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  Topic Review (Newest First)
02-13-2013 07:06 PM
Capt Len
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

Odd that no one has mentioned the use of a feeler gauge. Sort of useful in determining parallel flange faces after centering the coupling. This can be done after you know that the coupling and prop shaft are fitted properly( this may need the machine shop lathe )
02-13-2013 09:00 AM
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

It is possible that the vibration that you now feel is from the new flange, and the old transmission shaft not mating perfectly. The new flange surface should be exactly perpendicular to the axis of rotation of the flange. This isn't likely to happen unless you can get the transmission and the flange to a good machine shop.

However, you might try the following simple fix to lessen the issue; remove the bolts holding the prop shaft coupling to the transmission output flange. Align the holes so that the next hole on the propeller shaft aligns with any given hole on the transmission output shaft (move it one hole). Put everything back together, and try it out.

If the characteristic of the vibration changes, you confirmed my theory. If it changes for the better, keep it there. If it changes for the worse, try aligning a different set of holes.
02-12-2013 02:00 PM
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

Great news... I wonder if the vibration you feel now in the tiller was always there, but overshadowed by all the other 'bump and rumble' you had before....
02-12-2013 01:04 PM
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

As an update, we received a replacement flange and locking nut from a friend who came to visit us from back home. We also decided to replace the engine mounts, as one of the adjustment bolts spun in its rubber housing when I tried to adjust the alignment.

As we all suspected, the new flange had much longer teeth and gripped the transmission output spline much better. There was no wiggle between the spline and the new coupling, so Gary's point about the spline being made of harder metal than the coupling (and remaining undamaged) appears to be true. The old flange must have just been reamed out by the spline due to engine misalignment.

To complete the repair, first I installed the new coupling and spun on the locking nut. On the advice of a local mechanic I used a flat punch and a hammer to get the last little bit of torque on the locking nut, then used a cold chisel to calk it in and lock it in place.

Next was to replace the engine mounts. I borrowed a car jack and lifted one corner of the engine at a time, sliding out the old mount and sliding in the new. This was a relatively painless process that took an afternoon.

Finally came realignment of the engine. There are other guides out there on how to do this properly, but suffice to say that when I first checked the alignment on the old engine mounts, the transmission output coupling was probably 1/4 to 1/2 inch below the prop shaft coupling. This would explain the vibration issues, the worn cutless bearing, and the eventual failure of the coupling. The vibration and noise should have been a clue a long time ago, but it took separating the two coupling parts to actually see how bad it was.

After completing repair, we took the old girl out in the bay for a sail. Immediately we could feel and hear the difference. Our feet felt barely a buzz through the cockpit floor. The prop shaft swished smoothly straight through the packing gland where before it was a vibrating blur. With the new mounts, the motion of the engine itself had changed from a battering shake to a calm rumble. As we motored along, the cat took to perching with his belly on the companionway stairs like he was snuggled up to a purring mother.

If you haven't checked your alignment recently, I highly recommend it.

PS - On that last trip, I did notice more vibration transmitted through the tiller than we remembered from before. I feel pretty confident about my alignment job, so could there be some other reason why the rudder has more vibration?
02-01-2013 09:31 AM
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

I just looked in my Yanmar Parts Catalogue and the flange (item 26) looks different from the one in your picture. The one in the catalogue looks much deeper so more spline length. Attached is what I show. Is it possible you have the wrong flange.
01-30-2013 09:40 PM
Capt. Gary Randall
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

01-30-2013 09:40 PM
Capt. Gary Randall
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

any auto parts store will have feeler gauges,and good luck to you have a wonderful trip wherever you're headed baby will cross paths one day.......CaptG
01-30-2013 08:59 PM
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

Thanks Gary for the good advice. Unfortunately the hammer blows were my no-no. I used a wood chisel to pry the two coupling pieces apart. I think heat/dirt/rust conspired to glue the two pieces together. It was the only way I could get the coupling apart to get at the locking nut. Since the photos were taken I've filed off the metal bits at the edges of the flanges that got bent by the chisel, and polished it all with a fine scotch brite pad, so all that's left should be the pristine inner surface of the coupling discs minus a millimeter or two on parts of the very outer edges (outside of where the four bolts hold the coupling together anyway). Suppose that'll be all right?

From all the reading I've done the past few days, I'm pretty concerned about trying to get off the shaft coupling to take it to a machinist without destroying it and/or the prop shaft. If I could simply keep it attached and adjust the engine alignment to match, I'd be much happier.

Where does a person acquire a feeler gauge or dial indicator, generally? Is that an auto shop buy, a Home Depot thing, an industrial supplier? It'll be a new addition to my tool bag.

Thanks again.
01-30-2013 08:20 PM
Capt. Gary Randall
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?
01-30-2013 08:05 PM
Capt. Gary Randall
Re: Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

hello Jeff, I have done many many engine alignments, and I'm going to suggest to you by observation of the pictures that either your output shaft coupling or the shaft coupling or both were hit many times by a hammer that is a definite no-no. This is probably what initially started the problem. That is why I suggest that you have both couplings put in a lath at the machine shop,and the mating surfaces machined. Whenever I replace one coupling I always do this unless they are both in really good condition. The seal rides on the output shaft coupling which is more than likely damaged you will find the seal in the output shaft bearing housing I can plainly see it in the picture. There is no sense in making a repair that could cause more damage. Also to answer your other question about vibration, when you're engine is in neutral and you throttle it up about 1000 RPM you'll notice it really gets smooth. It should act no different when it is in forward or reverse gear if everything is in the proper alignment. You may have to ajust or shim the motor mounts to attain alignment to the couplings with a feeler gauge. I usually use a dial indicator but a feeler gauge will work fine I recommend 25.000 most of the time you need to use a hammer but never hit on the flange of either coupling. The shaft coupling can be hit on the body that surrounds the shaft and hold it in place. The transmission output coupling needs no hammer just the nut to install. When I use a hammer I always use a sacrificial brass rod or a block of wood. After looking at the pictures if you follow this practice you'll probably never have another problem with it. As said earlier make the correct tool out of an old socket using a hand grinder, or do it at the machine shop preferably half inch drive and torque the nut to specifications also using some Loctite if you can get some.
looking at the shaft coupling itself you'll notice a ridge on the inside as a mating surface, that ridge fits inside the output shaft coupling and if it is damaged in any way which I can clearly see it is, it could've been the cause of the problem. The correct assembly and alignment will not only solve the problem but it will also solve the cause as long as your output shaft bearing is in good condition. CaptG
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