Mysterious Clunk - 40hp rude

[Intermediate Mariner]

Hello,
This topic got mixed in with a prop thread so I wanted to start a new one since it's a totally different issue.

I am running a '62 lark IV 40 hp.

Take a look at this video (http://www.youtube.com/watch?v=QkMpGRl2Pas). You will notice a clunk at 16 seconds (right before I say "allright" as I was happy to get the clunk filmed).

I first thought that the dog may be slipping out of forward but as a test I adjusted the linkage (and took some away from the reverse side) to where it is in all the way and I still hear the "clunk". It only "clunks" once and only at mid-speed (not low or high).

Any ideas?

Thanks a million!

Shawn T
Wichita, KS

 

[Willyclay]

Re: Mysterious Clunk - 40hp rude

After watching your video and listening to the motor, it reminded me of my 1962 Johnson 75. It would "clunk" once at throttle-up but ran well without any issues. I finally identified a failed rubber motor mount that was allowing the powerhead to move due to load being applied. That caused the powerhead/exhaust housing unit to "clunk" against the inside of the cowling. Try the same running test in the video with the motor cover removed and see if you observe any significant movement of the powerhead at the sound of the "clunk". With the cover off, you may also be able to locate the source of the clunking sound better. Good luck!

 

[malinois]

Re: Mysterious Clunk - 40hp rude

is your clunk sound the same as the clunk you get when you put the motor in gear?

 

[boobie]

Re: Mysterious Clunk - 40hp rude

Sounds to me like your fwd gr and shift dog. Once they slip and "clunk" no amount of adjustment will help them as the edges of the gears are already rounded off. If you happen to end up replacing the dog and gr make sure you check all the mtr shift linkages especially under the p/h.

 

[samo_ott]

Re: Mysterious Clunk - 40hp rude

I have the same engine (less the clunk). On a different note, do you get it up to WOT when you say it is in the video as it sure does not seem to be at WOT.