Merc 470 wont turn over

[DBG]

I have an 84 Searay 260 EC w/ twin Merc 470's that are supposidely 4 years old. I was going across the lake yesterday at about 3800-4000rpm's and I heard some rattling, then the port motor sounded like it over-revved and quit. Now when I try to turn it over, the motor jerk's and the only thing that spins is the shaft that goes into the outdrive. I can turn the motor over by hand. (well with a wrench anyway) Any Ideas?

 

[DBG]

Re: Merc 470 wont turn over

anyone?

 

[Boomyal]

Re: Merc 470 wont turn over

Maybe something let loose in the outdrive, possibly the coupler, and allowed the motor to overrev, breaking something in the motor in the process. Does the motor try to start when you crank it?

 

[Bob_VT]

Re: Merc 470 wont turn over

You will have to give a better description. If you decide to turn the motor with a wrench you can do it but DISCONNECT THE COIL WIRE. If it should start you don't need to loose a limb.<br /><br />If it feels locked up remove your spark plugs and try turning it again.<br /><br />Bob

 

[DBG]

Re: Merc 470 wont turn over

Yes, I can turn the motor over by hand and it doesn't seem to make any noise. When you turn the key, the motor jerks, the the starter whines out while spinning the shaft going into the outdrive. I'm clueless.

 

[Elk Chaser]

Re: Merc 470 wont turn over

You gotta pull the engine and see what failed, could be as simple as a few bolts or as complex as a broken crank shaft in the engine or maybe failed splines on the outdrive shaft. Hard to say.<br /><br />Obviously the flywheel is intact but the connection between the flywheel and the engine is not, stop trying to turn over the engine because if it is something simple you may be creating more damage everytime that engine jerks.

 

[Blk-n-Blu]

Re: Merc 470 wont turn over

Possible timing chain / gear failure?

 

[TwoBallScrewBall]

Re: Merc 470 wont turn over

So the starter is turning the flywheel and everything back but not the engine.....<br /><br />sounds bad. If it was a loose ring gear the outdrive would not turn. If it was a timing chain the starter would not spin fast enough to whine since it would still be turning the lower end, and the pulleys would turn. Sounds like a snapped crank.

 

[DBG]

Re: Merc 470 wont turn over

That's what I am thinking, but forged cranks don't break that easy, and I wasn't pushing the boat that hard either. It rattled for a second then it died. Dunno. Only part that sucks, is I have to take it somewhere to get the motor pulled out. The back of the boat is too high to use a regular cherry picker, I need a chain fall or a forklift.

 

[DBG]

Re: Merc 470 wont turn over

6 sheared flywheel bolts.