Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => Engineering Techniques and Materials. => Topic started by: Bob K on January 25, 2016, 12:41:42 PM

Title: Replacing a Prop Shaft
Post by: Bob K on January 25, 2016, 12:41:42 PM
Prop Shaft Replacement   -   If you ever have to do this !!!

Fitting prop shafts during construction is straightforward in that you can mount the hull upside down on the workbench.  Faced with a completely seized prop shaft needle roller bearing on a fully detailed model limits options on how you can apply major surgery to the underside of a hull.  All other methods for removing the shaft had been exhausted.

Upside down was not an option.  Careening onto its side is possible providing you can make a jig to adequately support the hull to protect all the detail bits.  Two sections of shaped balsa with a support lining of soft rubber sheet against the hull sides, carefully clamped to the workbench. 

Using a Dremel / Rotacraft flexi shaft, carefully point grinding away at the original shaft sealing epoxy is a bit like preparing a dinosaur bone.  I also needed to preserve as much of the original skeg as possible.  Inside, the front support bulkhead had to be similarly cut away above the brass shaft tube whilst retaining the underside U to locate the new shaft.

(http://i1143.photobucket.com/albums/n626/bobkiralfy/HMS%20Amazon/prop-shaft-repair_zpsdphez8xr.jpg) (http://s1143.photobucket.com/user/bobkiralfy/media/HMS%20Amazon/prop-shaft-repair_zpsdphez8xr.jpg.html)
HMS Amazon

Success, with zero damage topsides.  I had been scratching my head for ages over how to get the shaft out.  I hope this method helps someone else.

(http://i1143.photobucket.com/albums/n626/bobkiralfy/HMS%20Amazon/HMSAmazon2.jpg) (http://s1143.photobucket.com/user/bobkiralfy/media/HMS%20Amazon/HMSAmazon2.jpg.html)
Title: Re: Replacing a Prop Shaft
Post by: raflaunches on January 25, 2016, 01:14:09 PM
Hi Bob


I remember a few years a go my dad and I had to replace the prop shafts on one of our large scale RAF ASRLs which had ovalised the bearings. The major difference between yours and ours was at least we could get our shaft out and we had a wooden hull which was a little more forgiving than GRP. But we understand your problem truly and you've done a brilliant job fixing the problem- probably like we did (judging by your first picture) you'd have thought 'oh no what have I done to my beautiful model?!!'. But perseverance and patience gets the job done. Well done mate. :-))
Title: Re: Replacing a Prop Shaft
Post by: Bob K on January 25, 2016, 01:50:45 PM
Thank you Nick.

I loved sailing my HMS Amazon, until the bearing seized and it became a dust gathering wall mounted static.  Now I can look forward to taking it to the lake again.  Must remember to strip and re-grease the shafts more regularly.  Very light grease with a touch of graphite.
Title: Re: Replacing a Prop Shaft
Post by: Shipmate60 on January 25, 2016, 01:52:37 PM
Bob,
SHG produce nitrile bearing ends that are a push fit in the tube and 4mm internal diameter.
So much easier to remove inner shaft, remove end bearings with pliers and replace bearings and if required the inner shaft.


Bob
Title: Re: Replacing a Prop Shaft
Post by: Bob K on January 25, 2016, 02:11:38 PM
Bob.  These are 2.00 mm / M2  shafts with sealed miniature needle roller bears both ends.  Very free spinning and watertight. 
Title: Re: Replacing a Prop Shaft
Post by: TugCowboy on January 26, 2016, 02:38:07 PM
Thanks for posting this up Bob. Looks like quite a thick hull you're working on there so good to know it works on all situations.
Title: Re: Replacing a Prop Shaft
Post by: Bob K on January 26, 2016, 02:54:38 PM
Not so much a thick hull, more an indication of how much sealing epoxy to cut through, both inside and out.
Turns out that with this type of needle roller bearing shaft system the inner shaft is not removable anyway.  Only found that out on the replacement.

Maybe I should have been a Dentist ?
Title: Re: Replacing a Prop Shaft
Post by: ballastanksian on January 26, 2016, 08:10:04 PM
I can imagine the noises eminating from your mancave Bob! She's a gorgeous model from what I can see of the stern :-))
Title: Re: Replacing a Prop Shaft
Post by: Bob K on January 26, 2016, 09:02:01 PM
Thank you.  HMS Amazon.  My first build.  Four years old now.
http://www.modelboatmayhem.co.uk/forum/index.php/topic,32820.msg356501.html#msg356501 (http://www.modelboatmayhem.co.uk/forum/index.php/topic,32820.msg356501.html#msg356501)