Multifuel Rythmic Shudder

[Wildchild467]

im not sure about the crank pulley, and the driven pulley of the compressor is variable diameter due to using the pulley to tighten up the belt. maybe ill try tightening up the belt some more. it flops pretty good at idle when the compresser kicks on. worth a try i guess.

 

[jhooah]

Old thread, but could the belt be stiff, causing it to have to straighten out after leaving the pulley, then bend back at the next pulley, similar to a cold low pressure tire inducing a bump till its warmed up, or holding the bump in memory (basically a stiff spot) and creating a vibration.
Just an additional thought, Change the belt 1st before digging into the insides, etc.
V/R W Winget

 

[rustystud]

Old thread, but could the belt be stiff, causing it to have to straighten out after leaving the pulley, then bend back at the next pulley, similar to a cold low pressure tire inducing a bump till its warmed up, or holding the bump in memory (basically a stiff spot) and creating a vibration.
Just an additional thought, Change the belt 1st before digging into the insides, etc.
V/R W Winget

More then likely the compressor was cycling on and off due to a faulty governor or unloader valves or air leak. Each time it came on it would shudder a little due to the extra load on the engine.

 

[Floridianson]

Start buy tightening up the air compressor belt. The easy way is to make sure the threads on the compressor and outer pulley are in good clean shape. Loosen the jam bolt that holds the outer pulley tight. Then start the motor and the belt will spin the outer pull up and tighten the belt. Shut down and tighten up the jam bolt.
Also this is something everybody should do incase you have to replace your air compressor belt. Remove the outer pulley off the compressor shaft, clean and very lightly lube it. I like very little never-seize. Then when or if you have a belt fail you won't be fighting the rusty threads and the belt tightening with go well. Make it a PM.

 

[rustystud]

Also this is something everybody should do incase you have to replace your air compressor belt. Remove the outer pulley off the compressor shaft, clean and very lightly lube it. I like very little never-seize. Then when or if you have a belt fail you won't be fighting the rusty threads and the belt tightening with go well. Make it a PM.[/QUOTE]

This is exactly what I did with mine. I took off the outer pulley half and went after the threads with a wire brush. Then I anti-seized the threads and reinstalled the outer pulley half. Works great now ! To tighten up the belt I would run the pulley half up tight then with the clamp bolt loose start the engine and give it a good rev. This tightened up the belt perfectly !

 

[Floridianson]

Yea I bet one weeks pay check that buy doing a PM on the compressor you might get away with no tools if you broke a belt in the field.
Also I have not seen a real pay check since 1981 but I did stay in a Holiday Inn Express last night.

 

[Wildchild467]

Yea its an old thread but it was not the air compressor cycling on and off. That is obvious when it kicks on and off with the air governor, no question there.

The belt is tight. You can hear it chirp when its not tight.

I 100% agree on the antisieze on the threads for the air compressor. I did all of that 4 years ago when I restored the truck. It has worked great ever since. A DROP of oil on the threads betwen the pinch bolt gap before you tighten it up or adjust it more helps a little too. PM is huge with these trucks.

I have determined the shutter is due to the fact the air compressor is out of phase with the engine crank shaft, similar to a balance shaft of some engines. If my memory serves me correctly, the air compressor spins .86:1 with the engine. This means for a brief period in time, the compressor would be out of phase with the engine crank shaft causing a little shutter or vibration. It seems like somebody told me once they were familiar with this and that the 2 cylinder compressors didn't do that. It has been like that for a long time and now that I have this new engine, it still does it a little. I'm not worried about it and think it is completely normal. It is not severe at all and I can barely feel it. i suppose if somebody got maybe a half inch longer belt and spun the compressor just a little slower, it might go away, but I am not worried.