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Charlie,
Thanks,... good info. Too bad they don't list all of the bushing dimensions. I'll check with Jim Ayers (M/T prop distributor) to see if he can tell me what the other dimensions are, but its my guess (based on measuring the bore in the prop flange) that they are 3/4", then stepped down to 5/8". I'll need to check again, but from looking at the sketch of the bushing, it may even be possible for the prop flange to have two steps in each hole. I'll check that tonight. When Jim Ayers and I last spoke, he mentioned something about a ring gear and I didn't pay that much attention. As I understand it, on Lycomings, the ring gear fits between the crankshaft flange and the prop flange. It seems logical that it would have 3/4" holes (to match the bushings). Also, from SI-1098G, the illustration shows two steps on the bushing, in addition to the shoulder. That's new information to me too. It would be nice to have the od's of each step. From what Jim said, the Lycoming bushings are internally threaded. Here again, SI-1098 doesn't clearly show if they're internally threaded or not. Mark S.
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Charlie England
Sent: Wednesday, December 15, 2004 5:33 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: M/T Prop Won't Fit PSRU
Mark R Steitle wrote:
I have been working to resolve a problem for more than a month now and thought I would query the group for a possible solution.
If anyone else is running (or planning to run) a 3-blade M/T electric prop with the RD-2C gearbox, I have discovered a mating problem in using this prop/gearbox combination for my 20B. The problem is the RD-2C prop flange comes with 3/8 id x 5/8 od bushings. The M/T prop has a stepped hole that is ¾" for the first 3/32" and then goes to 5/8". Tracy is not comfortable with drilling out the 5/8" bushings and M/T adamantly advises against using anything less than ½" prop bolts with this prop. So, I'm at a standstill until I can get this resolved. The only solution I can see is to press out the existing bushings and open up the holes to accept ¾" od x ½" id bushings. But that would require disassembly of the gearbox and some precision machine work, possible but not my first choice.
Mark S.
Lancair ES - 20B
(with a very pricey lawn ornament)
Mark,
On a Lyc the 6 drive lugs on a given installation are all the same diameter where they enter the prop, with no step. I'll bet that the 3/4" dia. step, if only 3/32" deep, is to allow mounting the prop directly on a Lyc prop flange without the flywheel (one lug in the crank flange has the oversize step on it to index the flywheel). Surely they don't expect <3/32" tall lugs to carry torque to the prop(?).
Attached is a snip from Lyc Service Instruction 1098G listing various drive lugs & dimensions, but I can't tell from the chart & drawing whether the .75" prop flange diameter necks down to 5/8" where it enters the actual prop. Why not call the US distributor for the prop & get clarification on whether they expect a drive lug (bushing) that's either 3/4"dia x only 1/16" high (can't be a full 3/32" or the prop might not seat on the flange), or a bushing that's 5/8" OD & 1/2" ID with normal height?
Neither sounds ideal, but if I had to choose, I'd go with door #2. :-)
Charlie
http://www.lycoming.textron.com/support/publications/maintenancePublications/serviceInstructions/SI1098G.pdf
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