old merc/mark question

[heath brinkley]

will a '64 merc 500 fit on a '59 mark55 midsection/lower unit ?

[crazy horse]

Heath, My book shows them both as 44 ci. if it's a 55A or a 58A. So I would say yes it should have the same bolt pattern . The only thing that might be differant is the gearcase splines, I don't see any specs in this book on the splines . I've done some swappin over the years with inline four stuff but I can't remember if the gearcase was a drop on.:)

[crazy horse]

This is a quick little ref. page out of a old manual.

[heath brinkley]

Thanks alot. I found a 55A 15" mid and lower and wanted to make sure it would work before buying it. Already have the merc500 but its a 20".

[Mark75H]

Heath, I don't know what year the change is, but there is a minor change in the bolt pattern for the back 2 studs about the time of your later motor.

All the front and middle studs will match for sure, as will the crank/driveshaft splines. Dave is right, both are 44's.

The change year might be the year they switched to the little wrap around cowl that covers the studs and nuts. Raceman calls this cowl the "jock strap"

If you have a late 60's motor it will definately not bolt up to a late 50's leg because of the back 2 studs.

I'm kinda thinkin' those motors won't fit.

[heath brinkley]

if the back two studs don't line up, would the other 6 be enough to safely hold it in place. Keep in mind this aint no pantywaist mark55 or mark58 this is a mighty merc500 were talkin' about.:D :D