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Discussion Starter #1
So this is my first inboard engine ever on a boat, let alone on a sailboat. It's a 13hp Yanmar 2gmf that is in great shape overall.

When I motorsailed her home I noticed something finicky about shifting. When I was fully throttled (regulated) down to about 830-850RPM and I shifted into gear I didn't hear a nice thunk sound and as a throttled up to about 900-950 the boat seemed to just drift then I felt it catch and start moving forward. I was worried the tranny was finished (maybe it is) and was PARANOID the entire trip home lol (65nm~). I had it do this again when I was testing it out in the bay before coming into my slip when shifting to reverse.

I noticed it would catch when throttling up. So instead I shifted to neutral (which always works fine) turned the engine up to about between 900-950 RPM (the gauge is tight to split 50rpm by eye) which is still BELOW the 1000rpm maximum I've heard to shift at, and shifted into gear and it went perfectly fine forward and reverse like that.

So I'm wondering if this is normal, I'm assuming it's not, and it's a sign the tranny is wearing out. I'm also assuming that since it does shift fine BELOW the "maximum" level the manufacturer recommends I can continue to use it that way for the summer (we are weekend warriors so there won't be more than 20hours or so on the engine by fall I bet). In the fall, if this sounds like it should be done, I can pull the tranny and bring it to a Yanmar dealer for a rebuild for peace of mind. Unless someone has any other ideas?
 

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I hope it's just linkage, but it sounds like you have a separate throttle and shifter. You might try disconnecting the linkage and manually shifting at the transmission, while tied to the dock. Just to be sure the throw is in the proper place. Most require a given amount of travel until a spring pushes the gear pack into place and further travel is of no consequence.

It's possible the reason it works better at higher rpm is there is greater friction, causing the worn plates or thrust bearing to expand ever so slightly and catch. If that's it, you could find it won't expand quite enough at any moment.

I would try any testing with the transmission stone cold.
 

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I had the same symptom with the same engine. I was worried that the clutch was worn & slipping until I discovered that the P.O. had filled the trans with ATF while the manual called for engine oil in that particular trans.

Changed to the correct oil and the problem went away.

ATF is commonly used in other Yanmar transmissions so it's an easy mistake to make.
 

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SloopJonB makes a good point. I would try changing the transmission oil and see if that makes a difference.
 

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Yikes. Yes, the wrong fluid could be a problem. Can't wait to hear if that's it.
 

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Discussion Starter #6 (Edited)
Thanks everyone, top of my checklist for the boat this week was a tranny drain and refill. Luckily ATF is bright red so I should be able to spot it quickly. If it is full of ATF I will drain\refill it a few times to get it out as I'm sure I can't suck out all of it on the first try. I'll snap a pic of the transmission plate to confirm what should be in it.

EDIT: pre-emptively picked up some Castrol 30w non-detergent oil as I've heard that is most likely what is required. I'll double check the nameplate before I dump it in though.
 

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Discussion Starter #7
UPDATE: I'm at the boat now. Finally got to the tranny. It's definitely a KM2A kanzaki transmission. Confirmed on the name plate.

So after much research here's my theory on these trannies slipping...

I searched Google and all over people say put SAE 30 oil in it. Even my yanmar manual says SAE 30w and that's it. I took a pic of the tranny plate and sure enough it clear as day says SAE 20/30 HD. The HD is IMPORTANT.

The fix for these cone clutches slipping is to gut the gearbox and devarnish the cones/gear cups with valve lapping compound. Ok. But why are they varnishing?

SAE 30 oil regular specifically says NON DETERGENT on the bottle. SAE 30 HD, well the HD stands for HIGH DETERGENT (not heavy duty like you might expect).

What does detergent do? Helps prevent scum and varnish.

So my theory is anyone with this issue is running into it because the wrong oil has been used because the manual (or at least alot of them) are wrong.

I just drained my box. It was overfull but was running SAE 30. I asked the PO and he said he used what the manual says... Not his fault of course. I'm refilling now with a detergent SAE 30 and will run it a bit then drain and refill repeat a few times to try and flush it.

Anyways, thoughts?
 

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I’m hoping fresh oil makes a difference, but going from 30 to 30HD doesn’t seem like a slipping remedy.
 

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Discussion Starter #9
I’m hoping fresh oil makes a difference, but going from 30 to 30HD doesn’t seem like a slipping remedy.
At least with the HD it can hopefully start breaking down the varnish IF there is any on the cones and cups. At least at this point the right stuff is in. If I have to pull it this winter and tear it down I will. For now it shifted immediately and smoothly each time while idling at the dock.

Part of the problem I think as well was too low of an rpm at idle. Yanmar recommends around 850 to 975. I had a good look at the idle today while cycling the new oil and it was barely chugging along at 800rpm. I dialed it up to 950-975 area and not only does the engine sound better but the shift was quick and immediate without and slipping (or jarring).

I'll find out next time off the dock either way lol. Like I said it didn't consistently slip, but a few times it didn't hit in gear all the way until powered up a bit. I may just be making a mountain out if a mole hill but for sure found out the wrong oil was in use.
 

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Fingers crossed. Sounds positive so far. The higher RPM may be creating more friction heat and more wort expansion. I think I may have said that already. If so, it could work for a while.
 

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Discussion Starter #11
Fingers crossed. Sounds positive so far. The higher RPM may be creating more friction heat and more wort expansion. I think I may have said that already. If so, it could work for a while.
Don't they all just "work for a while" anyway ? Lol. I think for now I'm ok because I'm in manufacturer spec. If it does it again and needs more rpm we will know for sure what is up. I'll update if anything changes!
 

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Discussion Starter #12
Well I've put over 200nm on my boat since first changing the tranny oil. Several dockings, lots of flat water and heavy chop motoring. So far everything has been running perfectly. She snaps in and out of gear beautifully and not a single slip.

I've changed the oil 3x since and each time it comes out cleaner. I thought I'd post in case anyone else runs into this

Idle speed: 900rpm~
Oil: 30w HD
Quantity: up to the tiny notch on the bottom of the dip. Or about 8oz.
 

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Glad I could help. :wink
 

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Discussion Starter #15
Update: 2 years and over 5000nm later on the transmission. We have only had 2x incidents where I caught the transmission slipping at low RPM. One of them was when I was leaving a lock and I drifted alarmingly close to the gate and one was while anchoring in a very tight oyster creek around crab pots and cross winds. Although it was only 2x over many thousands of miles they did remind me that after nearly 40yrs it's just due for a rebuild. The oil change and flush sure bought time though!

I'm pulling the transmission today while waiting on a new rudder to be fabricated anyways. An excellent rebuild shop is near me in NJ so I figure why not just get this done and stop rolling the dice. Especially while staring down a long motor up the Hudson river then Erie canal then st Clair river.

Price of new needle bearings, seals, cones, rebuilding the shift mechanism and various other usual wear spots bring it back to like-new condition with a 2yr warranty is 1700$. Seems fair after almost 4 decades of service.
 

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Update: 2 years and over 5000nm later on the transmission. We have only had 2x incidents where I caught the transmission slipping at low RPM. One of them was when I was leaving a lock and I drifted alarmingly close to the gate and one was while anchoring in a very tight oyster creek around crab pots and cross winds. Although it was only 2x over many thousands of miles they did remind me that after nearly 40yrs it's just due for a rebuild. The oil change and flush sure bought time though!

I'm pulling the transmission today while waiting on a new rudder to be fabricated anyways. An excellent rebuild shop is near me in NJ so I figure why not just get this done and stop rolling the dice. Especially while staring down a long motor up the Hudson river then Erie canal then st Clair river.

Price of new needle bearings, seals, cones, rebuilding the shift mechanism and various other usual wear spots bring it back to like-new condition with a 2yr warranty is 1700$. Seems fair after almost 4 decades of service.
my 3GMF engine is being replaced and our KZ2 transmission. Is also being reconditioned. Same as yours $1300 . This includes the damper plate
 
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Discussion Starter #17
my 3GMF engine is being replaced and our KZ2 transmission. Is also being reconditioned. Same as yours $1300 . This includes the damper plate
There's always something to do it seems. Speaking to my parts guy and the rebuilder these old km2a transmissions are one of the most expensive to rebuild. A few years ago the cone clutch soared in price and bas been sitting at 1100$ just for that alone. Apparently it's s magical piece of brass. It's still cheaper than a repower though I suppose.
 

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I always found it a pain to get the oil level just right when changing the transmission oil. It's supposed to just hit the notch on the dipstick when screwed in. I always overkill and then have to remove some.

A couple of changes ago I ran into this problem and was looking for an easy solution. Noticed a bottle of liquid hand soap in the counter. The little pump fit right over the dipstick hole. I cut the tube to match the length of the dipstick mark. I set this over the full hole and pump until it won't pump anymore fluid and the level is right where it needs to be. The pump now lives in the tool drawer.

Just felt like sharing.
 

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Is your transmission or an exact replacement out of production? I haven't had any luck with rebuilds and I think you're going to be a long way away, by the time you may need to collect on that warranty. That certainly doesn't mean this won't work.
 

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.....The little pump fit right over the dipstick hole. I cut the tube to match the length of the dipstick mark. I set this over the full hole and pump until it won't pump anymore fluid and the level is right where it needs to be.
That is a very cool trick!!! I am going to try to adopt it. I think I'll need to fashion a longer tube, rather than cut one short.
 
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