1978 Johnson 25hp lower unit or crankshaft?

[buffbenj]

25EL78C with shifter and steering controls (no tiller). Engine runs beautifully, but having repeated shifting problems. Have had it one year and have replaced clutch dog twice. Did it once myself with a used (but new looking) dog off of ebay and it worked for maybe 3 hours of easy running, then jumps out of gear from forward to neutral. Then had a trusted, experienced mechanic put a new dog in and he had a machine shop grind the forward gear a little. He also noticed my shifter cable was bent and range of motion hindered slightly, so he moved the cable half way down the shifter arm to improve the angle of arm movement. Worked great for about 5 hours, and now I cant go more than idle speed without it jumping out of gear (again!). The shifter and cable look OK and have good, smooth motion. I always firmly and swiftly shift it into gear. My question is, do I need to look at the driveshaft? Is this most likely a lower unit issue (given an experienced mechanic has recently had it apart), or is the driveshaft the most likely cause? If this werent such a doggone good running motor, I'd part it out. My mechanic is very experienced, and he SWEARS it needs a new set of gears and a new dog (Lower Unit Problem). But the fella I bought the boat from says this may be a red flag, since I have had the lower unit apart twice in a year, 25 hours total wear in a year, and now the dog (& gears?) are ruined again. I'm no expert, but each time the dog has been replaced and gears ground, they look darn near new. I have tried to put the parts diagram together in my mind, to try to tell what the driveshaft connects to at the powerhead (upper) end. Is it the crankshaft bearing? Could there be excess swivel/play in the driveshaft that is ruining my lower unit each time, maybe from a worn upper bearing in the powerhead? My mechanic swears no. The shifter cable is not the issue. I have temporarily removed it and it is impossible to keep the motor in forward gear manually at anything over idle speed. The thing is, if I can find a new set of OEM gears and dog on ebay or other site, I'm looking at over $400 + labor and new seals. I can do this investment, if the darn thing would last more than 25 hours. Found an identical replacement motor for $600, but 12 hours drive each way, or $195 shipping, with no warranty. Should I get a second opinion from another mechanic, and let him remove the lower unit? Removing the lower unit for a third time in 30 hours of use sure is fishy (or not, in this case, since the Crappie are starting to bite). Someone just shoot me...

 

[racerone]

Something is being overlooked here.-------If splines on the end of the driveshaft are good , then likely the spline in the crankshaft is good and all is driving properly.-------These things should last for years and years.---------Post pictures of the parts.----------At the window on the exhaust housing is there any up / down play when in neutral ?

 

[racerone]

Something is being overlooked here.-------If splines on the end of the driveshaft are good , then likely the spline in the crankshaft is good and all is driving properly.-------These things should last for years and years.---------Post pictures of the parts.----------At the window on the exhaust housing is there any up / down play when in neutral ?

 

[buffbenj]

No Title

I removed the exhaust housing window plate. Inside, there are two screws with a vertical rod. There was maybe 1/4 inch vertical play in neutral. The top screw was a little bit loose. The bottom screw was tight. I tightened the top screw with 1/4-1/2 turn clockwise, and now it is tight with no play. The light blue line in the photo is a flashlight. As for splines on the driveshaft, I know when I took the lower unit apart (the first time), splines were pristeen, in very good condition. So if there were play, it makes sense the splines on the driveshaft would be abnormally worn.
My mechanic seems to say that we have been trying to patch the lower unit together with used parts, and they fail. But these parts sure do look good when installed, almost new, with very little wear. I've already put $500 in it, and back to square one. New OEM parts seem to be hard to come by: at least $400 for the 2 gears and a dog, when a whole replacement motor is $600? really?

 

[gm280]

Your engine and exhaust and lower foot looks identical to my '76 40HP Johnson engine. And I know how those gears work on them pretty well. Do you know IF the mechanic replaces the detent balls and spring back when reinstalling the clutch dog? That does help the clutch dog and forward (and reverse) gears stay in place and not move around when running. If by change the spring is broken or even missing, it will be able to back out at will. And that can be the cause of the premature wear on both the gears and clutch dog. I'd take it apart again and check for those items and if they seem weak, replace them. They should need a pretty good amount of pressure to reassembly the spring, balls and slide the clutch dog back in place. If you can simple do that with out much effort, that is part of your problem. JMHO!

 

[buffbenj]

He's a reputable mechanic. I remember replacing the spring ball mechanism when I took it apart. I am quite sure he did too. I'm going to put it in the water just to see if tightening the top screw in the exhaust window makes a difference. I hope so! These screws hold the drive shaft in place when dropping the lower unit, correct?

 

[racerone]

No those screws are the connecter for the shift shaft !!!----------You might want to remove the screws for inspection.----Both those screws need to be put in to line up with notches in the shift rod.-----------Sorry, but the detent balls are only there to get nuetral.-These detent balls do not help keep it in forward or reverse .-Not at all.

 

[rolmops]

Did you at any point make sure that the clutch dog is fully engaged? If your shift shaft screws were loose,it means that there is play in the shaft that moves the clutch dog. The result can very easily be that the clutch dog is almost fully engaged but not quite and the result is that the edges of both the clutch dog and the forward gear are damaged . Putting a new clutch dog on a damaged forward gear just causes the clutch dog to be eaten up by the already damaged forward gear.
You must replace both at the same time and make sure that there is no play when they are engaged.

 

[boobie]

I agree with post # 5, and yes, I have worked on a "few" of them !!

 

[buffbenj]

So I need a mechanic to take the lower unit apart again, & be ready to replace forward gear, clutch dog, possibly reverse gear, & check the shift shaft & its screws& remind him that one of the shift shaft screws was loose, correct? He knows I am resourceful & can find replacement parts. He's made it clear that he is not enthusiastic about finding a set of gears for less than $500. This little motor is one nightmare!

 

[buffbenj]

So there is a way to make sure the clutch dog fully engages before closing up the lower unit with re-assembly? I certainly didn't understand how to do this when I replaced the dog the first time...

 

[buffbenj]

I put it in gear & the prop no longer turned. I thought that meant the dog was "fully" engaged.

 

[Faztbullet]

The new gears and dog will fix it right up as they are a 3 jaw dog and gear like the commercial units. These lower units didn't live long if out of adjustment as when OMC went to the bigger CI motor the units couldn't take the torque...

 

[rolmops]

how about you just buy another lower unit? It will probably be way cheaper.
http://www.ebay.com/itm/Lower-Unit-..._Accessories_Gear&hash=item4d2834695a&vxp=mtr

 

[buffbenj]

I can't make heads nor tails of the parts diagram of the exhaust shaft, specifically the shift shaft screws. Does anyone have another type of drawing, diagram, or photo of what the shift shaft and these 2 screws in the window, of what they do and how they work? Maybe my mechanic did not check them when refurbishing the lower unit last time? Found a set of gears and dog for $110 ebay, probably need to jump on that deal. Gonna back it down in the water first and try it since I tightened the shift shaft screw, (whatever that does)

 

[buffbenj]

By the way, my dog only has 2 jaws, not 3. Likewise, gears only have 2 gripping grooves I've seen 3 grooved dogs and gears, but not for my 25hp

 

[racerone]

The connecter for the shift rods is very simple !-------First there is no adjustment done there.----------The rods both have a notch that MUST be lined up with the hole when the bolt is put in,------Many mistakes are made there !!--------The adjustment is done at the shift lever up top.

 

[buffbenj]

I will check that before I put it in the water.