Grinding noise from MS3C gearboxes in neutral

[dragoon]

Just came over to Cowes and note that there is now a grinding noise like it's not fully disengaged when I go into neutral on the port gearbox. If I flip the throttle it goes away. Have tried lubricating the cable, oil looks fine, not slipping and not overheating.

Anyone have any thoughts on this?

Cheers Paul

 

[scottie]

The design of this box incorporates two cone clutches with the cones running on a helix which if unrestrained will engage gear. There is a vee shaped groove between the two back to back male cones in which the selector runs so it bee that your neutral position is incorrect and may require adjustment
Try with the shift cable disconnected and see if noise goes
Usually the box will try to engage gear by itself as a first sign of trouble

 

[dragoon]

Thanks Scottie. Will try as you suggest.

Cheers Paul

 

[dragoon]

Adjustment all seems fine, and the selector is definitely moving comfortably into neutral.

It doesn't do it every time, and only a tiny increase in revs stops the noise. Does the gearbox use centrifugal action to move the cones into neutral? I'm wondering if the idle revs need to be raised slightly?

Cheers Paul

 

[scottie]

No http://www.marinepartseurope.com/PentaPictures500/7521.jpg

 

[dragoon]

An update. I went back to the boat yesterday, to try and diagnose a bit further. I disconnected the gear linkage and operated it by hand. it seems it's not related to the stop position. But now I listen, I'm not so convinced it's the box and seems to be coming from the bell housing.

With a little more research, I learn that there is a damper plate in there, and the noise is consistent with rattling springs. This also explains why it goes when I blip the throttle - centrifugal force I guess. I suspect I'm going to need to change this plate though. A few questions.

- how long will the rattly plate last - i.e. With the few trips I make, is it likely to last until the end of season, and what does a worst case failure look like?

- I read that these plates are not Volvo made, but are an OEM supplied part. Does anyone have details of the OEM manufacture and part number? From what I can see this damper was fitted to a lot of engines and hasn't changed across the 40x range, except for being superseded by a replacement part at some point. Any guidance or experience here appreciated.

Feedback very much welcomed.

Cheers