Shaft Coupling Tightening, Castle Nut Alignment.

[Blaine Thorpe]

Well, the project to replace the shaft log hoses went well until this morning. I had everything cleaned up and ready to go back together ..... but when I went to tighten the shaft coupling for the Twin Disc 506 back on to the 1.5" tapered shaft, I can't get it the nut as tight as I would like it and put the cotter pin through the castle nut.

I am about 1/12 of a turn from getting the pin in. I could back off the nut by 1/12 of a turn, but every thing I know about tapered shafts, keys and castle nuts tells me I need to get it tight and leave it tight, no backing off.

This is on a 1975, 36' Convertible with 3208s and Twin Disc 506 gears.

Your thoughts and input would be greatly appreciated.

Thanks,

Blaine Thorpe

 

[captddis]

Not quite what you asked but most of the new shafts come with the nylok nut. No aligning needed and much easier. Any prop shop should have them.

 

[MikeP]

Your procedure is correct - it should not be loosened BUT first the nut has to be tightened to the proper tourque. What is the torque spec for the nut ?

Loosen it, determine the torque setting then
Tighten to that torque; if the slots do not line up, tighten it until they do. Do not loosen it.

This is the normal procedure for castle nuts - it is expected that they may be slightly overtorqued when getting the slots to align.

 

[Blaine Thorpe]

I wouldn't mind using a nylock nut, but would want to be sure I could still get the cotter pin in behind it for safety.

Not sure about the torque. I'll have to dig out the Hatteras manual. I was thinking it was probalby at least maybe more than I had on it when tightening. Won't be able to get access to the manual until Monday.

If not in the manual, I should have a torque spec book around here somewhere.

When I took them apart, they didn't seem all that tight.

Thanks,

Blaine

 

[yachtsmanbill]

1" X 8 TPI should be about 160 lbs give or take. Thats 80 lbs on a 2 foot bar. I put a piece of 2X4 between the blades on the wheel and the rudder and strut. Depending on the machinist that indexed the hole, it may not line up perfectly and you may need to run a drill through to clean it up. ws

 

[Blaine Thorpe]

I've been thinking about it, and believe that I might have to cut a new slot in the nut. It's not close to lining up with any of the existing slots. When tight, the hole in the shaft would line up with one of the corners on the hex nut.

I may pop the coupling off the shaft again, and start over to be sure there isn't anything holding the coupling from going on all the way. It looks seated, but won't hurt to check.

Can't get back on the boat until next weekend, so I have plenty of time to think about it,

Blaine

 

[MikeP]

I agree it's a good idea to check to be sure that everything is seating properly.

There's no need to cut new slots and it doesn't matter how much farther you have to turn it to the next slot. THey didn't cut new slots when they installed it originally. THe odds that a castle nut slot will perfectly align at the torque setting is pretty low...

Just torque it, turn it the additional amount necessary to fit the cotter pin and that's it.

 

[yachtsmanbill]

Well son, what I would do... If the wheel is seated, its seated. Period. Back the nut off and then turn the nut back down until the last set of holes line up. Take a feeler gauge and check the clearance between the nut and the wheel, and fit a brass or stainless washer in there. Maybe .005 on the fat side to make sure you get a good squeeze on it. Bear in mind the backlash on the hole/pin and lash in the threads. You can also try switching the nuts from P to S. You may get lucky.
Personally Blaine, I would drill a new hole; halfway from each side and then all the way through so that both sides line up. The tail end of the shaft doesnt do anything but give you a place for the cotter pin. Aquamet shafting is easy to drill. Use a sharp one! ws

 

[yachtsmanbill]

This is a stupid retraction... I thought you were re-fitting your props I think the coupling end is a finer thread, maybe a 1" X 12. The taper is definitely shorter than the prop end. If thats the case, try some neversieze on the threads and tighten, tighten, tighten. I doubt youll bust the threads off for an additional >1/12 turn. On the tugs, we take a slugger wrench to get that last little bit. IMPACT is easier than a torsional stretch. Is the key seated properly? It only takes a little bugger to hold you back.
How hard was the coupling to come off the taper? I dread doing mine. 2" shafts to boot. I want to change the hoses, clamps and repack.
Dont forget to check the alignment: primary on the hard, and then a final in the water. ws

 

[Blaine Thorpe]

That's the reason I took this apart. Looking at the shaft log hoses, that was the one area that I was concerned about. After getting them apart, I found the hoses had hardened, but in all they didn't look that bad.

Getting them apart was a lot easier than I thought it would be. I made a plate the the same diameter and hole spacing as the coupling so that I could use with my porta-power. I backed the nut off a couple of turns and used the ram just like you would to pull the wheels. The only ram I could fit in the space was a small ten ton cylinder. It didn't even come close to taking the full force. I would bet I could have pulled them with less than a five ton cylinder.

The nuts weren't that tight either. On the starboard shaft, I held the shaft by hand and loosed the nut. The port side was a little tighter. This just didn't seem right to me.

Using that same ram to pull the wheels off of the 1.5 inch shaft, it takes max pressure and a couple of hammer blows on the puller plates.

I'll take it a part next weekend just to be sure all is OK. Maybe I'll work on the other side to see how it fits as well.

I am leaning toward machining another slot in the nut if I still can't get them to liine up with the correct torque. Nuts are considerbly cheaper than shafts.

Attached is photo of the coupling puller plate and the prop puller plates that I made for use with a porta power.

Thanks for your the suggestions.

I'll let you know how it goes as we move forward.

Blaine

 

[captddis]

You are lucky. I replaced a shaft log hose on my 46 last fall. The ten ton porta power did not touch it, heat+ the porta power+ hammer did not budge it. Finally I screwed the spacer on the shaft, put some studs in and pulled the flanges together as tight as possible. Then put the slide hammer on the other end and had a guy inside with acetylene. Got it good and hot and slammed on the slide hammer and it gave! 6 hours later it was out.

 

[MikeP]

Yep - nothing beats the "Flame Wrench" when the going gets tough!

 

[Brian Degulis]

You should be able to tighten that nut the little bit more to line up with a slot on the castle. If you can't take the coupling off and warm it up a regular household oven at 500 degrees should work. If that's not available nice slow even heating with a propane torch will work. Make sure everything is clean a little very light oil on the shaft will help it to seat also. Do not losen it to get it to line up that's a taper and it must be completly seated making full contack and tightened to at least the minum spec. If you don't know the spec just get the thread size and go by the standard for that size. Remember to coat the threads with neversieze or similiar.

Brian

 

[Blaine Thorpe]

You are lucky. I replaced a shaft log hose on my 46 last fall. The ten ton porta power did not touch it, heat+ the porta power+ hammer did not budge it. Finally I screwed the spacer on the shaft, put some studs in and pulled the flanges together as tight as possible. Then put the slide hammer on the other end and had a guy inside with acetylene. Got it good and hot and slammed on the slide hammer and it gave! 6 hours later it was out.

I would have to agree that I was very lucky for two reasons.

1. That the couplings came apart easily without have to add heat and use any substantial force.

2. That I didn’t have any problems prior to taking them apart as they couldn’t have been installed correctly the last time they were installed. Neither the couplings nor shafts show any sign of wear or fretting.

Anyway, we are moving forward now, and will get them finished up next weekend.

Thanks again for all the input.

Blaine

 

[Blaine Thorpe]

Well, all is well with the couplings again. A little heat, a few blows with the hammer and a friend that has is significantly stronger than I am, and all is good.

Thanks all for your input.