Strut Realignment Help

[TDudley]

I was hoping that this forum would have some input on helping correct a possible situation I have with a miss aligned strut.

First the facts:

I am the proud owner of a 27' 1981 Hunter with a Yanmar 1GM. Last winter I pulled my motor, replaced my original brass shaft for a brand new SS shaft, replaced my old shaft coupling for a new one, replaced my old flooded transmission, replaced the cutlass, and replaced my old two blade for a three blade.

However, I did not replace my engine mounts. And to add insult to injury, my new shaft was one inch too long.

Well the jurry rigged set up i created to make it all fit failed to pass the muster. I had tons of vibrtation and shaking and an engine I knew was not only not aligned the way it need to be but was sitting a whole inch further forward in the boat then is should have been. And it was my belief it all started with the shaft being too long and having 25 year old engine mounts.

Well it was to be all fixed this winter. New mounts, re machined shaft, new clean coupler (since I bit the hell out of the last one instaling it) and a Proffesional allignment both out and in the water.

Well wouldn't you know it, I was told the strut was not true to the the stern tube. Now, I have read almost every ost on this trusted site concerning this condition and was glad to hear it was not an uncommon thing. And maybe even faitly simple (I use that word lightly) to fix. And since the condition does not appear to be from a bent strut and the strut is mechanically attached (for the most part), I am almost willing to take it on my slef.

But hear is the ultimate question. How does a DIY guy line up a strut with a stern tube. Is there some kind of jig I can build to insure that it is correct. Or should I just leave this one to the pros. Give me some thoughts, PLEASE. It is driving me crazy and I have a lot of sailing ot do this summer.

Thanks in advance

Tony

 

[Ed Schenck]

It is hard, really hard, with the rudder in the way. Without the rudder you can slide the shaft back so that it is fairly balanced in the cutlass. Then the forward end of the shaft should be pointing right at the center of the stern tube. With the shaft just an inch or so from the engine there is too much weight with the long shaft and the coupler. So you cannot tell if it is running true in the bearing.

An other way to visualize might be to think of a laser light centered in the strut. That light should go right through the center of the stern tube and strike the center of the tranny shaft. Now how do you duplicate that?

 

[Don12364]

My Experience

I presume your strut is of the bolt on variety rather than the glassed in type.
I found my strut extremely difficult to beak free of the bonding material which I suspect was Dow 5200. Removing the 4 bolts was easy though.

With the rudder removed I then offered up the shaft, through the stern gland and trial fit connected it to the gearbox flange via a flexible coupling.
Then I applied new sealant to the flange and bolted it back in place, all the while turning the shaft to make sure it did not begin to bind up through misalignment. On the whole this worked though, in retrospect it actually needed some packing under the strut to get the alignment right with the bolts fully torqued up. I was too eager and didn't dry fit it first.

The shaft was so heavy and so long it sagged between points where it was bearing - i.e. it sagged, only slightly, between coupling and strut so my end result was a small misalignment of the strut. This means that my cutlass still lasts very well but when removed shows more wear at the bottom of the forward end and again more wear on the top of the rear.
Apart from the very small increase in friction, there was no vibration or any other sign of problems; but then I have a 3 cylinder engine.
What I should have done was to use a hollow tube, which is lighter for its stiffness, as a temporary shaft whilst setting the strut in position. A 1" dia length of stainless tube would do provided it was straight and this is easily checked using Vee blocks and a dial gauge.

Re the vibration; I doubt that horrendous vibration would result unless there is horrendous misalignment. It is normal for things to go out of true when the prop is pushing the boat along using engine and mountings for the job. I don't see how these can be kept perfectly in line whilst under load anyway.
If the vibration is only at idle then those one lung engines are dreadful so you might need to increase the idling revs a little.
Also be aware that on some Yanmars the manufacturers recommend different stiffness of mountings for each side of the engine. The problem may be 'resonance'. This is when small differences in balance induce vibrations which just happen to occur at the resonant frequency of the mountings. This normally only occurs below idling speed but it can happen at higher revs. The trick is to change this resonant frequency to outside the rpm range normally used by either using softer mounts or harder ones.

My advice would be not to remove the strut unless absolutely necessary.
Also - think positively - you now have room to fit a rope stripper.

 

[Bill1565]

A friend of mine had a laser pointer that looked like a pen. we added duct tape to enlarge it, stuffed it in the aforementioned 1" ss tubing used a compass point hole in a piece of cardboard as an aperture at the other end and bore sighted the strut, shaft log and tranny shaft. My strut was not the correct one and was improperly mounted. Had to use 4 washers on each front bolt to depress the cutless brg into alingment.Made a huge improvement in the vibration. .

 

[TDudley]

That was my line of thinking, but the duct tape brought it all together for me. I was making it to hard by considering some type of tube/washer configuration. But the duct tape is the key. At least it lets me get an idea of what I'm looking at.

Thanks a lot for the info. Keep it coming.