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Md7a ms 191 mono shift reverse gear

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cdj

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"Hello,
Md7a is running great

"Hello,
Md7a is running great up until now.
Transmission will not go in to neutral while engine is running. Will shift to neutral while engine is off and stays in neutral with intermittent movement of prop shaft after starting engine.
I have removed control cable to trouble shoot.
Idle's at 800 rpm
Discovered the transmission leaks oil
Level got low, topped off.
I have the overhaul instruction manual and a parts catalog. Prices for parts at Marine Parts are shocking.

Has anyone had this problem and fixed it?

Time for a repower?

Thanks,
John"
 
It might be as simple as a re-shimming of the shift fork.
Screw 58, and shims 57. You might need to remove some shims in order to get the fork deeper into the V of the cone.
In worst case the cone has to be replaced.
 

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Thank you for the response. I replaced the dog and spring.
(part 52 and 53). It did not help. I cut off a small portion of the original spring and added it as a shim. This helped. It will shift into neutral from reverse but not consistently. Still cannot shift from forward to neutral. I am going to remove the extra spring I added and use shims as designed and see if that helps. I have also thought about making the groove deeper so the pin (part 55) will sit more firmly in place while at neutral. There is some slight sign of ware on the shoulder of the groove.

I located a transmission and various other parts from another MD7a with a damaged cam and will swap out the transmission if I have to but that is a last resort.

Thanks,
John
 
You have to be a bit careful.
The V-groove in the cone is NOT concentric with the cone.
If you were able to look at it all when assembled you would notice that the shift fork moves up and down.
To get the correct amount of shims, the box should be removed from engine.
Then remove shim and rotate shaft at same time. Just as the shift fork bottoms in the groove (resistance when turning), add one shim, and you are done.
The more shim you remove, the deeper the screw will go down and limit the fork going up. By 'adding' spring you may get a similar effect, but a dangerous way to go.
 
yes I discovered this. I started by adding too much extra spring and it would not move. I did this all without starting the engine. I removed the extra spring and put in a smaller piece. I "works" better but does not feel right. I remember how the shift felt when I first purchased this boat 2 years ago. Turning the actuator by hand it was a very positive snap into neutral. Now it is firm because of the extra spring tension but does not "snap" into place.

I'm curious which surface would be worn on the slide cone (part 25).

Also looking at the drawing again I'm now seeing spring and ball (part 47 and 48) maybe they play a part in this problem?

At any rate this seems like it is fixable with out replacing too many parts and maybe get many more hours out of this engine.

Thanks for your input.
John
 
Take out the shift mechanism and insert the fork into the groove. It should be next to no sideways clearance.
If it 'wiggles' in the groove, the cone is worn, normally.
A naughty trick, but gives some time, is to grind off at the bottom of the fork so it may go deeper into the groove and reduce side play. This only if the fork bottoms in the groove.
Not the official way, but works (for some time) if done right.
 
Ok, this makes sense. The fork I replaced was shiny and worn on the sides AND on the bottom indicating it was bottoming out. Thanks for the very logical temporary solution. Wish I'd thought of it before I purchased the extra parts and pieces. But it can't hurt to spare parts for a 30 year old engine!
 
Last edited:
Thanks haffimam37. I scribed a line to follow and took off maybe .0625 or a little more.
It works like new.
 
Enjoy it while it last.
Perhaps another 29 years?
What sometimes 'kills' it is too long stroke on the shift cable keeping pressure in the cone.
 
If you ran the gearbox low of oil you may have "galled" the surface of the cone clutch. This can cause it to bind in gear.
 
Thank you for the additional input.
What would be the fix if this was the case?
Replace the cone and the two gears? In the drawing above parts #21, 25 & 26?

John
 
Hi,
I didn't empty the gearhousing (#71) and it broke/cracked with freezing.
I want to take the gear housing of and have the crack melt.
Can somebody help me and tell me how to unscrew plug 85 ?
- Is it like a normal plug, eg turn left to take it of ?
- or can i just bypass the cooling and not cool the reverse gear ?
that's the simplest solution...

Thanks in advance, Bas.
 
Re: "Hello, Md7a is running great

cdj said:
"Hello,
Md7a is running great up until now.
Transmission will not go in to neutral while engine is running.

Hi John how did you get on with it in the end all fixed or?
(We have a similar problem) Graham
Click to expand...
 
haffiman37 said:
It might be as simple as a re-shimming of the shift fork.
Screw 58, and shims 57. You might need to remove some shims in order to get the fork deeper into the V of the cone.
In worst case the cone has to be replaced.
Click to expand...
A bigger pic
 

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Re: Md7a ms 191 mono shift reverse gear OH OH !

Umm found this looks like a bit of retaining ring
 

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