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Hey All...thanks in advance.

I'm stubborn.

I have a 2013 Troy Built riding mower with a 17.5 B+S engine. I have the standard problem with bending the intake (aluminum) pushrod, which I am certain is relate to overheating (happens less or can be avoided if I cut the 3 acres in sections). I keep a supply of them on hand and think I could probably change them blindfolded now.

I have this ritual when I start the mower now... I remove the spark plug and hand crank the engine a few times before starting it using a socket and a breaker bar, and I have noticed that there is often an odd resistance and a sound on the first crank...almost like the valve spring (I assume intake) refuses to compress and then does (or releases without the rod making contact).

Before I replace the cylinder head* I am hoping that some wise soul can confirm my theory that this will help and suggest any other options/repairs.

Like I said, I am stubborn, and prefer to keep things running rather than replace...I just replaced the inner tubes on my 42 year old snow blower (starts on one pull)

Thanks!


* I had to drill out and re-tap one of the exhaust bolt holes previously, so I am leaning away from a valve replacement.

Make sure your valve guide hasn't moved in the head, they tend to migrate upwards if they overheat/get too hot, and your spring will only go down so far, but your cam is still trying to complete the full cycle and something has to give. usually the push rod. Also, make sure all the cooling fins on the head are clear of dirt and debris to promote cooling and be sure you're mowing at full throttle (sounds counterintuitive, but more air flow=cooler engine)
if you don't mind, provide the engine model,type and code number so we can look up your specific engine and see what we're working with, these numbers should be stamped into the valve cover.

Thanks Scrub!

Model 31C707
Type 3346 G6
Code 130124ZD

Your description of the valve guide issue sounds spot on.

Are your valves missing their little caps?

Thanks Fish...caps in place, and I am not sure of the phrase, but the gap between the cap and the rocker arm gets checked prior to that manual rotation I mentioned.
(oil check done as well)

Delicreep said:

Thanks Fish...caps in place, and I am not sure of the phrase, but the gap between the cap and the rocker arm gets checked prior to that manual rotation I mentioned.
(oil check done as well)

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Valve clearance/valve lash.
What is the measurement you get?

I check both intake and exhaust.. .006 (intake) and .010 (exhaust)
The steel rod has never been re-adjusted.

Valves are a touch on the loose side, but I don't believe it to be your issue.
Exhaust .005 to .007
Intake .003 to.005

Scrubcadet10 said:

View attachment 67524

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Have you ever removed the engine shroud and checked the cooling fins and engine for grass, dirt, debris build up? Set valves at .004” and .006”, intake and exhaust. This is just a run of the mill single cylinder Briggs. Don’t baby it. Make sure oil is changed at needed intervals, check level periodically, and run it.
Visually check the valve guides to make sure they have not moved. If it keeps bending the aluminum push rod, obviously something is not right.

Thanks...I will begin using the new clearances next season. The engine is immaculately clean with no debris at all; the fan is fully operational

Will check the head this weekend and see if the guide has moved.

A lot of very good advice has been given here. What causes over heating. Among other things,
1. Debris/mouse nests under engine shroud clogging cooling fins. Take the shroud off and inspect.
2. While there go a step further and inspect the flywheel key. Look close at it. If the flywheel has moved off its key just a fraction it will affect the timing and overheat the engine.
3. As noted, past overheating will cause the valve guides to slip out and the valves will not open all the way thus bending a new push rod.

My guess, from past overheating the valve guides moved out of place and new rods will continue to bend until repaired. But first, insure you have corrected the original over heat issue.
My issue of a Briggs V-twin had huge mouse nests on top of both cylinders, sheared flywheel key, broken/bent push rods on one cylinder and valve guides extending out of position on the head.

Delicreep said:

Thanks...I will begin using the new clearances next season. The engine is immaculately clean with no debris at all; the fan is fully operational

Will check the head this weekend and see if the guide has moved.

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It's going to be a slipped valve guide as that's just what Briggs and strattons do..
They seem barely tight enough when they're new from the factory to work under ideal conditions and once they overheat just a little bit, things start slipping.
The entire pressed in is a bad idea on these but they're cheap and they don't want to spend money to make ahead that the valve guides would never even think about moving.
Regardless, fix it yourself and don't buy a new head because that's a waste and don't remove the head because that's not necessary.

I have fixed so many of these I've lost count.
There are multiple ways of doing it but the basic version that always works for me is too take out the spark plug and put the piston two or three inches down from top dead center on the compression stroke and then pack some rope or clothesline or whatever into the cylinder and then gently turn the engine clockwise by hand to push that rope into the valves to keep them closed.
Then pop the keeper, retainer and spring off of that valve so you can get to the valve stem and the guide.
I clean the area and the guide up really well with carb cleaner or brake cleaner and compressed air several times.
Then, I find a socket, deep well that's going to fit the guy perfectly for when I get ready to tap it into place.

Then I get the red loctite because it makes me feel better. I have no idea if it's even chemically possible at these temperatures to work at all but like I said it makes me feel better and I'm not had a single one fail so I continue to do what works for me.
I coat the outside of the guide with red loctite and then I tapped the guy back into place.
If you don't know how far, from doing it like I have, you can look with a flashlight inside the spring on the other valve to get an idea how far to drive it down.
I will caution that it does not get driven flush and it will stick up a little bit typically right around at least 3/16 to a quarter of an inch.
Then the important part. Stake the aluminum around the outside pushing it tightly in to the valve guide.
Many people have used a punch for this for years but I prefer a number two square bit which is also called a Robertson.
I hold it with my thumb and finger or I use some needle nose vice grips to hold it at an angle so I can place it just where I want it before I smack it with a smaller hammer I have.
The goal is to go in like a 45° angle near the top so you're pushing it in holding it tighter.
Don't get too close to the end where you would interfere with the valve stem coming through.
Now, there is another old trick for this which involves using a small Dremel tool and cutting a groove into the valve guide in the area that will be where you will later be staking and peening.
This way when you press the aluminum in, you are pressing into this groove which gives it an even better friction fit and like a land to hold it on.
This group doesn't have to be deep and nothing like have to thickness of the guide or anything crazy like that but rather just a little deeper than what your fingernail will catch on.

I did this early on but then I found it really wasn't necessary because I was fixing them left and right and never had any repeat failures so I just skip this step.

Then you wipe off all the extra squeezed out loctite and put some oil on the valve stem and place the spring and the retainer and the keepers back into place.

Then you place the cap back on tip of the valve stem and place the rockers and stuff back on and then turn the engine backwards a couple of inches so you can remove your rope which should still be sticking out of the cylinder from the end you left hanging out.
Then you set the valves and put the valve cover on and it will run and it should no longer bend the aluminum intake push rod.

Why not use Steel Push Rods instead of Aluminum ones? That might do the trick after you
check and adjust the valve guides.

DaveTN said:

Why not use Steel Push Rods instead of Aluminum ones? That might do the trick after you
check and adjust the valve guides.

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At best that would be a Band-Aid instead of fixing the real problem.
If you put a steel push rod where the aluminum one is already getting bit, you stand a very good likelihood of tearing the rocker arm.
You would think they would be stronger than this but I've seen a number of them on various different engines that actually rip the metal because they are pushing against a valve guide that has moved too far and they happen to be on an engine design that doesn't have an aluminum push rod for that extra level of safety margin or to be the weak link.

At a complete bare minimum you could reach in with a small y or fork shaped piece of metal or the tips of some needle nose small vice grips or even needle nose pliers or probably just a chisel or flatheaded screwdriver tip and place it against the guide at a 45° angle from the outside spring to the top of the guide and tap it a few times with a screwdriver on the top and then the bottom to move the guide back in towards the middle of engine about a quarter inch or so.
Then, if the engine stays cool enough, it might not move again and either push rod will work.
Unfortunately, and most of these situations the owner has not removed the shroud yet as they have just only removed the valve cover and if they remove the shroud they will find the reason for the valve guide slipping in the first place which is overheating.
You will typically find nesting from rodents or even birds or a lot of grass build up which can pack itself in tightly in the cooling fins and in the empty spot of the shroud above the head or you may also find lots of dark gray to black looking oily greasy grime and fuzz that clings to the fins and prevents them from dissipating heat and makes anything stick to them.
Another common reason or, the straw that breaks the camel's back in a borderline situation is the engine speed not being at the proper 3450 - 3500 or so RPMs or people who use a mower and get it up to full operating temperature which only takes about 15 minutes and then they lower the RPM when they're done cutting to idle speed which massively reduces the air flow and the engine temperature spikes as they ride it back to their garage to park it.
A good rule of thumb is if it's mowing or even moving, it needs to be at full operational speed.

DaveTN said:

Why not use Steel Push Rods instead of Aluminum ones? That might do the trick after you
check and adjust the valve guides.

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FWIW When ever I do a head job I replace the aluminium rod with a steel one .
Those of us who regularly do engine rebuild will have stories of alloy push rods worn so thin where they rub on the plastic guide blocks you an bend them between 3 fingers