URGENTLY in need of transmission advice/ideas

BobnLesley

BobnLesley

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We have a Yanmar 3GM30F and traditional propeller and shaft gearbox fitted; the engine starts and runs perfectly and reverse gear is equally good, but when we engage forward, we have a problem: At tickover it too is OK, but once we start to build-up the revs 50% of the time it works fine, but on the other half we get a shuddering vibration (to varying degrees) as the revs increase until about 16-1700rpm, whereafter it's OK again?

It's not a new problem, but having just relaunched - new cutlass bearing installed and stuffing box re-packed - it seems to have worsened from an occasional irritation to a serious danger; the worst incidents of shudder/vibration are much worse and all we can do is return to neutral and re-engage repeatedly, until we get a relatively smooth speed pick-up, a real pants-browner this morning as we were holding-off awaiting a lifting bridge in a 2 knot tide!

I can't see any problem with the gearbox/shaft connection, there's nothing around the prop or shaft itself and the engine mounts all look OK; any ideas?
 
Almost certainly a problem with the cone clutch within the gearbox. There's quite a bit in previous threads, including this one that gives the three options to look at sequentially:

http://www.ybw.com/forums/showthread.php?206387-Yanmar-2GM-gearbox-trouble

I had to strip mine down 4 or 5 years ago because it had exactly the same symptoms (especially with the gearbox oil warm - it worked fine if started from cold.

With the gearbox on a bench it's a quick job to re-grind the cones using valve grinding paste... so you should find the cost of materials is next to nothing, but a minimum of 2-3 hours of skilled labour may be needed.
 
I don't have a shaft-drive so this is pure conjecture ...... but if you had a misaligned or bent shaft this might manifest itself as an out-of balance vibration. If the cutlass bearing/stuffing box were worn perhaps they could cope with the misalignment but the new bearing does not have any play in it so the vibration is now effectively worsened and is transmitting through the hull even worse than before.

That sounds like it might have some engineering logic and would perhaps explain the symptoms that new bearings have made things worse?

Richard
 
BobnLesley said:
Thanks for the quick response guys, I'm getting the spanners out now to start by checking the cable's operation, clamps, etc. though I would have expected a problem with that to have effected forward and reverse gears equally? Will report back in a couple of hours; I really don't fancy a gearbox strip.
Read more at http://www.ybw.com/forums/showthread.php?206387-Yanmar-2GM-gearbox-trouble#WXywACelt8zPG8PX.99
Click to expand...
I bought from AV Mounts 1/2 Peachments price for the same thing
http://www.avindustrialproducts.co.uk/silent-marine.htm
 
You say that you have had the stuffing box replaced. Is this an old fashioned one with packing or is it a FACE seal one?

If the later, it may be that the spring pressure on the face seal is too great and it squeezes the moisture out of the face seal - result is vibrations much larger than you would ever expect. Action - re set the spring pressure on the face seal.

If its the conventional type with packing - ignore.

Good luck
 
First stop engine mounts. Could be as simple as loose mounts. Gearboxes are generally trouble free and if the oil is clean and up to marks doubt there is anything wrong internally.
 
Hi

If you have a flexible joint between your propshaft coupling and gearbox flange e.g. the R&D joint or similar, make shure that it has been reassembled correctly. If you get the bolts wrong they can lock the flexible joint when in forward (however the flexablity will return in reverse as the joint is pulled out.

The result with my engine when assembled wrongly was a bad "shake".

Good luck
 
Disconnected the operating cable to take that out of the equation and manually operating the shift lever, it seems that there is a nasty noise coming from inside the gearbox. Having been directed toward the local marine transmission guru, I've removed the gearbox and damper plate and taking all to him tomorrow morning, I'll let you know what we discover.
 
r_h was on the money with that old thread: The cone clutch and selectors are f****d and the local transmission guru's advised that we also replace bearings and the flywheel damper plate too whilst it's all in pieces - $1300 for the parts; I thought it was Volvo who were supposed to be expensive for bits?. Looking on the bright side, if it'd broken in a week or so's time, we could've been out in the boondocks of the Bahamas with no drive, then we would've been in deep do-dah!
 
There's not a huge amount of labour time in stripping it down and reassembling the gearbox (even if getting it in and out of the boat is a pain).

I'd be tempted to get them to spin the selector fork 180 degrees (they tend not to wear as much in reverse), resurface the mating faces of the cones with valve grinding paste and reassemble it with the existing parts.

You'll be amazed at the difference it makes and may not need the new parts for a number of years (or until after you've found a decent secondhand gearbox).

On the other hand, if you're planning on sailing to some very remote parts of the world, I'd understand wanting the peace of mind to get it all fixed.
 
...On the other hand, if you're planning on sailing to some very remote parts of the world, I'd understand wanting the peace of mind to get it all fixed...

That's us, we've already contemplated the 'what if' had the gearbox continued for another couple of weeks and then died in the Bahamian out-islands.
 
r_h said:
There's not a huge amount of labour time in stripping it down and reassembling the gearbox (even if getting it in and out of the boat is a pain).

I'd be tempted to get them to spin the selector fork 180 degrees (they tend not to wear as much in reverse), resurface the mating faces of the cones with valve grinding paste and reassemble it with the existing parts.

You'll be amazed at the difference it makes and may not need the new parts for a number of years (or until after you've found a decent secondhand gearbox).

On the other hand, if you're planning on sailing to some very remote parts of the world, I'd understand wanting the peace of mind to get it all fixed.
Click to expand...

Very timely as there's a thread here with a question about hours of labour. The guy said he was charged 4 hours for the workshop element, I assume he'd removed it and delivered it to the workshop.

I must admit 4 hours sounded excessive to split, lap and reassemble. Do you know how long it might take in a workshop for a KM35P gearbox (ex. 40hp Yanmar 3JH4E).

Not a job I've done but it looked more like 1 hour than 4 when looking at the manual.
 
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Bob

Was there nothing here? (NOTE I've just realised r-h has possibly given you these links but will leave the post here as it may be a bit more information)

Yanmar 3gm30 rough vibration in forward gear - Marine Engine
www.marineengine.com › ... › Diesel Inboard Engines Forum › Yanmar
Jul 3, 2008 - 6 posts - ‎3 authors

"Our 3GM30 has recently developed a very rough "shaking" vibration when engaging forward gear in idle to moderate rpm. Applying full throttle ...

https://www.google.com.au/#q=Yanmar+3GM30F+vibration
 
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