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  #1   IP: 74.100.94.148
Old 07-24-2011, 09:19 AM
LHilgen LHilgen is offline
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Unhappy Transmission Problem?

I would like some input if possible as I don't know what I need to do to address the following problem.

My Atomic 4 runs well but within a minute or two after putting it into gear (Forward) the decreases rpm and a noise can be heard (similar to a freezing shaft) following by a "bucking" sound and vibration. The engine stalls at that point. I checked the propeller shaft and it is free moving, so I don't blame the stuffing box. As the engine runs normal my guess is that the transmission is the most likely problem.

Your comments are appreciated. Thank you.

Lutz

Super Forum and I am blown away by your responses!!! Thank you.

Boat is located in Southern CA, Dana Point and regarding the engine I would say it is a 2:1 reduction gear (don't know for sure)..

I did go under water (boat is afloat) and the propeller and shaft are clean. Propeller engages in both forward and reverse. In neutral the shaft / propeller can be rotated "normal" (slight resistance - I assume from the stuffing box).

I will try to get a video/audio of the problem and will uncouple the transmission flange (Al's suggestion) to determine if the problem is unrelated to shaft & stuffing box. The noise is horrible but short lasting as the engine stalls within 5-10 seconds after the screaming begins. What worries me is the bucking vibration. I have not been in the engine compartment when it happens but would not be surprised if the atomic 4 "jumps onto my lap". This might be a video woth watching. By the way, ramping up the RPM to forgo stalling does not do a thing other than increase the bucking and screaming - not a good option.

Last edited by LHilgen; 07-25-2011 at 08:28 PM.
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  #2   IP: 64.252.208.121
Old 07-24-2011, 08:19 PM
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Al Schober Al Schober is offline
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Wow - I love a mystery! Two suggestions.
One is to check the propeller for fouling - don't know if a dive under the boat is easy or hard for you.
The other is to disconnect the shaft coupling from the transmission flange. Slide the shaft back about an inch and then try the transmission in gear.
Where are you located?

Al
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  #3   IP: 71.253.246.208
Old 07-24-2011, 08:27 PM
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Is it a direct drive or 2 to 1 reduction unit?
Is the problem in forward or reverse or both?
In forward on a direct drive no parts are moving inside themselves.
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  #4   IP: 148.170.241.1
Old 07-25-2011, 01:01 PM
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I suggest that the reversing brake band might be a hair too tight. What would happen is similar to trying to drive your car down the road with one foot lightly on the brake pedal. The brakes are just slightly dragging. In this case, it's a band brake. I could see that as the reversing gear spins within a too-tight brake band, the friction causes things to heat up until it finally offers so much resistance, it stalls the engine.
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  #5   IP: 174.65.54.224
Old 07-25-2011, 03:20 PM
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Post a video to youtube and link it here.

That is the best and faster way for us to see and hear what is really going on.
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engine stall, noise, transmission, vibration

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