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View Full Version : Spectra engine plate: is aluminum OK?


brunobl
08-26-2007, 07:20 PM
I put this on "the other" forum, but I thought I should hear the opinions of HF folks on this:

Due to my lack of experience with gassers during assembly/first few pull starts on the Spectra, the secondary engine plate (#125-43) key holes got worn down to the point that now the pull-starter pops off on every start attempt. I probably mis-judged the torque on the 4 bolts to keep the pull-starter permanently on, so the keyholes were damaged.

Of course the solution is to order another engine plate (and setting it right this time), but overseas shipping/customs/etc will keep the Spectra grounded for a long time while this is processed (electric starting is not an option for me).

I decided to replicate the CF engine plate and use it while the MA part doesn't arrive. I wondered which material I should make it from (CF in the required shape/dimensions is not available here). I initially thought of 1/16" fiberglass stock, but it occurred to me that the engine was not meant to be insulated from the bottom frame, so I settled on 1/16" aluminum sheet. This is just marginally thicker than the original plate, but since I originally had more clearance then the specified 0.020" at the clutch, the added plate thickness actually was a good thing IMO.

You see one of the original CF plate distorted/damaged keyholes and the home-made aluminum plate in the photos below.

Is there any obvious reason that I should not to use the aluminum plate? The engine aligned properly at the specified clearance, using this home-made plate. I don't plan on using it for an extended period of time (just until the MA part arrives) and wonder if there are any issues that I might have overlooked in my eagerness to get the heli off the ground again.

Thanks for your thoughts.

j.8
08-27-2007, 05:51 AM
Hi Bruno

The same thing happend to me, but the one you made out of aluminum
will be worn out to, at least mine did ( lower right key hole ).
I have used another one, made out of stainless steel, the last
3 month, without any signs of wear

If you change the fuel tubing, on the attachment screws frequently,
so that the screws donīt start to wobble,
then the key holes will last a long time on the original plate.

Bo Denmark

brunobl
08-27-2007, 07:16 AM
Bo,

Thanks for replying.
Yep, I had the feeling that aluminum might be a bit too soft for a definitive plate. I hoped it would last just enough for MA's part to arrive (things usually take 3-4 weeks to make it to Rio). I really like your idea of a stainless steel plate! It will probably last longer even than the original part. The thing is, I hand-filed the aluminum to shape, I guess it would take forever to do this on stainless steel. How did you make yours?

I might leave the aluminum on just to (re)start flying, and immediately start looking for some 1/16" stainless steel stock, and prepare myself for some serious filing.

Thanks for sharing your experience.

j.8
08-27-2007, 08:56 AM
I would say that it`s was absolutely serious work, fabricating that
engine plate of stainless steel, only using, a small hacksaw, drills and files,
but with a pot of coffee,some good music, and a day of your own ; ) then it`s done

I don`t want to disencourage you with the aluminun one,but after putting the heli back
together, aligning the engien, and then find out, that it aint gonna last very long.

Well perhaps I used som pour quality aluminum for mine, only thing I know for sure,
is that the stainless one, is not showing any signes of wear at all, and that`s after
3 months of use.

Only thing that is showing signs of wear now, is the screw` on the pull starter, but
I`ll rather replace them ; )

Regards Bo

brunobl
08-27-2007, 09:25 AM
Stainless steel it is, then.

Coffe won't be a problem. Got a good selection of MP3s to get in the mood for a bit of hours-long drilling & filing.

Thanks for the good idea.