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Irvine 46 prop 'backplate' key - how to mend/replace?


Jonathan M
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Not sure if I've described it correctly above (if not 'backplate' then what's the round thingy called?) but the key appears to have worn down quite significantly, giving rise to an excessive amount of rotation, say 30-45°.

 

How can I mend it?

 

Firstly, I assume the key's housing is tapered and I can drift it out, but I'm wary of damaging the presumably aluminium round thingy in the process.

 

Secondly, what material do I need to fashion a new key?  I'm equipped with a set of engineering files (Bastard, Second Cut and Smooth) and warding files in the same range, below which are two sets of needle files, plus a hacksaw and junior hacksaw each with a set of fresh blades, and I'm reasonably adept at accurate marking out using an engineer's square etc - but I'm otherwise ignorant and untrained in proper metalwork.

 

Alternatively does anyone have a useless old Irvine from which they're prepared to remove its round thingy and pop it in the post? ?

 

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Jonathan,

 

It looks like the metal fretted away from the inside as there is no key on the prop driver of an OS manufactured Irvine 46. There is a round hole with an internal flat cast in which locates on the crankshaft see below..

That prop driver could be built-up using Technoweld or similar low temperature aluminium welding product then filed or machined to fit.

 

Driver.jpg

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Andy

 

I suspect that the one I have isn't an original like the one pictured above (out-of-stock at the usual retailers).  The engine is obviously well used and was given to me complete with a very tatty Boomerang (no doubt not it's first airframe) which I binned.  There's also a thin hex-shaped nut used to pack it forward from the front bearing, which I'd ideally replace with a proper thrust-washer (if that's what it's called).  But it is a good runner and ideal for my Gangster.

 

I don't have access to any welding kit.  If I can't get a suitable replacement, occurs to me that I could either use J-B Weld metal epoxy to build the flat up (if that'd prove robust enough?) or tap in a steel grub screw with grippy threads (assuming that wouldn't unbalance things too much?)... or both?!

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Drastic measures needed Jonathan,

Only as a last resort, as I am searching for you too.

In my area, and hopefully, in your area, are aluminium welders who repair cylinder heads and alloy wheels damaged from cars.

Have used them a number of times, various jobs, and in seconds they could drop a weld in that small space, for you to file flat.

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I had a look around but they seem to be pretty rare. The part no is X-IRV46-4195

 

Its possible an ASP or OS driver would fit. That or you could just fit it and not worry. Once its all tight it will most likely be just fine. The prop drive on that OS40 fs i rescued last year is falling about laughing but the props dont fall off. 

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Since the engine has been attempting to make its only keyway through the prop driver, why not finish the job off and make a key from a piece of square hard aluminium alloy, brass or even steel.  If you make it a really tight fit in the prop driver and as close as you can get on the crankshaft flat, it should work.
Some 24 hour epoxy and a few hours somewhere hot (top of the hot water tamk or near the flue on the boiler), should bake the epoxy enough that the heat of the engine doesn't soften it in service).
 

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Looking again at the damaged driver, I’d say that someone has already tried a “repair”, filing out a slot and inserting what appears to be some thin folded metal to remake the D shape. Is this what has been done or is it a trick of the photo?

 

A suitable piece of brass, filed to fit the slot accurately and high temperature epoxied in place would be my solution if a replacement couldn’t be found. 

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Jonathan,

 

The one I pictured earlier is the OS manufactured one which is different to the Irvine UK manufactured one, neither are available from any of the supplier that still list it. It seems like there may have been a common problem with this part.

There should be a thin washer behind the prop driver which contacts the inner race of the front bearing so as Martin says this may have caused the problem.

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10 hours ago, Jonathan M said:

Thanks Denis, that can be Plan B.

 

Will see what John comes up with from his stash first... and/or if I can find an old Irvine 40/46/53 for spares?

 

Only one I have is slightly different, got a double flat, however if you look at both sides seems an easy task to round one up ? If it's of use PM your address.

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Gents, you've all risen to the challenge admirably!

 

I've had a long day away from home, but in a brief quiet moment I called Just Engines.  It turns out that the Irvine 46 (at least the OS produced ones like mine) used exactly the same prop driver and thrust washer as the OS 46AX, 53AX, etc - so I've ordered these from them.

 

Had this not been the case, then I'd have set about one side of John's double-flatted one with a file - however thanks so much for looking, really appreciated!!

 

Had John not unearthed his one, then I'd have gone with Robin/Martin's suggestion of a new brass key (I have suitable stock) with baked epoxy.

 

Had I done nothing, then, as Jon says, it wouldn't have looked pretty but it would probably have continued working (the thin hex nut is actually a good fit on the shaft and against the front bearing) until the original bodged key eventually wore away entirely...

 

Thanks to all for the help and advices! ???

 

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