Power head or Lower Unit ? 125hp, 1986

[sjdwallingford]

Here?s my story:

Replaced head gasket because of low pressure in lower cylinder. After changing, engine worked great. Never ran faster, although I heard a faint tapping noise, which was engine-speed related. At WOT, tapping noise was approximately 200 taps per minute. I believe the tapping noise became louder as the day went on (but I?m not sure). Later in the day, while pulling out of slip, I believe the prop hit the bottom at idle speed, however, engine continue to run great except for the tapping noise.

Next day, I pull out of slip and engine stops suddenly. Tried to restart, but the starter can?t turn the engine at all. I rotate the flywheel by hand in the opposite direction (CCW) (I could not turn it CW). Engine started and I made it back to the slip at which point the engine stalls again.

I took all the plugs out to inspect for aluminum splattering. Plugs looked good.

With the plugs out, I tried starting and, again, the motor locks. I rotate the flywheel CCW by hand and then I?m able to rotate CW by hand, although if I keep rotating it (e.g., 5-10 revolutions) it will eventually lock again and I have to rotate CCW to unlock. If I used the starter to turn engine, it locks within a revolution. Important observation: whenever the motor locks, the pistons are always in the same position.

That?s my story. As always, I appreciate any comments. Thanks.

 

[foodfisher]

Re: Power head or Lower Unit ? 125hp, 1986

Going with lower unit.

 

[sjdwallingford]

Re: Power head or Lower Unit ? 125hp, 1986

Foodfisher--

Care to speculate on what might be wrong with the lower unit? Thanks.

 

[Frank Acampora]

Re: Power head or Lower Unit ? 125hp, 1986

And I would suspect bad roller bearings on the big end of the rod, causing an eventual thrown rod. Possibly loose rod bolts. How did you come up with the 200 per minute at WOT? Neither the engine nor the lower would have this rate at WOT, assuming WOT is about 5000 RPM.

Drop the lower unit and test again. If it still locks up, I am correct that it is the engine. If it doesn't, then Foodfisher is correct. A broken gear tooth or two would act this way

 

[sjdwallingford]

Re: Power head or Lower Unit ? 125hp, 1986

Thanks Frank. I'll do as you suggest and drop the lower unit and try again.

The 300 taps per minute I thought was interesting because it didnt coincide with engine RPM, although it seemed to be proportional. It might have been a speedometer cable noise or something like that--i.e., possible red herring.

I found the fact that the engine would lock in the same position interesting--i.e., I could rotate 3 or 4 times before it would lock, but when it did lock, the pistons were in the same position. I also find it interesting that I was able to start the engine in this condition and power home to the slip.

Anyway, I'll drop the lower unit and see if the problem goes away. Thanks guys.

 

[jerryjerry05]

Re: Power head or Lower Unit ? 125hp, 1986

Try the gear oil drain first!!!
Any metal chunks or silvery oil.Then it's the lower.
If it only locks after every 2-3 revolutions either way and i'd guess a tooth or 2 has gone in a gear.Maybe?????

 

[foodfisher]

Re: Power head or Lower Unit ? 125hp, 1986

Foodfisher--

Care to speculate on what might be wrong with the lower unit? Thanks.

Frank and Jerry are the guys to listen to. Anyway the ability to back off the jam then go past it led me to gear meshing problems. The only gears I could think of was starter/flywheel in the motor. That left the lower unit.