Shaft to cutlass clearance

Strecker25

Well-Known Member
SILVER Sponsor
Nov 20, 2014
4,905
Rochester, NY
Boat Info
2002 410DA
Engines
Caterpillar 350HP 3126
Hey guys, very specific question I’m wondering (and think I know the answer)

i have nearly brand new cutlass bearings, 60 hours runtime on them. The engines and shafts were aligned multiple times (in water for the final alignment) and I have them to .004-.005 all the way around. No vibration, boat runs fine, etc.

After haul out I noticed the shaft has a noticeable gap on the outboard aft end of the cutlass and the same gap on the forward interior (towards the keel) part of the cutlass. Similar on both sides, slightly more exaggerated on the starboard. I’m talking about the gap between the shaft and rubber parts of the bearing. In other words, it’s like the shaft is cockeyed in the strut/cutlass.

No shaft play when pushing and pulling the shaft.

My suspicion is the way the boat is held in the cradle is flexing the hull slightly enough to cause this. Is that a reasonable explanation?

I just don’t want to wear the cutlass prematurely or worse yet score the shaft.
 
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"My suspicion is the way the boat is held in the cradle is flexing the hull slightly enough to cause this. Is that a reasonable explanation?"

My suspicion also and if that is the case, I don't like it.
Would love to see some all around and underneath pics of said "cradle".
 
"My suspicion is the way the boat is held in the cradle is flexing the hull slightly enough to cause this. Is that a reasonable explanation?"

My suspicion also and if that is the case, I don't like it.
Would love to see some all around and underneath pics of said "cradle".

i’ll grab some. It’s essentially stands that are part of a steel frame
 
Here’s a crappy one, I’ll get more. I have to put sling markings back on as they’re gone but the rear supports should close. The keel has 4x4 supports under it in I believe 5 locations resting on the frame. There are 3 stands/pads per side

Also to set context (as you know I’m a crazy person with alignment) we’re talking about .01-.03” gap between the shaft and the bearings rubber material on the areas in question

AB209C35-741E-4D31-951C-19A2136F175D.jpeg
 
something just dawned on me worth checking since I have no way of checking this issue once in the water (lake is almost never clear enough to dive the boat and see)

I will detach the coupler and check the coupler clearances at the transmission end. If it's out of alignment more than what I was while floating it should confirm my theory of some pressure flexing the alignment out
 
Any difference in the operation or gap/clearance of your transom door while on the hard as opposed to when she was floating?

good question, I’ll check tomorrow. Got a feeler gauge set to check the bearing clearance too.
 
I think the boat is well supported. The transom door is fine, alignment on the coupler at the transmission is completely tight, can’t get a .001 in it all the way around. The shaft wasn’t super tight in the cutlass even when new, but I can’t budge the prop in any direction when pushing/pulling on it.

I’m not going to sweat it at this point. I’ll monitor the cutlass for premature wear every year but other than that move onto the next problem

85CD8572-BDD7-47FC-B618-417FBE2D380E.jpeg
 
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I wouldn't pull the couplers apart but rather measure the distance between the shaft log and shaft at the four quadrants.
If those measurements are all the same I say you are pretty close. 0.006" at the cutlass over the length of the shaft between the strut and log will translate to a rather large number and be noticeable in the measurements at the log. But, regardless, all that will tell is possibly the engine has moved; highly unlikely.
Next did you repeat those measurements at the cutlass after rotating the propshaft?
I suspect it has always been there and not worry about it.
 
Your answer might be in the last sentence in your second paragraph in post #1: " I have them to .004-.005 all the way around. No vibration, boat runs fine, etc." So, are you fixing stuff that isn't broken………..

And to answer your question about the hull flexing……..Yes, they do. We don't have the room to store sexy square tubing frames like you guys do so we block up on a gravel yard. This isn't an apples to apples comparison but it is close: The 450DA is really 51'-10" and we use 5 sets of blocks under the keel and 5 pairs of stands under the chine so the hull is well supported. The last thing I do before climbing off the boat when she is being hauled out is to open and wedge transom, cabin entry, and all 3 head doors open to keep them from being pinched in the door frames as the boat's weight settles on the blocks and stands.

And my 1988 390EC would pinch its only door in the frame as well…………
 
I wouldn't pull the couplers apart but rather measure the distance between the shaft log and shaft at the four quadrants.
If those measurements are all the same I say you are pretty close. 0.006" at the cutlass over the length of the shaft between the strut and log will translate to a rather large number and be noticeable in the measurements at the log. But, regardless, all that will tell is possibly the engine has moved; highly unlikely.
Next did you repeat those measurements at the cutlass after rotating the propshaft?
I suspect it has always been there and not worry about it.

i did repeat the measurements and as a matter of fact the shafts were verified as straight and true last year. I did the dripless seals so while I had it all apart I took them to a local shop to have them checked

I’m all about preventative maintenance but I think this is truly a case of it ain’t broke, especially since the coupler alignment is perfect on both sides.

oh and when I reinstalled the shafts and seals I used the masterfab technique of a temporary sleeve to hold the shaft centered in the log and aligned the engine to it, so the shaft is perfectly centered in the log on both sides.

thanks for the input guys
 

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