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I'm getting ready to haul my boat to swap out the shafts among other things. I have a set of shafts ready to go, they have been checked out by a local shop and are good to go....I think? My boat has shaft extensions that are about 11 1/2" long between the transmissions and shafts. Is that standard on all gas powered 31's? I guess what I am asking is; am I going to be surprised tomorrow when I haul it and possibly find ou that my "new" shafts are not going to be the right length? My replacement shafts are about 82" long and I believe they came off an express. I have a Bahia Mar. Were they all the same length regardless of which model, assuming gas powered?

Craig-
The shafts in my gas powered 1972 FBC are 82 inches overall. That's from the front of the coupler at the transmission to the cotter pin hole at the prop nut and I have Spurs ahead of the props which add an inch or two.
I would guess that you will no longer need your 11.5 inch extensions.
Hope this helps.
Best,
Stephan

Thanks Stephan, so what you are saying is that you don't have the extensions on your shafts?

Of all the 31's Ive worked on, repowered or refitted, I never saw one with stub shafts.
Ive also ran into numerous different lengths on shafts. While very close to each other, not the same.

Craig G wrote:Thanks Stephan, so what you are saying is that you don't have the extensions on your shafts?

That's right, no extensions.

I'm thinking maybe having the shafts shortened and keeping the extensions. There is definitely very easy access where the shaft coupling meets the extension coupling unlike where the extension mounts on the transmission coupling. This will aid in alignment. Any other opinions? Should I shorten the shafts or get rid of the extensions?

Not an expert but why. Just another item to go bad. One long shaft has to be less maintence and less chance for an issue.. We have had our boat since 75 and I only remember pulling the shafts twice. Once to have cutlass bearings put in and when we repowered. Now you don't even need to pull the shaft for the bearings.

I'd love to see a picture of an 11" shaft extension.

An extension...?..or is it a Muff Coupling? That being two halves that get bolted together joining two shafts?

Either case..."IF" everything is 100% I am sure the extension is more then likely fine. I would not recommend.

Problem is I have a hard time believing an extension or muff coupling is running 100% true, balanced 100%.
Usually you can get them to run Pretty darn close...but not too often 100% especially if not assembled by someone familiar with setup and how to check.

What bugs me is everything you add to the system you detracts from 100%. Plus each item adds to the items that can fail or cause a problem.

On larger boats with low HP diesels...like recreational Trawlers...a Muff coupling is not a big deal...if shaft runs out a couple thousandths...nobody cares as the wheel turns so slow. But speed up the shaft rpm's like in gas motors for our boats ...a couple thousandths out is "felt", "causes problems" and would drive me Nuts.

Craig ... I have a spare set of shafts at my house that came off of a FBC that was doing a diesel re-power if you would like to do a comparison.
Where are you having it hauled ?

I'm not actually adding anything. These extensions have probably been there for 19 years when the engines were installed new in Italy. I have owned it for the last 10 of those years. I just ran it in gear at the dock, and both extensions are running true looking at them visually while spinning. The used shafts that I am going to install are true, but worn around the cutlass bearing area and stuffing box area. By cutting the aft end of shafts and putting a new taper, key way and threads on, I can have much better shaft surface where it counts. This seems like the easiest and most simplistic way to replace my 35MM shafts. It will cost about $100 per shaft for the machining. I don't know why they did it this way, but the shaft coupling is very accessible under the hatch. The accessibility of the extension at the transmission end is very challenging at best in between engine box and hatch. I don't see the harm in keeping it the way it is by shortening my shafts to fit. Remember, I'm not thinking up this idea to put extensions on and shortening the shafts. Someone already did that 19 years ago, and I kind of like it for access ability. Steve, I have a set also that are 82" long for now, and will compare them after haul out. I got weathered out today, so I didn't haul it, but I use Anglers Avenue DIY marina. It is very tight going under all the bridges though....no problem for you.

This isn't code is it??? we are talking boat parts right???? extensions ??? Muff Coupling???

JimmyG wrote:This isn't code is it??? we are talking boat parts right???? extensions ??? Muff Coupling???

Yeah, I guess that's what the kids are calling it nowadays.

Jimmy, you broke the code!

LOL! Next it will be dripless stuffing boxes!

Oh...I like a little drip at the stuffing box ;-)

Craig G wrote:I'm not actually adding anything. These extensions have probably been there for 19 years when the engines were installed new in Italy. I have owned it for the last 10 of those years. I just ran it in gear at the dock, and both extensions are running true looking at them visually while spinning. The used shafts that I am going to install are true, but worn around the cutlass bearing area and stuffing box area. By cutting the aft end of shafts and putting a new taper, key way and threads on, I can have much better shaft surface where it counts. This seems like the easiest and most simplistic way to replace my 35MM shafts. It will cost about $100 per shaft for the machining. I don't know why they did it this way, but the shaft coupling is very accessible under the hatch. The accessibility of the extension at the transmission end is very challenging at best in between engine box and hatch. I don't see the harm in keeping it the way it is by shortening my shafts to fit. Remember, I'm not thinking up this idea to put extensions on and shortening the shafts. Someone already did that 19 years ago, and I kind of like it for access ability. Steve, I have a set also that are 82" long for now, and will compare them after haul out. I got weathered out today, so I didn't haul it, but I use Anglers Avenue DIY marina. It is very tight going under all the bridges though....no problem for you.

To answer your question-

No, extensions are not normally used on 31's, gas or otherwise.
No, shafts do not "have" to be the same length for each side, although they can be.



Checking to see if a shaft/extension is running true by visually checking...the method leaves a bit to be desired in my opinion. But if it works for you...

They have worked well for 19 years, so I think I'm going to keep them which is the easiest and most cost effective way to replace my shafts. I'm just wondering though, without these extensions, access to the shaft coupling would be very limited on my Bahia Mar with 454s and B/W gears. What kind of access do you guys have to your shaft couplings? I'm thinking that might be why they did this in 1995.

Access is a pain in the Butt. I do half the work from inside the rear hatch...the other half from deck hatch.

I use Walters Clamp fit couplings and have shafts fitted to couplings.

...so to remove shaft. I have to loosen set screw, remove two clamping bolts, tap two blade screwdrivers into the back face of coupling to wedge open a bit. Shaft taps out. 10 minutes. Install is the reverse.

I finished the work on my boat. The shafts that I removed were 79 inches long plus another 11 and a half inches for the jack shafts as Frank and Jimmy's prop shop calls them. That would mean if I didn't reuse the jack shafts, I would need shafts about 90 inches long for my Merc 454 with B/W transmissions Bahia Mar. Any other Bahi Mars have a similar set up?

FYI, we used jack shafts and muff couplings on larger boats when we offered the hew owner the option of carrying spare shafts for a boat that didn't have the ability to store the shaft in the bilge,I'm trying to think if I could store a spare shaft in my 31 , we also used to attach the spare shafts to the keel ,a 60 ' boat had long shafts