m274 ...

M274 Mechanical Mule Knowledge Base
tbied2
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m274 ...

Post by tbied2 » Wed Jul 22, 2015 6:47 pm

well;;... it does not stay clean for long. after all the fourth parade, it is back to work. kinda hot out;;.. but cutting and splitting wood for winter now gives it time to dry out. also;;... keepin' an eye out for those pesky ground hogs and coyottes....... t ...................

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Re: m274 ...

Post by sergeant diessel » Wed Jul 22, 2015 6:51 pm

Nice 20 rds mag :)

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Re: m274 ...

Post by Auto Shop teacher » Wed Jul 22, 2015 7:55 pm

Nice, everything look so green, please send some of your excess water to Calif. we can use it! :wink:

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Re: m274 ...

Post by tbied2 » Wed Jul 22, 2015 8:20 pm

.... our rainfall for june and july is more than double this summer. some pretty big storms. blew down about six trees on my property, so i have a lot of firewood. also no electric for three days;;.. but i have a big generator. this is my pull start mule with the generator engine. it starts and runs great, but;... a little lacking in power sometimes. i think the regular mule engines are 14 hp;;.. and the generator engines are 10. if ya' want the gen eng to top out at 14,,.. you have to change the cam shaft and the rocker arms. ... but;;... just for puttin' around the yard with a few logs, ten horse power does ok. ................ t

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Re: m274 ...

Post by muleman7 » Thu Jul 23, 2015 5:32 am

The 2AO42 engine is different from the AO42 engine in the following ways"
1 The 2nd compression ring is cast iron and the oil control ring is a 2 pc set where the mule has chrome 1st and 2nd compression rings and a 4 pc oil control ring.
2 There is no copper head spacer thus the valve stem length for both intake and exhaust is 0.050 shorter from the keeper groove to the top of the valve where the rocker hits the valve.
3 The heads are identical for both engines and only the valves are different. The heads and piston assys I see on eBay appear to be the 2AO42 components.
4 The compression ratio for the 2AO42 is 6.9 to 1 and the mule is 6.5? to 1. After talking with an engineer that developed the mule engine he said they lowered the compression ratio to develop more low end torque since the engine would encounter varying loads and RPMs.
5 All other internal engine components are the same for both engines.

Check your ignition timing.
Check your governor to carb linkage and make sure that the carb will fully open.
Back off the governor low speed adj screw so it allows more travel.
With the engine running check that the governor does not hunt but comes to a set RPM for every position if it hunts adj the length of the throttle linkage to correct.
Were copper head spacers used with this engine and the 2AO42 heads?
Last edited by muleman7 on Wed Jul 29, 2015 8:03 pm, edited 1 time in total.
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tbied2
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Re: m274 ...

Post by tbied2 » Thu Jul 23, 2015 6:34 am

hey;;... that gives me a few things to checkout this weekend. i have been told by several old army mechanics that the generator engines were built to run at one speed/rpm ;;.. while mule engines run the whole rpm gamet for torque and power. the timing/duration of cam lobes and the ratio of the rocker arms were different for these two seperate uses.

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Re: m274 ...

Post by old man » Thu Jul 23, 2015 1:03 pm

Nice photo! and a good looking mule at work. I notice you have a flood light mounted on the front. I have 2 of them that I'm trying to rebuild. would you have photos of how you have the light mounted? It looks like it is at a nice level.
thank You
Steve

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Re: m274 ...

Post by old man » Thu Jul 23, 2015 1:05 pm

I must have hit submit a second time sorry

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Re: m274 ...

Post by Chuck W. » Sat Jul 25, 2015 10:25 am

1 The 2nd compression ring is cast iron and the oil control ring is a 2 pc set where the mule has chrome 1st and 2nd compression rings and a 4 pc oil control ring.
2 There is no copper head spacer thus the valve stem length for both intake and exhaust is 0.050 shorter from the keeper groove to the top of the valve where the rocker hits the valve.
Just for my own curiosity, I'd like to see the documentation for this, because:

TM 5-2805-258-24P ORGANIZATIONAL, INTERMEDIATE (FIELD) (DIRECT SUPPORT AND GENERAL SUPPORT) AND DEPOT MAINTENANCE REPAIR PARTS AND SPECIAL TOOL LIST for ENGINE, GASOLINE 10HP MILITARY STANDARD MODELS 2AO42-2 (NSN 2805-00-952-3927) and 2AO42-3 (NSN 2805-00-872-5971)

and

TM 5-2805-213-24P ORGANIZATIONAL, INTERMEDIATE (FIELD) (DIRECT SUPPORT AND GENERAL SUPPORT) AND DEPOT MAINTENANCE REPAIR PARTS AND SPECIAL TOOL LIST for ENGINE, GASOLINE, 14 HP MILITARY STANDARD MODEL AO42 USED ON PLATFORM, UTILITY 1/2 TON, 4 X 4, M274A2


Both list the same piston ring kit, NSN 2805-00-073-3020 (13214E8207) with the same ring numbers, top ring - MS13933-1, intermediate ring - MS13932-1 and oil ring MS1393-1

Both also list the same cylinder head assembly, NSN 2805-00-867-8744 (13214E8206)

All the internal parts appear to be the same to me. I've installed probably 8-9 gen set engines into mules with absolutely no problems or complaints of lack of power, etc., but always wondered why they were rated at different HP.

EDIT: More searching of the TM's may confirm tbied2's comments, the 10 HP cam part number is 13206E0571, and the 14 HP cam part number is 13206E8571. The 10 HP rocker arm part number is 13206E0700 and the 14 HP rocker arm is 13206E0701. Push rods are the same. Now to determine if this is due to different valves. If so, why do the head assemblies have the same part number?

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Re: m274 ...

Post by Auto Shop teacher » Sat Jul 25, 2015 12:07 pm

Hi Chuck, could it be that the generators are set to run at a fixed number of RPMs to keep the AC electricity as close to 60 cycles as possible? I know that mule engines have a much different carburetor and are expected to run well from idle to full throttle, so the main part being different is the carburetor. Whatever reason the government engines are rated at 5,000 feet, which using the old 3% horsepower loss for each 1,000 feet above sea level formula would cut down the power by at least 15% right there. That and the fact that most gov engines are SO de-rated on what they advertise they give you would put this argument more in the 'mental loss of power' rather than the factual 'real provable power loss'.

I suspect that either incorrect timing or a governor not adjusted properly, or clogged intake or exhaust is more likely the problem if both engines are mechanically sound.

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Re: m274 ...

Post by Auto Shop teacher » Sat Jul 25, 2015 12:12 pm

As to the difference if the government manuals rating the 2A042 mule engine with more horsepower than the same engine in the genset, could it be that the mule engines were rated BEFORE they set the 5,000 foot elevation requirement to rate engines at? Remember how your car loses power when you go 4,000 feet and higher in the mountains? I think we humans must work the same way in the 'thinner air'.

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Re: m274 ...

Post by Chuck W. » Sat Jul 25, 2015 3:07 pm

In the past, I thought I had done a pretty thorough comparison of the basic short-block numbers for the gen set and mule engine, and thought the difference in the two HP ratings was due to different carbs, governors, parasitic loads, etc., but now that I see these slightly different part numbers for the cam and rocker arms, I'm looking for printed documentation on the differences. I would think there were some engineering notes on the conversion to the mule. It's my understanding that the 2AO42-2&3 engines were also used to power pumps and welding machines, although I have never seen them in that application. Were they the same rated 10 HP? Interesting stuff here.

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Re: m274 ...

Post by tbied2 » Mon Jul 27, 2015 5:37 pm

hey chuck w. ;;;.. the old army mechanic who told me about the mule engines lives just down the road from ya'. i run into him all the time at knobcreek. he's a real hoot!! ,,,,,,,,,,,,,,,,,, smitty from oneonta.......... t .....................

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Re: m274 ...

Post by Chuck W. » Tue Jul 28, 2015 5:13 am

OMG!- J.D.! Did he ever tell you how to fix a magneto with a ball-peen hammer?

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Re: m274 ...

Post by muleman7 » Wed Jul 29, 2015 1:47 pm

G503 Reply

Thanks to Chuck for you have made me go back and investigate your concerns.
The following information has been taken from either:
TM5-2805-258-24P 1 Jan 1969 or TM5-2805-213-24P including Change 1 13 Feb 1984 And parts that I have.

Piston Ring Kits
2AO42 & AO42 list 5340-374-9707 for both engines?
Each Ring, Spacer and Oil Control are listed the same BUT;
Many of use have dissembled both engines and this is what I have found.
The 2AO42 Piston uses a 4-piece ring set plus the Top Groove Spacer.
The AO42 Piston uses a 6-piece ring set plus the Top Groove Spacer.
I am unable to explain the disparity but in the manuals 2AO42 Fig 5 pg 66 and AO42 Fig 17 pg 40 show the differences.
Pics of Items
AO42 Piston Ring Kit1.jpg
AO42 Piston Ring Kit
AO42 Piston Ring Kit1.jpg (231.48 KiB) Viewed 10620 times
Piston & Conn Rod Assy
2AO42 pg 31 lists FSN 2805-867-8752 Ord 13206E0640
AO42 pg 41 lists FSN 2805-925-0106 Ord 10941185
Pics of labels and assy
2AO42 Piston & -Conn Rod Tag.jpg
2AO42 Piston & Conn Rod Assy Tag
2AO42 Piston & -Conn Rod Tag.jpg (227.24 KiB) Viewed 10620 times
2AO42 Piston & Conn Rod Assy.jpg
2AO42 Piston & Conn Rod Assy
2AO42 Piston & Conn Rod Assy.jpg (147.71 KiB) Viewed 10620 times
AO42 Piston & Conn Rod tag.jpg
AO42 Piston & Conn Rod Assy Tag
AO42 Piston & Conn Rod tag.jpg (188.86 KiB) Viewed 10620 times
AO42 Piston & Conn Rod Assy.jpg
AO42 Piston & Conn Rod Assy
AO42 Piston & Conn Rod Assy.jpg (175.56 KiB) Viewed 10620 times
Valves
2AO42 Fig 2 pg 63 item# 163 Exh Valve 13206E0678 item# 169 Int Valve 13206E0677
AO42 Fig 15 pg 36 on pg 37 Exh Valve 10941184 Int Valve 10941183
Pics to show Keeper Groove to Top of Valve
AO42 Int-Exh Valve Part# Listing.jpg
AO42 Int-Exh Valve Manual pg 37 Listing
AO42 Int-Exh Valve Part# Listing.jpg (62.82 KiB) Viewed 10620 times
AO42 & 2AO42 Valve Lengths.jpg
AO42 & 2AO42 Valve Length Keeper Grove to Top of Valve
AO42 & 2AO42 Valve Lengths.jpg (161.66 KiB) Viewed 10620 times
Rocker Arms [The Same]
2AO42 Fig 2 Item 13 pg 63 line item 176 FSN 2805-867-8757 Ord 13206E0700
AO42 Fig 15 Item 9 pg 36, pg 37 FSN 2805-867-8757 Ord 13206E0700 and item #11 is apparently the rocker without the bushing
TM5-2805-213-24P Pg 36 Rocker Assy Pic.jpg
AO42 Rocker Arm in Manual Fig 15 item 9
TM5-2805-213-24P Pg 36 Rocker Assy Pic.jpg (105.49 KiB) Viewed 10628 times

Camshaft
The 2AO42 and AO42 parts manual list the camshaft assy differently. The 2AO42 lists it broken down and the AO42 lists it complete. This makes it very difficult to verify they are the same. I understand that the grind; lift and duration could be different and I have no documentation supporting either. I do have NOS units from John and Saturn Surplus. I will do further checking. One thing that I did find is that the Cam Gear is listed with different part #s this I will investigate further. All Cam parts could be the same for the AO42, 2AO42 and the 4AO84 except the actual cam for the 4AO84.
Yes the manuals list the same Ord# 13206E0571 for the camshaft but the manual pics show them in different configurations?

AO42 Copper Head Preformed Gasket 0.050 inch [Head Spacer]. I have not found a pic or a listing for this item. I understand the purpose is to reduce the compression ratio allowing more Low End Torque. Has anyone got a listing?

Thanks for the opportunity to share what I have found. This is a great Forum for the Mule Community. If anyone remembers Tom Brice and the Upper Room, Clarkesville, Georgia Tom and I were Partners. I started working with him in 1974.
Last edited by muleman7 on Wed Jul 29, 2015 8:16 pm, edited 4 times in total.
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