AO42 Lifter Replacement

M274 Mechanical Mule Knowledge Base
Post Reply
RBW
G-Staff Sergeant
G-Staff Sergeant
Posts: 63
Joined: Mon Nov 01, 2021 5:27 am
Location: Texas

AO42 Lifter Replacement

Post by RBW » Sat Dec 18, 2021 5:49 am

Hello

Got a set of lifters for the AO42 and plan to swap them out to check condition of the camshaft and see if I can resolve the valve noise issue. While the engine maintenance manual does not have specific instructions for lifter replacement, it looks like I can pull the shrouds, rocker arms, pushrods, and pushrod housings, then pull the lifters out with a pick or magnet. Is this correct? I'm familiar with this process from aircraft engines - I just don't want to get all the way into this and then find out that I have to still pull the cylinder heads. Thanks.


Curtis


Chuck W.
G-Lieutenant General
G-Lieutenant General
Posts: 5820
Joined: Wed Dec 18, 2002 11:00 am
Location:

Re: AO42 Lifter Replacement

Post by Chuck W. » Sat Dec 18, 2021 7:06 pm

You do know that the AO-42 engine is notorious for excessive hydraulic lifter noise? I doubt that replacing the lifters will do any good. I just add a cup of MMO at every oil change and don't worry about it.

RBW
G-Staff Sergeant
G-Staff Sergeant
Posts: 63
Joined: Mon Nov 01, 2021 5:27 am
Location: Texas

Re: AO42 Lifter Replacement

Post by RBW » Sun Dec 19, 2021 5:17 am

Chuck,

I have read that about the lifter noise. Running SAE 30 4-stroke air-cooled engine oil (Harvest King stuff from Attwoods just for the first change since out of storage). Put 1/2 cup of Marvel Mystery Oil in this. Ran a couple of gallons of ethanol-free 87 octane with about double recommended ratio of MMO, now running a couple of gallons of 100LL through it. Seems to be more valve noise on right side. Almost sounds like the impulse coupling of the magneto (but it's not - I can hear the impulse coupling kick in as the engine winds down when shutting it off). I'm familiar with lifter and cam issues from aircraft engines - wanted to check the lifter faces (at the cam lobe interface), cam lobes, pushrod sockets, and pushrod ends for spalling or heavy corrosion, bleed lifters to check for junk deposits, and check lifter barrel clearances. I figure lifters are cheap enough ($33 plus shipping for a set of four) that it's worth it to see what condition the cam is in.

Engine is pretty quiet on startup, but after a lap around the place, it is ticking pretty noticeably. May try a different kind of oil next time. Any recommendations on something readily available? Thanks for the reply.

Curtis

User avatar
ltsimp
G-Sergeant Major
G-Sergeant Major
Posts: 160
Joined: Sat Dec 04, 2004 7:11 am
Location: Delaware, Ohio

Re: AO42 Lifter Replacement

Post by ltsimp » Sun Dec 19, 2021 5:24 am

Curtis, please let us know the results of your endeavor. I am interested in your results. Good luck,

Warren Duchesne
G-Colonel
G-Colonel
Posts: 1769
Joined: Sun Dec 22, 2002 4:47 pm
Location: Monroe , La

Re: AO42 Lifter Replacement

Post by Warren Duchesne » Sun Dec 19, 2021 4:01 pm

Mule man use to say use risone oil treatment and he swore it worked.

RBW
G-Staff Sergeant
G-Staff Sergeant
Posts: 63
Joined: Mon Nov 01, 2021 5:27 am
Location: Texas

Re: AO42 Lifter Replacement

Post by RBW » Tue Jan 25, 2022 6:22 pm

Got the NOS lifters and pulled the left side valve gear apart. Engine had not been running for a few days, so any residual pressure in the lifters should have bled off. Plungers are fully extended and will not move at all. Two of the four new lifters would not move initially, but after dribbling some Kroil around the plunger, they freed up. Looks like it was some hardened corrosion inhibitor on the new lifters that stuck them in place. I'll eventually work on the old ones, see if I can free them up, and see how much crud is in them. No spalling on the cam follower surface, and the cam lobes are free of corrosion and very sharp, so I think the engine is good. Very minor pitting on the pushrod ends, but overall happy with how everything looks. Will continue to the right side, reinstall, and report on the results when I have it running again.

Curtis

RBW
G-Staff Sergeant
G-Staff Sergeant
Posts: 63
Joined: Mon Nov 01, 2021 5:27 am
Location: Texas

Re: AO42 Lifter Replacement

Post by RBW » Sat Jan 29, 2022 10:38 am

Well, new lifters installed and engine running. Valve train is actually noisier now. I don't think the lifters are actually pumping up, so now I have concerns about oil pump output. Going to pull the rocker arm covers, check the lifters for free play, and make sure I didn't do anything wrong. Wondering now if the three stuck lifters were actually making the engine quieter and the one that was free was making all the noise. Doesn't make a lot of sense so far, except for the knowledge that the AO42 is notorious for valve noise, so maybe that's just how it is. Marvel Mystery Oil, new filter, and new SAE30 non-detergent oil installed. May just run it for a bit and see how it does over time.

Curtis

User avatar
Grummanflyer
G-Sergeant Major
G-Sergeant Major
Posts: 183
Joined: Sun Oct 15, 2017 6:06 am
Location: Hills of Ky.
Contact:

Re: AO42 Lifter Replacement

Post by Grummanflyer » Sun Jan 30, 2022 2:31 pm

I have rebuilt my fair share of engines with hydraulic lifters and sometimes it takes quite a while for all the air to bleed out of them. A lot of times they rattle like a sack full of bottles when they first start and then they slowly start to quiet down but it's not uncommon for there to be one or two that take their time about bleeding out. When we rebuilt a lot of small block Chevy's and would have a "ticker" we would slide a .060 or thereabouts feeler gauge under the rocker arm while it was idling to temporarily unseat the plunger and move it a little further down in the bore. Then pull it out and it would refill with oil and be quiet. YMMV (your mileage may vary)

GF
I have guns.
You don't want me to have guns.
I won't give you my guns.
YOUR MOVE!

RBW
G-Staff Sergeant
G-Staff Sergeant
Posts: 63
Joined: Mon Nov 01, 2021 5:27 am
Location: Texas

Re: AO42 Lifter Replacement

Post by RBW » Sun Jan 30, 2022 8:12 pm

It seems to be a little better, especially at speed and under load. There is still a ticking that is very noticeable at idle. For the first few seconds on a cold start, I do not notice it, then it is pretty obvious and present at idle regardless of operating time or engine temperature. Using the old screwdriver stethoscope technique, the rocker arm cover bolts don't seem to make a lot of noise, and the lifter housings on the block seem very quiet. The most noise is actually from the passenger side magneto mount bolt, so I am wondering if I am hearing some noise from the magneto or governor. I'll continue to monitor, but I think the new lifters have quieted the engine down a bit overall, and operation under load seems to be smoother.

Curtis

Chuck W.
G-Lieutenant General
G-Lieutenant General
Posts: 5820
Joined: Wed Dec 18, 2002 11:00 am
Location:

Re: AO42 Lifter Replacement

Post by Chuck W. » Mon Jan 31, 2022 11:43 am

Have you tried running the engine with the belt removed from the blower? Possibly a blower bearing or tensioner failing?? Just thinking out loud!

User avatar
Grummanflyer
G-Sergeant Major
G-Sergeant Major
Posts: 183
Joined: Sun Oct 15, 2017 6:06 am
Location: Hills of Ky.
Contact:

Re: AO42 Lifter Replacement

Post by Grummanflyer » Tue Feb 01, 2022 11:55 am

Good catch Chuck. My mule developed a ticking, rattling noise once after using it at the airport all day. It just came on all of a sudden and while it idled, I looked everywhere for the source and could not locate it. I finally decided to just drive it and that's when it died. I got off and checked the fuel tank and it was bone dry. It was the dipstick pecking on the bottom of the tank with no fuel to dampen the vibration. Added one gallon and started it up. Noise gone ever since. I might have heard a story about a guy who might have put a long zip tie around a driveshaft on a car. Of course it only made noise when the car moved and the faster it moved, the more noise it allegedly made. Maybe the product of a wasted youth. :mrgreen:
I have guns.
You don't want me to have guns.
I won't give you my guns.
YOUR MOVE!

RBW
G-Staff Sergeant
G-Staff Sergeant
Posts: 63
Joined: Mon Nov 01, 2021 5:27 am
Location: Texas

Re: AO42 Lifter Replacement

Post by RBW » Sat Jul 16, 2022 1:33 pm

Well, I think I may finally understand why I have so much valve train noise. Turns out I didn't know about the shorter valve stems on generator heads. I have generator heads installed with copper spacers. I think that explains a lot of the noise, especially on initial start - the lifters have to fill all the way up to take out all the slack in the valve train. Guess I need to pull the spacers the next time I have the engine off.

Chuck W.
G-Lieutenant General
G-Lieutenant General
Posts: 5820
Joined: Wed Dec 18, 2002 11:00 am
Location:

Re: AO42 Lifter Replacement

Post by Chuck W. » Sun Jul 17, 2022 12:26 pm

The valves are the only difference if you start comparing part numbers between the AO-42 and the 2A0-42 engines. I also had no idea either until Charles posted his information some years back, some great stuff there. Charles and I had several heated discussions until he made me see the light! I always just thought the copper ring was the head gasket, not a spacer. Now we know! :D


Post Reply

Return to “MULE M274 Technical”

Who is online

Users browsing this forum: No registered users and 36 guests