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[richardabeattie]

I've always used the red plastic coupling with the brass inserts matched to the motor shaft and propshaft without significant problems but this time, however carefully I aligned things, the MFA 380 motor would not sit still.   When I tried to fix the motor firmly there was too much friction.  The propshaft is not bent so I suspected the U/J was not accurately made.  I tried enlarging the holes in the red plastic to give the central brass insert more freedom but no better.  So I removed it and joined the two halves of the coupling with a very short loop of thin cord with the knot in the middle for balance.  It works fine!  Not a solution for high powered motors but perfect for a 380 and vibration free.

[roycv]

Hi I remember once having a lot of vibration, after a bit I worked out that the shaft end of the coupling with a screw thread was not squarely locked onto the shaft.  A washer hard up against the threadless part cured it.
regards
Roy
 

[john44]

Hi, have you checked the brass fittings are drilled central. I had one that was a fraction off centre once, caused
bad vibration.


John

[richardabeattie]

As I said - I suspect the coupling is at fault but if the drilling is off centre that cannot be fixed.  My solution is working just fine.  Neither brass insert is threaded, both rely on a grub screw.

[Andyn]

These awful red plastic couplings have been covered on here countless times over the years. The solution (other than buying a proper coupling to begin with) is to bin the red plastic part and replace it with a tight fitting piece of silicon tube

[Martin (Admin)]

 I used to like the white HUCO couplings, they always spun true ... even on 6cc IC glow engines... very tough!

 Double / Kardan type couplings are excellent when motor / shaft or slightly misaligned!


      

[JimG]

As I said - I suspect the coupling is at fault but if the drilling is off centre that cannot be fixed.  My solution is working just fine.  Neither brass insert is threaded, both rely on a grub screw.

The grub screw fitting may well be the cause of the problem. Unless the shaft is a close fit in the coupling tightening the grub screw pushes it to one side of the fitting so it is no longer central in the hole. This puts the brass section out of balance. Better fittings use two grub screws opposite to each other allowing for better adjustment although it can take more work to get it right. (even beter would have 3 grub screws at 120 degrees which would allow for exact centering although ideally needing a dial guage when centering.)
Jim

[richardabeattie]

Huco couplings look good but cost far more and I'm not sure how you connect them to small diameter shafts - especially when the motor and propshaft are not the same size. Or do they take the same brass inserts as the red ones?   

[derekwarner]

Richard.....in fairness to the Manufacturer, the HUCO specification sheet indicates 1000 PRM as the maxinium speed for these 'Red' type couplings

These inserts would I believe be injection moulded, so the splined ID to OD tolerance would be governed here 


Derek

[richardabeattie]

Not understood.

[Martin (Admin)]

IE ... watch out for these red U/J coupling .... many reports of poor quality ....

NB: I've never had an issue with them ..... https://www.modelboatmayhem.co.uk/Builds/Puffer_Jan/Part_4.htm






 

[TheLongBuild]

Personally never had any issues with them.