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Hello. I'm new to the small engine repair scene.

I have a John Deere L118, B&S Intek V Twin 407777-0131-E1.

I just finished replacing a broken connecting rod and damaged piston. The engine has about 280 hours on it. I suspect the damage was from a mouse house on the cylinder head fins. That and probably low oil.

Anyway... it runs again. Seems fairly solid. I adjusted the valves and even took the carb apart and cleaned it. Idle RPM is about 1750... full throttle no load about 3100 RPM.

Here's the issue. When I go from idle/low and just slam the throttle lever to high... the engine races and or hesitates a few seconds... burps out some white smoke... and then runs fine.

Any clues? It runs fine beyond this fairly minor issue. I assumed the carb was dirty but I cleaned it out fully... no luck,

Could be a loose inlet valve guide or faulty valve stem oil seal or the head gasket is leaking.
Or some thing as simple as the rings are yet to fully bed in.
Installed wet the rings can take 50 or so hours to bed in, installed dry on a freshly honed barrelthey should bed in in 10 minutesunless you left it on low idle for extended periods.
Run the mower for 10 minutes then pull the dip stick
If whisps of white smoke come out it is a head gasket.
OTOH they are mower engines, not GP race engines so no reason to "slam" it wide open

I think I figured out the root cause of my original problem. Over time the gas line gets "fatigued" where it takes a right angle turn/bend near the battery on these mowers (L118). This causes it to collapse like a wet straw at times and not start. I was getting around this by blowing into the gas line whenever it happened (fairly rare). I thought it was only an issue during start. In this case I think it was not collapsing but restricting the gas flow as I pushed the throttle. I replaced the gas line and problem solved. For the record, I don't expect the mower to perform like a GP race engine... but previously it never had this behavior... so when it started having this behavior I knew something was wrong.

Having solved this issue there is still an issue after my original repair. Seems to have an issue once it gets warm. It hunts a little and makes a strange sound when not under load. I *think* the sound is a bit of a "bark" coming from the carb intake area. I see a little black puff at times when the air filter is off. I'm guessing this comes from the breather tube that is connected to the crankcase.

Any advice appreciated. I have fully cleaned the carb and replaced the needle and main gasket. No change.

Check head gaskets as was suggested by Bert.

slomo

slomo said:

Check head gaskets as was suggested by Bert.

slomo

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Yeah. White smoke out the oil tube.

Does that mean I just didn't torque the head gasket enough when I fixed my connecting rod? I have a bad feeling when I put the rings on the new cylinder I lined the gaps up instead of stagger them. I'm really hoping that's not the issue. Having to bust the crank case open again would be a PITA... but I'm learning anyway.

What do you mean didn't torque them enough. Did you not use a torque wrench and torque them to factory specs?

hlw49 said:

What do you mean didn't torque them enough. Did you not use a torque wrench and torque them to factory specs?

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Yes I did. I guess my question is... if the torque isn't right... an the gaskets are new... what else could be the issue? Warped head? Should I do a leak down test?

Leak down test is the best test you can do to diagnose the engine you can hear where the leak is, You will always get a leaking sound in the crankcase as you cannot seal the cylinder with rings. You can hear leaking valves and head gasket. I love leak down testers a service techs best friend.

bostonbear said:

Hello. I'm new to the small engine repair scene.

I have a John Deere L118, B&S Intek V Twin 407777-0131-E1.

I just finished replacing a broken connecting rod and damaged piston. The engine has about 280 hours on it. I suspect the damage was from a mouse house on the cylinder head fins. That and probably low oil.

Anyway... it runs again. Seems fairly solid. I adjusted the valves and even took the carb apart and cleaned it. Idle RPM is about 1750... full throttle no load about 3100 RPM.

Here's the issue. When I go from idle/low and just slam the throttle lever to high... the engine races and or hesitates a few seconds... burps out some white smoke... and then runs fine.

Any clues? It runs fine beyond this fairly minor issue. I assumed the carb was dirty but I cleaned it out fully... no luck,

Click to expand...

When you slam the throttle wide open you should get a slight hesitation since the carb. does not have an accelerator pump it depends on transition ports in the idle low speed circuit to do this and the transition ports can't supply the fuel the engine needs quick enough to keep up with demand.

bostonbear said:

I suspect the damage was from a mouse house on the cylinder head fins. That and probably low oil.

Click to expand...

Cleaning the cooling fins is a YEARLY maintenance item per your engine maual. These are air cooled engines. Neglect this and you are looking at engine damage as you found out. Clean the top of the engine block too. Should see silver aluminum all over the engine.

bostonbear said:

Yes I did. I guess my question is... if the torque isn't right... an the gaskets are new... what else could be the issue? Warped head? Should I do a leak down test?

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Every removed head should be checked for warpage. Get a 1/2" thick piece of plate glass from a glass shop. Not a lot of money. Take wet/dry sandpaper and level the head and block.

Torque the head in 3 steps in a criss-cross pattern. Start at 5ft lbs, 10 and 15 or what ever your max torque value is per your engine manual.

bostonbear said:

Yeah. White smoke out the oil tube.

Click to expand...

Could be the rings didn't seat if they are new. Or you didn't space them out properly with installing on the piston. Could of been a dirty cylinder bore if you honed or bored. That bore needs to be surgically clean prior to installing the piston. Scrub the bore with HOT soapy water, rinse and repeat. Paper towel with a little transmission fluid or Diesel. Look for a dirty towel.

Did you check ring end gaps?

All good advice. Thanks everyone.

At this point it would have been cheaper for me to buy a new lawnmower... but then I would miss all this fun

After completely eliminating all other possibilities:

1. The carb has been replaced... as well as the gas line and the fuel pump. I suspect regardless of everything else the carb had issues because it runs MUCH better at idle now.

2. Replaced both head gaskets and adjusted the valves. I do need to verify that the heads are not warped. Thanks for the glass tip.

3. Did a leakdown test after replacing the head gaskets and saw about 6% loss. Seems good to me.

After all this the mower runs poorly at full throttle. Hunts and pops out the breather valve. White smoke in the crank case. Runs even worse now under load and often stalls out. Must be blow-by via the piston(s).

Remember... I originally replaced a piston and both connecting rods.

* The piston I bought is a kit with the rings: part #793647
* I did not hone the cylinder walls... but I have the tool now.
* I did not take any great care in staggering the ring gaps previously. In fact, I have re-opened the crankcase and now see that while they were not 100% aligned... the gaps were fairly close (which is, I assume not great).

Plan now is to hone the cylinder walls, replace the rings, verify the heads are not warped... and hope for the best.

Question: The new piston is certainly not exactly the same as the old one. The rings are different as well. The part I am confused by is if I buy JUST the piston rings they have 2 versions. Before 06082400 and after 06082300. My ENGINE code date starts with 05 so to replace the old piston rings on the old piston I'm going with part #499604. Question is... what rings do I use for the NEW piston? Are the rings specific to the ENGINE or the PISTON? The piston is new (793647)... and the rings appear very different to me whe compared to the old rings... particularly the oil ring.

bostonbear said:

Question: The new piston is certainly not exactly the same as the old one. The rings are different as well. The part I am confused by is if I buy JUST the piston rings they have 2 versions. Before 06082400 and after 06082300. My ENGINE code date starts with 05 so to replace the old piston rings on the old piston I'm going with part #499604. Question is... what rings do I use for the NEW piston? Are the rings specific to the ENGINE or the PISTON? The piston is new (793647)... and the rings appear very different to me whe compared to the old rings... particularly the oil ring.

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I would say if you have the correct parts diagram, ordered the correct piston and rings per engine date code, should work okay. Obviously using OEM parts and NOT the cheapest OEM parts off ebay or amazon. Last deal was about "trying" to get around Chinese copied parts if possible with OEM box printing LOL. Buy your parts from a real mower shop or an online mower shop. Do this one time and could actually save you money.

"Torque to factory specs"... urrrhh... some years ago I had a torque wrench that didn't seem "quite right". I got a new one.

I had been torquing critical suspension and steering bolts to a third of spec. On highway cars, not lawnmowers. FK ME.

Never trust anyone.

Here's the update:

1. Question about what piston rings to use if you had a NEW piston on an engine with an OLD engine code. The answer is, the piston rings have BEFORE and AFTER codes. These codes refer to the engine code... but if you got the NEW piston you want the NEW piston rings (regardless of your engine code). The old rings flat out don't fit in a new piston. Note that the new pistons come with rings so this is normally not an issue. I'm not normal. So... the piston ring parts diagram BEFORE and AFTER really refers to the piston... not the engine.

2. The issue I was having was almost certainly blow by. The symptoms were: hesitation when going from idle to full throttle (followed by a big burp of smoke out the valve), white smoke in the crankcase, crank valve "popping" every 5-10 seconds at full throttle, eventual stalls but normally lots of hunting at full throttle (fine at idle).

I do not believe the blow by was caused by the head gasket(s) and I replaced the head gaskets multiple times and saw no evidence of a leak.

Took the engine apart (again) and did not find anything really wrong... but... when I first replaced the broken control arm and piston and put the engine back together:

• I did not take care to stagger the ring gaps.
• I did not hone the cylinders.

This time I did both of those things. During my original repair I also replaced the connecting rod on the "good" cylinder since I though it was a little damaged. When I did that I mistakenly "flipped" that piston 180 degrees. The piston looked to me to be symmetrical. The manual was very clear about the arrow on the piston head facing the fly wheel so I fixed that as well this time around. Note that, indeed, the pistons are NOT 100% symmetrical. The bottom side has a slight difference on one edge. Didn't notice it before. Not that there is also a "2" on one side of the piston. I assume that means it should align with the "2" on the connecting rod.

So... new rings all around (gaps properly staggered), put the old piston back to the correct orientation, honed both cylinders... and it runs. Fairly well. No more smoke in the crank case. No more hesitation when going full throttle. No more hunting or stalling. It's still making a noise I can't quite figure out. Might just be valves clacking... but waaaaay better than before.

Bummer. I strongly suspect that noise I'm hearing is rod knock. It would make sense since the original repair was due to low oil. I suspect the crankshaft is worn so there is a small amount of play. It runs and it cuts... but how much life does it have? Not sure. Quite a learning experience for me.

If the noise gets worse when the engine is hot and is reduced by using heavy oil additives, it is rod knock. Don't leave heavy oil additives in your crankcase unless you plan to just beat it to death.

Rods are cheap
SHort blocks are not
Your decision.
BEcause I charge for my time & the customer pays for parts rod replacement in your situation would have been a no brainer.
However the home owner never takes any account of their time because the time is not coming out of their pocket but the parts are so the temptation is to replace the minimal amount of parts rather than think about replacing everything that may have been damaged .

bertsmobile1 said:

Rods are cheap
SHort blocks are not
Your decision.
BEcause I charge for my time & the customer pays for parts rod replacement in your situation would have been a no brainer.
However the home owner never takes any account of their time because the time is not coming out of their pocket but the parts are so the temptation is to replace the minimal amount of parts rather than think about replacing everything that may have been damaged .

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Doesn't really have anything to do with time or $$. Has more to do with I have no experience with small engines and didn't think... "hmmm.... those wear marks on the journal are probably bad news." I'm doing this to learn so I will probably replace the crankshaft in the winter... Once I get it right... next project is a motorcycle.

I got into mower the opposite way round.
Motorcycles are a lot easier

bertsmobile1 said:

I got into mower the opposite way round.
Motorcycles are a lot easier

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You are out of your Lawn Royalty mind. You can't hardly fix anything on a cycle without dismantling the entire machine. Even checking the oil can be a two-victim job.

Must not be referring to Harleys, Old ones that is..

Richard Milhous said:

You are out of your Lawn Royalty mind. You can't hardly fix anything on a cycle without dismantling the entire machine. Even checking the oil can be a two-victim job.

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Not the ones I ride
They were made by the only company that ever made more than 25% of the worlds motorcycle for better than 20 years and it was not H D or Indian

It ain't Yamaha or Honda.