1977 Mercury 850 won't come out of forward gear.

[RandyJ]

I'm considering which way to go. Trying to help a friend with his lower unit issue. At first it would not shift into reverse. I removed the shift cable then used a screw driver to slide the shifter into forward at the engine. Now it doesn't want to come out of forward though I was able to push it enough to get it into neutral but the spring tension pushes it right back into forward. Need some helpful hints here. What's going on? Would it be better to just find a good used lower unit to swap over and if I did just what other models would the lower unit interchange with?... speaking of that, where can I find parts interchange information for mercury outboards?

 

[Mi duckdown]

Lower end is off. Vague info. Pics .?

 

[RandyJ]

What do you want a picture of? they all look the same on the outside...

 

[Chris1956]

Spring tension pushing it into forward? It should not do that. What is the condition of the gear oil?

Gearcases from inline 4/6 motors from the early 70's to the mid 80's should fit. Inline 4 motors have a 2.3::1 gear ratio which is a bit lower than the IL6 gearcases which have a 2::1 gear ratio. That could be an issue.

 

[RandyJ]

I haven't gotten to this engine but should have it out and check the gear oil tomorrow. I'm betting it is toast. He has NEVER checked the oil and the drain plug is in tight. I'll have to hammer it out with an impact driver. He said his service guy should have checked that 3 years ago when he had it serviced.... yeah, right....

 

[RandyJ]

I got around to it today. The gear oil looks superb... no sign of metal flakes or water contamination. I pulled the lower unit and was able to shift the gears by turning the shift shaft. At first I was able to get it to shift into forward, neutral, and reverse. I installed then it would not shift out of forward. When I pulled it back out it would shift into neutral or forward but I could not get it to shift into reverse. From the outside it looks like a very nice clean lower unit. Big problem to begin with is that the prop is frozen onto the prop shaft so I'm up against a real booger from the start. I don't want to destroy this prop or the lower unit trying to get the prop off.... The only good thing is that it's a stainless steel prop so can take a good bit of abuse from me. Rather than trying to force the prop until it comes off the hub or prop shaft I have it rigged up with a chain and 3 prong puller. Tomorrow I plan to get out my good size hammer drill and bang on the end of the puller using jack hammer mode with some tension on the prop to try freeing it up without tearing it up.

 

[Chris1956]

You can try using a 2X4 between the prop blades and the gearcase "neck" and prying the prop off. Make sure to pry on all prop blades and use penetrating oil on the prop splines. If that doesn't get it, the puller is the next option.

 

[RandyJ]

I've got it chained with the 3 point puller .... even put the jack hammer to it and it won't budge after being soaked with PB over night... not good prognosis. Going to be far cheaper to just find an old motor or good lower unit... sad to sacrifice a beautiful prop and nice lower unit...

 

[Chris1956]

well, maybe the prop hub will let go and you can salvage the prop blades and get a new hub pressed in. After the prop blades pull off, you should be able to get to the stuck hub and grind a split in it and crack it off with a chistle.

 

[RandyJ]

Yep. That's kind of a last choice alternative. I already wonder where I can get a prop re-hubbed around here. That job has gotten expensive and all the prop shops I knew of have gone out of business.

 

[emckelvy]

Something to remember, when the engine is not running, you have to turn the prop to shift cleanly into reverse. With the L/U on the bench, if it won't shift into reverse when you turn either the prop or driveshaft while shifting, it's got issues.

You're probably gonna have to burn the rubber hub out to get that prop off. If it were aluminum and not a $$$ stainless prop, you could just cut the prop up, but I assume you'd like to save the stainless prop. You'll probably need a MAPP torch, at minimum, to get it hot enough.

And be very careful, the rubber will catch on fire, and spit out burning chunks & bits. The prop could even spit itself off the end, with force, flaming all the way. Don't ask me how I know this!

G'luck with the disassembly and repairs. When you get it apart, check the shift cam and also the plunger that rides on the cam, for wear...........ed

 

[RandyJ]

Update.... the major issue with the hard shifting was the cables were too long and a big time boat shop had used wire ties to pull them up all nice and neat which caused a lot of hard turns for the cables. The adjustment for the cables was the biggest issue. Once I relieved pressure on the cables and backed off the adjustment the shifting and position of the shift control came into normal position. Not sure how I did it but by carefully feeling the gears and drive shaft as I turned them and shifted gears I finally found the "sweet spot" and got it all operating correctly. With new cables I put it all back together and have a very very happy customer who used the boat all weekend with no problems. We never were able to budge the prop off the shaft so now he knows he has a problem waiting to happen in the future.