6 HP E/rude gear box rebuild question

[Tim Frank]

1) Gear shift rod bushing and seal. The OEM manual is not as precise on this as I might have thought. There is a brass bushing that guides the shift rod as it exits the gearcase...it goes in a bore that also contains a rubber o-ring...which is sits between the bottom of that bushing and the bore bottom-shoulder. There is no real instruction on reinstallation.
I can press in a bushing with the best of them, but how critical is the compression or non-compression of that o-ring?

There was no real wear on that bushing, I was just going to replace the o-ring. The tech at the dealer where I bought the parts said that the bushing could stay in place....I could fish out the o-ring and reinstall a new one.
Obviously a job for a seasoned pro because I got the old one out easier than i expected, but getting the new one back was going to be more of a challenge than I was prepared to deal with to save a $6- bushing. That o-ring was very thick and not very pliable. Would have been a real blood pressure raiser.

Ordered the new bushing, ran a 5/16-18 thread into the old bushing, pulled it and it is all downhill now except for the clearance between the bushing bottom and the o-ring....if any. I can just reinstall to "about" the same depth if nobody has a better idea.

The question is, should the bushing be inserted: 1) to "snug up to" the o-ring
2) to actually compress the o-ring some amount....and if so how much....3) something else.

Since the manual is non-specific on this, and it is just the shift lever...little movement, it probably is not a critical issue, but there had to be some design intent and it would be nice to maintain that.
I have measured the depth of the bore, the thickness of the bushing, and o-ring, and it appears that in the original positions there was ~ 0.100" clearance between the bushing and the o-ring, which means the oring could move in the bore. That just seems odd to me....

Any ideas?

 

[bob1340]

Re: 6 HP E/rude gear box rebuild question

MMMMH--- I just replaced this bushing on my '71 8 HP. The bushing had a lip that the o-ring fit into so I just guessed the depth of the lip was how much the o-ring was compressed. I am guessing you have no lip on your bushing?

 

[Tim Frank]

Re: 6 HP E/rude gear box rebuild question

Right.
Just a smooth cylindrical bushing...OD ~ 7/16" ID ~ 1/4"
Length ~ 3/8"

 

[Vic.S]

Re: 6 HP E/rude gear box rebuild question

My 6hp is a mid 80s design so different to yours.

My judgement would be that if the O ring is tight enough when all installed to make an effective seal both on the shift rod and in the housing without being compressed then all that is required is to fit the bush to just snug up to the O ring to hold it in place when the gear shift is operated.

If it was necessary to compress it there would be instructions in the manual to get that compression absolutely correct. If the internal and external diameters are correct to make effective seals then its not necessary.

I agree though that 0.1" freedom for the O ring is surprising thats why I'd fit it just snug.

Just my thoughts for what they are worth.

(I cannot find such a beast as a 71 8hp.)

 

[F_R]

Re: 6 HP E/rude gear box rebuild question

The fat o-ring that goes in there is considerably compressed already. If you drive the bushing down against it, there is nowhere for the rubber to go when you shove the shift rod in it.

Actually, the service manual probably tells you to use the special tool to insert the bushing. That automatically sets it to the proper depth.

OK, so you don't have the tool. Look at the bore that the bushing goes in. See that chamfer at the top? Drive the bushing in till the top of the bushing is even with the bottom of the chamfer and you will be good to go.

 

[bob1340]

Re: 6 HP E/rude gear box rebuild question

Right.
Just a smooth cylindrical bushing...OD ~ 7/16" ID ~ 1/4"
Length ~ 3/8"

Well that sounds screwy!
What I would do is this. Place the oring at the bottom of the bore. Press the bushing in untill it just makes contact with the o ring. Lube the o ring with grease and see how well a 1/4 shaft fits. If it feels too loose tap the bushing down a bit and recheck it.

 

[Tim Frank]

Re: 6 HP E/rude gear box rebuild question

The fat o-ring that goes in there is considerably compressed already. .

Great point....which didn't consider. I measured the thickness of the old o-ring after I removed it. :redface:
What I need to do is put the new o-ring in place and then measure the depth of remaining bore and I probably will find that the "excess" has disappeared.

The bushing ID is actually .256 so a piece of 1/4" rod, cut to length, and threaded on both ends is perfect as a draw-bar to seat the bushing. A 5/16-18 tap threaded the old bushing beautifully for pulling with a 5/16" bolt.
The drawbar will offer perfect control for depth adjustment.

Thanks to all responders!

 

[Tim Frank]

Re: 6 HP E/rude gear box rebuild question

All back together and working beautifully.
Thanks for all responses.
Final word on the o-ring / bushing clearance/no-clearance was that with the new o-ring in place in the bore, the resulting o-ring thickness was greater and the bushing in its original position just contacts the o-ring....does not compress it, but keeps it firmly located.

For some reason the motor shifts much more smoothly, although since I did not replace anything but the gear-case seals, that does not really make sense.

Maybe it just feels better about itself with all the attention.