MERC 20 hp. Driveshaft trouble ahead?

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MOTION LINE

Seaman
Joined
Oct 9, 2004
Messages
74
One good friend told me that my merc 20 from 1966 has a rusty driveshaft and it will break any day (far out on the lake), I can remember some mercs braking the driveshafts in the 70ies but what years did MERCURY build decent(sainless) shafs or was it so that when the production was moved over to Belgium they wanted to save some costs and replaced the good American build shaft with a cheaper one?<br /><br />Is it safe to run my engine or is a drivshaft replacement mandatory?
 
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emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: MERC 20 hp. Driveshaft trouble ahead?

It would have to be terribly thin before 20 HP would cause it to break! On a 20HP, I'd be more concerned about the driveshaft splines rusting into the crankshaft. <br /><br />You could remove the lower unit for inspection to see if there's any issues. Apply a liberal coating of waterproof grease (or mfr's spline grease) to the driveshaft splines, but none on the top of the drivshaft. Replace the drivshaft O-ring if there is a groove in the drivshaft for one.<br /><br />If I recall most motors had stainless or bi-metal shafts by '75-'76 or so.<br /><br />HTH......ed
 
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Motor Boater Bill

Chief Petty Officer
Joined
Jan 29, 2005
Messages
488
Re: MERC 20 hp. Driveshaft trouble ahead?

I have a spare LU I bought on eBay and it has the bi-metal shaft, stainless from just above the water pump on down, but right above where the stainless steel stops it is rusted halfway through. I think it would eventually break at that point without a whole lot of torque. I believe it must have lived in salt water to get like that.
 
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