1977 OMC won't start

[VE8EV]

Oh, and the five bolts on the top fit very snugly but there's no reason for anyone to put Locktite on them. Use a #4 Phillips bit with a socket wrench. Don't try to get them out with a #2 Phillips screwdriver or you'll strip the heads out. Once they crack loose they come out easy. Don't use a torch either. There's an o-ring there that won't like getting cooked.

 

[jtrew77]

Just curious, do I need to find a uppergear case for a 120hp omc to replace this one, or can I use a upper from a OMC 400? I found on sterndrive.info website that all upper gear cases from 1973 to 1985 were the same except for the gear ratios. What would the effect be if I installed one with a lower or higher gear ratio? Just wondering if I can widen my search for a replacement.

 

[southkogs]

You need the same or at least REALLY close gear ratios that you can cover by "re-propping." You would have the problem of either winding out your engine or turning your boat into a slug.

I think yours is a 16:20

 

[jtrew77]

Thanks, what is a close gear ratio though? Mine is .8, 140Hp is .95. Is that close enough? What does a higher value of ratio do, or a lower one and how do you compensate with a propeller? Ideally I will either find the correct one or rebuild my current one, but wanted to keep my options open.

 

[wire2]

If the oil in the upper was quite low, the input cup/cone bearing (behind the ball gear) would have run dry and overheated. The roller cage gets destroyed and remains of overheated rollers flop around, possibly making the click sound. There's only a few bolts holding the top cover, pull it and look in there. I believe the bearings are Timken, part numbers will be on both the cup and cone, probably $25-$30 at a bearing supply. If you replace any bearings, check for lash between the gears, and add or remove shims to stay in spec. It will be outlined in an OMC manual.
And yes, you should be able to turn the ball gear by hand with the lower off.

 

[southkogs]

... what is a close gear ratio though? Mine is .8, 140Hp is .95. Is that close enough? What does a higher value of ratio do, or a lower one and how do you compensate with a propeller?

I'm not sure what numbers you're quoting (and I am waaaaaay past my scope of knowledge on this), but I think your overall drive ratio is 1.92:1 - meaning the engine turns 1.92 times to every rotation of the propeller. The 140HP should be 1.61:1. Which would (I think) mean the prop isn't turning as fast as it should ... so, you'd have to increase pitch (again ... I think).

You need someone "in the know" to help ya' on this part ... I'd have to ask the same question.

 

[jtrew77]

The numbers I was pulling are from http://www.sterndrive.info/id358.html

 

[southkogs]

LOL ... I couldn't figure out the .8 number, but that's 16 divided by 20. Now I see ...

I'm honestly not sure how well the re-propping would work. Hopefully one of the other guys will be able to answer that.

 

[wire2]

If you're still not able to remove the top cover screws, get a hand impact driver, ($10- $20), put the proper Phillips bit in it, place on screw and hit it with a hammer. They WILL come loose. But be sure you have it set for CCW rotation on impact.

 

[jtrew77]

got all but one out with the proper screwdriver, the last one is stripped pretty bad, so I'm getting a bit to remove the screw. I will need to find a replacement screw with whatever internal stuff I need Hope to have it apart this weekend and I will post pictures of what everything looks like.

 

[jtrew77]

Well got the final screw out and the gear that I can see looked good, so all that is left in the gear case is the ball gear(which spins freely now). The gears are jammed somewhere inside, so I am trying to get the pinion gear off and work my way down. Is there anything holding the pinion gear on the shaft or is it just a tight fit that I need to work off by prying? I removed the locking nut from the top of the pinion gear. I think the bearings are fried, but I need to get the pinion gear off to verify.

 

[Scott Danforth]

pinion should be pressed onto the input shaft. you will need a bearing separator and a hydraulic press. if bearings spun in housing, you may need a new housing. when replacing bearings, you will need to re-shim the box.