Briggs Intek 25HP with bent intake push-rod; WHY?

[grassy]

I have a Scotts S2546 mower with the B&S 25HP V-twin Intek... It was running fine one day, then the next it was running on one cylinder. Found no compression on the bad cylinder, pulled the valve cover to find the intake push-rod bent and floating around in there.

Now I can replace the push-rod for only about $6 but I'd like to know WHY it bent in the first place. Any ideas? Just a bad rod or...?? The exhaust rod looks OK. I can push the intake valve open by hand no problem.

It's weird that this seemed to happen when the motor was "off". So it bent when stopping the motor or trying to start or something? Maybe it ran fine with the bent rod until finally it popped out? So weird.

Edit:
Honestly I can't remember if I've ever checked the valve lash since owning this (maybe 5 years). I'm thinking maybe the valve clearance was way off. Either way too tight or loose which then caused the rod to bend somehow. I don't know. Will be checking the other (working) side soon to see how it's doing.

 

[Scrubcadet10]

Install the new rod and check valve clearances .
If you have the engine model # you contact Briggs and they can give you the procedure and valve lash specs.
It could just be the rod was fatigued and gave out. Where in The rod did it bend?

 

[bertsmobile1]

most of the time rods bend because the engine overheats and the valve gets stuck.
Rods are made weak for this exact purpose.
Overheating is usually because.
1) no one bothers to remove the covers & clean out the rings
2) using a higher grade of fuel
3) timing key is cracked so timing is slight out
4) incorrect valve lash
5) a hydrolock , although this usually blows the gasket before it bends a rod.

This is roughly the order.

 

[grassy]

Install the new rod and check valve clearances .
If you have the engine model # you contact Briggs and they can give you the procedure and valve lash specs.
It could just be the rod was fatigued and gave out. Where in The rod did it bend?

It's a 445000 series motor. 0.004" lash. The whole rod is bent along the length.

most of the time rods bend because the engine overheats and the valve gets stuck.
Rods are made weak for this exact purpose.
Overheating is usually because.
1) no one bothers to remove the covers & clean out the rings

Clean the piston rings? The head cooling fins are clean.

2) using a higher grade of fuel

Not this.

3) timing key is cracked so timing is slight out

Possible. The motor took a big hit a few years ago when the belt-guard/guide got sucked through the main pulley and bent the crankshaft. I suppose the push-rod could have been damaged by this as well way back then and it took this long to finally fail.

4) incorrect valve lash

HIGHLY likely.

5) a hydrolock , although this usually blows the gasket before it bends a rod.

Hmmm. The sparkplug on that side is wet with oil. So maybe oil is getting in there and locking things although I can't see that bending a push-rod. Blowing a gasket or bending the main rod maybe.

 

[Tinkerer200]

"1) no one bothers to remove the covers & clean out the rings"

Language thing here, he is referring to cooling fins, not piston rings, don't forget the passages running thru the heads around the valve guide castings. Also check for slipped valve guide. Guide should not exceed 1/8" above casting.

Walt Conner

PS: IF guide has slipped, I have a fool proof fix.
wconner5 at frontier dot com

 

[cpurvis]

Overheating, leads to valve guide moving out of head. The the valve spring retainer collides with it, bending the pushrod.

 

[grassy]

Overheating, leads to valve guide moving out of head. The the rocker arm collides with it, bending the pushrod.

I've seen that video. The guide(s) have not moved as far as I can tell. As mentioned, I can push the intake valve open all the way by hand.

 

[Fish]

A sticking valve can cause the engine to bend a pushrod when it drops momentarily if the valve sticks open briefly.

 

[bertsmobile1]

Well go back to the basics
The only reason why a pushrod bends is it is pushing up but what it is pushing on does not move
So what can be stopping the valve moving ?
only 2 things
1) it is stuck in the guide
2) it is stuck in the piston

This does not have to be a permenient thing.
So at running temperature the valve could be sticking while at room temperature it could be quite free.

 

[grassy]

I checked the other head and the lash is off. I don't know by how much but a 0.008 feeler fits easily so really loose. I took out the rod on this side and it looks fine.

One thing I noticed is that the oil under the valve cover is not the same oil in the motor. The motor oil is fresh and clear but the oil under the valve covers is syrupy and dark. Blocked oil passage or just old oil langishing? I don't think the original owner ever changed the oil because it was thick and dark as molasses when I first got the mower.

I think I'm going to change the rod, set the lash correctly, and cross fingers. I may try some of that seafoam crap or ATF or something to maybe clear out the oil passages (?). Then change the oil. Run it for a bit then check under the valve cover again to see if it's getting new oil.

Picture for those interested: