mercury 7.5 hp lower unit broken shift rod

[Michawilden]

I got a 80's 7.5 hp sail power mercury. I bought it for a couple of euro's ( I live in the Netherlands). Previous owner bought it with the boat and never used it but has been told that the gears where not working properly. I started the engine and it worked great, not pumping water but i didn't expect that anyway. The problem is that the motor sticks in first gear. I lowered the LU to inspect it. Expecting a mis allignment. However, when I dropped it, the shift cam stuck in the mid section in stead of the lower unit. It is obviously broken.
Now I doubt what I should do with it. I hoped you guys can halp me with a decision. Can I try to retrieve the other end by removing the shift rod bearing? Or do I have to dismantle the complete unit? I suspect that the other end of the shift rod still sticks in the shift cam and won't just fall out of the shift cam. If an end sticks out of the shift cam, is it even possible to get the cam out when I completely dismantle the LU?
The gear case sounds good, no weird bearing noises and no visually abnormalities. A second hand gear case costs about 75 euro's and this doesn't guarantee a proper working LU. What should I do? I got most of the tools to get the lower unit apart, I will have to manufacture a tool to remove the ring whish keeps it al in place. But is it al worth the time?

 

[Scott Danforth]

post a pic of what you have going on. Im trying to visualize your explanation. from the lower unit, there is a small stub of shaft that goes up to the tilt latch cam (plastic and held to the mid exhaust housing with two 1/4-20 screws). from there is a straight shift rod that goes to the two bevel gears in the cowl, then out to the shift lever

are you saying the tilt latch cam came out? or the shift rod from the lower is stuck in the mid section. the shift rod and bearing are normally retained in the foot by the water pump.

Also, when you purchase your water pump, use a dial caliper and measure the drive shaft diameter, in the mid 80's the 3.9-9.8 motors had two different shaft diameters 0.456" and 0.438" two different water pump part numbers

I can send you pics of my mid 80's 9.8 that I am in the middle of reassembly if it helps.

 

[Michawilden]

I'm not at home right now so I can't take a picture. In the following picture, The shift rod, number 40 is broken. The upper half is free and the lower half is probably stuck in the shift cam, number 48

 

[racerone]

???---Is clip # 43 holding it in there?----Not likely stuck in the cam.

 

[Michawilden]

#43 is a o ring to seal the shift rod. The case is that the lower end of the shift rod is in the shift cam, deep down in the lower unit. Even it this end not stuck. How do I remove it? It will at least stick a little but due to the oil. I cant grab it since it is al the way down in there, turning the LU upside down does not help. Therefor my question is what I should do. Dismantle the whole lower unit or save time and just buy another lower unit?

 

[racerone]

Maybe # 41 is the clip.---Note ----I have worked on more than one of these units !

 

[Chinewalker]

In order to fix this, you will have to disassemble the entire lower unit, regardless of whether the shift rod is broken or not. The shift shaft keeps the shift cam in place. Once the shaft is removed from the cam, the cam gets pushed forward by the spring loaded plunger in the propshaft. It is next to impossible to get the cam back in place with the unit intact.

Yes, 41 is the c-clip that keeps the shaft from pulling out. It is not hard to override that if the shaft is pulled hard enough. If that's the case, then the c-clip is floating loosely inside the gear case, lending yet another reason to pull the unit apart.

Not sure what would have caused the shift shaft to shear/break. Not a whole lot of force involved with twisting it to engage the shift plunger. And, by the 1980s, Mercury had finally embraced stainless steel shafts, so it should not have corroded to the point of breaking. I, too, would like to see pics of this project...

 

[Michawilden]

I made some pictures the other day. didn't have the time to upload them yet. Here they are:

The new and old shift rod. the shorter one came out of this lower unit:

I could inspect the lower unit, It seems that the other end isn't even in the lower unit anymore. I wiggled around with the propeller shaft and could see the shifting cam. I could see the splines. As chinewalker said, the cam is not oriented in the correct way so it will have to come apart. One thing I noticed that there was a little piece of metal down in there that blocks the rod so I have to try to get that out. I did not manage to take a decent picture. I will firstly remove the shift rod bearing.

I think that the previous owner trew away the other end. The end is not corroded nor does it look like a torque failure. I think that someone just wasn't carefull and broke the shift rod.
I bought an older engine for 60 euro's , I hoped to use the lower unit but this lower unit was in reasonable shape but the drive shaft was bend, So where the bearings in the lower unit. I can still use the good parts and sell the other parts in order to get my money back.

 

[Michawilden]

I managed to get the nylon ring out. Thread was very corroded. Heated the lower unit and then tried removing it but the ring just desintegrated. If I look at al the corrosion on the thread I wonder if the bearing carrier will come out. I have a puller I use for flywheels. I will use 3 hooks with thread and try to pull the carrier after heating t up. Will post a picture of the process.

 

[Michawilden]

Managed to pull the bearing carrier by using my flywheel puller. First installed the puller:

The carrier came out very easy but still a lot of corrosion or residue from being under water. The lower unit was also completely filled with snail shells

Next problem is the bearing. I can lift it a little bit by pulling on the prop shaft. About 0.05 inch. After that I cant get it any further. How do you pull the shaft without damaging it? Heat it up again and than pull by hand?

PLease give me some advise how to proceed.

 

[racerone]

Normally the shaft and bearing would fall out now.

 

[Michawilden]

So probably some corrosion on the bearing. I will heat it up again and then try pulling it. It is already loose but only for the first millimeters. It just won't go out any further.

 

[Chinewalker]

If you place the propshaft in a vice with soft pads, you can generally pull the housing away from the propshaft by GENTLY tapping the skeg with a hard rubber or plastic mallet. I do it by holding the housing horizontal, with the skeg away from me, and my hip against the driveshaft to support it. Heat does help, too.

 

[Michawilden]

I couldn't hold myself in and went on with the lower unit yesterday after school. I ended heating it up big time to get the first bearing out. I tried the gentle method but this did not get the bearing anywhere. I had put the lower unit in a vice with the propshaft pointing downward. Using an old pair of pliers, I gripped the prop shaft end gave a good smack with a hammer. The bearing could not resist anymore and gave way.

The outside was very rough, propably corroded. The innner part of the lower unit looked good however and the bearing looked and rolled good so I will still use it after a good cleaning. Removing the drive shaft was no problem. Loosening the pignion gear was no problem and the heat was still in the lower unit so I could pull it out without any problems.

This also looked in good shape. The impeller had died many years ago probably as you can see in the following picture. Will be replaced obviously. I will have to get an gear cover anyway so I will make an order. (The gear cover is number 65 in the exploded view)

After removing the pignion and drive shaft the forward gear was up. This one however was also stuck. I was not worried about any parts to come out but the forward gear could be a pain in the *** if it would still stick. Trying to pry with the propshaft did not get me anywhere so I started to worry that this would become the same problem as the backward gear. I thought that heating it up and then try to pry it out would work better so the propane burner came out again.
While heating up I invested the gears. They all looked fine, no chips or damages on any of the tooths and bearings where also in reasonably good shape. While I inspected I heard a sound come from the lower unit which was baking in the corner of the shed. The front gear just fell out. Winnnnn.

Here all the gears and the shift cam together:

All looked good in the gears and bearings and I could now hopfully see what was jamming in the gearcase. A reminder, something blocked the shift shaft. I could not see what was jamming in the gear case. Looking in the lower unit, I could not see anything down there but the shift shaft could still not get all the way down. After rambling the shift shaft a little bit around I could stick it al the way down.

However, I pulled it out and tried again and could again not get it all the way down. Looking down in the shift shaft bearing while shining a lamp in side the gear case I could see pieces of the retainer clip sticking in the hole all the way down. It was a little to big to get it out trough the shift shaft bearing. I heated the area around the shift shaft so I could get it out because it was really stuck.

The stumb was removed make the bearing more attainable. This helped and I coul get it out. Pulling it out I could see why it was stuck so bad. A lot of debris and a little corrosion got it to stick real bad. Removing it damaged the bearing but thats no problem since I got a good one from the other gearcase.

Now the half clip ( number 41 in the exploded view) could come out. It initially wouldn't come out but after some loving taps it fell out. It fell somewhere on the ground and could not find it. Doesn't matter, it is out. The shift rod could now go all the way down.

Plan is to clean the gearhouse from the inside and outside and sand it down so I can primer and paint it. I will keep you posted on the developments.

 

[Michawilden]

Cleaned up the gear housing really well. Sanded it down and painted it. It is not in the best shape but it is good enough for me. It look a lot better than before.

I cleaned the inside by using gasoline and rinse it out. Came out really clean. After letting it dry, I used compressed air to clear out the last spots.

Put in the shift cam and the shift rod. This was already a pesky job since my hands couldn't reach al the way down the case and the cam must be oriented properly. But after a few attempts I managed.

Put the shift rod bearing in place and locked it with the nut.

Now, the shift rod would not disconnect anymore so no worries there. The bearing could be pushed down easily, no need to heat it up first. Was now able to put in the forward gear. Beforehand I put in the shim ring which came out.

Gear in place:

Also no need to heat it up. A couple of wiggles with the prop shaft was all it took to get it in place.
Next was the pignion gear and the drive shaft: First the shims for the drife shaft bearing:

Next was tightening down the pignion gear after pushing in the driveshaft plus bearing:

By turning the driveshaft, the screw pulls itself in. Tightened it down by holding the drive shaft with a pair of tongs. Bended the pice of metel so it would not com free again.

Next was the prop shaft and the other gear. First installed the propshaft and the shim ring.

The backward gear had a ring around the bearing, The ring was little bit corroded and dirty so I cleaned that one up.

Seemed to go in the gear case pretty well. The ring was quite snuf in the gearcase but the bearing was a little but loose in the ring. Could push it down a little but it springed up due to the spring in the drive shaft.

Installed the big o-ring in the case for the bearing carrier. I also cleaned the bearing carrier with gasoline. ( sometimes I buy an old outboard with a tank. When there is still gasoline in the tank I keep that for cleaning purposes. Gasoline is suited to clean oil substances and especially for powerhead from mopeds. They tend to get al greasy and dirty and using gasoline cleans them really well.)

The bearing carrier in the gear case:

It is still not snug in the case. If i push it down it does not jam so I can easily pull it out again. I think that if I install the cover nut it will stay in place. I have not ordered the cover since I have to visit the shop. I can't order it online here in the Netherlands. We have smaller shops where one can buy impelelrs and stuff but not a big site where everything can be bought. Impeller is therefore also not yet installed. the housing however is now in place:

The old impeller looked like this:

I got a lot of pieces out of the cooling circuit but I doubt if I got every piece. I will use compressed air in the powerhead and hope some pieces will fly out of the water tube.

Last, I sanded down the prop to paint it. Heated it up and primered it. When I have time this week I will paint it black and I will order the cover nut and impeller. Then the tedious job of installing the impeller will begin. Done it before and hate it on these engines. Any tips on how to install the impeller?

 

[Michawilden]

I had found a site here in the Netherlands where I could buy the nylon cover. It was 5 euro's. I was afraid that it would cost like 20 euro's here so that was an advantage. Installed it with a pair of pliers. The gearcase is now closed and shifts fine. The prop shaft has a little friction when in neutral but I think that that will go away when it is filled with gear oil. The impeller will be arriving today or tomorrow. I ordered it from another site since it was 10 euro cheaper, even with the shipping costs.
Here you have the cover ring, number 65 installed:

When the impeller is installed I can finally let her snore again. Ik had run it when I bought it, It ran fine but still a little anxious. Hope all the hard work was not for nothing. In the future, I don't think I will ever open up such a corroded gearcase and just let it be.

 

[Michawilden]

Got the waterpump in yesterday. Installed it right away. This was not the first time I had this type of motor. I have had a 9.8 and a couple of 4.5 hp's. All where a pain in the rear to change the impeller. The key would not stay in place but yesterday I was lucky, it went in the first try. Finally some prosperity in this project. Getting the LU on the outboard took way longer than I hoped. I could not test if everything was properly alligned. It shifted good and the prop turned when I pulled the starter. Couldn't start it though, I had no time to let her run so I hope the water tube is in right.
Paint came out beter than I imagined. Colour is almost the same. Only a light stripe where the masking tape was on the midsection. ( the lower part of the midsection was in the same shape as the gearcase so it also needed painting). It now looks like this:

It will need gearlube and then I will test it. Propably saturday. Hope everything is alright. I would hate it if i have to pull the lower unit again( and mount it again, uggghh)

 

[Michawilden]

It runs and cools great. A strong pee shoots out from the side so it was all worth it and I dont have to pull the LU again( thank god) it is fall here so I will have to wait for spring since the boat out of the water.