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

[lightningrod]

I wanted to give back to this great forum my simple repair for an engine that I thought I had blown up. This is for the John Deere L120 Briggs & Stratton 20 HP Intek engine (2 cylinder) that came with L120 around the year 2002-2003.

I was starting my first mow of this season when I heard a tick in the engine. Shortly afterward, the engine spit and sputtered and quit. I was able to get it running again (barely) but after I removed the air filter cover I could tell that one of the pistons was pumping fuel air mixture back out thru the carburetor. I researched this forum which gave me clue as to a valve problem. After pulling the valve cover on the right side (right side if standing in front and facing the lawn tractor) everything looked OK as far as I could tell. Then I pulled the left cover to find one pushrod just laying down at the bottom of that area and bent! It turns out BOTH rods on that side were bent.

This was quite a revelation for me, since I'm NO gear headed wrench twister. I went to my local small engine shop and bought new rods for a total of $13.04 lol. I put them back in and it runs fantastic now! I couldn't believe it... I was ready to drop 2K on a used cub cadet down the road.

SO, the culprit is the bolt in the center of the rocker arm. It loosened up. It turns out that ALL 4 rocker arm bolts were hardly tight at all. The ones with the failed pushrods were the loosest. I tightened them down, replaced the rods and back in business. My L120 has over 600 hours on it, maybe others have had the same issue. Hopefully this will help, It's a very easy fix.

I'll edit and add pics thru my smartphone shortly..

 

[lightningrod]

Here are the rockers with the loose center bolt that I tightened.


Here's what my bent rods looked like.

 

[beenthere]

Glad you got r running again. Hope you adjusted the valve lash after putting in the rods.

 

[lightningrod]

Glad you got r running again. Hope you adjusted the valve lash after putting in the rods.

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:

 

[beenthere]

I suspect do a google search on the model B&S as well as serial number. Should be some .pdf info that tells how to set the clearance... likely will have to do with setting at tdc (top dead center) or some mentioned degree from that.
My first experience was this past winter with a 9 hp B&S, but was a good lesson. Found it all online.

For example, here is a youtube I just found.
Lawn Mower Repair Valve Adjustment V-Twin - YouTube

I posted a different video, but after watching it, the guy didn't really know what he was doing. This one looks much better.

 

[lightningrod]

Thank you sir, I will look into it! :thumbsup:

 

[lightningrod]

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

I dunno if it matters or not but, the rods I replaced were the ones that went down to the cam shaft, not the rods linked to the intake/exhaust valves. The rods that run to the valves have the heavy springs around them, right? I didn't mess with those.

 

[beenthere]

Yes, the push rods to the cam shaft. I'm thinking you are seeing the heavy springs around the valve stems. The push rods come up from the cam and push up on the rocker arm, that pushes on the valves. You want to adjust the rocker arms so there is the right amount of "lash" or clearance (don't want them too tight or too loose). Hope this helps.

 

[lightningrod]

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

OH! I see, so if I understand this correctly, according to the engine repair guy I talked to there should be something like .004 - .005 of an inch gap between the rod and rocker when set properly. Did I get that right? And the black set screw on the rocker is the adjustment for that?

 

[lightningrod]

And I bet the gap is needed for heat expansion of the rod.