbine main shaft just touches the brass centre of the bendix, this gives maximum available rubber to wear out and when it does wear out the shaft touches the brass and you can hear it, time to change the rubber
Peter R

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04-21-2009 07:41 PM  9 years agoPost 8
seattle_helo

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Seattle, WA USA

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Okay, all good to know. I'll set it up properly this next time round. Thanks for the info, Peter.

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04-21-2009 11:54 PM  9 years agoPost 9
MattJen

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UK

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On my PHT3 the rounded main shaft section where the ring engages is knurled.

Mine was on the SPH5 and PHT3 as well,

Just to add,
The alignment of the starter to the compressor nut is critical. Any change in this alignment may cause problems with the bendix engagement / disengagement. If the starter bendix does not disengage at the proper time (about 33,000 RPM), the starter becomes a generator and sends a very unwanted current to the ECU power board.
you do not as suggested wait for a metal on metal grinding sound before you change the O ring..

Matt

All The Best

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04-22-2009 12:25 AM  9 years agoPost 10
helibeli

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wales.uk

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As a matter of interest what system do full size helis use to start the turbine?

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04-22-2009 02:11 AM  9 years agoPost 11
Turbinator

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Nanticoke, PA

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Matt is right, if starter does not engage = trouble, big time!!

I unfortunatly had this happen. The starter motor is not designed to spin 90,000 RPM! The commutator in the starter motor actually flew apart and was in pieces in the end bell, worse yet that unwanted voltage Matt spoke of gets disapated in the ECU, namely into the power transistor. Mine got so hot it melted the solder that attaches the power transistor to the board and it slid down and shorted out accross the one next to it for the glow plug, needless to say it ruined the board . When ever you mess with this be sure on the first start and spool up the starter has disengaged.

I purchase my replacement orings from local Bearings and Drives Unlimited bearing house. Metric o-ring, 6X3BN70, 6 bucks for 10 of them, I put one in my 135 last year, one in the 230 this year, (all PHT3's)have 8 left yet. I guess they must be the right durometer or I am installing them perfectly!!! as they have lasted quite a while now.

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06-07-2009 04:17 PM  9 years agoPost 12
Torsten

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Germany

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hello,

i just exchanged the rubber o ring with a main rotor damper o ring.

seemed to hold up well.....until the starter motor did not disengage and spooled up with the turbine to idle rpm.

then i noticed it and shut the turbine off.

looks like the starter motor is just a regular car motor.

will have to exchange that one.

so be sure to realign carefully.

t

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06-09-2009 06:07 PM  9 years agoPost 13
seattle_helo

rrKey Veteran

Seattle, WA USA

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Thanks for the realignment warnings. Turbinator, I just now noticed your info about Bearings and Drives Unlimited. That's a good deal for 10 of them. Will order a batch now for future use.

helibeli, I believe many full size helis also employ an electric motor to spool up the turbine prior to ignition with jet fuel.

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06-11-2009 02:09 AM  9 years agoPost 14
chinnook

rrApprentice

Corpus Christi TX USA

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chinnoks use hydraulic start motors that spin the N1 gearbox for starting. Blackhawks use bleed air start turbines that turn the accessory gearbox for starting.

chinnook

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06-22-2009 12:21 AM  9 years agoPost 15
mikeflyz

rrApprentice

Westlake Village, CA

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Regarding full size helicopters, the smaller turbine helicopters (Bell 206 etc) use a starter/generator. There is no disconnect between the starter and the accessory gearbox. After start, the starter/generator becomes driven by the engine through the accessory gearbox. Once the generator is turned on, the starter then becomes a generator.

Mike
MA Fury Extreme, JetCopter SX

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07-26-2009 02:21 AM  9 years agoPost 16
seattle_helo

rrKey Veteran

Seattle, WA USA

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Okay, I have been flying the crap out of the big 500 this whole spring and summer but I must be mis-aligning my starter to the turbine shaft as I have now gone through two o-rings since I first posted this. That does not seem normal, does it?

I realize that alignment is critical- any specific tips to ensure the alignment is dead on? Obviously my methods are not correct.

nick

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07-26-2009 07:26 AM  9 years agoPost 17
PETER ROB

rrElite Veteran

Devon UK

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Nick,How many starts and stops?
Is it the JetCat "O" rings or the alternative replacement's?
Peter R

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07-26-2009 12:29 PM  9 years agoPost 18
Turbinator

rrApprentice

Nanticoke, PA

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I have the alternative orings in both my 135 and my 230. The 230 has had at least 50-60 starts on it andnstill has plenty to go. The 135 only 15-20 and the oring looks like new yet.

Alignment is critical to long life with any oring as if not spot on it geats chewed up quickly. I have no method suggestion, I eye ball mine and fiddle with it until it looks a perfect as possible. I put a wedge behind the bendix to keep it in the out poistion, about half travel to get it close, then use manual starter function and keep hitting it in/out and make any small corrections from there and loctite it down one bolt at a time once its to my satisfaction.

The orings can be ordered in a different durometer, that is what the 70BN on the end of the part # stands for, BN in BUNA N. The higher the number the harder the material. You can probably get different materials too like viton, silicon, nitrile, etc. I never looked into that but my first suggestion would be nitrile, but I am happy with the ones I got so far. If you get fuel or oil on the rings I'm sure that would give issue so watch out for that but most likely your problem is a up/down or side to side misalignment, that would give more grief then an angular misalinment but all need to be looked at.

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07-26-2009 03:48 PM  9 years agoPost 19
seattle_helo

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Seattle, WA USA

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Peter, using JetCat issued replacements and got between 55 to 60 starts per ring.

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