http://www.waterwaysworld.com/questions.cgi

[Patrick Vale]

Dear all,
I have a beta marine 38, with a PRM delta gearbox (no input shaft spline wear) driven by an R & D 'extra dampening' drive plate. Coupled via a double-cardan/constant velocity joint (from a london taxi propshaft), through a plumber's block to the stern bearing.
When engaged in gear, at tick-over (wound down to 550rpm), there is a distinct 'clonk-clonk-clonk' coming from the region of the gearbox.
At higher engine speeds, this noise seems to go away, although that could just be the engine drowning it out.
The shaft/cv join moves freely (with the force expected to drive a prop in water) by hand in both directions. The engine is angled down slightly on its mounts (adjustable screw-nut ones) so that the double-cardan input is slightly off-set.
My question is - should I worry about this? I have no nylon coupling between the gearbox and the prop/cv-join input shaft, so is this likely to just be 'clonky plumbers block'?
Should I raise the tick-over? It was wound down when the engine control lever insisted on increasing the rpm prior to engaging gear - there is now a correct control lever. I think the rated tickover is 750rpm. I will increase it.
Many thanks,
Patrick Vale

 

(cross-posted to http://www.waterwaysworld.com/questions.cgi)

Which seems to have replaced the title - should read 'Drive train clonking in gear'.

Edited June 3, 2013 by Patrick Vale

[Mike Tee]

Check page 31 in the manual -

 

Drive plate rattle at tickover: Check engine rpm (must be 850rpm min. in gear)

[MtB]

Sounds to me like a failing drive plate.

Why do you have an 'extra dampening' drive plate in the first place? Is there a history of drive plate probs?

 

MtB

[Bee]

First thought is the taxi propshaft, if you have conventional universal joints they should be set at 90 degrees to each other otherwise they will not work properly, umlikely to be the plummer block, not much to clunk there, apart from that I would just try to check for play and also fore and aft movement in every nut, bolt, key and joint you can find.

[RLWP]

Check page 31 in the manual -

 

Drive plate rattle at tickover: Check engine rpm (must be 850rpm min. in gear)

 

Well spotted! a very low tick-over sounds terrible

 

Richard

[Patrick Vale]

Thanks everyone for the replies - that would explain why the tickover is rated higher.

 

Mike the Boilerman - the PRM delta (predecessor of the prm 150) has a very finely toothed/splined input shaft, that is prone to wear if 'buffetted' around by the drive plate/hitting rocks etc.

The 'extra dampening' drive plate has a nylon bushing in a sort of web shape that transmits the drive in a 'springy' way - much more so than standard drive plate metal springs, which is supposed to lessen the likelihood of wear on the input shaft.

 

So I'm told!

 

Thanks Mike Tee for the manual spot! Really appreciated!