A moment of panic and a mystery

[Tim R.]

Completed the engine re-assembly yesterday. Double checked that everything was ready. Bled the fuel system and she started on the second try. She roared to life and immediately I heard a loud clacking sound that sounded like two large sockets banging together. I immediate shut down the engine and started re-checking everything including the valve lash and injectors. Vales lash was perfect and all injectors were firing. So I started her and quickly checked around the engine with a stethoscope to see if I could identify where the noise was coming from. Oil pressure was good. All I could determine was it was coming from deep inside the engine which could indicate main or rod bearings but the noise was not quite right for this. Too high pitched. Main or rod bearings are usually a little deeper.

I spent about an hour thinking and researching with nothing to go on. I finally fell back to my well honed troubleshooting skills; start with the simple stuff. So I removed all the belts and restarted the engine. No noise. So this means either generator, alternator or water pump. Re-installed the alt belt and the noise returned. Not the generator. Removed the belt and both the WP and alt spun smoothly with no play. Then I looked at the belt and found a spot where the inside was worn thin as is if it was being worn down with a spinning pulley without the belt moving.

I replaced the belt and all is good now. The mystery is how the belt got that way. It was running fine before I disassembled the engine. Very strange.

 

[Ross]

A worn spot on the belt is probably a defect in the belt as it is unlikely that the same spot of belt and pulley would make contact regularly.

 

[TomY]

When I was having belt problems, that's what happened.

With alignment slightly off, a substandard belt, when the regulator called for full output, the belt would first get a little nick in it. I don't know the sequence, but the belt must have stalled momentarily, then I suspect the main engine pulley would cut that little spot.

Then of course, every time the regulator called for full output from the balmar, it would hang up on that same spot, probably at the point it calls for full output, and cut it a bit more. This could go many cycles. But pretty soon, kaflooey, and it was gone.

That's all over now. First with better alignment(encouraged by Mainesail), a better notched belt(several suggestions), and lastly, Stu posting the magic 50% cut back switch idea.

We just returned from a few weeks of dragging the batteries down and needing full charge.

We did that all on the same belt, and it looks fine. Just very minor dusting. After the batteries sat for a week, a voltage checked showed them all over 12.7. Nice. Thanks guys.

Anyway, glad you found your problem Tim, keep an eye to see what may have caused the bad spot, in case it wasn't a defect.