Mercury 500 -69 rattles as hell, from upper part around the flywheel.

[Nozer]

Had the boat launched last weekend.

it runs good and smooth.

But there?s a loud rattling noise from the powerhead.
The sound has always been there, but it has increased, and now sounds VERY loud.

Its mostly when in idle or up to ? trottle.
When accelerating, the sound disapears when reaching about ? trottle.
Or it reduces so much it?s hard to hear. When on WOT, you cant hear it. (or very little)

Its a sharp rattling sound. When i took the covers off, it sounds like it?s coming from around the flywheel. Dosnt feel any loose parts when pulling the flywheel back and forth.

The sound is there all the time. Not any diffrence when it?s cold or warm.

The telltale is there all the time. And it dosnt seem to be overheated. It?s possible to put fingers on the cylinders without burning them.
And the telltale isn?t specially warm.

Nothing seems like i?ve fried the motor.
The cooling have worked all the time.

Rebuilt the fuelpump this winter, and the engine sounds good besides this damn rattle.

Anyone got an idea what to look for?

/Tobbe

 

[Laddies]

Re: Mercury 500 -69 rattles as hell, from upper part around the flywheel.

Check the flywheel flex plate, they tend to crack if the hub is pulled improperly and once in a while for no good reason.

 

[emckelvy]

Re: Mercury 500 -69 rattles as hell, from upper part around the flywheel.

I had an old Merc 1000 that sounded just like it had a bad upper bearing and when I went to pull it down, heard the flywheel go 'crink' 'tink' and discovered the cracked flex plate. All around the hub as described. You can check this by removing all the center bolts on the flywheel which hold the flexplate assy to the center hub.

If it's not a cracked plate, highly suspect that it's the crankshaft upper ball bearing. You can pull the bearing cap for inspection, after removing the flywheel and stator.

But, if the bearing is bad you'll need to pull the powerhead and "split the cases" since the bearing on a '69 should be pressed onto the crankshaft. As I recall at least.

If you're lucky the bearing will come out with the bearing cap and it's relatively easy to drive out the old bearing and press in the new one. BCA 6206 or equivalent, get one cheap at any auto store.

Be sure to replace the crankshaft seal and bearing cap O-ring while it's down.

Well, maybe you'll get lucky and it's the flex plate! HTH...........ed

 

[Nozer]

Re: Mercury 500 -69 rattles as hell, from upper part around the flywheel.

Thans for the tips guys =)

Went out to the boat today with my toolcase, and it was the flex plate that was broken.

Had cracks all around it, so the center part was "loose".

Nice that problems can be so easy to fix sometimes =)

/Tobbe