Mercury Mark 5 Lower Unit

[Buccaneer]

Gathering new bearings and seals to put the gear housing
back together on the Mark 5, and still have not been able
to verify one thing.
Is there suppose to be a roller bearing in the "Water Intake Housing" piece?
When I took the Mk 5 apart, there was a bearing there, but there
was a non original bushing pressed on the prop shaft that the
bearing rode on.
I had some MK6 spare parts, and it’s "Water intake Housing" piece
had no bearing in it, just the seal…….. not to say that there wasn’t
one in there originally.
I plan on using the Mk 6 shafts when I put the MK5 back
together, as they’re in better shape.
Help appreciated!

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Attachments:

Prepare to be boarded!

[hotrod]

I looked at the Mark 5 and Mark 6 parts lists. There is no bearing in the water intake housing, only an oil seal. The seal is not illustrated in the illustration, just listed with its part number. The lower driveshaft and prop shafts each have 2 bearings for each shaft (one needle bearing and one ball bearing per shaft). The needle bearing is pressed into the gearcase housing for each of the 2 shafts. These bearings each have their own part number and they are not illustrated (they cost $1 each back then). Pressing them into the gearcase is the first step in gearcase assembly per the instructions. Each of the 2 shafts also has a ball bearing on them. Each bearing has its own part number. I don’t know if Mark 6 parts can be installed in a Mark 5 case. You may have to do some measuring and possibly shim as needed for gear mesh & clearance. There may be a Mercury website for more info.

[Buccaneer]

Hotrod, thanks for the reply. It seems that the prop
shaft wouldn’t have enough support with the
ball bearing so far away from the prop, but guess
Mercury knew what they were doing. Not sure of
the thoughts of guy that put the extra roller bearing
and bushing my Mk5 prop shaft though!
The Mk5 case looks, and measures identical to the
Mk6 case. The Mk6 has spiral gears and a different ratio,
so I’m told I’d have to use the Mk6 prop as well.
Thanks!

Prepare to be boarded!

[Buccaneer]

Found the following (in the photo) from the
Mercury manual explaining the differences
between the Mk 5 & 6 gear boxes.
Both require to be set up with .003 to .005
backlash.
What’s the proper way to measure backlash
on outboard gear boxes? I have a dial indicator,
but no clue how it would be set up. Believe
I have a magnetic base for the indicator, but
of course it’s not going to work on the aluminum
housing 🙁
The manual gives no clue that I’ve found so far.
Your wisdom most appreciated!

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Attachments:

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[RICHARD A. WHITE]

Here is my thoughts… If you are building the MK5, you "should" be able to take all parts out of the MK6 case and just install them into the Mk5 case, benefits, it looks like the MK6 gears would allow for more speed as the are faster, if my math is right and I did not use a calculator so I could be wrong… Check the gear lash after installing and you should be good to go… Reading further is shows the 5 prop as being smaller, that would let the engine wind up a bit more, and the pitch is different, LOL…so they might just be equal…
Gosh I love Engineers……That last statement may not be true 🙂

Good luck and I hope I did not cornfuze you any more than normal 🙂

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[Buccaneer]

Thanks Richard, just have to figure out now "how" to
measure the backlash.

Prepare to be boarded!

[dave-bernard]

lift up on the drive shaft and push in on the prop shaft should be just a small amount of play. this should be done dry.no grease.jmho if you don’t have tools.

[Buccaneer]

Thanks Dave, I’ll probably end up doing as you suggest,
but am still curious what the "right tools" are.

Prepare to be boarded!

[RICHARD A. WHITE]

Reading this, I am thinking like Dave, push prop shaft in, then check how much up and down travel you have on the drive shaft.
Attach indicator to the drive shaft, and have tip of indicator touch gear case, check travel and see what it is…

just thinking out loud……

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[hotrod]

Another consideration from a Merc service manual: The original Mark 5 gearcases were machined deeper where the prop shaft ball bearing seat is. Thus they used a spacer between the ball bearing & the seat. The "replacement" housings were not machined as deep for the seat and this eliminated the use of the spacer. You will have to figure out if you need the spacer or not.
(The 2 needle bearings were used in the KF5 & MK5 & MK6 gearcases but only illustrated in the KF5 parts illustration.)

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