Help...my merc 50 rattling and shaking

[jasonyoung]

Hi...my 2 stroke merc blueband 50hp mid 80s i think started rattling and grinding last trip...seems fine under load but when i slow down or idle it making a racket...got video(sorry it long)...you can see it going great but when i slow down the noise begins...been reading horror stories on net about big end bearings etc....any ideas or advice be greatfully appreciated.

 

[jimmbo]

Did you the cowl wrap and top cover off and look around to see if anything is loose?

 

[jasonyoung]

Hi..i took off cowl and wrap...sounded like it coming from under flywheel...a rackety rotor sound...been advised remove spark plugs and try to see if flywheel loose while boat is on land....tried on loch but felt tight...going today so i let u know

 

[60sboater]

Sounds strong under load. I wonder if the something related to/with the starter may be loose.

 

[Chinewalker]

Not common, but the flex plates on the flywheel have been known to crack on them. Usually right at the hub, along the bolt holes. Once they get spinning, they act as a gyroscope, so they don't do anything, but at idle, they bounce around a bit. Pop the top off and take a look at the flywheel. If the outer rim moves independently of the center, you're onto it... Don't run it any more until you figure it out, though, as it can take the stator with it...

 

[jasonyoung]

Thanks for replies...had a look yesterday but no movement in flywheel.. tried pushing and pulling it...going back up today with some tools..will take off flywheel see if i can see anything loose or broken once it off.

 

[CharlieB]

Those old flywheels are bolted to the hub, it is easily possible to 'clock' them incorrectly making the timing marker seem way off. You can remove the flywheel without removing the hub. Sometimes there is a second 'cover' plate on top of the actual flywheel plate so you may not be able to see if it is cracked until that cover comes off.

 

[Chinewalker]

Yep, mark the hub and plate with a Sharpie to get them aligned again when you're done.

 

[jasonyoung]

Thanks...brought boat home yesterday...removed 8 bolts and flywheel came off...took spark plugs out...spun flywheel before i took it off after plugs out...no noise...when flywheel off no cracks or signs of anything broken...think next step is to remove hub with a puller tool and see if any broken bearings or connectors etc...have to order tool from ebay

 

[Chinewalker]

Any evidence of the flywheel hitting the stator? I had a 50 come into my shop once with a broken crankshaft. Motor still ran, as the break was at an angle, right under the top main bearing. The bearings supported the crank enough that it still worked, albeit noisily.

You can remove the upper main bearing cap by removing the stator, followed by the four bolts holding the cap in place. Gently and evenly pry the cap out with a pair of large flat blade screwdrivers, taking care not to mar up the machined surfaces of the housing.

 

[jasonyoung]

Thanks i remove the four bolts i think u are talking about tomorow...see what i find underneath..will post pics of what i find thanks again

 

[jasonyoung]

https://youtu.be/vvBUgzYtBfY
think it fixed...the 8 bolts werent tight down when i took off flywheel...were terrible to turn either way...so im hopin noise was play on flywheel being not fastened down tight...i greased bolts and put it back together...tightened right down.. started it and ran for good 40 mins...even tried in gear...no noise....i couldnt get big centre bolt free thats why i decide not to try force it as i know not about engines...i think it running as normal...put a vid up..thats what it always sounded like...cant hear rattle no more...thanks for all advice...going to launch tomorrow and have a good run...got electric as spare just in case...let u know thanks again

 

[jimmbo]

There was quite a rattle at 25 sec

Considering how far above the water pump is, I'm surprised it is pumping water. Anyway, put the cowl on and take it to the lake.

 

[jasonyoung]

https://youtu.be/9HrwT7n9_Hc

Went great...but panicked when seen white smoke/steam at idle after going full throttle...thot a gasket or wrong mix...burnt off eventually...launched boat with engine down....as it slid off trailer it sunk a bit until whole boat was in...so im assuming that it got wet and the smoke was in fact steam...all good now