1988 70HP Mercury Lower Unit

[bwhalerman]

I just finished installing new cover plate, gaskets, impeller and re-installed the lower unit. The motor was in neutral when I removed the lower unit. When I reinstalled the prop it spun freely as it is supposed to do. I put the throttle at the console in forward. As designed the prop only turned to the right. But, when with each turn there was a click. Maybe the gear spline is not seated properly? When moving to reverse the throttle control at the helm is stiff and doesn't move too far. I was thinking I need to drop the lower unit and recheck the gear seating spline. Any opinion on what I described. Also, I have rebuilt three carbs. The motor starts on the first try and will need to go to the river for better adjustment. As I was reinstalling the barrels that hold the throttle cable in place I had to turn both barrels to reinstall them. Could this have any effect on what I described about the prop situation.

Thank you very much

 

[GA_Boater]

The prop noises sound right. Neutral spins free, Reverse is locked in both directions and in forward it's locked in one direction and the dog clutch clicks in the other. You're OK.

Shifting into reverse can be hard with the motor off because the gears aren't meshing. Turn the prop a little and try it. Don't force the remote control into reverse or the shift cable can be stretched.

The barrels are easily turned when taking the cables off or putting them on. On the throttle cable, make sure the carb plates are closed at idle and fully open at full throttle, adjust the barrels as needed. The shift cable should move the shift lever under the carbs about the same amount for forward and reverse, again adjust the barrels for equal movement.

 

[bwhalerman]

I was just thinking some more about what I wrote and figured that when i turned clockwise by hand and felt the click that it was probably locked in the correct way. Being just a bit cautious as I wasn't exactly sure and would rather have my observation confirmed than doing something stupid. FYI, I have found this site to have very helpful information and timely response to questions. Thank you very much.

 

[Texasmark]

That clicking is the overrun clutch in F gear and as Georgia said, it's on the rear of the F gear and front of the clutch dog which rides on the prop shaft. Purpose is to allow the prop to free wheel any time you decelerate, like when you are coming off plane and chop the throttle. If it locked like R does, your teeth could be embedded in your windshield if you had one. I had an OMC engine lock up at WOT once running 35+, without the ORC and had there been a windshield, that would have been my situation.

 

[bwhalerman]

That clicking is the overrun clutch in F gear and as Georgia said, it's on the rear of the F gear and front of the clutch dog which rides on the prop shaft. Purpose is to allow the prop to free wheel any time you decelerate, like when you are coming off plane and chop the throttle. If it locked like R does, your teeth could be embedded in your windshield if you had one. I had an OMC engine lock up at WOT once running 35+, without the ORC and had there been a windshield, that would have been my situation.

Good information, thank you. This motor was running great last year. I bought it and the boat/trailer in December 2014. It's a 1989 17' Boston Whaler Montauk. Got an unbelievable deal and in excellent condition. I've added new starter, plug wires, solenoid, rectifier,and last month rebuilt the fuel pump, 3 carburetors and so I decided while I was at it to rebuild the water pump. This was my first go round with dropping the lower unit so I decided to pull it because on the last trip out the horn sounded. I haven' t checked the thermostat yet as I learned that is somewhat unlikely to fail (but it is on my replacement list). It appeared that the lower unit had not been dropped for quite a while. Mud inside, upper and lower seals in the cover plate were nearly impossible to extract. Had to purchase a new cover plate. So now everything is back together again and like I said before when involved in something I've never done before I always think its wise to get advice from others who have been there before.

Thank you very much for your input.

 

[Texasmark]

Glad to be of assistance as I'm sure are the others responding.

 

[bwhalerman]

Now that the water pump job is finished and all the good advice considered I decided to change the lower unit oil before taking my boat to the ramp to adjust the carburetors. When I drained the oil it looked a bit like cream was in the oil. Up to this point I only ran water into it with hose attached to do the initial carburetor settings. Obviously water got into the lower unit somehow. I pulled the lower unit again and with the diagram nearby removed each part and confirmed every piece in the order shown on the diagram. I installed a new cover plate that came with upper and lower seals already installed, ran a generous bead of silicone to separate the cover plate from the exhaust.

I also pulled the shift assembly housing to confirm condition of seals and gasket. At this point I asking if anyone thinks the water tube seal is installed properly from one side versus the other. It seems to fit either way its placed. Whatever the source of the leak it didn't appear to be significant. Last year when I changed to oil before storing it the oil looked as though it just came out of the bottle. Any ideas would be appreciated.

 

[bwhalerman]

I just found the problem. There was so much crud in the lower unit that apparently some got under the gasket below the cover plate. Fixed everything and its good to go. Also the water tube connector is designed with a reveal on the pump housing side so that must be installed over the tube on the pump housing which apparently I did correctly.

 

[Texasmark]

Glad you got-r-fixed.

 

[bwhalerman]

I just found the problem. There was so much crud in the lower unit that apparently some got under the gasket below the cover plate. Fixed everything and its good to go. Also the water tube connector is designed with a reveal on the pump housing side so that must be installed over the tube on the pump housing which apparently I did correctly.

Well almost fixed. I discovered after install I only had forward gear. I dropped the lower unit again because when doing the last install the shift shaft lifted out of the tube with the bushing assembly. At the bottom end of the shaft it has teeth but when i reinserted it into the tube/housing it didn't appear to mesh with anything on the bottom end. I visually inspect the bottom and did not see any matching teeth. I figured this may have caused the lockup in forward gear.

Yes I am new to this and want to learn it for future work but I looked through manuals for my motor and don't see anything on this issue. I don't understand why the end of the shift shaft doesn't mate up with any receiving end in the bottom of the gear case. It appears as i look down the tube that I see the bottom and the sides appear to be smooth.

If I can't get this thing wrapped up I guess its off to the boat yard. Any suggestions would be appreciated. It's late and I need to fight another day:=)

 

[Texasmark]

Forward only means that the shifter cam is not connecting the cam follower inside the prop shaft which means the spring that pushes the clutch dog (a sliding gear locked to the prop shaft used to engage the gears) is engaged in the rear of F gear. to get to the other two gears, you have to apply pressure to that cam follower to push it back into the prop shaft. Part way pushed back is N and fully is R.

The shaft from above comes down to the lower unit with a splined end on it. That spline is inserted in a splined (on both ends) collar which, reinstalling the lower unit is fitted on top of the shift shaft splined stub in the lower unit. The LU stub bottoms out when pushed on, but can come up out of it's mounting when removing the LU. Coming up and out of the mounting allows the shaft splines to also come out of the "shifter cam" which is the pivot and securing mechanism for the cam. With out the pivotal axle, if you will, the cam has nothing from which it can exert leverage on the cam follower and you cannot shift as a result.

Corrective action is to try your luck at fishing the shifter stub out, looking down through that small hole, lining up the cam female splines and finessing the male splines back through the cam and then wiggling all that so that you can push the shaft on through the cam and stub it in the lower mounting hole in the LU casting........lots of luck.

The alternative to that is to drain your LU oil, pull you prop, then unbolt (2) and remove your carrier bearing, then remove the prop shaft with the clutch dog and cam follower. Following that you have to fish out F gear and it's thrust bearing and shims (keep count of the shims and where you found them)......The F gear will lay flat in the LU housing and you can fish it out under the drive shaft pinion, without having to remove that. Thence you have a clear view and the access you need to hold the cam in place with a pair of long nose pliers while, with the other hand you finess the shifter stub down as I said above.

Replacement is the reverse of the removal. Before you reinstall the LU with a pair of vise grips, set the cam to the center position which is N then slide the shift rod coupler from the mid section down onto the LU splined shaft...a little lube would be inorder to help next time you remove it. Set your remote control shift lever to N. Ensure your water tube is lined up. put a small amount of grease on the drive shaft splines (sides only) excluding the top which could interfere with proper seating and if the LU won't go that last ? to 1 inch, turn the crankshaft while applying upward pressure on the LU till it eases on up

Then don't forget LU lube and you should be good to go. Sounds like a PIA but just have the engine on the boat, tilted fully up after draining the oil and it's not that bad......getting the mind set to tackle it is 80% of the job.

Good luck,
Mark

 

[bwhalerman]

When I look down the shift shaft tube I see a cam with a depression in the center and on the prop side I can see what appears to be a small pin. In another post about a similar issue it was written that turning the prop and stopping just before a click is heard takes the spring pressure off the cam and then it can move freely.
At that point insert the shift rod.

I don't understand some of the mechanics involved. Am I supposed to somehow move the cam in some direction which will then provide the opening into which the shaft is inserted?

 

[bwhalerman]

Okay, looks like I am making baby step progress. My lower unit is sitting in a workmate opening. With the prop on the shaft the lower unit is pitched down about 15 degrees, more of a diagonal angle, prop up to the left and front of the lower unit down in the workmate. Based on a number of things I have read I lifted the lower unit out of the workmate and now with the LU upright and parallel to the floor I can see that what before looked like a solid cam with a small dimple, well that dimple is now open. When I insert the shift rod into the opening it freely spins in both directions with out engaging receiving splines. So, I guess I'm moving forward but don't understand the final step to make this link up occur.

 

[Texasmark]

Okay, looks like I am making baby step progress. My lower unit is sitting in a workmate opening. With the prop on the shaft the lower unit is pitched down about 15 degrees, more of a diagonal angle, prop up to the left and front of the lower unit down in the workmate. Based on a number of things I have read I lifted the lower unit out of the workmate and now with the LU upright and parallel to the floor I can see that what before looked like a solid cam with a small dimple, well that dimple is now open. When I insert the shift rod into the opening it freely spins in both directions with out engaging receiving splines. So, I guess I'm moving forward but don't understand the final step to make this link up occur.

I think I read you. You are talking about looking down the hole where the shift rod enters the lower unit and seeing the cam but no splines. If that's true then as I mentioned, the cam has moved out of position and this is not unusual as the front end of the prop shaft is hollow for a distance toward the prop. In that hollow end of the prop shaft is/used to be 3 ball bearings (essentially spacers that adjust for differences in spring pressure when LU is assembled at the factory.

Next, moving toward the front of the prop shaft, inside the hollow front end is a spring and next the cam follower (a metallic cylinder with a dull conical point on the front end and which has a hole in it from both sides which is where the roll pin is attached which connects to the the clutch dog (spring and ultimately affects the dog) to move it back and forth during the shifting process.

Cam pressure against that spring moves the clutch dog, making it shift gears so you always have pressure against the cam. That pressure is the problem and is why if you can align the splined pivot hole with the hole in the LU casting that you are looking down through you are mightly lucky. Just resolve yourself to the fact that you will wind up pulling things out as I said to get at it from the inside......the mental decision is the hardest....just keep track of how the parts came out and put them back in, in reverse order.

 

[bwhalerman]

View attachment shift tube.pdf this is a visual example of what I am seeing. When my LU was mounted in my workmate it was resting in a diagonal mode. After reading some other posts on this site of people with similar problems I learned that I needed to have the LU upright and parallel to the floor. When I did that the view I am showing you appeared. Before that manipulation what I saw when looking down the tube was a similar view but the cam was just dimpled now it has a hole that wasn't there before. I believe I also read somewhere that if you beat the front of the LU with a rubber mallet it may be possible to get the receiving spline to appear.

Obviously, I'm struggling a little to understand procedural options (I'm a visual guy, need to see to understand) on the one hand I've read where this cam can be coaxed into the right position to receive the spline from the shift shaft into the cam and on the other hand the prop has to be pulled as you noted. You wrote that I am lucky- not sure what that means. I hope it's something that is positive lol. I feel at a crossroad now. If there is no way to get this done without pulling the prop I'll do it. I certainly have the will to get it done and have no problem jumping in to do it. But, all of this stuff is learning curve right now.

 

[Texasmark]

Where I'm looking is blurred beyond recognition in the PDF. On me telling you you're lucky, I'd have to look hard to find that statement as I never thought where your are or headed was a lucky situation. If you were to drain the LU oil, you would have a better chance of fishing the cam back into alignment. I agree banging on the front of the LU with a rubber hammer can jar it in place.

Tell you what you might do. Drain the LU. Then take an aerosol can of Brake Parts Cleaner, with the LU vertical, like it is when running on your boat, and the drain plug and oil out of the LU and spray down in the hole a few times. This has the possibility of removing the oil around the cam which should remove most of it's surface tension so that you would have essentially a dry cam and dry slots where it rides. Then banging on the front of the LU you might get it to move.

Then if that doesn't work or you see part of the hole, get a stiff wire and see if you can get it to move around. I really think the spring pressure on the cam follower will make this most difficult but "nothing ventured, nothing gained.....or lost.

 

[bwhalerman]

Thanks for all of your advice. Now I think the decision has been made by forces greater than myself. The e ring dropped into the bottom of the shaft housing. Attempted to fish it out with my magnet on a flexible stem and it decided to wedge itself between the side wall and the cam. Now there is no alternative. The prop shaft must come out. That is for tomorrow or another day.

Good news...got the e ring.hahaha anyway, but now the stuck magnet has made my decision for me. Could be worse, right? Now I'm going to learn even more about my outboard. I'll report back when I'm finished. Again, thanks for your time and advice and all who pitched in. This is a very helpful site.

 

[Texasmark]

Iboats sells either the Seloc maintenance manual or you can buy time on the www, renting the manual. I had the Merc OEM and rented the Seloc here.....takes only a minute or two to get in. I liked the Seloc. I hear others on here gripe about it. I know not what went with them but I know what went with me. It's fast to acquire, inexpensive, and can help you through the next step. Confidence, slow pace, pay attention to how you undo things and it isn't (shouldn't be) that hard.

Simplistically it's:

1. Remove the prop and thrust washer

2. Unscrew the 2 screws and pull straight out on the bearing carrier assy that surrounds the prop shaft. If prop shaft tries to come out with it, don't let it.

3. Grasp the prop shaft and work it out and under the drive shaft pinion gear. The F gear may or may not stay in place when you do this. I'd hold something against it to keep it in place for now. With the prop shaft out, notice the front end of it. That's your cam follower that follows the detents in the cam that you are after.

4. Carefully catch the side of the F gear and work it out with it's thrust washer being careful of any thin, easily damaged shims and remember how many and where you got them. The F gear radial support bearing cone should come out with F gear leaving the race in the LU casting. Get under the side of the F gear and inch it out allowing it to lie on it's side as you fish it out from under the drive shaft pinion.

5. You should now be looking at the cam. Pull it out, paying attention as to which way it comes out and look it over so that you are familiar with it. Stick it back in it's grooves (in the LU casting,one slot above and one below, and work your splined shaft into the hole and into the cam....see 6 before you do this step.

6. If you have access to parts and iboats may sell what you need, you might put in a new oring seal on the bearing carrier you pulled out after removing it's two mounting screws. Also in that carrier are 2 back to back prop shaft seals that you might change.....back to back to seal what's inside inside (oil) and what's outside outside (water). Last, add a new shift shaft seal while you are at it. The vent and drain ss screws have gaskets under them. Get new ones for them too plus some extras for the next time you change LU oil.

7. Installation is the reverse of the removal.

Good luck. Want more, ask.
Mark

 

[bwhalerman]

Thank you Mark, I ordered parts this morning, seals, shims, spring...I'm dedicating Saturday to the task so I can cleanly setup my work area and get this done right the first time. I own a small business and every day goes into 12+ hours so I decided to budget 6 hours on Saturday for nothing but this job. I'm divin in lol

 

[Texasmark]

I'll follow along Saturday so if you have any questions I'll help or point you to someone who can.