Prop shaft coupling alignment

Hey CCF,

I just finished replacing the cutlass bearing in the strut on my 1999 Sport. The shaft that was in the boat was not a double taper so I had to cut it out. I was also unable to remove the engine/trans in my garage. Anyways, the new double taper shaft was a breeze to install and torque to spec. My question is, since I did not move the engine, trans, or strut in any way, what would the coupling alignment procedure look like? The shaft flange butt up flush with the trans flange with little force. I used a feeler gauge with hub bolts finger tight and I could not slip the thinnest feeler in any portion of the hub. Does this mean I am properly aligned? Thanks for the help!

DHMcFadin wrote: Hey CCF, I used a feeler gauge with hub bolts finger tight and I could not slip the thinnest feeler in any portion of the hub. Does this mean I am properly aligned?

Dominic,
No, you missed the concept. The .003 is the max DIFFERENCE side to side and top to bottom. This indicates the faces are parallel which in turn indicates any angular misalignment of the shaft to the trans/engine. IE, the shaft needs to run straight back from the trans/engine. Also, keep in mind that alignment starts at the strut. The strut needs to be aligned first so the prop shaft runs close to center in the log side to side top to bottom when the shaft turns freely in the cutlass. Then the trans/engine is aligned to the shaft. Considering how your cutlass was so worn, I highly recommend you start over with the alignment and, at the strut.

BTW, don't assume that the alignment was correct just because you didn't move the engine.

MrMcD wrote: The bolts need to be loose so they don't affect the flange fit. Then check with your feeler gauges. I always try to get my fit below .002. Last time I was under .0015. You did not mention the size of your smallest feeler gauge. I think .003 is considered the high side of acceptable but tighter is always better.

Thanks for the reply. My smallest feeler is .0015. I will disassemble and re-verify! This is why I love this forum! Thank you!

8122pbrainard wrote: DHMcFadin wrote: Thank you for the insight. My smallest feeler is .0015. The only reason I assumed the alignment was good was 1. The cutlass bearing that came out was evenly worn. 2. The prop shaft had no grooves or marking around the shaft log. 3. The boat ran smooth prior to the cutlass bearings needing to be replaced. I only replaced the shaft because I wasn’t able to remove the engine and trans and the boat didn’t have a double taper shaft. But I will disassemble everything and re-check using your instructions. I appreciate the help very much! Dominic, To possibly clear up any confusion, let me explain checking for the max .003" difference another way.. Lets say you use a .010"feeler gauge and on one side it's tight between the flanges. Then, the max reading on the other side between the flanges should be no more than .013" or no less than .007".

OHHHHHHH

Thank you for clarifying that! It’s not the I need to rely on the smallest feeling, it’s that whatever size I use needs to “feel” the same all the way around.

Sorry for making that difficult!

8122pbrainard wrote: DHMcFadin wrote: OHHHHHHH Thank you for clarifying that! It’s not the I need to rely on the smallest feeling, it’s that whatever size I use needs to “feel” the same all the way around. I had a feeling!! 8122pbrainard wrote: Dominic, No, you missed the concept. The .003 is the max DIFFERENCE side to side and top to bottom.

No pun intended? Lol

I’m glad y’all told me to check. The engine needs to come down and to the right. It’s more than .004 out of tolerance. Looking from behind the trans, I can fit .004 at the top and left side of the coupling but can’t fit .0015 on the right and bottom. Will have to adjust.

8122pbrainard wrote: Dominic, Aligning the engine to the shaft can at times be frustrating. As an example, when you move the engine, the centerline of the trans output shaft can change. Think out the moves in your head before making the actual adjustment.

Thanks! I think I will also be battling the old motor mounts as well. I thought about replacing those too but the rubber spacers don’t have any cracking and feel soft/supple so I think they are ok. Penetrating oil will be my friend.

MourningWood wrote: Also, if you have the means to take some of the weight off the mounts (via Hoist, cherry-picker, or other) it greatly simplifies the process. Even lifting a corner helps greatly, esp. with lateral adjustment, which it sounds you may need.

I unfortunately don’t have any of those handy but thanks for the suggestion.

If you have not already done this you should remove all the bolts at the coupling, back off the shaft enough so it sits free, it will sag a little due to its weight. Watch and see where it wants to sit naturally.
Now spin the shaft, you may need to lubricate your cutlass in the strut.
Find the spot where your shaft spins most freely. We refer to this as the Happy Spot.
This will probably be a spot where you are lifting slightly on the front of the shaft while turning the shaft. You can cut a short piece of 2x4 wood and use it as a support to support the front of your shaft in the Happy Spot once you find it. I cut a small V in my piece of 2x4 to help hold the shaft. I think mine was about 4.5 inches long with a V cut at the top.
The bottom of the boat is tapered and if your 2x4 is the right height you can slip it forward or aft till it supports the shaft perfectly. Now align the engine to the shaft in this position.
If the shaft is in the Happy Spot there will be no stress on it when it is connected.
Aligned properly the shaft when connected will spin with little effort. I have the plastic cutlass which does reduce drag but my shaft spins with one finger easily.
To answer your question on how to lower the rear at the coupling you can play with it and do what works for your boat. I was able to move mine, I lubricated each of the adjustment threads and the pinch bolts and shafts that needed to slide. I think I actually tapped a flat blade screwdriver into one of the pinch bolt slots to open it slightly. Tapping on the mount also helped encourage them to slide as needed.
A bad alignment will force you to grab a blade with a full hand and muscle it to turn.
Plan to spend 3 hours fine tuning, with this in your head if you get it done in 2 hours you will be excited. It can take time.
Mark