Bent prop shaft

[FredM]

I hit a submerged object and bent my prop shaft about .019" (19 Thousands of an inch). I have managed to straighten it to within .009" which can't be seen with the naked eye when rotating the prop by hand. Is it worth trying to have it straightened anymore or should I just leave it to overhaul time?. The motor is an early 80's 18hp Mercury with forward controls and electric start. <br /><br />PS Is the reverse lock supposed to engage in neutral as well as reverse (mine does) or should I adjust the linkage so that I am able to tilt the motor when the shift lever is in neutral?<br /><br />Thanks - Fred

 

[alcan]

Re: Bent prop shaft

Hi Fred<br /> I don't know what the tolerance is on your prop shaft. I,ve got one to strighten out also. Yes your reverse lock is working properly. You need to have it locked in neutral so when you pull the starter the motor doesn,t try to get in the boat with you.

 

[ob]

Re: Bent prop shaft

FredM, I wouldn't run with anything short of .002 runout on a propshaft.The rotational imbalance will wear out your carrier bearings and at .009 will shake like a pig.You may be doing your lower unit overhaul sooner than expected.Also attempting to straighten it while installed will reek on your propshaft bearings.How did you arrive at the .009 ? Are you using a dial indicator on the propshaft or the prop hub?

 

[FredM]

Re: Bent prop shaft

Thanks Alcan - Didn't think about the pull start scenario. As far as the prop shaft goes, it appears the standard propellor with the rubber mounted hub would have some inherent run-out anyway, which leads me to think that .009" should be ok. I've also seen adverts from machine shops offering a straightening service to within .002" of true. I know strickly speaking it should be straightened but being relatively new to the outboard scene (I'm an auto mechanic and auto eletrician by trade) I'm not sure what's acceptable and what's not. (My manual doesn't get into shaft tolerances). - Thanks for your help

 

[ob]

Re: Bent prop shaft

Fred ,Ive been a rotating equipment mechanic for most of my adult life.Trust me on this one ..009 is considered excessive for something as small as a propshaft.It's your motor.

 

[FredM]

Re: Bent prop shaft

Thanks OB sorry I didn't see your post until after I replied to Alcan. Yes I used a dial indicator and the .009" is measured at the end of the shaft near the retaining nut thread. Interestingly there was no vibration at all from the motor even at the initial .019" - it was only when I was flushing the motor that I found the problem. If there is any doubt I'll remove the shaft (which is easy enough on this model) and get it straightened. I'll put a new rear bearing and seal in while I'm at it. - Thanks