Help! Reverse now stalls motor

[kcford]

Am posting on behalf of friend. He recently pulled an Ericsson 32 to do bottom paint and replace cutlass bearing. Owner also reported bad vibration when motoring. The boat was ramp loaded onto trailer and both forward and reverse were working properly during loading (although with vibration). The prop was removed and cutlass bearing replaced with no issues. He noted that the shaft was touching side of shaft tube at hull - bad allignment.

When boat was splashed, motor started normally, but instantly stalled when put into reverse to back off trailer. Forward was fine. In slip, the motor was properly aligned to shaft once shaft was centered in tube. Still stalls motor in reverse only. When uncoupled, motor does not stall in reverse. When uncoupled, the shaft can be freely turned by hand both directions. Once recoupled, it stalls motor when going to reverse. In water inspection of prop, strut, etc. looks normal. We are stumped! Any ideas?

[erps]

When uncoupled, the shaft can be freely turned by hand both directions. Once recoupled, it stalls motor when going to reverse.

I would suspect a bad motor mount that is drastically altering the alignment of the engine/shaft when torque is applied in reverse. If it were me, I would have the engine cover off and carefully watch the engine movement and the movement of the throttle linkages while the motor is being shifted from neutral to forward and then reverse. I would suspect that the alignment is changing so badly as to bind the shaft in the cutlass bearing or that the engine is shifting and pulling the linkage to the throttle or kill cable. If that ain't it, I would probably rub a lot of hair off my head, because this sounds like a head scratcher.

[sailingdog]

I'd second what ERPS said. Did your friend check the engine mounts recently?

[kcford]

Originally Posted by erps

I would suspect a bad motor mount that is drastically altering the alignment of the engine/shaft when torque is applied in reverse. .

I left out some details for brevity. The engine/shaft has been observed during shifting and no significant movement was observed. The alignment was poor when it was loaded on the trailer, but reverse was working OK. NOTHING was changed regarding alignment while on trailer. Here is my "grasping at straws" advice and logic today: Reverse worked when loaded on trailer, but not when launched from trailer. Therefore, something he toucherd while on trailer is the problem. Only items touched was prop and cutlass bearing. The prop is a feathering prop; unknown model, which was disassembled to remove. Although in-water inspection didn't reveal problem, I think next step is to go back on trailer, remove prop, and test reverse.

[sailingdog]

If the engine isn't shifting on the mounts... then my guess is that the prop isn't working properly... and your friend isn't getting any power in reverse. That might also account for the vibration your friend was describing.

[FSMike]

I would be curious to see if the gear shift/throttle has somehow been accidentally misadjusted so as to shut off the fuel when put in reverse. I don't think that is the problem from your description (engine runs in reverse when disconnected from shaft), but it's another slant on things.

[JimsCAL]

I had the same thought as Mike. Is this a single (both throttle and shift) or double (each separate) control? Single controls are trickier. You might try disconnecting the throttle cable and control the engine speed locally, then shift from forward to reverse and back and see what happens.

[klem]

Is there a chance that your idle is set too low? I have seen many people chasing problems around simply because their engine was idling at 100rpm too low. To FSMike's comment, the engine model is not stated but idle should be controlled on the engine not in the shifter. There are some older engine's that don't have an idle setting and use split throttle and shift levers where idle is controlled by the throttle lever but the throttle lever should not be moved when shifting.

Is it just stalling out or is it crashing to a stop? Have you tried spinning the shaft by hand in both directions to make sure it rotates freely?

Your feathering prop may very well be the culprit. Can you adjust pitch between forward and reverse? If so, is there too much pitch set in reverse?

[kcford]

Thanks for the replies.

The shaft does turn freely by hand in both directions, both coupled and uncoupled.

I had not thought of the possibility of fuel being shut off when shifted to reverse. Will check that, although since it doesn't happen when uncoupled, I don't think this is it. I don't recall the control configuration other than it is two controls on the pedistal.

Regarding the prop, which I think is most likely culprit, we confirmed in the water that the blades cannot interfere with the rudder or p-strut in any configuration. The motor instantly dies when shifted to reverse, but we do not hear anything that sounds like the prop striking anything. Is it possible that the prop was assembled wrong and the pitch is far to great in reverse? Could this stall the motor? I would not have thought the motor could be instantly stalled regardless of pitch. Severe pitch plus too low idle speed is sounding like a possibility. Won't get a chance to check until the weekend.

[kcford]

Update... I think this is headed in a new direction. By repositioning the motor such that the prop shaft is against the bottom of the shaft log, we can now shift into reverse without killing the motor. Odd thing is, you can't get rpm above idle even with full throttle. Our new theory is that the prop strut is misaligned with the shaft log. It was working with a worn cutlass bearing, but not with a new bearing.