Hi all,
A mate of mine has a Yanmar 2GM20 in his S&S 34 which has been partially submerged, ruining the starter motor and causing significant corrosion of bolts etc.
He needs to remove the gearbox assembly and has removed the 8 6mm bolts around the periphery of the housing containing the gearbox, but the assembly refuses to budge.
We are assuming there is nothing else we need to remove in order to extract the gearbox assembly, and that the problem is the splined shaft from the gearbox is frozen (rusted in) in the clutch plate.
We think the assembly is just like the attached pic.
Can anyone shed any light on this?
Are we missing something?
All suggestions greatly appreciated.
regards,
Allan
Just a thought; have you placed the transmission in the neutral position. If the transmission oil has not gone a milky colour I doubt water has got inside the gearbox to cause rust.
If you think you have removed all the bell housing bolts and nothing else is holding the gear box captive I would say the input shaft is rusted on the the drive plate/ flywheel / crank shaft..
If you think this is the case I would fill the void between the bell housing and the engine block with diesel and walk away for a few days you might have to keep repeating the process.
If the engine gear box is out of the boat .Id lay in side ways so the diesel and or CRC or some thing you like to soak into the shaft and drive plate
Block one of the holes in the bell housing roll it over so the other hole is above the input shaft and fill the bugger up come back in a week or so but make sure the shaft is covered.
You need to keep the input shaft soaking so it has a chance of releasing
Only Yanmars Ive worked on had hydraulic pumps mounted on the engine in small excavators.
So with out a drawing of the engine / gear box drive mechanism I'm a little vague
Select to expand quoteTKNick said..
Just a thought; have you placed the transmission in the neutral position. If the transmission oil has not gone a milky colour I doubt water has got inside the gearbox to cause rust.
Thanks TKNick - I THINK we've had it in neutral, I'll check that. You're right - water may not have got into the gearbox, but were taking it off because of the large of corrosion crud inside the bell housing.
Will post the outcome
regards
Allan
Select to expand quoteHG02 said..
If you think you have removed all the bell housing bolts and nothing else is holding the gear box captive I would say the input shaft is rusted on the the drive plate/ flywheel / crank shaft..
Yes, that's what we think HG.
If you think this is the case I would fill the void between the bell housing and the engine block with diesel and walk away for a few days you might have to keep repeating the process.
If the engine gear box is out of the boat .Id lay in side ways so the diesel and or CRC or some thing you like to soak into the shaft and drive plate
Block one of the holes in the bell housing roll it over so the other hole is above the input shaft and fill the bugger up come back in a week or so but make sure the shaft is covered.
You need to keep the input shaft soaking so it has a chance of releasing
Good idea - engines' still in the boat which makes reorienting it a bit more difficult, but it's worth trying.
Only Yanmars Ive worked on had hydraulic pumps mounted on the engine in small excavators.
So with out a drawing of the engine / gear box drive mechanism I'm a little vague
Thanks HG - we'll post how we go with this
regards Allan
There must be some sort of drive plate that the input shaft slides into thats rusted up.
Perhaps ring a yanmar dealers and ask for a price for a dive plate and ask a few questions? might give some sort of idea
www.sailnet.com/forums/gear-maintenance/40708-yanmar-2gm-tranny-separation-help.html
These guys ground off the two spokes on the vent on the bell housing and then use a socket to remove the drive plate so this would be your best solution 
Google is your friend 
from the above link
did the same job last week. billangiep is right, knock out a few spokes of the vent. Then you can get a number 12 socket in and unbolt the drive plate from the bell housing. I think there's six bolts. You'll need to turn the engine to line up each bolt with the hole you've made in the bell housing. Then the trannie will pop right out with some gentle persuasion. Then you've got a drive plate stuck on the spline. Some WD40 and a pipe should free it from the spline but my mechanic said 50% of drive plates break before they're unfrozen.
from the above link
from the above link
Select to expand quoteHG02 said..
What sort of out come did you end up with Datawiz?
Waiting on my mate to attack it next weekend - will keep you posted
Select to expand quoteDatawiz said..HG02 said..
What sort of out come did you end up with Datawiz?
Waiting on my mate to attack it next weekend - will keep you posted
There is a vent hole in the gearbox dipstick cap, so if it's been submerged, it will have salt water in the oil. Don't ask me how I know this.......
When you remove it ideally you should renew the bearings & seals, & deglaze the cones. Although since mine had a swim, the bearings & seals have lasted over 200 hours, but they're a bit noisy and it does leak a litttle when fully warmed up. It had quite a bit of corrosion inside, but still goes fine. But the deglaze was essential. They are very simple to work on, so long as you have a manual.
I agree that so long as all 8 mounting bolts are removed, it will be rust holding the shaft in the flywheel drive plate, there's nothing else. Neutral or not won't affect it.
Good luck with it!
Graeme
