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-   -   Reverse only partially engaging (http://www.sailnet.com/forums/diesel/71271-reverse-only-partially-engaging.html)

scove 01-12-2011 01:29 PM

Reverse only partially engaging
 
Reverse is only partially engaging in our Kanzaki KM4A (transmission for Yanmar 4JH3E). When engaging reverse the shaft starts to spin in reverse but doesn't spin any faster as more throttle is applied. The problem is reproducible with the control cables disconnected. And sometimes it works just fine (but most of the time it does not). No problems in forward. Any suggestions on what this might be or how to troubleshoot this further or even fix it?

Faster 01-12-2011 01:37 PM

I've had similar situation with a Hurth gear.. it seemed the cam on the shift lever didn't fully engage the slider that moved the plates internally. I removed the lever/cam assembly and had a welder build up the cam a bit and it worked for years again after that....

Different gear, though...

MacGyverRI 01-18-2011 02:55 AM

try changing the fluid/filter and make sure it's going fully into gear.

JimsCAL 01-18-2011 10:16 AM

Sounds like the reverse clutch is slipping. May need a transmision rebuild.

Northeaster 01-20-2011 07:17 PM

1st, try unhooking the shiter cable from the trannsmission shift lever, and manually push the lever into reverse, to see if that makes a difference (the cable may need adjusting, if that's the case)


If that doesn't help:
If it is a cone clutch design, like the km2a on my older Yanmar 2GM, you (or a mechanical friend) can take it apart and apply a bit of valve grinding compound on on the drive cone, and then lap this against the reverse (and forward if you like) drive gears to take off any glaze that may be making it slip in gear. I did this on mine, and it has worked great for 3 years now.

It does not take alot of force to lap the drive cones in this way, so just a half dozen - a dozen or so (1/4) turns while applying pressure between them as you turn them. You are only trying to take off the glaze, and do not want to actually wear the parts with the abrasive valve grinding compound. Wipe / rinse off the compound when finished and re-assemble.

scove 01-21-2011 03:52 PM

Thanks Northeaster. I've managed to reproduce the problem with the cable disconnected and yes, it's a cone clutch design (or so I'm told). I'm not equipped to take it apart at the moment but will look for someone along the way (Grenada to St. Maarten) who can help with that.

Faster 01-21-2011 04:28 PM

Quote:

Originally Posted by scove (Post 689429)
Thanks Northeaster. I've managed to reproduce the problem with the cable disconnected and yes, it's a cone clutch design (or so I'm told). I'm not equipped to take it apart at the moment but will look for someone along the way (Grenada to St. Maarten) who can help with that.

Try the guys at the Boatyard in Tyrell Bay, Carriacou if you're not already past there.

scove 01-22-2011 11:11 AM

Thanks Faster. I checked there on the way down but unfortunately Uwe was out of town at the time and it's not on our itinerary on the way back :( I wish it was as it's a wonderful little island. We could have spent weeks there but other people's schedules have forced us to move on early on the way down and skip it on the way back. The more we're out here the more we are starting to really understand (at a deeper than intellectual level) Bruce Van Sant's rule for meeting people while cruising. "Pick a time or a palace, not both".

r.furborough 01-23-2011 08:30 AM

You have received some great information from Northeaster, but before tearing the transmission apart check the adjustment of the actual shift mechanism on the transmission and the detents that actually hold the mechanism is gear. I had a similar problem on my Kanzaki KM3A fitted to a 3GM30F. Turned out to be adjustment and a weak detent spring.

The transmission manual should have details of the adjustment specs along with a diagram.

scove 01-25-2011 09:52 PM

Transmission manual ... yeah, good suggestion but boat didn't come with one :( Need to try and track one down.

I'm going to start by changing the oil. I'm going to use my oil extraction pump to try to get the old stuff completely out and maybe do it a couple times to really flush it. See if that helps before getting more drastic. It should be done anyway.


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