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74 40 hp gear case issues

P

Patrickstar74

New member
Just installed this engine and took it out for a test run Sunday. Power head wise it seemed good. Idled good ,revved good. All in all pretty smooth. Here’s the issues. First off it seemed to be a total dog. At WOT the boat barley moved. I think top speed was around 8 mph. The motor it replaced was a 55 hp and there was no comparison. Then as we were just putting along the motor started bouncing horribly, then quit and continued running. Soon after it kicked out of gear. I was able to put it in gear and continue on. Then after about another 10 mins of putting around i had stopped and then went to go in reverse and it was stuck in forward. Wouldn’t come out no matter what I did. Got it home pulled the lower unit apart and found the cradle on the dog clutch had fell off the clutch and wouldn’t allow it to move. So I put everything all back together , filled it and test ran in barrel. And all seemed fine. Well took back to the lake and it made it about 6 feet from the dock and did it again. So my question is it this just from wear or is there something else that could be causing this. Maybe misadjustment of the shift cable? I’m at a total loss here. I just don’t want to throw new parts in this before I pinpoint the root of the problem.
 
I see two issues here. First, 8 mph means either it is running on only one cylinder, or the throttle isn't opening all the way. Up to you to diagnose it. Secondly, it is impossible for the cradle to get out of the clutch dog----IF it is assembled correctly. Of course, there is the possibility of worn dog, gear, linkages, etc. Again, we cannot see nor diagnose it from a distance.
 
Agree with the above post.-----Was the pivot pin installed correctly ?-----Did you have the lower unit off the motor and upside down when assembling it ?----And are the 2 bolts in the brass shift rod connector installed correctly.----This is simple work , but easy for the novice to make mistakes.----Sorry if I am blunt here.
 
fdrgator said:
I see two issues here. First, 8 mph means either it is running on only one cylinder, or the throttle isn't opening all the way. Up to you to diagnose it. Secondly, it is impossible for the cradle to get out of the clutch dog----IF it is assembled correctly. Of course, there is the possibility of worn dog, gear, linkages, etc. Again, we cannot see nor diagnose it from a distance.
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ok well the motor is hitting on both cylinders, that’s been verified. Long before it even hit the water. I later found the prop may have been slipping, never actually got to verify though. The lower unit was never apart before the first run. And it was totally removed and upside down when I found the cradle had came out. As I think about it more I’m leaning towards a misadjusted cable only due to the fact that the shift lever is the only thing that actually holds that cradle in the clutch. I will tear back apart tonight and see what I find.
 
No, the shifter fork holds the cradle in the clutch dog and it can't get out---unless the pivot pin is removed.
 
racerone said:
^^^^^-----Agreed again.
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ok...where could this problem lie? Nothing was ever apart and everything is connected properly. (Well when I put it back together) and the screws in the brass piece are in correct and tight. I pulled the cover before I left the lake just to see if that was the issue.
 
I say that somebody took the cradle pivot screw out at one time.----A common mistake when changing oil on these.----The oil drain plug is on the bottom near the front !!
 
racerone said:
I say that somebody took the cradle pivot screw out at one time.----A common mistake when changing oil on these.----The oil drain plug is on the bottom near the front !!
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So I found this was causing the shifter bind. Is there supposed to be a screw here?
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There is a wee screw / pin on the side of the gearcase.-----The side of the bottom half.----That is the pivot pin for the shifter fork.----Plus the oil drain screw on the bottom of the lower half.----Post #7 says that " everything was connected properly " but are you sure it was if a screw was missing.-----So now I think the lower unit was full of water and you should take it apart ASAP>
 
racerone said:
There is a wee screw / pin on the side of the gearcase.-----The side of the bottom half.----That is the pivot pin for the shifter fork.----Plus the oil drain screw on the bottom of the lower half.----Post #7 says that " everything was connected properly " but are you sure it was if a screw was missing.-----So now I think the lower unit was full of water and you should take it apart ASAP>
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no the pic wouldn’t load for some reason. What I’ve found is this. The lever on the engine connects to another lever that goes upwards towards the flywheel. Well when you give it throttle the plate advances and and if you try to pull it out of forward that lever hits the plate. I’m sorry I can’t remember the name here but I know it’s used to advance timing. The name is just slipped my mind. If I could upload the pics it would be easy to understand
 
Armature plate is what it’s called in the breakdown. And that plate moves very freely. Is that supposed to? I’m wondering if my power loss was a timing issue. But one thing at a time lol
 
Well today when I got to looking that’s what I’ve found. That armature plate was stuck behind the lever not allowing it to shift. So that is my current situation
 
That assembly is an interlock to prevent shifting at high speeds. Throttle must be at a "slow" setting in order to shift. And you cannot advance the throtlle to "fast" unless it is in gear. Simple if you don't try to make it complicated.
 
A lot of guys who are smarter than I am are responding here. Make sure to keep that in mind as you read this... I don't see anywhere in here where compression is mentioned. I have had outboard motors run and operate smoothly including revving up good when not under a load, but put them in gear and they just don't have any power. I am learning to be very suspicious about compression on these older motors.... Have you checked compression? Its not going to solve these problems your having in the gear case but if its too low it could defiantly influence your decisions about how much effort/$$ to put into the problem... I own a 1974 Merc 850 so Im right there with you! but I have been told by trustworthy experts that putting money into my old Merc is probably a bad idea.. Looking forward to hearing how this turns out. Good Luck. Peace
 
BoatDope said:
A lot of guys who are smarter than I am are responding here. Make sure to keep that in mind as you read this... I don't see anywhere in here where compression is mentioned. I have had outboard motors run and operate smoothly including revving up good when not under a load, but put them in gear and they just don't have any power. I am learning to be very suspicious about compression on these older motors.... Have you checked compression? Its not going to solve these problems your having in the gear case but if its too low it could defiantly influence your decisions about how much effort/$$ to put into the problem... I own a 1974 Merc 850 so Im right there with you! but I have been told by trustworthy experts that putting money into my old Merc is probably a bad idea.. Looking forward to hearing how this turns out. Good Luck. Peace
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UPDATE-
Took it out last night for a test run. I had adjusted the shift cable and also put the spare prop on. Few things I noticed. 1 the boat did this time try to plane. It wasn’t plowing through the water like last time. Had more speed but not much. But definitely better. It did pop out of gear one time but I pulled the cable off and shifter it in at the motor and no more problems after that. Also it did run somewhat better with the cover off which leads me towards the carb. So I need to find information on 2 things. Carb adjustment and also the correct way to adjust the shift linkage itself. As in at that brass coupler. Or is there another adjustment? Or is it strictly at the cables ? All in all last nights run was a win in my book. It went out under power and came back under power so I’m not complaining
 
There is no adjustment feature at the brass coupler.----The screws go into that with notches lined up with the holes.----I repeat , no adjustment at the coupler.-----There is adjustment right at the shift lever up top.
 
Check for spark that jumps an actual gap of 5/16" on a test device.----Very common for those motors to run on one cylinder.
 
racerone said:
Check for spark that jumps an actual gap of 5/16" on a test device.----Very common for those motors to run on one cylinder.
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found a bad plug wire. Haven’t ran it yet. Replaced plugs also. Still trying to figure out how to adjust the shift linkage. Also could someone explain the cut out switch on the side of the motor. What exactly is it’s purpose
 
Get your eyes off the cut-out switch. The worst thing it can do is not work. It's job is to prevent a runaway condition in neutral.
 
fdrgator said:
Get your eyes off the cut-out switch. The worst thing it can do is not work. It's job is to prevent a runaway condition in neutral.
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Another thing I’m noticing is that with the throttle lever pushed to wide open the butterfly in the carb on is about half open. At first I thought it was a cable adjustment but I noticed the same thing if I use the lever on the side of the motor. When I turn it to fast it’s the same way. Does it pull own with vacuum as it’s running or is there something I’m overlooking here
 
Either it is not in forward gear, OR somebody has messed with the fuel saver rod in the throttle linkage on the side. Or both.
 
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