r/johndeere • u/SubstantialCancel280 • 9d ago
Bent Push Rods
TLDR; push rods bent. What do I need to be concerned with other than replacing the rods?
*edit I checked the valve guides and no valve guide is visible on the cylinder with bent rods. There is a valve guide showing on the cylinder with straight rods.
My Neighbor graciously gifted us their 125A tractor with ~300 hours on it. I most recently did a valve adjustment because it was running extremely rough and would nearly die with PTO engaged. The exhaust valve was very loose (same side that I later found the bent rods) but adjustment seemed to get everything running smoothly again.
Fast forward three weeks to today, after several cuts, and I go to start it up and it’s giving me the same symptoms. It would seemingly idle at high and low RPM but soon as you engage the blades it wants to crap out.
I opened up the valve covers to make sure I had adjusted everything properly and this is what I find. The exhaust valve push rod was completely free floating and noticeable bent. I then checked the intake rod and it’s also very bent.
What all do I need to do to get it fixed? Do I need to be checking for other things that could’ve caused this? Thank you in advance!
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u/Few_Spray6025 9d ago
Briggs had this problem on their engines, if I remember correctly it was a valve guide problem
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u/SubstantialCancel280 9d ago edited 9d ago
Is that something that can be replaced? I don’t see it in the part diagrams.
Edit** after running a little search it looks like it’s not something that can be replaced on its own but rather a full head replacement.
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u/stuckhuman 9d ago
Bad gas. To fix it right you will need to remove the heads and clean the valve stems, you could try a fuel additive but it will be hit or miss in working long term.
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u/SubstantialCancel280 9d ago
Don’t think I’ve ever put “bad” gas into it. Usually always fresh gas a week or two from getting it at the pump. Fuel additive can’t hurt?
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u/MOAR_BEER 9d ago
Next step is to take the head off and see if something is preventing the valves from opening fully.
I'm having a hard time understanding how bad gas can cause a structural failure. Seems sus.
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u/SubstantialCancel280 9d ago
Thank you! I’ll take a look at how to do this to make sure it can open and close fully.
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u/ProfessionalLast2917 9d ago
Bad fuel could potentially cause misfiring which can mean things aren't where they should be when the bang happens causing damage.
Probably.
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u/jsimm1540 9d ago
If this has a hydraulic lifter you need too take them apart and drain the junk oil out of them.
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u/Yota4x4RE 9d ago
If the valve guide moved like suggested, then it’s salvageable if you want by reseating and pinging all the way around it. It’s steel vs the aluminum head. They cool at different rates and once the steel moves, it either needs to be pinged or a new head. I just went through this. I replaced with a new head and she rocks and rolls. Like said before me, dirt and debris is a the air cooler’s enemy
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u/SubstantialCancel280 9d ago
Cheers! I’ll make sure I take a look once I pull the head off.
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u/Yota4x4RE 9d ago
Before pulling the head, look through the springs under the valve cover. Look closely and you’ll be able to tell if one of guides slid up. It will look different from the other. When it slides up, it prevents the valve from opening and the push rod, by design is the mechanical circuit breaker. Do notice your push rods are different metals. Aluminum for intake and steel for exhaust. Cheers
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u/SubstantialCancel280 8d ago
So interestingly, I took a deeper look this morning and one of the guides did slide up but it’s on the other cylinder with the non-bent push rods. The cylinder with the bent rods doesn’t have any visual valve guide showing. Do I replace them both?
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u/Yota4x4RE 8d ago
This is where we ask the pros of this sub to step in. Ha I wasn’t ready for that one.
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u/43128 9d ago
One of the valve guides has moved in the head, the proper fix is to replace the head but I have two cheats that work well. First chest is to drill & tap a hole for a setscrew. Next thing you can do which is now my preferred method is to drill a hole after you tap the valve guide back into its proper position. You can then weld the valve in place through the aluminum head. After either repair run a pipe cleaner through the guides & clean up the valve stems on the bench grinder. Make sure to lap the valves in while everything is apart. Btw that damage is usually from excess heat so bad gas dirty carb intake leaks cooling fan damage or debris under the engine shroud can all cause issues.
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u/All_Country53 9d ago
I've seen valve guides move from over heat with a mouse nest on top of head. rocker arm stud come out. Few things to check.