30-40 and 44 Merc Crankshafts
Quote:
Originally Posted by
MTECHMARINE
Reference
MARK 40
MARK 50
MK55 SMALL TAPER
MERC 300 - 500 THRU MID 60'S LARGER TAPER 40 and 44's
With correct end caps and flywheels will all these interchange??
And I have been told different cranks have different finish grinds on the crankpins. older are looser (smaller diameter) Which have what??
Been Evinrudin' for years, now back to 1st love "Sandcast" Merc 4 bangers! Need to refresh my knowledge base. Thank you. BILL
OK, here's the basics that I'm aware of...
Difference between 30 and 40/44 cranks is just driveshaft spline.
From there, there are two basic sizes to the rod journals. Early are .880" OD, later are .882" OD.
Early would be Mk40, Mk50 and early Mk30 and Mk55. Early 30 and 55 have a forging number 400-2 on #4 and the area where the bottom ball bearing runs did not clean up all the way down, the forging steps down. These are all small taper for the flywheel
Late had various numbers, but were machined all the way to the bottom, allowing room for double seals. Those were mostly big taper for the flywheel.
The rub is, I have seen a few 'transition' models (manufacturer reserves the right to change specs at any time) where the big journals were on a small taper... or was it other way around?
So, best to measure the journals.
All these will fit a 40 or early 44 with appropriate parts. Be careful though, with the later 'solid' top bearing cap... there are two lengths. The short is for the later-yet 44 cranks with the thick (approx. .100") top counterweight. You need the long, same length as the slotted cap version, for these cranks.
Hope this helps.
Jerry Wienandt
Trident Racing