canvassing opinions...

[Bernadette]

ok here's another question i have for the forum:

whats the usual practice when installing a fexible mounted engine...

are cv joints and/or flexible couplings and/or thrust bearings installed as well?

bernadette

[Thad]

I think the usual practice is to mount the engine with proper alignment and just let it wobble around. I also think that a cv joint with thrust bearing is the best practice but the money issue raises it's head with equipment and fabrication cost. Engines must have their own thrust bearings internally but they have torque and vibration issues that complicate solid mounting as was common for many years.

[Todd D]

Normally the transmission is directly bolted to the shaft flange. Some people like to put a flexible coupling between the shaft and the transmission, but it certainly isn't needed.

[Ian McColgin]

First, nothing here applies in any way to V-drives, belt drives, or any other system where there cannot be a straight line out the transmission and reduction gear out to the prop.

On any boat you should be able to keep allignment close enough that a CV joint is not needed. "Flexable couples" are not so much flexable as just not steel to steel connections. They are quite lovely for dampening minor vibration caused by poor engine tuning or an unbalanced prop - like you really should knock that barnicle off. The flexable couple will also dampen the vibration of the most modest misalignment.

All three of these factors are more likely on a wooden sail boat than on a power boat due to the side bashing the engine mounts take while sailing, especially into a head sea, and the effects of just plain less use and - reduced warm-up/running time ratio - more abusive use that sail boat auxilary engines get.

In an older wooden boat, you may have so much hull movement that flexable mounts are also a good thing. Like the couple, this is not so much flexable in any big angle sense as vibration absorbing. At age 70 Goblin got flexable mounts and it was wonderful. Goblin's hull could wrack so much on a beat that the interior door nearest the main mast could not be closed if open or open if closed when on a hard beat. The flexable mounts allowed the relativly short shaft (into a flexable couple) to partly drag the engin back closer to perfect allignment and absorb vibration.

If you have incurable vibration even when the static allignment is correct, the prop is balanced, and the engine is in tune, then try just the flexable couple first. If you add must flexable mounts, make sure they are up to the prop thrust. I have seen instances where vibration was made worse by flexable mounts where they were not indicated.

Don't use either flexable couple or mounts in place of proper allignment. Even when you must use them, the static allignment should be as perfect as you'd do with conventional couple and mounts. Can't stress that too much. These are not CV or U joints. The thrust of the prop gets to the boat through the engine mounts. But in the dynamics of an older sail boat, flex couple and maybe mounts can help keep the fastenings in the boat and your fillings in your teeth.

G'luck