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Honda 40HP outboard cavitating while on step

N

NWT Boater

New member
Good day,
Recently my 40HP outboard honda motor started cavitating when the boat is on step, have check the foot and even order and installed a new foot and it is still happening. Anyone out there have any ideas? Currently thinking the hydraulic ram is not staying in trim position once the boat is on step. Anyone have a similar issue or possible fixes.

Aaron Martin Hay RIver NWT Canada
 
Hi,

I think I might suspect a slipping prop hub for something like this.

If you're starting out with the engine tilted out, if the trim system is "slipping" or moving it should simply be forced all the way in by the thrust of the prop.

I've seen lots of trim systems that don't have the power to trim out at speed but I don't recall ever seeing one trim in due to thrust.

Just my experience and opinion though.

Good luck
 
racerone said:
Measure the transom.-----Post the actual dimension here.-----Why would you order a new lower unit.
Click to expand...
we drifted into a rock with the engine down and prop engaged less than trolling speed and it the cavitation started to happen when when we were returnig to our cabin, asssumed that the bottom end was damaged.
 
You probably spun your prop hub.

You will likely need to replace the prop.

Sorry for the glum news but it's waaay cheaper than a transmission.

There are several options for props available but if you were happy with the performance of the one you have, just use the part number with the same blade count, diameter and pitch.

Diameter and pitch will be stamped into the hub near the root of one of the blades.

Example: 11 1/4 X 12
The first number is the diameter.

If you post your frame number and model (A or D) I can help you with finding the one you want.

Always use a new thrust washer with a new prop even if the old looks ok.

Good luck.
 
Thank you, the boat and motor are at our cabin and I will not be back there until June 29th, I will check and psot the information once I return on July 8th.
 
There are a couple of methods to check and be sure the prop has spun the hub.

The.quickest way to find a very weak/loose hub would be to ....

First, for safety, remove the emergency stop lanyard so that there's no way the engine could start.

Then, with a helper slowly rotating the propeller by hand (doesn't matter which direction),
shift the outboard into gear.

With the transmission in gear, select the strongest person present and have them try to turn the prop. It might move the slightest amount (thousandths of an inch) due to clearances in the shaft splines and transmission components but, for the most part, it should not budge. If you find that you can force it to turn by hand, it is BADLY spun.

A badly spun prop hub can usually be seen if you simply take it off and look at it. The rubber will be obviously distorted and might even be partially missing.

For one you might not be able to move by hand but still suspect, would be to simply mark the inner hub or the end of the prop shaft and make a corresponding mark (a Sharpie marker works) on the outer hub then take the boat on a short run getting up on plane (Step).

If the marks you made are no longer aligned afterwards, that is the proof you need to begin shopping for a new prop.

Good luck.
 
Maybe I'm not too smart, but I've never purchased a new prop. There are lots of guys out there that sell them used. You can look on ebay and find whatever you're looking for from guys that buy scrap motors from repair shops and part them out. Props are expensive. Usually, when I'm shopping for one, I'm not absolutely sure what pitch I want, so I might buy a couple and return the one that I don't like. That's just me though. I like to have a couple of extras and different pitch props for different things.
 
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