Merc 18 5995557 Shearing Drive Keys

[JDusza]

I have an 18 Merc, 5995557, that I just put new bearings (crank and drive shaft) and seals. Started it up in a barrel. Much quieter, lot less rattling and no more squeaking. Shut it down and wouldn't restart. Found the drive key sheared right in half. Installed another one and same thing. Starts, runs, shuts off and then won't come back. Broken key.....
So, why is it shearing keys?
Thanks,
J

 

[Laddies]

Re: Merc 18 5995557 Shearing Drive Keys

Some one did not torque the flywheel to the proper torque originally and if it contuinues it's because the crank and flywheel taper is not cleaned up properly a good taper holds the flywheel when torqued properly all the key is for is to index it till it is tightened.

 

[Bosunsmate]

Re: Merc 18 5995557 Shearing Drive Keys

As above crank must be clean and also the flywheel taper, no grease etc and tightened to correct torque
Check your timing isnt too advanced at start up too

 

[JDusza]

Re: Merc 18 5995557 Shearing Drive Keys

Nailed it! Thank you. Cleaned up crankshaft with emery cloth. Cleaned up flywheel with emery and magnet. Measured key and shaft slot to be sure. Put it back together and torqued the flywheel bolt. Starts first pull. Ready for try-out.
Thanks, again.
J