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M8 Prop Adaptor - HELP!

Can anyone find one of these please?

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Graham Davies 310/08/2020 10:38:49
98 forum posts
45 photos

Morning all,

Due to some localised Geography issues (The ground was 6ft too high and at 45 degrees to where it should have been at the point of landing...), I have bent the prop adaptor on my Tempest.

The motor is an (otherwise excellent) unbranded 4250-600kv, from a now dry source. So going to the manufacturer isn't an option.

The adaptor is a a 3 bolt design with the following dimensions:

Thread: M8

Thread length: 25mm (would prefer 30!)

Rear recess diameter: 11.0mm

Rear recess depth: 7mm

Bolt hole diameter: 2.7mm (x3)

Bolt centre diameter: 13.15mm (Measured; likely specified at 13mm)

Boss thickness: 9.7mm

I have shown edge to edge dimension between the bolt holes as this is easiest to measure.

Does anyone know where I can get a similar boss? I found what looked similar on HK, but there are sufficient differences to make it unsuitable.

I cannot use a collet boss because I had to cut the shaft to get the battery far enough forward.

I don't want to buy parts in the hope they will fit, as it's close to being cheaper to replace the motor.

If anyone can recommend a part, or has one in their spares box, I will be eternally grateful!



adapter 1.jpg

adapter 2.jpg

adapter 4.jpg

kc10/08/2020 12:23:28
6643 forum posts
173 photos

Could it be the same as this one?

If you take a chance and buy that then also spend 14 pence and get this shaft that might just be the spare shaft you could use otherwise.

If you are in a rush then consider trying to straighten the adaptor - they are soft and can be 'bent'  straight with a little care. 

Edited By kc on 10/08/2020 12:31:08

Graham Davies 310/08/2020 12:40:41
98 forum posts
45 photos

Hi KC,

Thanks for your reply.

Sadly, no. I bought one! It has 14mm BCD and the recess is 10.5mm, so no dice.

I tried to straighten the adaptor, but it's very hard to identify where the bend starts without a few things I don't have (ideally, I'd put it in a lathe and use a dial test indicator to find the onset of the bend. I sold my Myford a few years back. If I still had it, I could not only straighten this one, but make some spares!)

Back to the drawing board!


Keith Berriman10/08/2020 12:46:20
780 forum posts
11 photos

Maybe look at Airtek hobbies the have lots of adaptors shown on their motor range

Colin Low 210/08/2020 13:32:39
3 forum posts


I'd email or speak to George at 4-Max. He's got a range of adaptors and shafts etc.


Graham Davies 310/08/2020 13:41:55
98 forum posts
45 photos

Thanks Keith,

Nope, nothing there.

They do have replacement shafts that may fit, but this would really only be to salvage the motor into some other model as reversing it and using a collet adaptor is likely to need extensive rework of the model. Still, if I end up replacing the motor, at least it stops the old one becoming a paperweight!

Keith Berriman10/08/2020 14:02:51
780 forum posts
11 photos

Hi Graham. Just looked at my Airtek motor adaptor and see the difference one option have a look at Fusion Logic motors they maybe nearer your needs

kc10/08/2020 14:22:53
6643 forum posts
173 photos

Putting the adaptor onto the motor and levering the prop nut by hand often straightens the soft thread enough.. The main thing is that the prop seats on the flat face nicely and the nut is tight.

You could always contact your local model engineering society and see if anyon can help make an adaptor - chances are if he is a real engineer he will straighten it by hand though!

In the right hands a 'Birmingham Screwdriver' is a precision tool!

Simon Chaddock10/08/2020 16:05:33
5774 forum posts
3055 photos


If you are stuck and as the bend does not look severe I could straighten it and check it runs true in the lathe.

No charge.

PM me and I will send you my address..

Graham Davies 311/08/2020 08:28:48
98 forum posts
45 photos

Hi Simon,

Thank you for the kind offer. That's what makes this forum so good.

Unfortunately, had I realised this was going to be such an issue and the original bent adapter so scarce, I would have left it alone. I attempted a repair and I would now not trust it, so it's purely a 'space model' now.

The sad fact is I can get a new motor for between £17 and £50 depending on which route from China it takes (!). The bit that irritates is the variability in specification and supply. I hear a lot of chat about Chinese purchase routes; I personally would prefer to pay £40 for a motor I can get spares for than £25 for one that becomes an ornament after yet another of my creative landings!

But again, thank you for the offer; that really is good of you,


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