Export thread

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.

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?

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.

Scrubcadet10 said:

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?

Click to expand...

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

bertsmobile1 said:

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

Click to expand...

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

2) using a higher grade of fuel

Click to expand...

Not this.

3) timing key is cracked so timing is slight out

Click to expand...

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

Click to expand...

HIGHLY likely.

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

Click to expand...

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.

"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

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

cpurvis said:

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

Click to expand...

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.

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

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.

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:

The oil passage in those engine is big enough for the push rod to fall into the crankcase. The valves are lubed by splash/vapor so there isn't a lot of oil movement into the head area.

grassy said:

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:
View attachment 45424

Click to expand...

After installing the new pushrod and adjustments, leave the valve covers off and the plugs out, and turn the engine over by hand a few times while you watch things....

Also look at the action of the rocker arms, and see if they all travel about the same distance, a bunch of engines had cam problems about 15 or so years ago.

Deere parts guy says they see the intake rod bend a lot. A sacrificial part when anything is out of whack. After putting the new rod in I found the lash to be way too tight. There was no clearance at all. That could be what bent it... hopefully...

Almost ready to try to fire it up. Without thinking I had removed the carb before doing a compression test so I have to get it back on before I can test. I really need new fuel lines too. What are they 1/4"? I have some 1/4" Tygon but it's too thin wall for the clamps. So much to do

Take a piece of The fuel line to a parts store, they should have it!

Well it fired right up. Only thing is, at idle it's knocking like crazy. I can't remember if it did that before or not. At high/running RPM I can't tell if it's knocking or not.

I have no idea why anything I did would make it knock, maybe it always did this. At low RPM it's so bad that it sounds like a diesel.

Listen:
https://vocaroo.com/i/s1NW2WkVMRqE

Make sure that the engine mounting bolts are tight. If the engine is loose, it will cause a knocking noise.

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.

Click to expand...

Thick oil is one of the signs of overheating

We seem to be going in circles but always end up at the same point.

Well it fired right up. Only thing is, at idle it's knocking like crazy. I can't remember if it did that before or not. At high/running RPM I can't tell if it's knocking or not.

Click to expand...

If it is a pre-ignition knock then both the pressure and temperature will skyrocket thus causing the valves to stick
If it is a loose rod knock then the piston could be hitting the valve.

If it was sitting in the shop in front of me I would be pulling the plugs and placing a rod on top of the piston.
Then with gentle down force on the rod rotate the engine several revolutions feeling for a click when the piston broaches TDC which indicates a loose rod.
I do this because I am adverse to supplying customers new engines out of my pocket.


I feel there is a lot more to this story than we have been told and you have been sold a mower with a hand grenade masquerading as an engine.

After doing some mowing I think the knock was always there (at least since I have owned it). So for the last 5 years or so has been working OK for me.

There is no question this mower has been severely abused. Oil never changed, belts routed all wrong, bad blades, bad wheels, bent crankshaft, and all manner of problems. I took it on as a cheap mower and never expected it to last this long. Now it's kind of a friend that I try to keep going.

I wish I hadn't taken the carb off because now it seems to have an air leak or something. Getting some minor backfire/stuttering. Ah well... Damn.