Getting the shaft

"I know this is not a pure Cru

"I know this is not a pure Crusader question but here goes, while working on one of my engines a mechanic noted that the shaft log was "wobbling" slightly when the boat was in gear, I had him check the alignment and he said he found that all of the engine mountings were loose and that he could not get the engine perfectly aligned because the propeller shaft was bent. He claimed he could see the back of the engine moving while in gear tied to the dock. Well being the skeptical person I am I chose the hottest day of the summer (Saturday) to climb into the engine to see what he was talking about and do all the fun gas filter checks and changes. I could see the shaft log (packing gland) wobbling slightly I could not really see the back of the engine moving though. Here are the questions. 1. Does this sound like a bent shaft? I have a vibration at idle forward with this engine but at no other speed. 2. Is there anyway to check the shaft short of pulling the boat removing the shaft and checking?
Thanks for any information anyone can give me."

"Sorry, but he is right: Coupl

"Sorry, but he is right: Coupling misalignment alone won't do that. The shaft has to come out.

Jeff"

thanks jeff

thanks jeff

"Scott:

There's a good

"Scott:

There's a good chance the shaft isn't centered in the log...the alignment wasn't done properly.

If the shaft is bent, the wobble usually doesn't go away with a speed increase. Also, if the shaft is bent, you can't get the alignment correct.

If the coupler isn't too rusty, you can do a quick assessment by separating the flanges and reconnect them. mark the two and then measure your existing gap, at the 4 spots in between the bolt holes and write them down. separate the flanges, rotate one 180 degrees and remate them. repeat the 4 point measurement. if the 'wide' spot moves to the opposite side of the circle, its time to get the shaft checked.

The only way to accurately check the shaft is to remove it and support it on a series of V-blocks."

"I was told that he could not

"I was told that he could not get the alignment done. He said he could only get it within 2 thousands (of an inch?). Anyway, the coupler is not rusty at all so it should be relatively easy to separate. How easy is it to separate the flanges, do I have to loosen the packing gland first?"

"2 thou? Sounds mighty close

"2 thou? Sounds mighty close to me. Note that it is possible to have a coupler bent or misshapen as well as the shaft. Recheck the coupler after moving ONE flange 180 degrees as well, to check the coupler trueness."

That is what I thought as far

That is what I thought as far as being mighty close. But the mechanic says the wobbling of the shaft log is what is telling him that the shaft is bent.

"Yes indeed...rule of thumb is

"Yes indeed...rule of thumb is 0.001" per inch of diameter of the coupler. Crusader say 0.004" with the 5" flanges they put on mine.

How easy to separate...that's a loaded question. If they are fairly rust free and the alignment isn't bad, you should be able to separat them by hand, once the 4 bolts/nuts are removed. If he just checked the alignment, this should be real easy.

If you're gonna crawl down there and check, make sure the shaft is centered in the log first or you'll be wasting your time.

No need to mess with the packing gland."

Any other way to make sure the

Any other way to make sure the shaft is centered other than to look? I thought I read somewhere you need to move the shaft horizontally and then vertically to "find" the center???

""Any other way to make su

""Any other way to make sure the shaft is centered other than to look? I thought I read somewhere you need to move the shaft horizontally and then vertically to "find" the center???"

Pretty much true, with the caviat that it is important for the shaft to exit the cutlass bearing centered as well. Actually, that is more important than centering in the log. You can have perfect coupler alignment and have uneven cutlass wear. With a somewhat "floppy" 1 1/4" or less shaft, over a span of many feet, even this inspection calls for care. You can usually look at the forward part of the bearing (with the shaft in) to check for an uneven wear pattern."

"Concur with Dave...will admit

"Concur with Dave...will admit i assumed the boat was floating and that the factory alignment of the drivetrain was a) proper & b) still pretty close - not good on either.

Will add that when the shaft is centered in the cutlass bearing, it will rotate, by hand, with minimal force. My 1.5" shafts can be spun with my small, old, worn-out hand. this will get you close w/o a haul....drawback is if the bearing is worn, the center may be "large"."

"Ok, that brings into mind tha

"Ok, that brings into mind that I CANNOT spin my starboard prop by hand very easily either in or out of the water. The port prop pretty much spins like yours does. I had the cutlass bearings checked this spring before launching and the report was that while they are showing some signs of age (8 years) there is no abnormal movement or wear on them. I have also looked the cutlass bearings while the boat is on the hard and there does not appear to be uneven wear ie a "cocked" shaft. But that stb shaft is a bugger to turn."

"There you go....either the sh

"There you go....either the shaft isn't aligned or, as I recently found out on mine, the bearing can fail on the inside, where the normal inspection doesn't detect a fault.

If you pop the couplings, you can do the 'move the shaft to find center' exercise. I've found a set of 2x4s can be used to 'hold' the shaft at this preferred position. One day i'll rig up a v-notched piece of plywood. you can then assess how freely things 'spin' and adjust the shaft's position if needed.

My dynamics professor had a saying: Aligned systems exhibit minimal friction. Excess friction accelerates wear. Wears costs money."

"Do you have a vibration or is

"Do you have a vibration or is this just something he noticed?

I've seen brand new shafts wobble but run fine with no vibration, especially shafts smaller than 2". If he has .002 alignment and it does not change when the coupler position is rotated versus the transmission, go boating.

If he actually has .002 and tells you he can't get it to align, find a new mechanic, he is either doing his first engine alignment (at your expense) or trying to sell you some work you don't need.

I would do as suggested above and separate and check the location of the shaft in the port. If there is still some question, put a dial indicator on the flange, both at the transmission and at whatever locations on the shaft you can access. A bent strut will also cause a shaft to wobble. If you have trouble spinning the shaft by hand, loosen the coupler bolts and see if that changes anything. If t doesn't, chances are it is binding in the strut bearing and is probable pinching doe to a bent or misaligned strut.

Make all checks twice, once with the coupler bolts tight and one with them loose. If you see a difference, the tightening of the bolts is causing the problem, meaning simething is misaligned or bent.

Good luck,
Rick"