Driveshaft water tubes, 18-35hp motors

[johnyrude200]

Hello All,

I have been noticing that quite a few of the motors I work on either are missing these, or the o-rings at either end are missing/worn out. No big deal replacing o-rings.

Now on the older 18-20-25’s, this may create a big problem where water starts filling up the exhaust housing and finding it’s way out where ever it can (the exhaust pulses seem to keep it from getting up into the powerhead…but that’s still not good).

The newer 20-35’s, the cooling system will just plain not work right.

My question is has anyone tried fabricating these water tubes on their own out of round aluminum with a couple of o-rings at each end? The reason I ask is nearly every 18-20-25 I work on (early 70’s thru ’76) is missing this. While the motor still can run at a correct temp, it’s still not something I send the motors out the door looking like for obvious reasons.

I don’t think it would be necessary to cut a recess in each end of the tube to hold the o-ring in place, but figured I’d see if anyone else has tried this. The tubes are 7/8" O.D at the o-ring recess, and about 1/8" thickness. This tubing is pretty inexpensive online in aluminum, graded to resist corrosion with structural strength. Lengths are 7-7/8 (longshaft), 2-7/8 (shortshaft).

[wiscoboater]

Without the small "recess" in the tube for the Oring, would it not creep out of place with engine vibration?

[frankr]

I consider that tube to be an important item that needs to be there. That said, I see no reason you can’t fabricate your own if you have access to a lathe. (Easy to form the grooves on the lathe).

[johnyrude200]

Couldn’t agree more frank on those water tubes; not sure why people discard them so often. You can get away without them on the older motors, but those ’77-thru 32 cu. in. motors won’t pump water without them!

[frankr]

Maybe you can get along without them on older ones, but they are there for a reason. They create an isolation tube for the drive shaft AND the bottom end of the crankshaft with it’s seal assembly. Being an old salt water mechanic, I realize how much that means when it comes to rust damage to the splines and crankshaft seal. It is damage that sneaks up on you unnoticed till it is too late.

[johnyrude200]

agree, there certainly is a difference in water output without the tubes in the older 18-20-25’s too. I guess folks reassemble things and have extra parts, yet don’t think that means anything 🙄

Here’s a 15hp I took apart last night that was seized due to this very issue. The upper driveshaft seal bearing was so stuck with salt that the customer thought the motor had seized. My website explains the story more so I won’t bore people with the rest of the details. After I removed this (and the bearing), the motor was totally fine (replacement parts aside). There was no o-ring on the driveshaft.

[fleetwin]

OK, am I the only one that doesn’t understand what oring(s) you are referring to? Your picture shows a 9.9 missing the upper driveshaft oring…

[johnyrude200]

on the 18-35hp motors (old and new), they use a water tube on top of the impeller housing to create a shield from exhaust pulses entering via tiny holes atop the housing. Both styles use 2 o-rings at each end of the tube to seal it up. I’m assuming this creates a water seal up the driveshaft housing, and if this o-ring at the top of the driveshaft is missing, allows water to work its way up into the drive/crankshaft articulation/splines.

The 9.9/15 upper driveshaft bearing housing (for lack of a better term) has a couple of other seals too. They don’t have a water tube like the larger HP motors, but this one (pictured) was seized up with salt up there.

[Mumbles]

quote johnyrude200:

The 9.9/15 upper driveshaft bearing housing (for lack of a better term) has a couple of other seals too. They don’t have a water tube like the larger HP motors, but this one (pictured) was seized up with salt up there.

Later 9.9/15’s, you’ll have to check which years, use two lip seals inside the crankcase head with no O ring on the shaft instead of one seal with an O ring. Besides making the shaft harder to install, OMC probably felt the O ring was unnecessary with two lines of defence below the splines. Using the later head on an early motor is a simple upgrade to do while the powerhead is off.

[frankr]

I’m surprised we haven’t confused anybody yet concerning the "old" 18hp. The isolated drive shaft chamber first appeared on the 1958 35hp Lark/Super Quiet, and the 50hp, plus the redesigned 10hp. The 18/20/25hp didn’t get it till 1968. Until then, the crankshaft end stuck down into the nasty exhaust/water environment. That’s why they used that baffle plate to shield it—which didn’t do much good.

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