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  #1  
Old 05-10-2010
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Shaft alignment with a dripless seal

Hi people, this is my first post and I need advice on aligning the shaft on my newly installed Yanmar 20, My boat is a New Zealand built H28 and just before I purchased her she had a dripless seal installed. The old engine was a 12hp single, which blew up, I installed my new engine fairly easily but continue to have problems with noises from the shaft. The problem Im having is that when they removed the old stuffing box and installed the drippless seal the shaft is no longer held in a central position, it can move around when disconected from the gearbox becase the only thing holding it is the cutlass bearing at the prop, this makes it difficult to find the true central position, During the last antifoul I removed the shaft and had it checked, replaced the cutlass bearing and when the engine was replaced a new three blad prop was fitted. The engine mounts appear very soft on the Yanmar, some say too soft but it is hard to beleive that Yanmar cant make an engine mount to suit their engines, and replacement mounts (polyflex) are over $1000 with the coupling. Anybody had any similar experiences??
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Old 05-10-2010
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I have a dripless seal on my 13hp Yanmar and it did require checking the alignment when I had to remove the shaft. It's not that the process is difficult, merely that it can be time consuming. Even with a stuffing box though, you should be checking alignment when disconnecting the shaft from the trannie.
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Old 05-10-2010
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Quote:
The problem Im having is that when they removed the old stuffing box and installed the drippless seal the shaft is no longer held in a central position, it can move around when disconected from the gearbox becase the only thing holding it is the cutlass bearing at the prop,
That sounds pretty standard.

Quote:
this makes it difficult to find the true central position,
Hang the shaft so it's centered in the shaft log and then adjust the engine to match up to it. The dripless seal is in a rubber bellows. You adjust the carbon seal so it's centered around the shaft by shifting the rubber bellows one way or the other before you tighten the hose clamp.
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You don't say what kind of dripless seal. PSS, Volvo or ?
BTW: I had an H28 once. But as erps said you need to center the shaft in the log and align the engine to that. Yanmar mounts are soft, especially when new. I actually used an isolation unit when I installed a Yanmar in my H28. 30 years ago so not relevant here and I did it because it would be difficult to align the new installation with the existing shaft. I would have needed to raise the motor by several inches which would have interfered with the hatch.

Some will recommend changing the mounts but I would try a good alignment first.

Gene
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Downunder,

My boat, engine and setup is different than yours but I recently fitted a PSS dripless shaft seal and had the same question as yours before the engine alignment was done - "How do we know where the shaft is in the shaft log before we do the alignment and bolt down the engine?" Below is what we did, it might help you in your situation.

We moved the engine forward a bit (1-2") to disengage the shaft coupling from the transmission. The engine was still there so we could know where the TX coupling was. We then moved the shaft at the shaft coupling from side to side, marking the extreme position the shaft reached on both sides before it touched and stopped at the shaft log. Based on that we established a approximate center. When keeping the shaft at the center we could see if we were off and by how much. Another way to look at it was by seeing how much to the side we were able to go on each side. So far as we were equidistant from the Tx coupling center we were fine. Same method was used for up down.

Hope the description above is clear and it helps you.
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Thank you all for a rapid response! the seal is a PPS and I have tried nearly all of your suggestions in one form or another, with limited access (lying under the pilot berth and only able to get one arm in there) and the boat in the water, Ill just have to keep trying, I have not pulled back the bellows to check the shaft is central in the deadwood sterntube but will definately be trying that next time the boat is out for antifouling, I figure if I cut 3 small wedges and wedge it at centre then align the motor to the shaft. The motor moves on the soft mounts that much that when you start or stop the motor the shaft bangs on the stern tube( Yanmar says the stern tube is too small in diameter ) not much I can do about that!
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You will need to loosen the stainless collar and slide it forward. There are two set screws in each hole (one locks the other) and they say you should not reuse them. The gland will leak but not so much that the bilge pump can't keep up. You will then be able to slide the flange back from the transmission and can check shaft log centering. Done creatively you can minimise the leak by holding the collar against the carbon seal while you do this. It will be pretty easy to see if it is way off. The shaft does not need to be perfectly centered in the log, just enough so it doesn't bang into it as the motor moves around. Once properly aligned the motor should not move the shaft much at all except perhaps while starting.

I just installed a PSS and aligned it in the water. It turned out I needed to raise the aft end of the engine a bit to align with the shaft and at the same time raise it slightly to center in the log. I used a razor blade between the loosened flanges to check alignment. I checked resistance while inserting the blade between the flanges. The bellows on the PSS pushes against the engine. It was easy to tell what needed adjustment by how much resistance I met while pushing the blade in.

Sorry if that isn't very clear.

Gene
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