1986 Hunter 31 Strut Replacement

[Dfisher]

Hello All,
I decided to got through with the purchase of a 1986 Hunter 31. The engine runs great and the survey checked out okay with the exception of the prop shaft being disconnected from the transmission. The previous owner reported that there was a strong vibration. I know that the cutlass bearing was replaced and only has a couple of hours on it but the surveyor noted approximately 1/32 of play between the bearing and prop shaft. The boat is currently on the hard getting a bottom job so my first step is to pull the shaft and have it taken to a machine shop to make sure it is straight. If that checks out, I'm moving onto cutlass bearing and alignment. Surveyor said they mounts felt secure and does not think they are bad. My question is, with the boat already on the hard should I go ahead and replace the entire strut. I talked with the hunter store today and the strut comes with a new bearing so I would save on the labor to remove the old one and install the new one. I can't spot anything wrong by eye with my strut but I really don't want to put the boat back in after only doing the cutlass and then have to pull it again to replace the strut. If anyone has any history with strong vibration caused by a bent strut it would be greatly appreciated. The previous owner noted the vibration / shaking was so bad he could get it to full RPM when in gear. Thanks in advance

 

[IH82BL8]

I haven't dealt with this before, but it sounds like the problem is an alignment problem where the shaft couples with the transmission. I'd investigate that before spending money on a new strut.

 

[woodster]

if your strut is not bent or cracked in any way or its bronze does not have a pinkish color to it there should be no need to replace it ...you prop shaft could be worn out of round where it goes through the cutlass bearing ...bent ....or the prop could be eccentric on the shaft...or the coupling to the gear box could be the problem .....the 32th of an inch play makes me think you need to pull the shaft and mic it for thickness and check and see if the taper is true ...there are about a dozen this in the drive train aft of the gear box that could be out of whack so if you are pulling the shaft check them all and if the shaft is worn replace it with a new one with the coupling mounted and face true by the machinist along with a new cutlass bearing ...also ck the alignment of the strut to the stern tube ..when all that is satisfactory the load it all up and re alien the engine and gear box to it ....also check your prop for balance and good seating on the taper it may need lapping if it is not seated correctly...hope this helps

 

[Tata duende]

Seems 1/32nd play at the strut bearing would not give the level of vibration the PO noted; I would check the straightness of the shaft between where it exits the hull and the strut. Easy to do, just put a measure (anything) between the hull & shaft about mid-point and turn the prop, see if you are getting any variation as you turn it. It is not uncommon for a yard to get a strap under the shaft as they lift the hull and bend it slightly, and it will result in serious vibration.

 

[kloudie1]

Another in agreement.. If it is not pink and not bent.. don't mess with it.. Changing the strut is an exacting job that requires a lot of time and effort to line it back up with the transmission outlet flange.. The strut is not fit nor is it positioned positively, so when ya remove the old one, a lot of measuring and shimming and thinking goes into bedding it correctly..

 

[Dfisher]

sounds like I should start with the shaft. I will be going to the boat to remove that shaft next week. Do you remove the coupler from the end of the shaft and then pull the shaft out of the boat or remove the prop from the shaft and pull the shaft into the boat. I'm thinking the prop shaft may be bent based on what we saw when we yanked the boat - about 1/4" of the strap was over lapping onto the shaft and when I spun the prop you could see the strap goin up and down slightly. As far a measuring the diameter of the shaft, is there any published information about what size it is suppose to be?

 

[woodster]

If it's a 1 inch shaft if it measures 1.000 it is good to go. If it measures .980 it is marginal at best ...personally I would replace it because that is .020 less than new and close to 1/32 worn but some may disagree

 

[Dfisher]

Great info. Thanks woodster

 

[woodster]

there is a chart some where on the net for telling you the ware factor and how much is allowable i will try to find it and post it ...it may be in the cutlass bearing search where it tells you the max and min of the shaft i will try to find it

 

[woodster]

here is the chart and it states .03 to .008 on the chart if i am reading it correctly

http://www.pacificmarine.net/engineering/propeller-and-rudder-bearings/cutless-bearing-clearance.htm

 

[Tata duende]

I noticed in the pics you posted that you have a feathering prop on the boat. That could actually be the source of the problem, if one of the blades in not fully 'opening' to match the other it would cause all sorts of imbalance.

 

[Dfisher]

It is a feathering prop but myself and the yard checked it out and both sides seem to operate smoothly

 

[Tata duende]

Just a long shot then but double check that not only are the blades moving smoothly, but are they opening to the same angle. If not an equal angle you will have a different pitch on each blade; I potted the prop and thought, 'Ahaa', but Oh well! Anyway, if not the prop then I would go back to the bent shaft theory. Also, you had said that the shaft was disconnected at the coupling; try looking at it from inside while someone turns the prop for you; is it turning true, or is the packing gland (if mounted with a rubber hose connection) showing movement.

 

[Dfisher]

That's a good tip. I will have the machine shop check that out as well