lower unit reseal

[dutch420]

Hi guys gonna reseal a couple lowers but never done one yet a walk through would be great
One is from a 72 70hp chrysler.. 2 peice
Other is from a 71 70hp but skeq is bent so i wanna use my parts 73 85hp to transfer the parts to but never done this help if ya can
And not sure what i need

 

[Frank Acampora]

Re: lower unit reseal



You will need a seal for the drive shaft (located under the water pump), a seal for the propshaft (inside the rear bearing carrier), a seal for the shift rod, and two new seals for the fill and drain plugs.

There is a large O-ring between the gearcase and midleg.

Gearcases are either two bolt or three bolt. Three bolt is shown in the photo. This refers to the number of studs holding the gearcase to the midunit. Several of the studs have small O-ring sealing them at the top, under the nuts and I believe the front stud has a small O-ring at the bottom in addition to a locating bushing.

The only complex seal is the shift rod. You first remove the old one by threading in an appropriatly sized lag bolt and pulling it out. You then press in the new seal steel cup up and rubber side down. Use something appropriatly sized (I use a socket) to press the seal until it is snug around the shift rod. The shift rod should not be tight, but should move smoothly and relatively easily--there should be some drag on it though. Since this seal can be pressed tighter, often it is not necessary to replace it. You simply press it until it seals against the shift rod.

Do not try to salvage a gearcase with a damaged O-ring groove or midunit flange. Sanding down the gearcase and/or midleg meeting flanges will change the gear lash and lead to premature gear wear.

 

[dutch420]

Re: lower unit reseal

Ok great frank .. Now do i need to add any "gasket maker" inbetween the two piece.

 

[jerryjerry05]

Re: lower unit reseal

Putting "parts" from one unit to another will usually require shimming with special tools.
That what your gonna try?

 

[dutch420]

Re: lower unit reseal

Hey guys thanks for the info... Yes jerry thats what i would like to try my 1971 70hp has a bent skeg but every thing else ie good .. I had a 73 85hp i used for parts lower did not work right i seperated the 2 piece and the drive shaft came right out of the gear case.. Now it had a lot of metal shavings in it to.. So i would like to use the gears and what not from the 71 and put it in to the 73 that has the undamaged gear case....
Now i also have a 72 70hp im gonna put on me boat and wanted to reseal it to.. ..but frank gave me some info on how to do that. Just i am taken a stab in the dark in the other too

 

[Frank Acampora]

Re: lower unit reseal

No "goop" is necessary for the parting line between the gearcase and midunit. The O-ring is sufficient seal if the surfaces are clean and in good condition. However, a thin coating of RTV silicone or anaerobic sealer could not hurt.

As I remember, the lower drive shaft bearing sets the gear lash and there are NO shims. The cup simply sits in the recess of the midunit (second photo).

However, there are different shims for the forward gand reverse gears on the propshaft. The thickness of these set the lash of both gears with the pinion. More later.

The pinion must be set with a (according to the factory) NEW pinion nut. However, you can re-use the old nut if you either squeeze it slightly in a vise to deforem it again or you re-stake three sides with a punch. Either method deforms the threads slightly, making it a self-locking nut. Again, If I remember correctly the pinion nut must be torqued to 80 INCH pounds. This overcomes the resistance of the deformed threads and sets the pre-load on the two tapered roller bearings carrying the drive shaft.

Now, back to gear lash: Most Chryslers of this age were set up loose, according to an old Chrysler mechanic I knew. You may very well be able to replace the whole gear pak into another gearcase and still be within tolerance. When you do, spin the shaft without the waterpump or seal so you can "feel" the gear mesh. If it is smooth without any grumbling or grinding, it will probably be good.

And, as an aside, the two piece lower unit while very nice looking is not nearly as good as the one piece. If you find a one piece engine that is trashed, for cheap dollars, you can transplant everything of yours onto the one piece midleg and lower unit. You will then have a better performing engine with a better choice of props AND about 2-3 MPH more top end. I alreade did this on a 90 on the boat in the avatar and proved that it does indeed get 2-3 MPH more.