Yanmar 3GMF - Removing The Transmission

[Joe Mullee]

I have a 1983 Hunter 34 with a Yanmar 3GMF engine. I've done everything anyone has suggested to stop the knocking between 1100 - 1800 RPM's while in forward and it won't go away. In fact it's getting worse so I think it's time to have the Kanzaki transmission rebuilt as others have suggested. My boat is on a mooring at Dinner Key Marina in Coconut Grove, FL.

Here are my questions:
1) Do I need to haul the boat to remove the transmission? I'm wondering how the shaft is handled during the removal process.
2) Is removing and re-installing the transmission something I should have a Yanmar service technician do? Besides basic winterization and scheduled fluid changes all I've done is basic replacing of the fuel pump, alternator, impellars, belts, starters, mixing elbow, and maybe a few other simple tasks.

Thanks for any advice.

Joe Mullee

 

[woodster]

how much overhead do you have in the engine room...also if you get it free of the block do you have the room to maneuver it out of the hole and get it topside....you should be able to split the coupling on the shaft to the tranny by taking out the four bolts that hold it together and slide the shaft aft ...that will give you some room ....kloudie may have some things to share about this as well

 

[Cool_Change]

Hi. Removed mine for rebuild on a 2000 H340. Shouldn't have to haul out provided coupling to shaft comes apart and you have room to slide that down so the transmission can then slide off the spline gear from the engine. In my case I also had to loosen then engine mounts and slide it forward. The transmission isn't overly heavy...can carry by hand once out. While it was off being worked on I also took the opportunity to replace motor mounts...you might consider same.

 

[Claude L.-Auger]

Hi. Removed mine for rebuild on a 2000 H340. Shouldn't have to haul out provided coupling to shaft comes apart and you have room to slide that down so the transmission can then slide off the spline gear from the engine. In my case I also had to loosen then engine mounts and slide it forward. The transmission isn't overly heavy...can carry by hand once out. While it was off being worked on I also took the opportunity to replace motor mounts...you might consider same.

I removed mine on a mooring...by myself. I even removed the flywheel and clutch plate. You'll need someone's help to re-install it because of the engine angle and the cramped space provided by the access in the stern cabin. As mentioned, undo the coupling and slide the shaft back. Fairly simple job to remove but you'll feel like a pretzel when doing it. Hope the pics help. Good luck.

 

[kloudie1]

Interesting.. Claude, how did you get it out? the access hole aft of the engine?
Two other "hi-jack the thread" questions: What is the canister with water hose to port of the engine bay? what are the angle iron "runners" just above the flex engine mounts?
Joe, Note tthat Claude pulled and replaced the rear main seal on the engine.. While you are in there, that is probably a great thing to do too.

 

[Claude L.-Auger]

Interesting..

Claude, how did you get it out? the access hole aft of the engine?
Yes and put it back through the same access hole. But as mentioned I needed help to support the weight from the top of the engine.

Two other "hi-jack the thread" questions: What is the canister with water hose to port of the engine bay?
When I bought the boat it had dual refrigeration systems: 110V and an engine driven compressor. What you see is the heat exchanger for the engine driven system. Seawater went through that before going to the engine. This has now been removed.

What are the angle iron "runners" just above the flex engine mounts? The engine driven compressor was mounted on the port side and had a hefty iron support bolted to an angle iron mounted on the engine mounts. I always thought the starboard side angle iron was there only to facilitate engine / shaft alignment by making the height even with the port side.

Joe, Note tthat Claude pulled and replaced the rear main seal on the engine.. While you are in there, that is probably a great thing to do too.

.

 

[Fast Ed]

My trans was removed by a professional, and here is how he did it. A small hydraulic scissor jack was placed on a board under the engine. Engine mounts were loosened and the engine jacked off its mounts. This provided room for the trans to slide aft after the coupling was undone. He had it out in under an hour!

 

[Charles Erwin]

Are you certain the gear box is the source of your symptoms?

Have you definitively ruled out the flex plate, motor mounts, shaft (for run out) and alignment, coupler, cutless ? Is the propeller straight (no blade deformation), prop balanced, and solid on the shaft ?

Understand it is possible the gearbox is the culprit but It is extremely unusual that 'knocking' - in a limited and definite RPM range - implicates the transmission.

And -- it would be a great disappointment to spend time and treasure on the gearbox only to find out it is not the source of your symptoms.

Charles

 

[Richard Bryer]

I am with Charles here- Mine developed a knock at about the same range a few years ago. I changed the prop shaft from the old bronze to ss and it went away. According to the prop shop, the run out was borderline on the old shaft, but I wonder if the old bronze ones develop some sort of flexibility as they get old