Merc 280 heavy vibration felt in hotfoot at 4000 and up???

[Djohns]

Help! :confused:

I have a very strong vibration coming from the engine that I can feel directly in my hotfoot. I initially checked under the cowl and found black soot from what resembled the serpentine belt. I replaced the belt. The flywheel was tight and the idler pully and alternator spin freely. DDT shows no faults and compression is good. I just serviced the lower unit and it looks good?? no water intrusion, shaft spins freely? I will borrow a cle to rule out the lower unit.
What am I overlooking.
Afraid to damage engine if it turns out to be an engine bearing.
Any other ideas?

Thanks S&F!

[gmacrae]

Might be worth taking the prop in to be balanced?

[D.B.S]

Black gunk under the fly whywheel most of the time is the top bearing.

[john j 80 viking]

Prop hub may be slipping.

[Jay Smith]

Might take the prop off and rotate prop shaft and see if its took a lick and is bent...I'd also remove the plug and look at the LU oil and see if there are any gremlins lying there...

Jay

[Djohns]

Thanks everyone for some good ideas and suggestions. Problem showed up after experimenting with Mercury Tempest. Swapped back to Lightning ET, vibration still there. The propellors use a flow torque solid hub on the 1 1/4 fatshaft. Don't believe you could spin this hub??? Engine doesn't slip, just vibrates. I checked all bolts; jack plate engine ect.. Sportmaster prop shaft spins freely and does not appear to be bend. I will change water pump and evaluate driveshaft. I quess if this does not pans out I will spin the motor minus lower unit and check for vibration. "I do not hear any strange engine noises" This is a 2000/2.5 with 120 hour on engine. Leakdown number 2/4/6 = 2%, 1,3,5 =6-8%.
If I still don't see anything, I will pull front half, inspect reeds and stare at rod bolts.
Please keep the good ideas coming. Really helps out

Thanks,
Dave

[sschefer]

You mentioned black soot and replacing the belt. I'm not at all familiar with that engine but if it has an external alternator on it, check it. Maybe a loose pulley, bearings shot, threw a winding... I dunno, just swags. If it doesn't have an external alternator then check the flywheel for a loose, broken or missing magnet.

[Djohns]

Thanks!

280 has an external alternator. I will double check it again.

Dave

[Djohns]

Still can't find the problem. Question? Could a flooding injector or failing reed cause engine vibration?
Engine idles fine and runs great on the hose?
DDT shows no injector or ignition faults??
Will take back to the Lake; run to 4000+ and do plug check to see if I see anything.

Thanks everyone!

[Markus]

The propellors use a flow torque solid hub on the 1 1/4 fatshaft. Don't believe you could spin this hub???

I don't think this is your problem, but there have been cases where those hubs have been way out of balance.