Theory and Practice of Engine/Shaft Alingnment (2)

[Slowboat35]

Following the useful inputs in the original thread I've done a little research and as pointed out the gearbox output flange of the old Yanmar 3GM30 had holes centred at 78mm while the TMC60 gearbox flange (on the new Beta) are at 82.5mm, although both are on a 4 inch flange.

As the fitting company re-used the old Centaflex coupling it seems they must have re-machined the Centaflex's coupling to fit the new TMC's spacing.

It was pointed out that this is a likely cause of the deep rumbling transmission noise and vibration I am experiencing.

Is such a 'mod' considered normal or acceptable practice? In reality what chance would it have of being successful?

I am trying to narrow down the several possibilities as the solution to the noise is proving elusive.

Any further inputs?

 

[Tranona]

I am not sure it can be re-machined as the bolts run in tunnels through the body of the Centaflex. Maybe they used an adaptor plate. You have only posted a photo of the installation with the old Yanmar. It would be helpful to see the Beta installation.

 

[Slowboat35]

I'll have to look at that - I wonder how they fitted it then?

 

[doug748]

I think Tranona is correct, I can't see how the Centaflex could be altered in that way.
Adaptor plates have to be very accurately machined as a lip engages on the output to centre the thing, the holes and bolts play no part in this. If it is not done properly you could end up with the shaft not running concentrically with the gearbox which would be very dodgy.

It's a different thing to alignment but is easy to test like this:



Or you could use an engineer's scribing block or even a lash up with a pencil or scriber.

As mentioned a photo would help a lot.

.

 

[jwfrary]

A photo says 1000 words!

 

[Slowboat35]

I'll get one in due course!

 

[Moodysailor]

Definitely a picture when you get a chance, but I'd be equally interested in how it is centered, as post #4 above says.

Usually, the gearbox flange has a 'female' register inside the bolt PCD, this matches to a 'male' one on the coupling (or vice-versa). Either way, it's imperative that these are exactly the same size and matching (male-female, same diameter) or it will be impossible to accurately align the parts due to the tolerances in the bolt holes.

The fact that the PCD of the holes is different causes me to question this, as I've seen cases where these are mis-matched in the past - with different diameters, or same female-female. That the coupling was machined or modified rather than replaced with the correct specification warrants investigation here, IMO.

 

[fisherman]

Took me a long time to trace the source of vibration, the female register in the gearbox flange was ten thou off centre. 2in dia shaft heavy to run out that much, on a 1.1:1 box, 200hp. The supplier had the nerve to tell me that was within tolerance. Found it intially by accentuation, very long lever, set on a fulcrum very close to the flange, end against the register. Worked out by ratio that it was about ten thou, dti confirmed it. Engineer sleeved it for me.