Mercury Mk 5 & 6 Gear Cases

[Buccaneer]

I tore apart the gear case on my 1953 Merc Mk 5.
The prop shaft is in rough shape. I thought perhaps
the shaft from my "parts" Mk 6 may work, but see
that the prop shafts are different, as the Mk 5
has a bigger bearing step in the middle for the
cartridge. My Mk5 has the water pump above
the "shoe" piece as does my Mk6. Looking at
diagrams, it appears that some Mk 5’s had the
water pump impeller on the prop shaft, instead
of the drive shaft. My Mk 5 had straight cut gears,
and the Mk 6 had bevel cut gears.
Is is possible to switch guts from the Mk6 and put
them in the Mk 5 gear box? (Mk6 gear box is toast)
The Mk 5 diagrams show two different prop shafts,
one of which is the same shaft as the Mk6.
So confusing!
Your wisdom appreciated!

Prepare to be boarded!

[jasonh]

The quick answer is no. You can the other way, mark 5 guts into marks 6 housing, with a spacer and proper shimming. The water pump on propshaft would be from the predecessor to Mark 5, the Super 5 KF5.

[jasonh]

Also, the props are different

[Buccaneer]

Jason, Thanks for your reply. I guess the reason I’m confused is,
both my Mark 5 & 6 have the later style water pumps driven
by the drive shaft, but yet the Mark 5 must have an earlier
or different style prop shaft. I haven’t done any measurements
yet, but the gear housings on both the Mk 5 & 6 look the same.
Then again, I have no idea what the previous owner(s) may
have done…… for all I know I may have a MK6 gear housing
with MK 5 guts in it.

Prepare to be boarded!

[Buccaneer]

In looking at the diagrams on MarineEngine.com, the only see one difference
between the Mk 5 & Mk 6 gear box guts, and that is…..
A. Different prop shaft ball bearings (Mk6 is thicker)

Between the Super 5 and the Mk 5 & 6, there’s several differences of course….
A.Prop shaft
B. Pump Cartridge vs. Water intake housing
C. Gears
D. No Lower drive shaft (no neutral clutch on the Super 5)

So if my MK 5’s prop shaft is different than my Mk 6’s, then
I either have an early Mk 5 with the Super 5 style shaft,
or someone’s mixed and matched parts over the years 🙁
Will think about it more tomorrow!

Prepare to be boarded!

[Anonymous]

mark 5 has neutral shift super 5’s don’t. super 5 water pump is on the prop shaft mark 5 it is on the drive shaft.

[Buccaneer]

Dave, my MK5 has the neutral shift and water pump on the drive
shaft as you say, (like my Mk 6) but the prop shafts are different.
What I’m trying to work out is if I can put MK6 guts in my
MK5 gearbox. So far, I see no differences in the housings.

Prepare to be boarded!

[Anonymous]

I think one has straight cut gears and the other has spiral cut. you may be able to interchange complete lowers.

[Buccaneer]

When I find out if I can turn my gear box into a Mk6 unit,
I’ll let you know! Thanks.

Prepare to be boarded!

[Author]

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