Evinrude 20 HP loss of propulsion

[BigEddieM37]

I have what appears to be the identical loss of propulsion problem that was posted by another member in an older inquiry http://forums.iboats.com/showthread.php?t=110339 However my engine is an Evinrude 20HP from about circa 1988-ish (I don't have my manual in front of me at the moment.)

A reply to that earlier posting indicated that there might be a problem with a rubber grommet between the outer hub & prop that is slipping. I looked in both the owner's manual and service manual and can't seem to find this rubber grommet.

I've only been the owner of this engine for about 8 months now and have experienced this loss of propulsion problem at moderate to high cruise speed twice now while out on the water. Slow down, stop, pause briefly, wait, put back in gear and then it's ok again for the rest of the day. I'm worried that one time it won't fix itself and I'll be calling tow boat services. Why would this slippage, if that's what this is, be intermittent? Is there any history that this a common problem with this engine?
Suggestions appreciated.
Thanks.

 

[tashasdaddy]

Re: Evinrude 20 HP loss of propulsion

it's common problem with props. take a permanent marker, and draw a line, completely across the prop center metal to metal, if it is still aligned after he problem it's not the prop. this is the back side of one of my spare props, you can see the inner ring, the rubber hub, and the outer ring of the prop. the rubber lets go and slips, the slits are the thru hub exhaust.

 

[BigEddieM37]

Re: Evinrude 20 HP loss of propulsion

Should I merely be replacing this rubber grommet on general principles since who knows when or IF it was ever done previously by the previous engine owner(s). Do I need any special tools to remove the prop and replace this rubber grommet? Is that all that should be replaced? I've never taken one apart before. I see a big nut in the center of the prop. Just hold the prop itself still and loosen the center nut with a wrench? Is that all there is to it?

Another fellow with whom I work said that cavitation could very well be what I'm experiencing. How DOES one confirm that cavitation has occured? I hear that topic mentioned as well from time to time.

 

[F_R]

Re: Evinrude 20 HP loss of propulsion

It would be unusual for the hub to slip only once then be OK the rest of the day. You are probably experiencing cavitation. You tell the difference by the process of elimination. Mark the prop as mentioned. If it's ok, it's cavitation.

Remove the prop by removing the large nut and slide it off. You cannot replace the hub by yourself, a propeller shop has to do it. But you can just replace the whole propeller.

 

[BigEddieM37]

Re: Evinrude 20 HP loss of propulsion

F_R,
Maybe it IS cavitation. Interesting. I will mark the prop with a marker as suggested and then look at it. Yes it DOES lose propulsion and then after slowing down to a crawl and then slowly restarting up again she's fine. Purrs like a kitty.

I'm assuming that there's really nothing I can do to remedy this cavitation thing?

Thanks for the helpful insight. I learned something.
Ed

 

[F_R]

Re: Evinrude 20 HP loss of propulsion

Cavitation is a simple thing but with many causes. The simple part is that it is an air bubble around the prop. Causes range from the motor being mounted too high on the transom, tilted too far, weeds on the lower unit, something on the boat bottom making bubbles (barnacles), and more.

Here where I live, weeds are the major problem. On some installations, a single blade of grass hooked around the gearcase can set it off.

 

[Silvertip]

Re: Evinrude 20 HP loss of propulsion

Just to add a bit of information. That grommet is not a grommet, its a rubber bushing that's bonded to both the propeller hub and blade area of the prop. A prop shop must make this repair which is why you can't find the "grommet".