install R&D coupling

[mheelis]

We have westerbeke diesel engine and sillete sonic drive on our gemini cat. We have had to replace the original flex coupling with and R&D coupling and the difference is 4mm. We understand the gap needs to be exact. We have aligned the motor mounts etc. Any ideas, tips someone else may have done when they encountered a similar problem?

[chris95040]

Some more detail may help. I'm not sure how you aligned the motor mounts if the couplings aren't in reach of each other but I may be misunderstanding.

(BTW I've always been instructed to align the engine without any plastic flexible coupling in place. You get a much better feel with the feeler gauges if it's just the transmission output coupling pressed against the prop shaft coupling. This of course requires being able to slide the shaft fore and aft to make up the difference between when the flexible coupling is in place and when it is removed.)

Are you saying that this new coupling is 4mm less fat (along the shaft axis) than the previous one? What's stopping you from just sliding your prop shaft forward 4mm to make up the difference? You may be able to make up the difference by locating your shaft coupling 4mm further aft, but it would require drilling a new spot for the set screw.

[atoll]

Originally Posted by mheelis

We have westerbeke diesel engine and sillete sonic drive on our gemini cat. We have had to replace the original flex coupling with and R&D coupling and the difference is 4mm. We understand the gap needs to be exact. We have aligned the motor mounts etc. Any ideas, tips someone else may have done when they encountered a similar problem?

does the sonic drive side of the coupling only have 2 bolt holes?
if so there are guides that need to fit into the sonic coupling.

on the gear box side
edit
you might have to increase the thickness of the adaptor plate by 4mm as the aft end also has guides in the r&d coupling,and the inner side has a lip for alighnment to the gearbox coupling

link to sonic page
http://www.sillette.co.uk/documents/SonicCatDrive2.pdf

http://www.sillette.co.uk/sillette_downloads_page.html

[mheelis]

Hi, and Thanks, Atoll, it seems you have been down this road before? The Gemini needs 2parts R&D 910-21 which are bolted together with a metal square bar between them, we have removed this and are having a new one machined 4mm larger with all the recess's. This should bring it into a gross alignment which will be fine tuned with feeler guages ? fingers crossed it will be close enough.
Thanks again for the response.
"Cheers" Gemini 34.

[atoll]

Originally Posted by mheelis

Hi, and Thanks, Atoll, it seems you have been down this road before? The Gemini needs 2parts R&D 910-21 which are bolted together with a metal square bar between them, we have removed this and are having a new one machined 4mm larger with all the recess's. This should bring it into a gross alignment which will be fine tuned with feeler guages ? fingers crossed it will be close enough.
Thanks again for the response.
"Cheers" Gemini 34.

yes I have a prout 37 cat with a sonic mk1.
and yes increasing the adapter plate/bar thickness should do the trick.

getting exact alignment Is quite difficult but the flex coupling is quite forgiving!

best thing to do is to measure the gap from one side of the output flange to the input flange,and measure at 90degrees,,180 deg,270deg,and 360deg all should be equal if in alignment vertically and horizontally.

parallel misalignment is more difficult to correct but using a set square from the input flange (sonic) to output flange(gearbox) and turning 360 deg will show if the gearbox needs moving up,down, left or right,then re check parallel alignment.

checking for parallel misalignment is best done first