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914 Servo Problem -- broken copper wiper -- is there a fix?

 
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Gilles



Joined: 16 May 2020
Posts: 33

PostPosted: Sun Mar 28, 2021 2:53 pm    Post subject: 914 Servo Problem -- broken copper wiper -- is there a fix? Reply with quote

Le 24/03/2021 à 02:33, PCahill a écrit :
Quote:
Quote:

Gilles,

I think everyone on this list would benefit from knowing about an equivalent motorcycle servo for a lot less cash! I looked myself for such a part... no joy!


Paul and all,
Went flying today and could retrieve the servo in the hangar.
Fortunately the invoice was still attached to the package, so here goes :
Kawazaki Ninja ZX10R Exhaust Valve servo Motor.
My buddy found it on eBay in 2016 for $14.99
[img]cid:part1.5B6B12A2.BD198EA2(at)free.fr[/img]
FWIW, --
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr


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Gilles



Joined: 16 May 2020
Posts: 33

PostPosted: Sun Mar 28, 2021 3:03 pm    Post subject: 914 Servo Problem -- broken copper wiper -- is there a fix? Reply with quote

Le 29/03/2021 à 00:52, GTH a écrit :

Quote:

Fortunately the invoice was still attached to the package, so here goes :
Kawazaki Ninja ZX10R Exhaust Valve servo Motor.

[img]cid:part1.70339923.F05A279A(at)free.fr[/img]

--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr


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PCahill



Joined: 05 Feb 2018
Posts: 6

PostPosted: Sun Apr 11, 2021 5:17 am    Post subject: Re: 914 Servo Problem -- broken copper wiper -- is there a Reply with quote

ALL FIXED! See below for details.

Thanks to everyone for suggestions on repair or replacement of my 914 turbo servo with the broken wiper. I learned more than I ever wanted to know about this system; here are some notes to make your life easier and cheaper for when you have a similar problem!

First, I bought a used 914 servo through eBay as a quick fix in case other, more time-consuming searches failed. I didn’t use this servo and now have it as a spare. Per another contributor’s suggestion, I also purchased a used “Kawasaki Ninja ZX10R ZX1000J exhaust valve servo motor 21174-0005” through eBay for a lot less money ($25). Confirming one of the comments I received, this Japanese-manufactured Kawasaki motorcycle device appears to be a drop-in replacement for the 914 servo, other than having a hexagonal rather than round pulley. That is, the Ninja servo appears to have the same wiring, the same case, the same circuit board, and critically, the same gear and wipers. I’m also keeping this part as a spare. There are plenty more on eBay for less than $35, or new for about $300 on the web, which is still about $200 less than the Rotax-supplied part (warning: different part number!)

As one person pointed out, my broken wiper may have been the result of a manufacturing defect. Maybe so. However, when I bought the plane from the builder in California in 2018, the engine only had about 200 hours over the last 12-years, and my plane now sits for months in the winter inside a cold hangar in Ohio. Therefore, it is also possible that the dielectric grease caused the wiper to stick to the circuit board, initiating a crack one day upon power-up. I’m not impressed by the design of this servo – because the servo rotates bidirectionally, in one direction the wiper drags, and in the other direction the wiper plows through the grease, which I picture has putting a lot of force on a small part. The design must work OK for almost everyone, though.

Ultimately, I installed a gear, including the wipers, that I received from Ronnie at South Mississippi Light Aircraft (www.flysmla.com). Ronnie had a bag of failed servos “next to his desk” and I accepted his offer to pull a good gear and wiper out of a servo with corroded electronics (the wiper is in perfect condition). This used gear and wiper work perfectly; the TCU + servo appear to be self-calibrating upon start-up. It would make too much sense for Rotax to offer the gear + wiper as a spare part. Unfortunately.

The overall repair isn’t too bad… only confusing to diagnose for a novice. If the orange TCU caution light blinks immediately upon power-up, then a sensor or wiring problem is the likely cause. If the orange caution light comes on for a second or two (as it should), goes off, and then a few seconds later starts to blink, then the problem is more likely with the servo (like my problem). Watch out for, and don’t lose, the 3 mm diameter brass “thrust plate” on the wire clamp on the pulley. Also keep the aluminum sleeves in the rubber mounting grommets, which may or may not arrive with your used part. The Rotax-Owner website has an easy-to-follow video about properly adjusting the cable to the waste gate.

Thanks again to everyone for your advice


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