Merc 85 crank drive splines.

[BB46]

I have a 4 cyl mid 70's 85 Mercury outboard that didn't want to drop out the lower unit. Splines were locked together. I heard that was pretty common.

Thing is. The splines on both ends and especially in the engine crank shaft side are really in bad shape. Very rusty,corroaed, and pitted to where I don't believe they would hold together under power.

Is this also common? Next question. Are the splines directly in the crank and thusly make the motor junk or is there a piece between that needs replaced?

I know or 3 of these right now and need to know what my options are.

BB46

 

[emckelvy]

Re: Merc 85 crank drive splines.

Yup, the crankshaft splines are "broached" or otherwise formed/machined into the end of the crank and cannot be repaired (at least by any reliable, economic method).

The accepted method of fixing this would be to pull the powerhead, split the crankcase, and replace the crankshaft. Of course while you're inside it'd be a good idea to check out rings, bearings, etc and renew as required. New seals & gaskets too!

A pretty common problem with these. The end of the driveshaft is somewhat exposed, whereas the older crankshaft bearing end caps had a "snout" on them which provided a bit more protection to the driveshaft/crank area from water splash.

Combine that with a lack of maintenance (pulling the lower unit down every few years to replace impeller or at least inspect and then lube-up the driveshaft splines), and the driveshaft rusts away in the crank.

Or, the O-ring seal on the driveshaft (and in later models on a 'carrier' pressed into the end of the crank) fails and lets water in the splines.

You'll find tons of little Twins like this. Folks will run them as long as they pump water, maybe for years and years. Then when the impeller goes, you can't get the motor apart because the crank and driveshaft have become One.

That's why it's important to service these once in a while, if for nothing else but to grease the splines.

A few months ago I picked up an '89 Evinrude 6 hp with stripped-out crank and driveshaft, pretty new for a motor to have these probls. So it's not a problem limited to Mercs.

But then again, worked on a 1955 Johnson 5.5 hp this summer that looked and ran like new and had perfect driveshaft/crank splines. You just never know until you open 'em up. Lots can happen over the years.

At any rate, hopefully amongst all the dead motors you'll find a good crankshaft. Otherwise, eBay might be a good place to look for parts. Or your local Craigslist.org .

Any crankshaft from a 4-cyl, 66 C.I. 800, 850, 85, 80 or 75 should work.

HTH & G'luck........ed