John Deere L120 Briggs & Stratton 20 HP Intek Valve Pushrod Issue

[beenthere]

And the black set screw on the rocker is the adjustment for that?

Yes, and a lock nut to tighten and hold the set screw in place.

 

[lightningrod]

Thank you for all your help. One of the rods is ticking at start up but once it's warm it's quiet. So I will definitely get the tool to set proper clearance and get it done

 

[Richard001]

OK with a little searching on the internet, I found some specs for your engine. Found this here:

http://www.mytractorforum.com/280-s...ies/242387-briggs-statton-repair-manuals.html

Also have attached the appropriate PDF.

View attachment 466536

As you can see, the valve clearance is done with the engine cold.

I looked at you valve photo and you do not need any special tools. A flat blade screwdriver will work for holding the adjustment screw while you tighten the lock nut.

Loosen the lock nut, turn the adjustment screw to get the proper gap, then hold the screw while tightening the lock nut.

One more thing. Do not run the engine anymore before you adjust the valves, you may end up burning up the valves if they are not set right.

Richard

 

[lightningrod]

Thank you for the great advice Richard001 and beenthere. I appreciate all the help. I will get a feeler gauge like the one in the video posted on page 1 and get it done. The engine man in the video even advised adjusting the rod clearance every year. I had NO IDEA...

He even said something about it rolling over hard at start up.. I've seen that happening also, so I absolutely need to do the adjustment.

You guys have been SO helpful! :thumbsup:

 

[Gator6x4]

Thank you for the reply. The small engine repair guy mentioned that too, but I don't have the know how or tools to do it. I just put the new rods in, tightened the rocker arm bolt in the middle that holds it in place (it has a square looking spacer directly underneath it where it fastens to the engine) and luckily it runs.. I dunno how long it will last. I ran it for 3+ hours today after the repair.

Any advice on how to do this adjustment would be greatly appreciated :drink:

I think the BS engine and Kohler engines have what is referred to as "positive stop" on the rocker arms. Tighten to X inch pounds, replace the valve cover and start the engine. No valve lash or valve adjustment required.

One should tighten the rocker arm down with the pushrod removed. After tightening the rocker arms insert the pushrods into the lifters, and fabricate a tool by using a screw driver and plastic tie holders. Place the plastic tie over the end of the lifter, insert the end of the screw driver and rock the lifter back, opening the valve just enough to slide the push rod in place under the lifter. Careful, don't jerk the vale open with the fabricated tool. Remember a piston could be in the top position and you could damage the valve or piston.

The tool to do this with looks like a small engine rod with the cap removed and a medium size flat washer bolted to the rod with a rod bolt. Place the rod on the rocker arm in such a manner that places the washer under the front lip of the rocker arm, rock the rod down, opening the valve allowing clearance to insert the valve.

 

[lightningrod]

Hi gator, did you see the video on page 1? It also specifies .004 - .006 of an inch in the PDF linked in this thread.

 

[Gator6x4]

Hi gator, did you see the video on page 1? It also specifies .004 - .006 of an inch in the PDF linked in this thread.

It has been several years since I actually worked on a positive stop engine, but the clearance was achieved by a different length push rod for the exhaust and intake valves. This is why most repair manuals would caution about inserting the pushrods back into the same location they were removed from.

A positive stop engine does not have "valve adjustment" mechanism built into the valve train. You have the rocker arm, a rocker arm pivot, a threaded nut or a threaded stud and the push rod. Some engines have a threaded post sticking up instead of a threaded stud which you place the rocker on. You then screw the nut down to a specific inch pound.

 

[imabass]

Keep an eye on the push rods bending again. There was a flaw in these engines that the valve guide will migrate in the head. When this happens it prevents the valve from opening and the when that happens your push rods are the weak link and will bend. You can look through the valve spring to see if your valve guide is migrating up. It will push the valve seal out of place as well.

What causes this is a combination of oil leaks and debris collecting on the cooling fins on the head which restricts the proper cooling of the head. As the aluminum expands at a faster rate than the valve guide it will allow the guide to migrate out of its hole. There is a fix but will require disassemble of the head and pressing out the valve guides and drilling and tapping holes in the head to insert set screws to better hold the guide in place.

 

[lightningrod]

Yes sir, thank for contributing to this thread. Since replacing the rods I've discovered that mice had built homes in the nooks of the engine. I've been able to remove most of the debris after some of it actually caught on fire while I was mowing! I agree that there definitely was a cooling issue and I should further clean the cooling fins on the cylinder heads.

After finding the rocker arm bolts loose, I'm hoping that was what led to the bent rods. Although, I can't rule out that the valve guides haven't migrated as you've described.

How can I check for migration of the valve guides?

 

[lightningrod]

Keep an eye on the push rods bending again. There was a flaw in these engines that the valve guide will migrate in the head. When this happens it prevents the valve from opening and the when that happens your push rods are the weak link and will bend. You can look through the valve spring to see if your valve guide is migrating up. It will push the valve seal out of place as well.

What causes this is a combination of oil leaks and debris collecting on the cooling fins on the head which restricts the proper cooling of the head. As the aluminum expands at a faster rate than the valve guide it will allow the guide to migrate out of its hole. There is a fix but will require disassemble of the head and pressing out the valve guides and drilling and tapping holes in the head to insert set screws to better hold the guide in place.

View attachment 467235

So, I checked the valve guides and it appears they haven't moved.
Thank you so much for your insight, I will keep an eye out for this!

I set all the rockers with .004" of clearance with the feeler gauge just as described in the video posted on page 1. All I can say is wow.. It purrs so nice now. No rickety slop under the valve covers. It rolls over effortlessly at start up. I'm very happy with what I've learned here and I am very grateful to all of you that have contributed to this thread.

But that's not all I did. I removed the top cover and found the BIGGEST NASTIEST mouse house that I've ever seen! I got out the shop vac and cleaned it all up, what a mess! IN my opinion this was definitely a contributing factor in the overheating which caused the rocker arm bolt to loosen, which led to the pushrods failing. I also cleaned the air filter, it was caked with rodent debris. Pics to follow.