Propeller Shaft Question (revised)..

CJM

CJM

Member
Aug 26, 2010
84
CT
Boat Info
1986 250 Sundancer /
2000 340 Sundancer
Engines
5.7 Merc /
Twin 7.4 Horizons
The boat -- 2000 Searay Sundancer 340, w twin 7.4 Horizons Inboards..

What is the minimum acceptable clearance between the front of the propeller (boss) and the back of the strut that holds the cutless bearing? The shaft is 1 1/2" diameter..
 
What are problems with the shaft the clearance on mine is 1/4 inch off top of my head my boat is still in water. The only way it could change is if your coppler on forward side of trans slipped other wise you are concerned about nothing.
 
It's been said before, and is worth repeating - don't put out information that is misleading. If you're not sure about something, then please refrain from posting. Once it's "out there", you can't get it back, and someone else may pay the price.

In this case, there are several factors at work, each of which can effect the minimum acceptable clearance between a prop and the aft end of the cutlass bearing. The first is water flow through the bearing. Enough clearance must be maintained such that sufficient water can flow into and through the cutlass bearing to both cool and lubricate the bearing / shaft. An old rule of thumb is to provide for one shaft diameter of clearance, but like most blanket rules, this one isn't perfect, and can result in excessive clearances as the shaft diameters go up. But the next question you have to ask is: what is my actual clearance when the boat is running, versus the static clearance when the boat is idle, and the gap can be directly measured. Motor and transmission mounts flex, so as more throttle is applied (in forward) the clearance is reduced. At full throttle, the clearance is at a minimum, just when you need the most water flow. So, this variability has to be accounted for.

The clearance here also changes over time - as mounts age, the rubber durometer changes, the mounts take a set, and the clearance starts to shrink. So, again, you want to allow for that. And, there is a more pragmatic requirement for the strut to prop clearance. Someday, you're going to want to pull that prop, and if you can't get a puller plate behind it, that simple 20-30 minute job just became a lot longer and more expensive, since some poor soul now has to corkscrew his way into the tight confines of a bilge and pop the shaft loose.

Bottom line - 1/4" is too tight. If that's the static unloaded clearance, it's got to be almost zero, or may be zero, under load. It's also not enough to fit a conventional puller between the prop hub and cutlass bearing. Now, it is likely that the motor mounts have aged and sagged, reducing the clearance, or maybe the shaft was replaced with one that was a hair shorter than original sometime in the boats life, or maybe the strut is out of position / bent. There is a bit of adjustment in the mounts themselves, since they are slotted, but you'd have to loosen all 4 of them, and see if the motor and transmission can be slid back a hair. I doubt you'll get much out of that though. If this was my boat, I'd look long and hard at the mounts, and see if they have deteriorated. If so, they need replacement. Without knowing more of the boat's history, it's hard to comment beyond that.

Dale
 
Thank you for your response. I also have approx. 1/4" clearance. (only on the port side shaft).. Now what would be the best option to gain the appropriate clearance?... Replace the shaft with a longer one ? Could I try a "shorter" prop? Different coupler?
 
The adjustment is on the front side of trans in the coppler it can be slid back . Have your boat yard send a small guy in there and move the shaft back the shaft is fine.
 
Thanks Vandal. It looks like you have the same boat... I was under the impression that the shaft and the coupler are tapered and non-adjustable. and the "set screws" lock the shaft to the coupler. Have you actually done this on your boat?
 
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MasterFab, thank you for your well worded answer. Now a lot more of us know what's involved with that.
 
GFC - thank you for the kind review. It's nice to know someone reads this stuff for content.

CJM - you are correct in that the shaft is tapered at both ends (double tapered shaft) in the 340 with V-drives. You really need to get a handle on what has happened, and the boat history, which we don't have , is key here. It's possible you have a prop with the wrong hub dimensions on the boat, or as we mentioned before an incorrect replacement shaft, loose or deteriorated engine mounts, etc. If you crawl in there and look around, I'd bet something will become apparent.

Vandal - I would very much like to know how, specifically, you intend to adjust the shaft position on a boat with double tapered shafts, such as the 340 in question here?

Dale
 
MasterFab nails it. IF and that's a big if....the port side is only a shorter shaft issue, I would lengthen it with a dampener and replicate that on the starboard side. I doubt my thoughts are correct, but I try to look at things from a different angle.
 
Thank you for your input. I was on your site and I see that you have "been there, done that".... I have recently obtained this boat and the previous owner is deceased, so the history of "what happened" might be a little difficult to get.. I was told by a mechanic that the best option is to replace the shaft with a longer one. He checked and said they made different lengths... (my research stated 68" is correct) I just wanted to see if there were other options... I was thinking about a shorter hubbed prop but I'm still researching... Thanks again..
 
I wouldn't order an new shaft until the cause of this issue has been identified. You lost a good amount of clearance somewhere, somehow, and that should be where you focus your efforts. An extended shaft won't repair worn out engine mounts or some other issue that is the true cause.

Dale
 
Thanks, Dale.. They were thinking that the shaft was replaced with an aftermarket one that was shorter... I'll check the mounts when I get a chance...
 
dpmulvey said:
MasterFab nails it. IF and that's a big if....the port side is only a shorter shaft issue, I would lengthen it with a dampener and replicate that on the starboard side. I doubt my thoughts are correct, but I try to look at things from a different angle.
Click to expand...


It works just the other way on a v-drive with ZF transmissions where the shaft passes thru the gear case. The coupler is on the front of the transmission so if you put a flexible shaft coupling between the coupler halves, the net effect is moving the shaft forward, not backward, by the thickness of the flexible joint.

Be I haven't seen where the OP says what transmissions he has............
 
fwebster said:
It works just the other way on a v-drive with ZF transmissions where the shaft passes thru the gear case. The coupler is on the front of the transmission so if you put a flexible shaft coupling between the coupler halves, the net effect is moving the shaft forward, not backward, by the thickness of the flexible joint.

Be I haven't seen where the OP says what transmissions he has............
Click to expand...

Good catch. Thanks.
 
Velvet V-Drive (I believe 5000).
 
Thank you all for your advice..... FYI -- I found a company www.gcsmarine.com that sells a product called a "drivesaver" that is supposed to help with vibrations... The "drivesaver" bolts to the transmission flange and then the shaft coupler bolts to it... They have specific "savers" for all transmissions and torque ratings.... For my application it's 1" thick, so it might be what I need.... They also sell "run-dry" impellers that can run without water for 15 minutes (yeah I needed one of those 10 years ago).... I am going to research this more over the winter, but thanks again........
 
Please re-read Franks post. I'm kinda embarrassed that I didn't catch what he did because I have the V-drives he is referring to. If you have the same V-drives and use a shaft saver, you will end up shortening the shaft.

A pix is worth a thousand words. Look at the spec drawing on the right. The letter "E" is where the shaft would exit the drive. That's facing the bow.
 
Yes, through further research, the coupling attaches to the flange on the front of the transmission. I have read that there are different types of couplings (tapered, solid, or split) depending upon the shaft... I believe the non-tapered couplings can be adjusted.I'm going to have to get in there and check. Thanks again..

 
Okay, I am going to revise this thread again. (I haven't done much to it over the winter).. I did get down in to the engine compartment and check things out. The "engine" mounts are the issue (MasterFab Called It).. The port mount of the port engine is "cocked" towards the bow, this looks to be the culprit on why the shaft moved forward. The mounts will have to be replaced. Can this be done by raising the engine slightly, or should it be removed? Opinions?
 
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