Clunk when taking off after reverse

[formulaben]

No, since the clunk only occurs after there has been reverse thrust, (more than just shifting into reverse, thrust above idle). (Plus I don't have a prop puller )

That's precisely why you should remove it, to check the condition of the key/keyway! It may be the key is damaged but the fitment is still tight enough that you cannot move it with only your hands, but the high torque of the motor is shifting it side-to-side. I highly suggest (again) removing it and installing a new key. At the very least, this will eliminate the prop as a possibility. If you can't do that, then take a Sharpie pen and mark it after it has been in FWD, then go dunk it again and after hitting reverse see if it has shifted concentrically...

I went back and re-read your original posts. When you said "the prop is bottomed out against the stop" what exactly does that mean? Do you have a tapered shaft or is it splined? Can you post a picture?

[iliketoski]

Ben, I just reread what I wrote as well, "bottomed out against stop" is not a valid statement. I get what you are saying now, and that may be a good step to take. However, I would think that if the nut is tight against the prop, (it is) and I have now verified that the space between the prop and strut is not changing (which I verified by measuring after forward and reverse thrust), I would think the prop is not moving. Although, (and I would hate to think) if the key is damaged the prop could be turning on the shaft to cause the clunk, but I wouldn't think there would be enough give (short of total failure), to create the clunk symptom.

Thanks for your suggestions.

[Woodski]

@iliketoski: Ben has a good suggestion. The torque of the engine and resistance of the prop can allow the prop to rotate on the shaft even with the nut relatively tight. A narrow or worn key (probable cause as key is softer than shaft) will allow the prop to rotate back and forth even if no fore-aft movement can occur. Sharpie mark on prop / shaft / nut will allow you to troubleshoot. You should also be able to slightly loosen the nut and then rock the prop back and forth to confirm this theory.

[iliketoski]

Woodski,

Thanks for the explanation, while I a little skeptical of this being the cause, this is certainly a valid item to check.

[iliketoski]

Quick update, pulled the prop this week and checked the key. Both sides of the key had a groove cut into them. I turned the key 90 degrees, this may be the root of my problem. Problem is, I won't know now until spring :-(.

[formulaben]

If the key is damage, you need a new one. You can probably get one locally.

https://www.bakesonline.com/detail.aspx?ID=1462

[justgary]

Quick update, pulled the prop this week and checked the key. Both sides of the key had a groove cut into them. I turned the key 90 degrees, this may be the root of my problem. Problem is, I won't know now until spring :-(.

So did you perform the test that Ben proposed in posts #4, #20, and #26? You keep explaining away why you shouldn't have to do any of the tests we propose, and yet you have not found the true source of the problem....

How hard was it to remove the prop? Did it pop right off with a tug, or did you have to use a puller and then threaten it?

[iliketoski]

I didn't take the prop off and run it, I saw this of no value as the issue occurs when there is thrust. Obviously no prop, no thrust, no problem.

Since the dealer removed the prop, I was not able to do mark as Ben suggested, They removed and inspected the shaft, taper and fit, Yes they did need to use a prop puller and threatened it :-). They said all look perfect except the key. They did not have one in inventory but were confident I'd have no issues by reusing if rotated 90 deg. There was more risk in having the key in its old position since the wear in the key is the plane of the sheer force. Now I have full thickness at the stress point.

Edited November 29, 2014 by iliketoski

[justgary]

I agree on rotating the key, but if you have a transmission issue it is not obvious that no thrust equals no problem. It is usually much better to actually do a test than explain why you don't need to.

Personally, I think that the key is the problem, but the primary way to have that problem is with a key that is too tall (keeping the prop from contacting the shaft taper properly).

If the old key was OK but the prop was slipping on the taper, you should lap the prop to the taper. It should not slip when installed properly.

[formulaben]

On second thought, I was wrong. It's definitely your transmission. Go get a new one.

[iliketoski]

Since the problem started years after use, I really didn't think the problem was the prop not seating properly on the taper and key. If the key was too high it would have surfaced long ago, same with the taper.

I appreciate all the suggestions, I'm hoping I have it solved. WITHOUT REPLACING THE TRANSMISSION

[iliketoski]

Well, now that spring has sprung and I splashed the 'bu this past weekend, I'm happy to report the issue has been eliminated (clunk when taking off). So you don't have to read the thread, it was a slight movement of the prop on the shaft, that over time caused nicks in both sides of the key, small but evidently enough for the prop to move on the shaft. I actually just rotated the key 90 degree put prop back on tightened up problem solved.

Moral of the story, sometimes (rarely) it is a small inexpensive solution.

[iliketoski]

I wanted to update on this topic.

This summer, (after rotating my key 90 deg) I started to feel an oh so slight tap that was reminiscent of my original issue.  So I decided to pull my prop again.  Low and behold the  same thing was starting to occur, a small nick in the sides of the key.  So I installed a new key.  I was very surprised to find the difference in size between the old one and the new one.  It was obvious that my old key was worn, and allowing a slight gap that allowed the prop to slip oh so slightly.

After years of use (and over 1200 hours) , keys do wear.  An inexpensive maintenance item.  $9.

[Advoka]

On 11/14/2016 at 7:13 PM, iliketoski said:

I wanted to update on this topic.

This summer, (after rotating my key 90 deg) I started to feel an oh so slight tap that was reminiscent of my original issue.  So I decided to pull my prop again.  Low and behold the  same thing was starting to occur, a small nick in the sides of the key.  So I installed a new key.  I was very surprised to find the difference in size between the old one and the new one.  It was obvious that my old key was worn, and allowing a slight gap that allowed the prop to slip oh so slightly.

After years of use (and over 1200 hours) , keys do wear.  An inexpensive maintenance item.  $9.

 

[Advoka]

Hi. Did you have any images of the key? I think my boat has the exact same issue...when I go I reverse with a bit of throttle a crazy clanging and banging sound starts under the boat at the prop/rudder area..... scary...sounds like the propeller is banging off the rudder.

[BlindSquirrel]

13 hours ago, Advoka said:

Hi. Did you have any images of the key? I think my boat has the exact same issue...when I go I reverse with a bit of throttle a crazy clanging and banging sound starts under the boat at the prop/rudder area..... scary...sounds like the propeller is banging off the rudder. 

If you remove the prop, you’ll find the key. It’s a piece of brass about an inch long and a 1/4 inch wide. 
 

https://www.bakesonline.com/prop-key-for-1-18-shafts-only.html

[Advoka]

Cheers...did this solve the issue of the major banging from the propeller when it's in reverse.....mine sounds like it's metal banging on metal and clanging and loud banging where you think you've wrecked the engine? No issue in low/idle revs in reverse.

 

[justgary]

3 hours ago, Advoka said:

Cheers...did this solve the issue of the major banging from the propeller when it's in reverse.....mine sounds like it's metal banging on metal and clanging and loud banging where you think you've wrecked the engine? No issue in low/idle revs in reverse

If you have clunking noise in gear it could be several things.  Perhaps check for the following:

• Loose prop
• Severely worn strut bushings
• Loose coupler
• Bad damper plate
• Low transmission oil level
• Bad transmission