After having the prop shaft replaced, I continued to notice vibration on short trips to and from the lake. This year while on a 4 week cruise, I noticed vibration and finally significant leakage from the shaft strut which was being shaken loose. This was repared but vibration continued. Another shop recommended alignment of the engine which improved but did not eliminate the vibration. I get 5.9 to 6.1 kts at 2300 rpm. I have a 2GM20, Prop specs unknown except 2 blade, should be 13 x 13 per manual. Alternator is right up the the wall on port side. I have been told the mounts are not what Yanmar would spec, they are too stiff. Is there a reference source that would give a proceedure for re-assembly that would allow the entire train to be centered and aligned? Thanks
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Yard work perhaps
To align the engine, you need to first determine how out of whack it is. Disassemble the flange that holds the shaft to the transmission. Chances are the shaft will flop slightly, valdidating the problem. If you run a playing card around the flange and it gets stuck in one spot while showing considerable play opposite, that will validate as well. Now you simply adjust the motor mounts until the distances all the way around the flange are 1/1000th inch. Then reassemble.
To align the engine, you need to first determine how out of whack it is. Disassemble the flange that holds the shaft to the transmission. Chances are the shaft will flop slightly, valdidating the problem. If you run a playing card around the flange and it gets stuck in one spot while showing considerable play opposite, that will validate as well. Now you simply adjust the motor mounts until the distances all the way around the flange are 1/1000th inch. Then reassemble.
Have Your Prop Checked!
It made a world of differnce on my boat (Legend 37, 3GM35F) when I had it checked. One of the 2 blades (stock) was 1/2" out of pitch from the other. Had it fixed and it became smooth as silk. If your boat is several years old, never reconditioned the prop, hit something at some time(included wrapping a lobster/fish pot on it) then go for it! P.S. They can go out of wack from normal running, also.
It made a world of differnce on my boat (Legend 37, 3GM35F) when I had it checked. One of the 2 blades (stock) was 1/2" out of pitch from the other. Had it fixed and it became smooth as silk. If your boat is several years old, never reconditioned the prop, hit something at some time(included wrapping a lobster/fish pot on it) then go for it! P.S. They can go out of wack from normal running, also.
Get your prop rebalanced
Jeff, Your problem is very similar to one I had. Your prop needs rebalancing. Many times the prop is bent when service yard folks press it off the shaft to do a cutlass bearing replacement. You can't tell by looking at it, but a good prop shop will use computer-aided balance machines and tune it to original specs. It's relatively cheap - about $40-50.
Jeff, Your problem is very similar to one I had. Your prop needs rebalancing. Many times the prop is bent when service yard folks press it off the shaft to do a cutlass bearing replacement. You can't tell by looking at it, but a good prop shop will use computer-aided balance machines and tune it to original specs. It's relatively cheap - about $40-50.
I'll chime in with $.02.
I went through the alignment process several times this spring. Bill nailed it with checking for alignment with this exception. All the support components up to the prop shaft flange are flexible and when you disconnect the shaft flange from the transmission flange, it will *flop* a bit and that is normal. The key is whether the shaft is centered in the log when the engine is aligned to it. As Bill said, the flanges should mate to .001" or .2 mm. If you'd like, I posted an overview of centering and alignment in the Cherubini section. A variable you mentioned also was re: the mounts. Are they not the original? The Yanmar mounts are soft to 1) minimize buzz at higher RPM and 2) accommodate the shaking a 2 cyl diesel has at low RPM. Since replacement of those are a PAIN (I've read), check your alignment first, then the prop before worrying about the mounts. For those that had the stamina to read this far, a 13x13 prop seems a bit odd. The suggested prop for my 2GM20F in a smaller, lighter 280 is 15x12. Any thoughts?
I went through the alignment process several times this spring. Bill nailed it with checking for alignment with this exception. All the support components up to the prop shaft flange are flexible and when you disconnect the shaft flange from the transmission flange, it will *flop* a bit and that is normal. The key is whether the shaft is centered in the log when the engine is aligned to it. As Bill said, the flanges should mate to .001" or .2 mm. If you'd like, I posted an overview of centering and alignment in the Cherubini section. A variable you mentioned also was re: the mounts. Are they not the original? The Yanmar mounts are soft to 1) minimize buzz at higher RPM and 2) accommodate the shaking a 2 cyl diesel has at low RPM. Since replacement of those are a PAIN (I've read), check your alignment first, then the prop before worrying about the mounts. For those that had the stamina to read this far, a 13x13 prop seems a bit odd. The suggested prop for my 2GM20F in a smaller, lighter 280 is 15x12. Any thoughts?
Thanks for all of the input, I'll definitely take the prop to a service shop in the spring for a tune up. Will check the Dia. and Pitch too. The mechanic who aligned the engine last summer had to do it in the water and could not check the shaft strut. He said he would normally want to get to .001" or less but wound up with .003" as the alternator was up against the engine box. I'm thinking it needs to be looked at again next spring before launch to check and realign the strut to allow the engine to be pushed back into the center of the box before final alignment with the coupling. Any further thoughts?
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