AO42 Mule vs 2AO42 Power Plant Engine Differences
Posted: Mon Aug 17, 2015 9:01 pm
I will attempt to list and show with pics the differences between the AO42 Mule and 2AO42 Power Plant engines.
First a short introduction. The major internal Long Block engine components appear to be the same. They both are 42 cubic inch displacements and use identical Cylinders, Pistons, Crankshafts, Camshafts, Hydraulic Lifters, Push Rods, Rockers and Heads. The Valve Train differences are the Valves and the use of a 0.050 Copper Preformed Head Spacer/Gasket along with a different set of Piston Rings for the AO42 Mule Engine. One of the engineers that helped develop the Mule engine said they dropped the Compression Ratio to produce more low RPM Torque since the engine would run under varying loads and RPMs where the Power Plant engine ran at a constant RPM and varying loads. I have no engineering data to explain the TMs reference to the Power Plant 10 hp rating and the Mule rating of 14 hp. Remember the muscle car adage increase compression increase hp. The compression on the Mule is around 125 #s where the Power Plant is around 145 #s.
The following chart is a pic of an Excel spreadsheet where I have listed the Valve Train parts including the FSN and ORD #s for both engines. Some of the parts did not have FSN #s so those cells are blank. I also listed the TMs / Month-Year published and referenced the fig #s and Item #s to make it easier to check.
Spreadsheet pic listing Valve Train components and Piston Rings
Camshaft from Emory Mule Supply
Left Head is a 2AO42 and the Right Head is an AO42 notice the height of the Valve Stems
Closeup of the 2AO42 Head the top of the valve is nearly flush with the valve spring keeper/rotator
Closeup of the AO42 Head the valve is 0.050 longer from the keeper grove to the top of the valve it sticks above the valve spring keeper/rotator
These are valves from each engine the top one is a 2AO42 valve and the bottom is an AO42 valve
This is a Piston Ring set for the AO42 engine the #s match with the spreadsheet pic
This is a piston with rings for the AO42 engine
This is a piston with rings for the 2AO42 engine
I will post a pic of the Copper Preformed Head Spacer/Gasket later
I hope this clearly documents the differences as I see it. From my experience using the 2AO42 Long Block for the Mule I find it more responsive with better power. But I have not tested it over the full RPM rage fully loaded. I will save that for another day and edit this post
Copper Head Spacer measuring 0.065 thick
Copper Head Spacer in comparison to micrometer
Copper Head Spacer installed in the head
I used a digital caliper to measure the top of the groove to the top of the valve and found:
The 2AO42 valve measured 0.200
The AO42 valve measured 0.250
The Copper Head Spacer measured 0.065 and the 0.015 difference must be for crush allowances when the head is torqued
First a short introduction. The major internal Long Block engine components appear to be the same. They both are 42 cubic inch displacements and use identical Cylinders, Pistons, Crankshafts, Camshafts, Hydraulic Lifters, Push Rods, Rockers and Heads. The Valve Train differences are the Valves and the use of a 0.050 Copper Preformed Head Spacer/Gasket along with a different set of Piston Rings for the AO42 Mule Engine. One of the engineers that helped develop the Mule engine said they dropped the Compression Ratio to produce more low RPM Torque since the engine would run under varying loads and RPMs where the Power Plant engine ran at a constant RPM and varying loads. I have no engineering data to explain the TMs reference to the Power Plant 10 hp rating and the Mule rating of 14 hp. Remember the muscle car adage increase compression increase hp. The compression on the Mule is around 125 #s where the Power Plant is around 145 #s.
The following chart is a pic of an Excel spreadsheet where I have listed the Valve Train parts including the FSN and ORD #s for both engines. Some of the parts did not have FSN #s so those cells are blank. I also listed the TMs / Month-Year published and referenced the fig #s and Item #s to make it easier to check.
Spreadsheet pic listing Valve Train components and Piston Rings
Camshaft from Emory Mule Supply
Left Head is a 2AO42 and the Right Head is an AO42 notice the height of the Valve Stems
Closeup of the 2AO42 Head the top of the valve is nearly flush with the valve spring keeper/rotator
Closeup of the AO42 Head the valve is 0.050 longer from the keeper grove to the top of the valve it sticks above the valve spring keeper/rotator
These are valves from each engine the top one is a 2AO42 valve and the bottom is an AO42 valve
This is a Piston Ring set for the AO42 engine the #s match with the spreadsheet pic
This is a piston with rings for the AO42 engine
This is a piston with rings for the 2AO42 engine
I will post a pic of the Copper Preformed Head Spacer/Gasket later
I hope this clearly documents the differences as I see it. From my experience using the 2AO42 Long Block for the Mule I find it more responsive with better power. But I have not tested it over the full RPM rage fully loaded. I will save that for another day and edit this post
Copper Head Spacer measuring 0.065 thick
Copper Head Spacer in comparison to micrometer
Copper Head Spacer installed in the head
I used a digital caliper to measure the top of the groove to the top of the valve and found:
The 2AO42 valve measured 0.200
The AO42 valve measured 0.250
The Copper Head Spacer measured 0.065 and the 0.015 difference must be for crush allowances when the head is torqued