JD L120 Engine Problems

bz1 · Aug 18, 2011

Does anyone know if this series JD has had many engine problems. I have a friend who's 2006 L120 engine crapped out with only 80 hours. The repair shop told him those engines were junk with many problems and short life. This engine just quit and won't run. Turns over really easy like blown head gasket, bad valves, hole in piston, or something like that. Haven't taken it apart yet. Just wondering if this engine is a bad design like the shop is telling us? If the engine has problems does anyone know what typically goes wrong?

mulerrich · Aug 19, 2011

Yes, these 100 series JD have had lots of problems. I have an LA 130 with the kohler courage 23 horse v twin. Blown head gaskets(twice) and bent pushrods. The Courage series engines are very cheap. I am looking to repower mine with either a BS Vanguard or Kohler Command either one is better than the Courage line of motors.

jinman · Aug 19, 2011

I would pull the spark plug(s) and see if each cylinder had good compression. I'd also disconnect the engine kill wire and see if the electrical system is putting out a good spark to the plugs. Finally, I'd check for fuel problems by removing the air filter and pouring a tablespoon of gasoline into the carb throat. Put the filter and cover back on, and turn the engine over while hooked up normally and see if it tries to start. If so, it is probably a dirty carb float bowl or stuck float needle valve. Those seem to be common in the JD small engines (Kohler and B&S, but NOT Kawasaki).

You just can't trust somebody who says, "These engines are junk so yours is probably shot." That's just a invitation for them to do a huge replacement and repair bill. Any shop worth their salt would say that they see lots of problems but need to check the engine for symptoms. If the engine was locked up or had a thrown rod, their comment might make sense, but to call an engine junk just because is won't start is irresponsible in my opinion.

jenkinsph · Aug 19, 2011

I have an L130 which has the Kohler Command engine, has a label on the top front of the engine. What engine does the L120 have?

I agree with Jinman for the most part a good diagnosis is in order, blanket statements such as "piece of crap" make me run away.

bz1 · Aug 19, 2011

Thanks guys. This engine is a B&S engine. Not sure which one off hand but I think it's a 20+ HP Intek engine. Haven't checked the compression yet but it doesn't act like it has any, i.e. it turns over very easy and very fast. So it's not just a fuel problem but it could be several other things like I mentioned in my original post. My friend told me today that he checked for spark and that was good. Then they stuck a rod down into one cylinder and turned the machine over. The piston did not move. Broken connecting rod or crank? Strange thing is that the engine doesn't make any weird noises when turning over. You would think you'd hear a clunk. Given the symptoms even the JD dealer says that he'd just replace the motor. So I suppose when my friend told them about the piston not moving that might of elicited a response to replace the motor. Anyone know where one gets a good deal on a new motor.

jinman · Aug 20, 2011

Here's an engine that's a little more horsepower, but probably as cheap a replacement as buying an exact replacement from John Deere.

BTW: If the flywheel is turning and producing a spark, but neither piston is moving, then it could be something as simple as a shearpin broken and the flywheel loose and spinning without moving the crankshaft. I would sure do a teardown to see what the real problem is before spending lots of $$$ on a replacement engine. To see if the crankshaft is moving when the starter is engaged, look under the engine at the pulleys attached directly to the crankshaft. Something fishy seems to be going on here.

Kyle_in_Tex · Aug 20, 2011

jinman said:
Here's an engine that's a little more horsepower, but probably as cheap a replacement as buying an exact replacement from John Deere.

BTW: If the flywheel is turning and producing a spark, but neither piston is moving, then it could be something as simple as a shearpin broken and the flywheel loose and spinning without moving the crankshaft. I would sure do a teardown to see what the real problem is before spending lots of $$$ on a replacement engine. To see if the crankshaft is moving when the starter is engaged, look under the engine at the pulleys attached directly to the crankshaft. Something fishy seems to be going on here.

+1, good possibility Jim. I'm not a fan of the big single cylinders (except old iron Kohlers and such).

Need more info, what was operator doing and what did they experience as the motor quit running? A simple backfire could shear the key, or hitting something hard with the blades.

Kyle_in_Tex · Aug 20, 2011

Product Specification for L120 Lawn Tractor

Says its a Vtwin. I haven't heard much bad press about these.

bz1 · Aug 21, 2011

Good idea to check to see if the crank is turning. My friend says he didn't hit anything while mowing, nor did the machine backfire or anything like that. He's very very meticulous about how he maintains his stuff and careful about how he uses his stuff. All his stuff is kept looking brand new. So I don't think it was abused in any way. I'll have him check the crank rotation.

bz1 · Sep 8, 2011

Yep, the crank is rotating just fine. I did find out today that he has not checked some other simple things that should be checked like the main fuse, the seat safety switch, the brake safety switch, etc.. We'll look at those things next. One odd thing. The manual says the parking brake has to be on and the brake pedal depressed for the machine to start. He has never had to engage either one to get the machine to start before. Is the manual wrong or perhaps the design has changed?

jinman · Sep 9, 2011

bz1 said:
. . . One odd thing. The manual says the parking brake has to be on and the brake pedal depressed for the machine to start. He has never had to engage either one to get the machine to start before. Is the manual wrong or perhaps the design has changed?

My LA145 requires the brake to be depressed to start, but it is my choice on whether I engage the parking brake lever or not. If I engage the lever, I can remove my foot from the brake pedal. I suspect your friend's brake pedal safety switch has been out of adjustment, internally bad, or jumpered around (in that order with jumpered being a very slim possibility). Safety switches are notorious for going bad and his may have been bad for a very long time. In an unrelated, but similar switch story. I used to be able to start my Kawasaki Mule in gear even when the manual said it had to be in neutral. After about 350 hours of use, it finally started to work that way. You just never know. . .

bz1 · Sep 12, 2011

OK, I brought the machine to my house with the intent of figuring this out and fixing it. First thing I checked was fuel and there was no fuel going into carburator. I pulled the plugs, good spark, then my was to perhaps squirt a little gas into cylinders and seeing if it would fire. I checked to see if pistons were moving when turning the engine over by hand - nope, neither piston moved. Bad sign. Removed the engine and opened it up. Both connecting rods were trashed and a big chunk broken out of cylinder wall. Bad problem, basically trashed engine. The guy says it just quit, no noise or nothing. I really didn't expect this to be so bad. I suspect the problem was low oil even though he swears it was OK. I only drained about a cup of oil from engine before I opened it up. There should be more than that right? The big end bearing surfaces on the rod were pretty scored up. Oh well, new engine time. Anyone have any comments on what to replace this with? Same engine model or something else? Thanks.

Markcuda · Sep 12, 2011

Anyone have any comments on what to replace this with?

A owner that will keep the proper amount of oil in it.:laughing:

Kyle_in_Tex · Sep 12, 2011

5 years old with only 80 hours....hummmm...I'd be looking for rat's nest or mud daubers nests blocking the cooling fins under the top cover.

Oh, and also an owner to put oil in it.

If you go into a lawnmower shop, the synthetic Briggs Oil (I think still) offers to double the warranty if you use their synthetic oil.

jinman · Sep 13, 2011

I think I'd measure the bolt pattern and output shaft diameter to be sure my replacement was the same. I don't think I'd go back with the original engine. If you can find one with a low oil shutoff feature, that would be good. There are lots of places on the internet selling engines.

It appears the shop owner's comment in the original post may have been closer to correct that I thought.