63 Merc 9.8 110 lower unit problem ( shifting)

[Scott53]

my 63 merc 9.8 110 has shifting problems and could use some advice.I can't always get it into forward. I've taken the lower unit off and tried to shift with pliers on the shift shaft(short).It seems to shift in N-R. I've worked on powerheads and coils and points but no experience on the gear assembly.I know I could try to save some money and do the repair myself.What could be the problem with the shifting and how hard is it to disassemble and reassemble.

 

[Texasmark]

Merc uses a twisting cam arrangement on a lot of the engines. The splined shift shaft protruding from the top of the lower unit is connected to a pivoting cam with 3 detents for FNR. The detents are at a different distance from the pivot point forcing a "cam follower" pin inside the front end of the prop shaft to move up and down the inside of the prop shaft to the corresponding position. This movement is spring loaded and pinned to a sliding gear called a clutch dog which does the actual engaging as it is forced up and down the prop shaft. It's pretty bullet proof if you keep your lower unit oil clean and waterless. How's yours?

As I recall the rear bearing carrier, which is immediately in front of the prop, is retained with a spanner nut threaded to the inside of the LU housing. The last time I removed a prop shaft I just got a piece of pipe and made my own turning with a strap wrench to remove the nut. Need to clean up the exposed threads with a wire brush and apply lots of high quality penetrating oil first.....wasn't easy for me to get mine out due to corrosion.

Once the spanner nut is backed out/removed, you can grasp the ribs of the bearing carrier and pull it out...a sliding hammer tool will be helpful....Harbor Freight has them. Once out the prop shaft will come out right behind it if it didn't come out with the bearing carrier assy.

Now, how about a picture of the prop shaft and clutch dog. We'll go from there.

Mark

 

[Scott53]

Sorry to get to you so late.I've been busy on my boat project and other chores.When i drained the oil it was grey and soupy.I'll try to work on that on Monday.Your info is great.Let me get back to you.

Scott53

 

[Texasmark]

Grey and soupy is water, not as much as when it is milky yellow, but you have a leak somewhere:

Driveshaft seal under water pump housing;

shift shaft seal where shift shaft goes into LU;

prop shaft seal inside the R gear bearing carrier...the thing you pull out after you remove the spanner nut;

fill and drain screws.

Need to check for rust and corrosion, probably on the clutch dog, or between it and the prop shaft which is keeping you from shifting. The dog needs to move smoothly against the spring force up and down the shaft. Since F is your problem I'm going to guess that the dog either can't slide all the way forward or the spring is binding and can't provide the required thrust to force the dog up against F gear.

Wouldn't hurt to have a look at your F and R bearings while in there. You can fish the F gear and bearing out without having to remove the drive shaft/pinion gear. If you have any shims pay attention where they are located and ensure that you get them back where they belong upon reassy.

Mark

 

[Scott53]

Good morning Mark

I started to take apart the gears this morning.No problems so far.I took some pictures of the prop shaft and clutch dog for you.There was water in the lower unit when I drained it again.Not a lot but some.I'm having a problem with the forward gear.I can't see how I could remove the gear with out taking the drive shaft pinion gear off .Is this normal?

S

 

[Scott53]

​Good Morning Mark

I've been working on the gears today with no problems with the disassembly.The rear carrier and driveshaft came off good.I took some pictures of the clutch dog and drive shaft.The clutch dog seems ok with no corrosion.Drive shaft looked ok.I was going to take out the foward gear like you mentioned and it seems to be engaged in the drive shaft pinion gear.Can't see where the gear could come out with out taking off the drive shaft gear.

 

[Scott53]

I'll try this again.( 2 attempt) Having problems with the post.I'll try to send with out photos.I started working on the gears this morning with no problems .The clutch dog and pin looks ok. The drive shaft looks ok .I'm trying to remove the forward gear and I can't see where I can remove the gear with out taking the DS pinion gear off.Any suggestions?

 

[Texasmark]

The dog should slide freely up and down the slot in the prop shaft against the spring resistance. The pin in it should go all the way to the front of the slot in the prop shaft by itself. My original assumption (hope) was that the spring was restricted somehow and it couldn't go all the way thus was unable to mesh with the rear of F gear adequately. The tips of the gears on the dog need to be sharp (points intact, not sharp enough to cut you) like the teeth on the blade of a hand saw, not rounded off on the tips. Same for the rear of the F gear where the dog mates.

You should be able to fish out the gear any shims and the thrust bearing by reaching in with a hook and grasping the bottom of these parts. Then slide them out under the drive pinion.

Will keep checking for the pics. If you do a post preview and they show up there they should be good to go; works for me.

Mark

 

[Scott53]

I'll try to pull out the forward gear light you said.I've been trying to take the DS pinion gear to get to the forward gear and not getting anywhere with that.I'll let you know what i see in the rear of the housing.

 

[Scott53]

I'll try to pull out the forward gear like you said.I've been trying to take the DS pinion gear to get to the forward gear and not getting anywhere with that.I'll let you know what i see in the rear of the housing.

 

[Scott53]

I'm taking a break this afternoon.My work bench is outside in full sun and it's 80 out.I'm on some meds that make me sick if I'm in the hot sun for a while.I'll continue later this early evening.

Scott53

 

[Scott53]

Mark

I finally got the forward gear out.The bearing did not.The bearings look good.The shift shaft has a little play up and down.The shift cam was working rough when the shaft was all the way down.The play seems to be about 1.5 cm + or -.I put a large screwdriver under the shift cam and forced the screw driver down making the shift cam go up.I did this a couple of times and checked how it moved.It seems to be better but I can't believe that my solution to this is correct.Should there be any play in the shift shaft up and down.?

Scott53

 

[Texasmark]

The cam is wedged into an aluminum casting with casting limits up and down. F gear is minimum cam pressure, aka spring in the prop shaft and cam follower, the point on the front of the prop shaft are all the way forward for F gear. If you had a problem with R where maximum pressure is against the spring inside the prop shaft then I would say yes "wobble of the cam" MIGHT be a problem.

Keep looking. You haven't found the "smoking gun" yet.

Mark

 

[Scott53]

Mark

How is it going today?The forum seemed to be down this morning.Could you tell me the position of the shift lever for F-N-R.I might have it wrong.Up is at 12:00 (R).One click at 1:00 (N).Down at 4:00 (F).My motor engages at the 12:00 position then one click at around 1:00 for N with no engagement after.

 

[Scott53]

Mark
How is it going today?The forum seemed to be down this morning.Could you tell me the position of the shift lever for F-N-R.I might have it wrong.Up is at 12:00 (R).One click at 1:00 (N).Down at 4:00 (F).My motor engages at the 12:00 position then one click at around 1:00 for N with no engagement after.