'71 25hp propshaft detent question

[Bindernut]

Got another question on my 71 25hp Evinrude (25102S).

As shown in the service manual, the prop shaft has a hole in the shaft that carries a spring-n-ball detent setup for the clutch dog. It snaps it into forward, reverse, and neutral.

The trouble is this...
The prop shaft was bent, so I scored a complete 18hp lower unit with wornout gears/dog on ebay for parts. I don't know the exact year of the 18hp lower unit donor, but it's the same as mine.
The donor's prop shaft doesn't have the hole for the detent setup, but I installed it anyway. Now, the dog depends on the detent on the shift lever assembly (up on the powerhead) to hold it in gear. It doesn't.

With the old prop shaft the dog/gears did not jump in either forward or reverse. But with the donor prop shaft it jumps in forward. The clutch dog and gears have very minor wear and were fine before so they should be fine with the new shaft too...or so I would think.

Anyone else ever have this problem? I think I'm going to have to crossdrill the 18hp shaft for the detent spring setup to hold it into gear. Anyone see a problem with doing this?

My friend also has a '73 25hp Johnson on their pontoon. This motor doesn't have the detent setup on the prop shaft either... We just replaced the dog and I milled the gears to remedy it's gear jumping problem. It's working fine, but we would consider drilling this one for the detent too if it would be beneficial to preventing wear.

Sorry for the long-winded post...

 

[Dhadley]

Re: '71 25hp propshaft detent question

Drilling the shaft is a very real option, no problem.

Cutting the engagment lugs on the gear & dog can present some problems. If you go thru the hardness it won't last long. If you're lucky it'll be fine. Seen both scenarios.

 

[F_R]

Re: '71 25hp propshaft detent question

I always update the prop shaft by drilling for detent. Much better system, but it won't prevent jumping if the dog/gear are worn. Yours must be about at the critical point if it was OK with the detent but not without.

The biggest advantage of the detent is it causes the dog to snap into gear quickly so the dog ears don't bang around so much.

Since you mentioned that you do milling, I assume you know about drilling stainless steel. Anybody else who is inexperienced is in for a surprise. You know what I mean.

 

[Bindernut]

Re: '71 25hp propshaft detent question

Thanks for the info. I wasn't sure if that detent system was something different between years or between tiller/console models. (My rude is a tiller, that Johnson is a console, the donor LU is from ???).
I was considering drilling it right away, but held off because I was impatient to get it back together after my water pump incident first time out this year. That's what I get for not taking the time to ask about it earlier! LOL
Yep, I'm real familiar with working with stainless...most of our repairs at work are on stainless food-service machinery.

The story behind the milled gears...cuold be a post all by itself...
A local (Merc & Honda) boat shop parts counter guy suggested we might be able to swap the forward and reverse gears to use the other unused engagement surface on the gears. Ermm...can't do that on this LU, the Fwd & Rev gears are different!
Well, we've got a turret jig on the Bridgeport @ work. I had to rebuilt a clutch setup on one of our machines that looked like a very large version of an outboard clutch dog setup. Figured it wouldn't hurt to play around with the gears from that donor LU so I chucked it up and milled the engagement surfaces with a carbide cutter. I got em cleaned up by removing only .005" of material. I don't think it milled through the heattreat layer, but even if it did I'm only out about 30 minutes of time after work one day. Those LU gears are hard! Don't even bother trying this with a regular tool steel cutter...
The gears turned out really nice, so we tried them on that 25 Johnny on the pontoon along with a new dog/cradle assembly. It's working like a champ for now. Not bad for "free" gears...better than another $400 of parts anyway!
I think we're gonna tear down that LU after this season and add the detent setup on this motor too.

 

[R.Johnson]

Re: '71 25hp propshaft detent question

Bindernut: You just did the possible. I like reading post's like this.

 

[Bindernut]

Re: '71 25hp propshaft detent question

Just posting a quick update on this.

I cross-drilled the replacement prop shaft and installed the detent spring/balls. After working around my jinx this year...whenever I get a day off, it's either raining or blowing 20-40mph...I FINALLY got it out on the lake last weekend for a couple hours. Works great! No more jumping out of gear.

The Johnson on the 'toon with the milled gears is holding up for now. We're gonna run it this season and tear it down this winter to crossdrill it's prop shaft too. I'll find out how those "free" gears are working out then.

Happy boating everyone and thanks for the help!