Replacing a straight shaft engine coupler in the water

jamesrladd

New Member
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May 29, 2015
9
Chattanooga, tn
Boat Info
Passage 450
Engines
Yanmar 4jh2
I am looking at buying a 97 420AC with 7.4's. One engine reportedly had loose bolts on the engine coupler and it wallowed out the factory holes and the the bolts eventually sheered. The current owner had new holes drilled and reinstalled the original coupler. That engine now has vibration issues. I think a new coupling is in order. The boat appears to have tides dripless seals. Can a new coupling be installed with the boat in the water?
 
I am looking at buying a 97 420AC with 7.4's. One engine reportedly had loose bolts on the engine coupler and it wallowed out the factory holes and the the bolts eventually sheered. The current owner had new holes drilled and reinstalled the original coupler. That engine now has vibration issues. I think a new coupling is in order. The boat appears to have tides dripless seals. Can a new coupling be installed with the boat in the water?

maybe, depends on how much room you can slide the shaft back before the prop hits the rudder

that being said, I’d be asking the current owner to fix any alignment issues including this work before signing for a purchase.
 
I don't know how you are going to get the shaft back enough to replace the coupler. As above, I'd have the owner do it, fix the vibration issues, before closing.
 
I'd have the owner do it as well You don't want to risk that what if there's damage to the motor I wouldn't buy the boat until it's fixed and smooth as butter
 
I don't know how you are going to get the shaft back enough to replace the coupler. As above, I'd have the owner do it, fix the vibration issues, before closing.
If it is a Sundancer why does the shaft need to move back?
They move forward to split the couplings right?
The shaft would only need to slide back if there wasn't enough room forward of the coupler to slide it off of the shaft.
I don't know that boat but I could do what he is asking on my 400DA with the Hurth gears...
 
I don't know which way the motor moves or the transmission moves but if you had the engine coupler bouncing around on that crankshaft it could not have been good for the bearings pistons rods all that
 
Why didn't he just replace the coupler when he took it out to drill new holes I would suspect it would be out of balance but I don't know I'm just trying to gather information myself
 
If it is a Sundancer why does the shaft need to move back?
They move forward to split the couplings right?
The shaft would only need to slide back if there wasn't enough room forward of the coupler to slide it off of the shaft.
I don't know that boat but I could do what he is asking on my 400DA with the Hurth gears...
It’s an aft cabin. But how are you going to get any leverage to move the shaft?
 
Ah, sorry. His data says it is a Sundancer. If it is an Aftcabin then he has straight shafts right?
That’s what I am thinking but don’t know. Either way you’ll need to move the shaft and you’ll need leverage to do that.
 
That’s what I am thinking but don’t know. Either way you’ll need to move the shaft and you’ll need leverage to do that.
The shaft can slide easily with the boat in the water; it better or there is something else wrong. The thing to watch out for is deflection on the seal so it isn't damaged and to limit the distance it will move back; the bore in the gear the shaft runs through will support the shaft (again Sundancer). If it is a Sundancer the shaft only needs to be moved back a couple of inches so the coupler can be lifted out - at least that is how my 400DA was.
I've had all the running gear apart on my 52DB but I don't know if there is enough room to get the couplers off with the props on (straight shafts).
 
The leverage is not the problem....the distance between the rudder and prop is. On straight shafts you have about 2" of play before the prop hits the rudder. The shaft goes into the coupler 3+" so backing the shaft out of the coupler is problematic in the water.

Their are multiple advantages of getting the boat out of the water. First and foremost....you can check the shaft to ensure that it is straight. Replacing the hub on a bent shaft will not fix anything. Second, it is a good time to replace the Tides seals.
Finally.....checking the prop to make sure it is not the source of the problem is a lot easier.

upload_2023-6-5_9-13-14.png
 
I can tell you that on my boat there is enough room to replace a complete tides seal assembly (on the hard) by sliding the shaft back until the prop touches the rudder so I Know the coupler can be changed on my boat. Nothing I would attempt in the water though. With my luck there would be an oh shit moment and the rest would be history. Ymmv.
As far as the op’s boat goes, several years ago a late 90’s 370 or 380 AC, can’t remember, on our dock broke a transmission on a big block gasser. A marine mechanic changed that tranny in the water at our dock in a few hours, so I’m guessing the coupler can be changed based upon me being able to slide the shaft back enough to get the shaft half of the coupler off to replace my tides seal and the fact that a mechanic pulled a tranny out of a very similar boat in the water. Nothing I would do, too much reefing and flexing on the tides seal but I am always a little over cautious.

BE1CAC08-46C6-4013-A38E-455CF9642D2F.jpeg

I had room to work, others may not.
Get the seller to get your prospective new purchase in order unless you are getting a good deal and you want to deal with it.
 
I've got a 370 AC on the hard, with props off, and I can confirm you can split the coupler a good 6 inches and get a puller in there. The transmission coupler has a center nut, but if you change the coupler, you may need shim adjustments (velvet drive) and a new nut. They are preloaded at assembly time for the correct play. I had to replace the coupling nut on mine as the old one came loose. I'm hoping just a new nut won't mess with the pre-load.
If you remove the 2 half circle covers on the bulkhead, you might get another 4 inches of clearance going aft.
In the water might be a challenge on clearance.
 
Thanks for all your feedback. I was looking to worst case my potential outlay as the seller is fairly motivated in his pricing; $61K. I need to factor in that the 7.4s with 1400 hours could be considered a ticking boat bomb. The oil filters appear to have been changed less than 100hrs ago but over six years ago on the calendar; so very little recent use. I do plan on having a full survey including compression and borescope. However, I may need to rethink this buy from more of a hull value approach as a repower could be imminent.
 
I could have used that level of survey. Ran great, responsive, close on wot, but 1250 hrs. Water intrusion on 5 cyl. Both exhaust manifolds and risers leaked for years and 1 internally.
Already worked once but terrible job im finding.
 

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