Causes of bent pushrods

Discussion in 'General IH Tech' started by phurst, Jul 17, 2012.

  1. phurst

    phurst Farmall Cub

    Ok, bone headed dropping of a lifter into the valley aside, I was mucking about under the valve cover because of a banging noise, and a miss. The culprit was a bent pushrod. Before I slap a new one in and call it a day (assuming I ever retrieve my lifter), I'd like to figure out (or at least make a good guess) as to why the pushrod got bent in the first place. So, what are some common causes of bent pushrods?

    My 196 has less than 50k miles on it, rocker arm assembly appears to be in great shape with good oiling. No scarring on the tube the rocker arms are on, and it was installed correctly, with the holes pointing up (9 stand, welded rockers). The only thing that comes to mind as far as abuse is that the PO somehow switched the #3 and #4 wires on the cap, which obviously made it run very poorly, backfiring out the carb, etc. No idea if something like that could cause a bent pushrod. What else should I be investigating before I button it all back up?
  2. RD Durham

    RD Durham High Wheeler

    A number of items can contribute to a bent push rod.

    Most common is a sticking hydraulic lifter which can end up with enough of a gap between the top of the lifter and the push rod that the push rod can get sideways and end up bent.

    Metal fatigue over the years can also cause a push rod to bend.

    Pretty rare but it can happen when you have a bad engine backfire. Especially on a Scout V8 numbers 5 and 7 sparkplugs fire on after the other and though rare you can get a cross fire between the spark plug wires. Shop manual specifies that number 7 sparkplug wire be routed around the carburetor and then to number 7 sparkplug while number 5 sparkplug wire goes in front of the carburetor. You can also get a sever engine back fire in a four cylinder IH engine if you have a burn out exhaust valve. The 196 I had several years back had a burned out exhaust valve and would really backfire when the engine was turned off, a few times it bent a push rod when the engine tried to run backwards after turning off the engine.
  3. phurst

    phurst Farmall Cub

    Ok, so I guess I really should get that lifter out to check it out. It is my understanding that it is "bad juju" to replace a lifter though. Something about it causing rapid cam wear.
  4. phurst

    phurst Farmall Cub

    Here is the offending rod, by the way.

  5. jauringer

    jauringer High Wheeler

    It's "bad juju" to install a new cam and run the old lifters. It's fine to install new lifters with an old cam.

    Might as well pull them all and either clean and check, or replace them while you're in there. Check the bottoms for cupping as well.

    BTW: I went through the entire process of tearing mine apart, cleaning, and then putting them back together just to buy a new set for $100 and be done with it. IMO, it's not worth the effort being 40 year old lifters. (assuming yours are OE)

  6. Afireinside2285

    Afireinside2285 High Wheeler

    The only one I ever bent was running very old varnished gas,which I guess caused the lifter to stick. I replaced it and drove the scout for many months after till I sold it.

    Good luck
  7. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

    A sticking valve in the valve guide or a piece of carbon holding the valve open can also cause it.
    A sticking valve is pretty common on an engine that has sat for a while.

    If the bottom of the lifter is worn to a cup, chances are good that the cam lobe is bad also.
    You can put a new lifter in but it won't last long and will just put more metal in the oil.

    Best to just replace the cam and lifters, use break in lube and use an oil with plenty of zinc(ZDDP) or use a zinc additive in every oil change.
  8. Mark Pietz

    Mark Pietz High Wheeler

    Once I floated the valves on a freshly rebuilt 196. Pistons kissed some of the valves, and it took me a while to figure out while I kept dropping odd pushrods - some rocker arms (early style) had cracked and the damage was invisible until the loading from higher rpms opened the cracks, letting the rods drop into the engine. Of course, some of them looked like pretzels when I retrieved them from the bottom of the pan.
  9. phurst

    phurst Farmall Cub

    Ok, lifter is out, and a new set of lifters and pushrods will be at the parts store in the AM. Is there an easy way to check for a stuck valve? Do I need a spring depresser?

    Sent from my ADR6350 using Tapatalk 2
  10. Bryan G

    Bryan G Farmall Cub

    Back around 1980 my Dad was goofing around in the Country Squire, driving fast up our gravel driveway then locking up the brakes and getting her sideways. In the process the engine shut off and when he restarted it he found it had bent a rod, or several as I recall. Never did get an explanation of just why.
  11. Thomas

    Thomas Dreams of Cub Cadets

    ---Timing off #1 TDE, when you should time off #8 TDC, could very easily put a valve too close to the piston's uprising, causing damaged that would come with an "interference engine". This would include a bent pushrod, but more likely a bent valve. I would check the valves, but that's just me. Backfire would be possible, but that's going to find a means of escape rather than a means of resistance, power & destruction.

    ---Then you have the possibility that your oil is too thick for the engine. 40W is the heaviest oil that was recommended and is still recommended from when I contacted Southland International and asked them to look for me. They said if the books said 40W was the highest, 0w40 would be the best all-around solution, 0W30 if I ran SEA30 and the usual 10W30 & 10W40 "... if that's the way you feel". I still don't, nor will I ever agree with 20W50 in an engine that runs 40W tops. Try putting 20W50 in a new car that runs 5W30 and see what happens. 30W is considered a hydraulic oil as well as our oil filters are hydraulic filters... ~hint, hint~ Too much pressure if you're running Lucas Oil Stabilizer at all, especially if using Lucas OS and 20W50 oil... no idea what you're running, just saying.

    ---When installing the rocker assembly, you do not line the timing mark up with 0. You line the leading edge of the counterweight on the haromic balancer with 0. That's roughly 35 degrees BTDC. Pretty much the sam ething the FSM/FRSM states... you do have them no?... and even Chitlons says "On 4-196 and 8-304, 345, 392 engines turn the crankshaft until leading edge of balance weight on crankshaft pulley is aligned with the zero degree mark on the timing indicator before installing rocker arm assembly". The reason is that this will be the lowest possible area on all* lobes, so there will be the least amount of force on the components when installing... against the rediculous theory behind timing that recently included the misplaced pi... pi... ~ahem~... NM... that is 35 degrees further than you need to be, which brings you to the top of a few lobes.

    -... It could very much be that the pushrod was seated on the edge of the lifter and not on the plunger cap itself... then again, it could be from installing the rocker arm incorrectly, the wrong oil, incorrect timing, heavy load... or too heavy a foot.

    ---Oh, and next time you drop a lifter into the valley, try a flexible claw retrieving tool or use that magnet to try and pull the lifter into view and stand it up so you can get the magnet on the flat or cup and pull it straight up and out. Use a narrow magnet with a rubber cup around the sides and the side of the magnet won't be so easy to stick to the lifter bore or grab the lifter. When you use a lifter tool, understand that a good engine has just enough room for the lifters to sit in the bore and there is no side-to-side slop, so... you will have to sort of chisel away at the varnish that is on the bore so the lifter will come out. Pull and push the lifter to break down the varnish, don't try and pull it the first time. That will cause even the best of lifter tools to lose grip of the lifter. There's not much for them to grip in means of a groove... if the retaining spring sits in the groove as well. At best, you have about 1/32" of a lip to grab. the lifter will fall away if you don't work with it. Haste makes waste.
  12. Jay Tabor

    Jay Tabor Banned

    ih engines arent interference engines, says so in manuel.
    way advanced ignition timing has caused bent push rods, seen it, fixed it.
  13. phurst

    phurst Farmall Cub

    Well, when I got the rig, timing was set at 32* TDC with no vac advance, presumably to bump the idle up due to the wires being in the wrong order. Knocked like hell the first time I tried to drive it. The PO only put 20 miles on it before getting rid of it to me. Sounds like it's either that, or the swapped plug wires. Either way, new lifters and pushrods going in when the rain stops. I guess we'll see how it goes.
  14. Jay Tabor

    Jay Tabor Banned

    what I deduced from the things i found when the scout came to me for repairs, homeboy had been cruising the freeway and went to pass, during down shift-acceleration . .. things went bangedy bandgedy bang
    found half the cylinders had bent pushrods and some had the p rod sticking thru the rocker arms!
    I thought and thought and looked and looked for da answear...hmm
    something told me>>>>>>> HEY CHECK THE TIMING!
    SO i did, the guys had set the static timing to about 20 -30* btdc,[ or more cant remember the nightmare details] something like that.
    so i added total mechanical advance and total vacuum advance to the static timing and looking at the cam/valve chart I could see that the sparkplugs were firing while the intake valve was still OPEN.. and the piston was a long ways from tipperary . .
    so what i figured was- seeing as how it was mostly all intake pushrods bent to look like pretzels..................... and stuck thru the rocker arms . . . .

    that the spark was happening way too soon and the igniting gas was slamming the valves shut and so the valves got pushed up to the seat faster than the pushrods could get out of the way, and whammo!
    after i set ricky racers engine timing back to 5* btdc where ITS SUPPOSED TO BE, they drove off in their scout happily ever after..
    I had checked for valves being stuck-nope-
    broken valve springs-nope...
    valves seating- yep..
    snap-on combination wrenches in the cylinders -nope....
    had oil, good flow to top end...
    nothign wrong with cam- that a peek down thru the heads at each lobe could determine..
    good compression in cyclanders- yep.
    replace a half dozen rocker arms and pushrods and a miscellaenous lifter or two . .
    things were fine in the rocker arm assembly set up and op..

    so I feel that it was way advanced timing that caused the carnage . .

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