Vibration / Shuttering

[LuckyPenny]

I have been having a contiunious problem with shuttering / Vibration. I am running a 21 Foot CC with a Johnson 100HP (1979).<br />Anyway, between 1900 and 2100 RPM the entire boat shutters. Above and below this, she runs fine. Any suggestions?

 

[alcan]

Re: Vibration / Shuttering

Hi Lucky<br />Just some ideas here. Damaged prop, bent propshaft, damaged motor mounts/isolaters, damaged pivot tube bushings,or the tube itself. Check closely for bent/out-of-line damage. You my not have hit anything, but someone my have hit you.

 

[LuckyPenny]

Re: Vibration / Shuttering

Thanks. the only visable damage or irregulatory is scuffing on the leadind edge of the prop. and a very small ding on one of the blades. Would that be the cause?

 

[alcan]

Re: Vibration / Shuttering

Maybe. Maybe one of the blades is bent more than you think. Take your prop to the prop shop or dealer and have it looked at. Put a dial indecator on the prop shaft and check run out. Things don't have to be completly distorted to cause problem. A little out of ballance here a few thousands bend there. How about the flywheel? Did you take a look see there at all? Loose magnets, cracked flywheel,Etc??

 

[Hooty]

Re: Vibration / Shuttering

I think alcan is on the right track but just for grins, try a prop with 2" less pitch and see what happens. You might be lugging the engine.<br /><br />c/6<br /><br />Hooty

 

[LuckyPenny]

Re: Vibration / Shuttering

If it were the flywheel or loose magnet wouldn't I be getting some heavy vibration at high idle?

 

[crstrode]

Re: Vibration / Shuttering

For what it's worth, I just bought a 1977 Evinrude 85 HP. First time out I thought it was running OK, but with some vibration. I also suspected a bent prop.<br />Lo and behold, after about 20 minutes the fourth cylinder finally kicked in for a few seconds at a time. The boat set me back in the seat withthe extra power, and the vibration went away!<br /><br />(now you know how little I know about outboards!)<br /><br />OK now how do I check the coil from the #3 cylinder without the rest of the motor? No spark from #3, even after swapping plugs.<br /><br />The boat and motor are now 120 miles away, and I was planning on checking the coil, buying a powerpack and new sensor in hopes that one of these high $$ parts will fix it.<br /><br />What resistance should I be seeing on the coil wires?<br /><br />Carl<br />Cheney, WA