# JD L120 Engine Problem



## the professor (Sep 16, 2010)

Sudden loss of power this weekend, down maybe to 2/3 normal. Barely enough to run mower deck. Mower was extremely low on oil (sorry). I checked the fuel line, changed the fuel filter, changed the air filters, cleaned off dust and debris, no difference.

Been looking at this forum and think it could be a problem with right cylinder. I pulled the right plug and the motor started and ran about the same. Pulled the left plug and the motor wouldn't start.

I'm no mechanic, but when I pulled off the cylinder caps, they both looked exactly the same. How can I tell what is wrong?


----------



## Hoodoo Valley (Nov 14, 2006)

What's the condition of the plug wires and connections?


----------



## the professor (Sep 16, 2010)

I can send a photo, but, they look practically brand new. 

If it is a rod, would I be able to see just by removing the cylindar cover? I took off the cover and I can see the rods and they were fine, but they could be bent or broken further in.


----------



## Hoodoo Valley (Nov 14, 2006)

Have you checked the valve clearances? That would tell you if they were broke or bent. Likely the push rods are fine, but who knows. Have you also conducted a compression test on both cylinders?


----------



## the professor (Sep 16, 2010)

No. I thought I'd check the forum to see if there were any "doh" fixes before I got into anything really technical. I've never done a compression test before. I have a service manual for the machine that gives you step-by-step instructions including what equipment to get.


----------



## Hoodoo Valley (Nov 14, 2006)

Well, I'd check to see if you have spark at that cylinder first I suppose if you haven't already. You had mentioned the push rods and so the bit about the valve clearances.


----------



## the professor (Sep 16, 2010)

Okay, I finally was able to find time to check the cylinder for a spark. Both cylinders are getting a spark, but only the right side is working. Also, the throttle doesn't seem to be doing anything, the engine idles the same no matter where I set the throttle.

Any thoughts?


----------



## Hoodoo Valley (Nov 14, 2006)

Throttle hooked up? Vacuum leak in the manifold for that side? Sticking valve? Did you check valve clearances?


----------



## the professor (Sep 16, 2010)

Valve clearances are okay. Rods looked good. If you have a stuck valve, will the rockers and rods still move?

After I checked the valves and rods, I fired up the engine and there was a single, pretty loud metallic clang and then just normal engine sounds. Throttle is working (I had done something stupid) and the lefthand cylinder is working great. Just can't get the right side to fire up.


----------



## Rattosh51 (Sep 10, 2008)

"extremely low on oil"
Like how low? This could've caused some damage to the engine.

"only the right side is working." "lefthand cylinder is working great. Just can't get the right side to fire up."
Which side is it? You said both sides were getting spark, so that rules out the coil, spark plugs and wires. That pretty much leaves the internal part of the engine not working, whatever side it is...


----------



## the professor (Sep 16, 2010)

Well, the verdict is in...it is a broken connecting rod. Afraid this goes beyond my meager skills.


----------

