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Allis? 3-71 governor issue


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Old 12-08-2018, 12:47:48 PM
glennh glennh is offline
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Default Allis? 3-71 governor issue

The new sawmill powerplant 3-71 is has finally fired. Given the lack of bearing noise or heavy smoke, it has been deemed "good enough to use". This engine is assumed to be from an Allis Chalmers HD7 based on the orange, and olive drab paint under the much newer yellow respray, and the Allis Chalmers branded filter element in the add on bypass oil filter. The air intake and control linkage also seem to match photos of an HD7.

After much cleaning and scraping of oil sludge, and fuel system flushing, along with an injector replacement and under valve cover tune up, the engine ran well, and ran from idle up to a speed that sounded like high idle.

The problem came when I tried to shut it down. Pushing the speed control all the way took the engine to low idle, but shutting the fuel shutoff did not kill the engine. I had to shut the air damper to make the engine die.

A close examination of the governor shows that it will not allow the control tube to go to the no fuel position. Unhooking the control rod allowed about 3/8"more travel in the racks. The idle speed screw? was turned in far enough to stop the control rod, and an the stop lever on the top of the governor has a link to a slotted tab that limits it's travel. The air damper is also linked to the stop lever so that both close when shutting down. All of this linkage appears to be original Allis.

Anyone have any idea why the governor and air damper would be set up this way?Click image for larger version

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  #2  
Old 12-08-2018, 12:52:46 PM
glennh glennh is offline
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Default Re: Allis? 3-71 governor issue

Note: In the side view of the governor, I had already backed out the idle screw enough to allow the fuel to shut off. It was originally turned in below the level of the lock nut.

Another note: I may not be looking at the idle screw correctly. Shouldn't the fuel shutoff be completely independent of the idle adjustment? Maybe by moving the pivot point of the control rod?
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Old 12-08-2018, 01:23:28 PM
Norm W Norm W is offline
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Default Re: Allis? 3-71 governor issue

Be aware that the air cut-off is for emergencies. It's use can ruin the seals in the blower. I'd have to check my books, but from my meager memory I think what you are calling the "Idle Screw" is what they call the buffer screw. It is used to eliminate surging at idle. It should be turned in only enough to stop the surging, if it is turned in further, it will raise the idle speed.
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Old 12-08-2018, 01:38:33 PM
Sonny Reese Sonny Reese is offline
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Default Re: Allis? 3-71 governor issue

I had a 3-71 in Oliver super 99 gm, and it had a cable running to the dash for shut-off. Also it did not have emergency air flap. thanks; sonny
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Old 12-08-2018, 02:20:10 PM
The Diesel Doctor The Diesel Doctor is offline
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Default Re: Allis? 3-71 governor issue

You have a real vintage 3-71 there. What is the S/N? You have a variable speed governor. The idle screw is on the rear of the governor 1/4 inch NC thread. The buffer screw is on the side of the governor. 3/8 NF thread, The lever on top is used to position the gov, in the run and shutdown mode. Looks like it was set up to shut the engine down by shutting down the gov. and air at the same time. Disconnect the rod between the gov and the air shut down. Install a spring on the shut down lever to hold it in the run position. Start the engine and then shut it down with with that lever. Back out the buffer screw a turn then adjust the idle with the screw on the back. Turn the buffer back in until you hear the RPM rise then back it off till the RPM drops. Remove the valve cover and clamp a vice grip on the control rack so you will have control when you try the above. AL
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