Merc 250 prop shaft question

gibbsb

Cadet
Joined
Sep 7, 2003
Messages
19
Being new to boating after 30+ years, I find that either things have changed or my memory loss is worse than I thought! Anyway, after a few minor prop skirmishes the last few months, I had to replace the plastic drive hub in the prop. After reassembly, I noticed that the prop shaft appears to be slightly bent. I'm talking a few .001", but you can visually see it when rotating the prop. The prop appears to rotate in plane, but if you watch the hole in the center of the shaft, I can detect a little off center rotation. I need to know the permissable runout on the shaft, and if it is bent, how big a job is it to replace it? Are manuals available for this motor? It is an '04 250 Saltwater. For the past few months, I have noticed a slight vibration at about 2K. If I have rods in the port storage rack, they rattle. Above or below that speed, it seems smooth. I have not hit anything hard enough to have any visible damage on the prop. The final blow came on Saturday. Doing about 10mph in 40' of water, I grazed a treetop. Not a solid hit, but just enough so I felt it. All help is appreciated.
 

ehenry

Commander
Joined
Jan 6, 2002
Messages
2,393
Re: Merc 250 prop shaft question

There are manuals for your engine. When you get the shaft out I'd take it to a machine shop and have it straightened. Its alot cheaper than buying a new one. I bent mine bad last year and they straightened it for $33 instead of a couple hundred for a new shaft.
 

gibbsb

Cadet
Joined
Sep 7, 2003
Messages
19
Re: Merc 250 prop shaft question

Thanks for the info. I have ordered a manual and parts book from Mercury.<br /><br />Barry
 

sledhead041

Seaman
Joined
Jun 8, 2004
Messages
61
Re: Merc 250 prop shaft question

The max run out you should run is 0.009in. Any more then this and you will have vibration and seal problems. I never had any good luck with bending the shaft back. It seems that once you bend the shaft into its plastic state it weakens the shaft up a lot. It also makes a difference in where it is bent, the closer to the micro weld the more likely it will break off next time.
 

gibbsb

Cadet
Joined
Sep 7, 2003
Messages
19
Re: Merc 250 prop shaft question

Where is the runout measured? At the outer end?<br /><br />Thanks
 

gibbsb

Cadet
Joined
Sep 7, 2003
Messages
19
Re: Merc 250 prop shaft question

OK, I've ordered the manual and the parts catalog. Are there any special tools needed to replace the prop shaft? I own a repair shop and have an assortment of pullers, presses, etc., so will I need anything else? Where is the best source for parts?<br /><br />Motor is a Merc '04 250 Saltwater<br /><br />Thanks in advance,<br /><br />Barry
 
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