Motor mounts

[motthediesel]

I wanted to try some different engine mounts to see if I can take some of the wet-dog shake out of the old Lehman-Peugeot on our 27FC. I know there's an element of risk in re-engineering something like that, but I thought some slightly softer mounts might help. Having the engine more free to move could be a problem with a ridged driveline, but our boat is equipped with a Federal flexible coupling, so I think it should be OK. Did all the 27's come equipped with those, or did someone add that later?



As I understand it, the Federal couplings still require careful alignment, but they do allow for some movement, so ideal for this setup. I didn't know how hard it would be to change mounts out, but it was pretty easy. Those clamp-rod mount connections help because you can slide them right out sideways.



Here's what the new mounts look like.



Now it's just a matter of aligning the shaft, and that will take a bit of doing. I have a lot of experience with tuning inboard runabout shafts, but this is a bit different. There must be close to 7 feet of shaft from the coupling to the stuffing box, so I first need to determine the vertical location of the shaft, then go from there. Then too, the final alignment can't be done until the boats back in the water, so I just need to get it close now.

Tom

[Sprig1]

That looks like the same engine shaft coupler I have. What kind of engine mounts did you buy? I should probably do the same thing.

[motthediesel]

I got these from Go2 Marine:

https://www.go2marine.com/DF-206-Series ... gine-Mount

[motthediesel]

Having thought some more about this, that seems like a very long length of shaft from the coupler to the stuffing box without support. The general rule seems to be a maximum of 40xdia, so in this case (1.25" shaft) 50". Some of my older books say to never exceed 50xdia, which would be 63". Without measuring, I'd guess it's way over even that number in our boat.

I rooted around in some old posts here and found that at least some of the later A27's did in fact have an intermediate shaft bearing. That sounds like a good idea, now I wonder how much of the vibration in our boat is the result of shaft "whipping" ? And whether that flex coupling might in fact be making it worse, not better. One solution might be to add a bearing, but I can see no way to do that without removing the fuel tank -- and I DO NOT want to go there if I don't have to.

Tom

[Sprig1]

That's a good thought on the length of the shaft. Could it be that your turning such a big prop that's causing more vibration ? Taking the fuel tank out is not so bad. I took mine out and cleaned it put and put inspection ports in. It wasn't very dirty.
I'm wanting to try a bigger prop on my boat I have one I just don't know if the shoulder is the same.
Keep up all the good projects.

[motthediesel]

Yes, it could be that our giant 19" (with it's insufficient tip clearance) prop has added to our smorgasbord of potential vibration sources. I really feel that a lot of the "noise" we are hearing underway is really cause by the vibration of various panels. So this unsupported shaft thing is definitely something that I would like to address.

You said getting the tank out was not that bad, do you have the single 70gal tank in your boat? It looks like getting it out would be a grim job to me, but maybe I'm missing something? Did you get it out forward through the engine compartment, or back into the stern cabin?

Tom

[REO]

I don't know about the long unsupported shaft issue, but Betamarine sells motor mounts for that engine that are supposed to reduce vibration. My mounts look like yours, and when I sent them a photo they recommended the new mounts. $100 each. Seems a bit costly--but maybe they will improves the shakes.

[Sprig1]

Tom sorry I never saw your question. I'm sure you have done it by now. It came out the back fairly easily. I hope you are enjoying the summer. I haven't even had my boat out of the slip maybe soon.