Transmission Mystery!

[Scott T-Bird]

I described earlier this year how I pulled my tranny out. I eventually took it to Mack Boring and they did a rebuild, essentially they replaced the drive cone which was worn. I have a Yanmar 1GM with a Kanzaki KM2A transmission. Happily, we finally put the boat in the water and yesterday I was able to check it out. The yard had put the boat in the water and started up the engine but had not run it in gear having just pulled it over to a slip. The first thing I noticed was that when I shifted to forward the boat went in reverse and vice versa. The shifter on my wheel pedestal is essentially vertical in neutral, forward for forward and backward for reverse as is logical and it's labeled that way. So I took it for a spin and it seemed like when I shifted the lever backward to run the boat forward, the normal rpm never got developed and it felt very sluggish. The boat ran smoother when going backwards.

So I complained to the yard thinking they positioned the linkage wrong. But the response was that there is only one way to position the linkage at the shift lever on the transmission. The mechanism connecting the gear shift lever to the pedestal was never touched - no reason to. I called Mack Boring. Their response is that there is only one way to install the drive cone. As to the shift lever, it is at neutral when the lever is at an angle of 45 d angled up and toward the drive shaft. When in forward the shift lever should be moved down in the direction of the drive shaft and the position would be near horizontal, when in reverse the shift lever should be moved up (toward the engine) and the position would be near vertical. They suggested that we observe if this is the case.

So today that is what we observed. The shift lever is consistent with the way Mack described it except that the engine performance is not consistent with the real forward and reverse. Here's where I'm confused. Today, I spoke with 2 service guys at Mack Boring (one was out of town but did make a call to me). The first one said that there is a different ratio for forward and reverse, the other thought that the gear ratio is the same both ways. I think it is different. My boat yard manager pointed out the high pitch whine that occurred only when the transmission is engaged in the (new) forward position. He said that whine is consistent with 'gear reduction' for reverse and says that it is noticable on virtually every boat he operates. When engaged in the (new) reverse, the engine sounds like it normally should sound for forward. The manager also noticed a distinct performance difference like I did. When he mentioned the distinct engine sounds, I realized what had seemed odd to me when I tested it out last night as well (but I couldn't put my finger on it at the time). After we discussed these things at the boat is when I called Mack Boring again, and it was the 2nd guy who was skeptical that there is a performance difference or a different pitched engine whine between forward and reverse. However, he did ackowledge that I would know my boat!

BTW, I didn't change the prop either, but it strikes me that if I were to change the prop to the opposite rotation, then everything should work perfectly normal with no need to revise any of the linkages. The tranny was rebuilt several years ago ... is it possible that they changed the prop at that time AND modified the linkage at the shift lever on the tranny?? So now, the shift lever is normal but the prop rotation is wrong?? It is a confusing problem.

Both Mack and my yard are being cooperative but the wasted time is distressing. Mack did suggest using a (whatsitcalled) photo-timer (can't remember the term) to guage the rpm of the engine and the rpm of the shaft to verify the gear ratios in forward and reverse. The yard is not sure they have one that works and will distinguish a difference between forward and reverse. We're working on it again tomorrow. The expected ration in forward would be 2.62:1

Any thoughts would be greatly appreciated!! Pictures show engine pulled out during the winter. I can't really tell the position of the shift lever in these photos.

 

[Scott T-Bird]

BTW, the problem is still that when the pedestal lever is shifted to forward, the tranny shift lever is shifted to reverse and vice versa. It is confusing because this mechanism was not touched during the whole ordeal. It only seems logical that previously, the tranny shift lever was operating backwards somehow, but we can't figure out how that could have been since it only can be installed one way.

 

[Ross]

Study the linkage arrangement some more. All you need to do is lead the cable from top to bottom or from left to right instead of from botton to top or from right to left to have this sort of change.

 

[Rich Stidger]

I think you have TWO problems

First, I think Ross has the solution to the shift lever direction issue. Changing the linkage arrangement will reverse the motion. Do you have any pictures of the engine before it was pulled for the transmission rebuild? Maybe those would show the cable configuration.

Second, it sounds like the correct forward (shift lever pointed toward the shaft) produces the transmission ratio for reverse. Take Mack's suggestion of getting a photo-tachometer and measuring the engine rpm at the front drive pulley and the transmission output rpm at the coupler. Do this for both the forward and reverse engagement.

Then get back to Mack with the results.

I don't believe in coincidences. If the transmission is behaving differently after the rebuild, something must have happened to cause that effect.

We'll all be waiting to hear the results!

 

[RichH]

Ross is probably correct. The linkage has probably been reversed.

 

[Maine Sail]

Problem...

The problem could be that when Mack Boring removed the shifter arm from the tranny, to pull the case apart, they put it back on 180 degrees out facing the engine as opposed to facing aft?

There looks to be a gold sticker with green arrows on the transmission housing. They appear to show to rotation of the shifter shaft for forward & reverse. When you put it in forward and the shaft moves the way of the arrow points then the problem is internal. When you move the shifter and the shaft moves opposite the sticker the problem is linkage.


If the arm was reversed:

1) Loosen bolt on shifter arm.

2) Slide shifter arm off spline and almost 180 to align with the blue line..

3) Tighten bolt and connect shifter cable..

 

[Scott T-Bird]

No, the linkage couldn't have been reversed because the cable and the rod would then have come from the bottom, thru the hull. In my mind, the only thing that could be reversed is inside the tranny that causes the gear reduction for reverse. What would that be? The throw on the shift lever (at the tranny) is correct for forward, the rotation of the shaft is correct for forward (clockwise when looking at the prop from the rear or counter clock when looking from the engine toward the shaft log), the boat moves in forward ... the gears behave as if it is in reverse. I agree, the photo tach will tell the story. The problem is that the yard may not have one that works, and Mack Boring is reluctant to make a trip just to do that. Between them, somebody has to work it out. I'll have to force that issue this morning.

Personally, I think the issue is inside the transmission ... which means pulling the boat out, removing the front woodwork and trim, pulling the engine off the new motor mounts and setting it on the cabin floor, removing the tranny and starting from scratch. All wasted time. I'm inclined to think that I can quickly solve the problem by simply replacing the prop with a new one that has the opposite rotation. Is that viable? I wouldn't have to change anything else if this solution works.

 

[Maine Sail]

Scott...

No the linkage couldn't have been reversed because the cable and the rod would then have come from the bottom, thru the hull.

Scott,

You're thinking in the wrong planes (see post above)..

P.S. I have the PDF version of the Yanmar service manual on my computer which includes the KM2A transmission and the orientation for the shift lever of the KM2A is identical to those photos above. Mack Boring or your yard screwed up. The problem is NOT internal. I just looked a the internal gear diagram and it is impossible to assemble it to work backwards as the gear splines would not even mesh.

Flip the shifter arm to about 1:30-2:00 position and you should be running in no time.

 

[Scott T-Bird]

Thanks for reply MS, I haven't read it yet ... we must have been typing at the same time ...

 

[Maine Sail]

Thanks for reply MS, I haven't read it yet ... we must have been typing at the same time ...

I'll be glad to send you the service manual but it is a BIG file (almost 15 mb). Just PM me you email address..

 

[Scott T-Bird]

Thanks for that diagram ... that is exactly how the linkage and the shift lever is assembled now and it is the only way it could have been assembled in the past. As I said in the earlier post, for the cable linkage to be assembled wrong, it would have to come up from the bottom which is simply not feasible.

As I said before, the throw is correct for forward, the prop rotation is correct for forward, the boat moves in forward, but the engine output performance behaves like it is in reverse. MS, do you understand what I mean by a distinguishing difference in pitch when the tranny is in reverse as opposed to forward?

 

[Maine Sail]

As I said before, the throw is correct for forward, the prop rotation is correct for forward, the boat moves in forward, but the engine output performance behaves like it is in reverse. MS, do you understand what I mean by a distinguishing difference in pitch when the tranny is in reverse as opposed to forward?

Ok now I'm confused??? here's what you said in the original post..

The first thing I noticed was that when I shifted to forward the boat went in reverse and vice versa.
So I complained to the yard thinking they positioned the linkage wrong. But the response was that there is only one way to position the linkage at the shift lever on the transmission.

Huh.....????

Your photo shows the shifter arm facing forward at 9:00 and it should be at about 2:00. Your original post description fits the arm being at 9:00 yet your most recent post says that it spins in the correct direction now just sluggish??

 

[Scott T-Bird]

MS, it is a little confusing as we are typing at the same time ... I do have the SELOC manual for all Yanmar engines in my vintage and it is very helpful. One question about the photo I included. The photo was taken before the tranny was removed for rebuild ... I can't tell but does the photo seem to show that the shift lever is 180 d off? That would explain everything. It would explain to me that it was assembled backwards sometime in the past to install a prop with the opposite rotation. Does that sound feasible to you? I'm still thinking that my solution would be to change the prop.

 

[Maine Sail]

As I said before, the throw is correct for forward, the prop rotation is correct for forward, the boat moves in forward, but the engine output performance behaves like it is in reverse. MS, do you understand what I mean by a distinguishing difference in pitch when the tranny is in reverse as opposed to forward?

Ok now I'm confused??? Here's what you said "before" in the original post..

The first thing I noticed was that when I shifted to forward the boat went in reverse and vice versa.
So I complained to the yard thinking they positioned the linkage wrong. But the response was that there is only one way to position the linkage at the shift lever on the transmission.

Huh.....????

Your photo shows the shifter arm facing forward at 9:00 and it should be at about 2:00. Your original post description fits the arm being at 9:00 yet your most recent post says that it spins in the correct direction in relation to the gear shift position on the pedestal but now just sluggish??

As I said in the earlier post, for the cable linkage to be assembled wrong, it would have to come up from the bottom which is simply not feasible.

In your situation this is NOT true and not always the case. If your shifter arm (blue line in edited photo) was removed from the splined shaft, and put back on in the wrong position, 9:00 vs. 2:00, the cable would still come from the same direction (above) yet the tranny would shift backwards when you hit forward.

With the shifter arm in the 9:00 position moving to forward on your pedestal is actually reverse on the tranny.

With the shifter arm in the 2:00 position the forward position on the pedestal is forward on the transmission..

In both situations the cable still comes from above. Once you move the shifter arm on the transmission through 12:00 everything reverses operation..

Your whine may be caused by the forward gear not completely engaging due to incorrect orientation.

 

[Witzend]

It would seem likely that MS has the correct solution, but that the boat yard would have had to bend the bracket that the cable mounted to. In your pic it is vertical allowing for proper alignment to the shift arm as installed by your yard. MS diagram has it at an angle for proper alignment with the shift arm at ~135deg from where it is installed now. Look at this bracket, can you tell if it has been re-bent. Ask the installer it they re-bent it. Also MS picture has another piece to the bracket that does not show in your pic. Has that been inadvertently left out?

 

[Tim R.]

Scott, changing the prop will only compund the problem. Spin the shift lever on the tranny 180 and see how that works. Also, you can put the tranny in gear, decompress your cylinders and turn the engine by hand to check the ratio.

 

[Scott T-Bird]

I know that the linkage at the wheel pedestal is a separate issue which can be resolved, so I am trying to resolve everything from the shift lever to the prop ... I'm still believing that at some point in time, somebody changed the prop to the wrong turn and then resolved it by changing the shift lever so the gear would be consistent for forward and reverse. I could chech this out I suppose by feeling the prop ... maybe I can find a photo that shows the prop close enough to look at the rotation. I'll look and post one.

 

[Maine Sail]

Pardon my

Pardon my poor MS Paint skills.. The cable still comes from above in both situations yet one is reverse and one forward..

Proper rotation for your transmission is:

Forward = clockwise when viewed from the stern
Reverse = counter clock wise when viewed from the stern

This means you should have a right hand (stamped RH) rotation prop.

 

[Ron20324]

How fast does the boat go in forward- or have you had it on the water?

 

[Scott T-Bird]

I think you are helping me to resolve this. The 9:00 position would be forward as the shift lever was positioned before the drive cone was installed this year. The 2:00 position is neutral as the shift lever is now installed. The shift lever on the pedestal is now reversed. The tranny and the engine had a re-build about 10 years ago when this could have been messed up and the shift lever reversed as a solution. I couldn't know for certain. What I don't understand is the specific parts that cause the gear ratio in forward and reverse. Is there supposed to be a different ratio? I think I remember the first guy form Mack saying that forward is 2.62:1 and reverse is 2.13:1. If this component is reversed somehow it explains why what should be the correct rotation is actually reverse.