bolt size for prop shaft coupling

[tartansailboat]

I may need to remove my drive shaft in order to get at some keel bolts which are leaking and need to be re-torqued. I will have to press out the prop shaft from the coupling and want to purchase some longer, hardened bolts for this job. What is the correct bolts size and thread pitch? And any idea how long a bolt I will need to press out the shaft. I will use the trick of inserting a socket just a bit smaller than the shaft and tighten the bolts to press out the shaft.

[hanleyclifford]

The threads in the gearbox output coupling should be 3/8" x 24 (NF). Rather than turning into the threads, I would install long, say, 4" threaded cap screws with nuts and flat washers to apply the torque on the fully threaded (into output coupling) cap screws.

[tartansailboat]

Hanley, thanks for the information on the technique. I was afraid of using the threads in the output coupler to press out the prop shaft. I am assuming that the holes in the collar of the prop shaft are clearance holes and that the holes in the output coupler flange are threaded. The washers and nuts go on the outside of the prop shaft collar and you hold the bolt from turning with a wrench on the hex head of the bolt while turning the nuts to squeeze the collar against a socket (or similar piece). I have heard that you need grade 8 bolts for this job, is that your opinion?

[hanleyclifford]

Yes, grade 8 can take the torque without stripping.

[tartansailboat]

I checked with McMaster, they only sell the fine thread in grade 8 at $4 each for 4 inches. Again, thanks.

[tenders]

I've done this three times in the 20 years I've owned my boat, and while I did not need Grade 8 fasteners I did require a substantial repertoire of Grade 8 obscenities.

It's a horrible job, perhaps made worse in my circumstance with the V-drive which places the transmission directly over the coupler with very little access to swing a wrench, or even fit bolts beyond a short length between the transmission and the coupling.

The next time I have to do it I'm cutting off the coupling with a Sawzall and buying Don's split coupling.

[sastanley]

hanley & tartan...I am dense..I am afraid I don't understand what you two are talking about. Tartan, can you take a picture when you get this set up? I used your first plan with progressively longer bolts to press out the shaft with a couple of sockets. It was very tedious as tenders commented. Moyer didn't offer the two piece couple just yet last year when I was doing this project, although I may do the same thing as tenders..cut it off and buy the split coupler (if I ever need to take it apart again..)

[hanleyclifford]

Shawn - The procedure is essentially the same as the way you did it. The only difference is that he will be using nuts on the threaded cap screw to apply the pressure rather than turning into the threads in the coupling.

[tenders]

...and will be using smaller-diameter bolts to fit cleanly through the coupler holes (on the engine side and the shaft side) so as not to chew up the threads on the couplings.

[hanleyclifford]

...and will be using smaller-diameter bolts to fit cleanly through the coupler holes (on the engine side and the shaft side) so as not to chew up the threads on the couplings.

I had not thought about doing it that way with, say, 5/16" - 24 NF, but I see your point. However, I do think the threads in the output coupler will stand the torque if the cap screw is stationary.

[tartansailboat]

I will take pictures tomorrow but I have already ordered three grade 8 bolts, 3/8x24x4"long fully threaded. In my setup, a direct drive A4, there is no room behind the flange on the transmission to put a nut even it I were to use a smaller size bolt, say 5/16. So the only way I can see pressing out the prop shaft is the way Hanley suggested, i.e. fully threading a long 3/8x24 bolt into the output flange, then using (grade 8) nuts between the hex head of the bolt and the prop shaft coupling, to squeeze the coupling against a socket or a stack of washers, to press out the shaft. That technique sounds much less risky than trying to screw the bolt into the threads with the same socket (or washer stack).

But I am confused as to why you all think this is such a tedious process. I have excellent access to the engine, the T30 has the engine just aft the mast with a cover box which is easily removed. The reason for my concern about time is that I will probably have the boat yard help me in this process and at their rates, from what you both say, this could cost me a lot.

I would think that with a 4 inch bolt, it would only take one or two passes with a socket or washers to drive out the shaft, what am I missing here?

[tartansailboat]

As promised, here is a photo of my prop shaft, output coupler and transmission flange. Clearly there is no room behind the flange to put a nut if I were to use smaller diameter bolts (5/16) as was suggested rather than thread new longer bolts into the flange to used with nuts ahead of the coupler to press out the shaft.

There is another alternative, that being to make a new dummy flange out of say 3/8" steel with three 3/8 clearance holes. Then I could unbolt the output coupler, slide the prop shaft/coupler back a few inches, install the new longer 3/8 bolts and use a nut on the back side of the dummy flange with the socket trick to push out the prop shaft. That technique would not stress the threads in the original transmission flange but its more work to make the dummy flange.

Do you all feel confident that if I screw the longer bolts into the original transmission flange and use nuts ahead of the output coupler to press out the prop shaft, that I will not screw up the threads on the flange??

BTW, the reason why I think I need to separate the prop shaft from the coupler is that I also have a pillow block between the transmission and the stuffing box, and the output coupler will not slide back beyond that pillow block. And finally, the reason for this whole exercise is to get a clean shot at my leaking keel bolts some of which are under the prop shaft.

[hanleyclifford]

If you go to the on line catalogue on this site and check "specialty tools" you will see TOOL_06_135 which carrys the theme of your plans nicely.

[tartansailboat]

Hanley, Now you tell me! thanks, I will call Ken and see if the bolts they supply are grade 8, looks a lot less risky than my original scheme using long bolts into the output coupler.

[tenders]

If you have room to swing a wrench around that coupler, and have the ability to push the shaft aft several inches without banging into the shaft seal with the coupling or the rudder with your prop, then this will simply fall into the "slow work" category rather than "abhorrent PITA" category. Count your blessings!