Bending pushrods

bdunegan

Member
Have a Briggs 24hp intek twin that bends exhaust valve pushrods. I can put a pushrod in it, leave rocker arm loose, roll over by hand and it will bend pushrod. Valve spring is compressing same as intake valve spring. I can push valve spring by hand, pushrod is seated in socket in rocker arm socket, other end seats in socket also. Verified nothing in either socket, leave rocker arm loose, roll over motor, and bends pushrod. It's almost like pushrod is too long, but it is exact same as intake pushrod. I noticed that while rolling motor, intake pushrod spins, exhaust does not. Any quick response?
 
Sounds like camshaft timing is "off" and piston and valve are getting in each other's face.
 
I agree with Bob cam timing is off.

So fil in the blanks. Has this just start out of the clear blue or have you had the engine open and did some work to it
 
Don't mean to sound outrageous, but it was given to me two years ago with bad steering. Turned out only roll pin. I have mowed with it two years with no trouble. This year, valve cover gaskets were leaking so I took them off to reseal. Took first one off, and everything looked fine. Took second off and all that was there was a broken intake valve. No exhaust valve at all, so that side was definitely not doing anything. Mower took a while to start, but like I said, I have used it two years with no problem! I have witnesses! Had another identical with a broke rod, so I pulled pushrods out of it, they are identical. Put back together, set valves, and rolled it by hand, and exhaust pushrod bent. I thought maybe wrong length after all, so I took specs to lgs and got two more. Put one in, this time leaving alve a little loose, rolled over and bent it too! Motor has never knocked or used any oil, but it has been running on one side. I made sure pushrod was seating both ends in the sockets, and I double checked that nothing else was in there. I know previous owner and knowing him, he never had it apart. Just puzzled as to where the other piece of the intake pushrod and the whole exhaust pushrod went?
 
Well since it cannot be running on the cylinder with bent push rod then have you tried to push the exhaust valve in to make sure it is not locked up in the head it self?? Since that cylinder has not been running good chance the valve it self is stuck tight and if that is the case good chance you will have to pull that head and work it over real good to free up that valve
 
If that is the case do the rocker move as they should and are you installing the push rod correctly? If you can push the valve by hand then it has to have some thing odd going on or. Maybe you are only pushing the valve in a small amount of the real travel so they get hard past where your pushing them in and bending the rods
 
I can push the valves in, they both do have stiff valve spring tension, but I can move them. I have verified three ti es that the pushrod is in correctly. The rockers move freely on both valves. I put a new intake valve pushrod in at the same time I put the exhaust in, and it is operating the rocker just fine, and I am able to push the exhaust valve with spring in the same distance that the intake valve is compressing with the pushrod. It is just acting like the pushrod is too long, but it isnt.and like I said, I can leave the rocker loose with a huge gap, and pushrod still bends rolling it over by hand. I know something is not right, but I can't figure it out. The plunger ( not sure what it's called) in the head on the bottom end where the pushrod seats, is it possible that it's pushing out too far, and if that is the case, it would have to be camshaft problems, correct?
 
When it comes to the bent push rod competition. Briggs wins all titles hands down.

Just do a web search for Briggs bent push rods and you will be busy for at least a year or two looking and reading page after page on the subject.

People will say that the intakes push rod is aluminum. But it is not nor is steel like the exhaust push rod. Whatever it is it is easily bent.. You could try replacing it with a steel one (both are the same length). It seems to help on some engines..

Sorry but you could not give me anything with a Briggs Intek engine. If you looked into it. You may be surprised to find that they were designed for just a 200 hr life..
 
What is happening is the valve spring retainer is hitting the end of the valve guide when the rocker tries to open the valve. Its pretty common for them to loosen up and walk back and forth in the head if the engine overheats.

Have you had the cover off the flywheel? Either that cylinder head is plugged tight with dirt and trash and no air can circulate through it,

Or else the engine was run low on oil at one time and that head overheated and that was when the valve guide moved.
 
I have had all covers off when I first got it and cleaned everything out. It wasn't clogged up then. As to running low on oil, I can't answer that because previous owner possibly could have ran it low. What is solution, remove head and replace valve guides? I would just like to know where broken piece of intake pushrod and complete exhaust pushrod went to. I am no genious, but I don't think there is any way they could have gotten back into the crankcase so someone must have had valve cover off at some point.
 
Thanks for all the help, didn't know it was possible for an entire pushrod to get back into the block through return oil galley passage, but found out it is, so it looks like a good summertime teardown job to fish out pushrod. Also will be removing head to check out valve guides. I do have a good head to replace with tho. Any pointers or things to watch for when removing the sump? I have done them before but never on a twin. Thanks again everyone!
 
The best repair is to replace that cylinder head. That is what we recommend at the shop where I work.

Like your post above, you probably need to remove the sump and see if there is any pushrod or parts of pushrods in the sump. losing a pushrod through the oil drain hole has been known to happen in Kohlers and Kawasakis, so it may be possible on a Briggs as well.
 

All good ideas here and probably wrong.

Check to see if the valve guide is coming up out of the head. If it does it doesn't let the rocker press the valve down as it should, i.e. the push rod doesn't have full travel and it bends. It doesn't matter if it's aluminum or steel, it will bend.

I don't know how many pushrods I replaced before I read about this on a small engine forum. I just pushed the guide back into the head took a small chisel and staked it in. NO problems after that, still have that mower and i still runs great. No need to remove (or replace) the head.
 

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