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Hi all, new member trying to help a friend. I’m not a small engine expert but worked on cars.
My friend’s John Deere Series 100 125 Automatic with 20 HP Briggs V Twin has a replacement engine with some use. The engine quit and seems out timing. After watching YouTube videos I’ve checked the valve adjustment, fuel delivery and has spark. Engine had a starter and flywheel ring gear replaced. It’s not the fuel solenoid.
The engine was pulled and this model doesn’t have a decompression lever, cam looks okay and timing marks line up.
With spark plugs out and ground to head both have spark. I haven’t pulled the flywheel yet but trying to eliminate any other possibility before pulling it.
Flywheel doesn’t feel loose, owner did hear a loud sound when it quit. I never heard it yet, engine spins fine then every once in a while a backfire. The valves and push rods all go in and out don’t seem bent.
Besides a sheared flywheel key any possibilities? A small engine repair guy doesn’t think it’s the flywheel key. Saw the engine and felt it turn with crank case cover off. Nothing seems damaged inside and saw the camshaft lined up and cam condition and timing.
Cylinder compression was at 140 lbs for #1 (left side facing forward) and 160 for #2 (right side. I thought it was good amount although 20 lbs difference a bit concerning.
Any diagnosing thoughts and ideas would be great. My friend doesn’t have a lot of money and we’re trying to help although small engines admittedly are not my forte.
I don’t mind pulling the flywheel to check for a sheared key but wondering if there’s anything else it could be or to check?
Thanks

The mower is a series 100 125 automatic. Valve cover number 441577 0113 e1 if it helps.

Hobbesnmina2001 said:

The mower is a series 100 125 automatic. Valve cover number 441577 0113 e1 if it helps.

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You already pulled the engine and opened it up to look at camshaft. Pulling the flywheel to check for sheared key is not as much work as checking the camshaft.

You said starter and ring gear have been replaced. If the flywheel nut was not torqued to 150 ft pound it very well could be a sheared fw key. I would check it.

And these flywheels are torqued to 150 ft-lbs instead of the 130 ft-lbs listed on the Power Portal site. Must be done using a torque wrench and not an impact. Many DIYers think they can just get by with an impact. Over torquing with an impact will lead to cracked flywheels or stuck on flywheels. Common automotive harmonic balance puller is used to pull the flywheel..

Thanks guys, I’ll check that. Removing it is not the issue I just hadn’t gotten to it yet and it never hurts to ask questions.
Hadn’t thought about the impact wrench part, that makes sense. I have torque wrenches so that’s not a problem.
Interesting on the different torque specs. The dealership gave me a sheet that said 200 inch lbs on the crankcase cover bolts but I went with the sheet from the new gasket that says 325 inch lbs. I converted into 27 ft lbs by dividing it by 12.
Hope everyone had a great Thanksgiving Day!
Have a great day!

Yes originally it was 200 in-lbs then increased to 300 in/lbs, and now it is increased to 325 in-lbs.

And that Sump gasket from Briggs might be faulty as I had two of them to fail in short order. One the customer only made three passes on his lawn. The hole were chased to clean the threads all three times. Currently have a aftermarket sump torque to only 25 ft-lbs as had three holes to pull out going to 27 fl-lbs. Heli coiled those holes and can be torqued the 27 ft-lbs but I decide to only go to 25ft-lbs this time around and the gasket is holding fine. The customer done cut 5 acres since i installed the after market gasket.

The Briggs gasket looked like vanilla file folder paper and the aftermarket was dark red and felt a lot better.

Just make sure you have check for the flatness of both the crankcase and sump mating areas. Also note if the gasket blows again replace the PCV valve assembly.

Thanks guys the flywheel key was it. Sheared and flywheel moved. After replacing it and torquing it to 150 ft lbs the engine fired up immediately on the first try!
I plan on doing more small engine and equipment work, maybe pick up not running units. It looks like a fun hobby. If I run into this again I’ll be checking the flywheel key before pulling the engine and dropping the crankcase.

Thanks again, take care and have a blessed weekend!

Question what’s a good aftermarket gasket brand name and online sources?

Usually I cut my own if I do not have some left over in a rebuild kit .
Be very careful with the thickness because the thickness of the gasket controls the end play in the crank .
They used to come in packs of 4 to 6 of different thicknesses when they were sold as a stand alone item however I only seem to be able to get complete kits now days
Most mower shop that actually repair engines will have draws full of partial gasket kits and in particular crankcase gaskets

bertsmobile1 said:

Usually I cut my own if I do not have some left over in a rebuild kit .
Be very careful with the thickness because the thickness of the gasket controls the end play in the crank .
They used to come in packs of 4 to 6 of different thicknesses when they were sold as a stand alone item however I only seem to be able to get complete kits now days
Most mower shop that actually repair engines will have draws full of partial gasket kits and in particular crankcase gaskets

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Glad you got it fixed. Rarely is it a sheared flywheel key.

Hobbesnmina2001 said:

Thanks guys the flywheel key was it. Sheared and flywheel moved. After replacing it and torquing it to 150 ft lbs the engine fired up immediately on the first try!
I plan on doing more small engine and equipment work, maybe pick up not running units. It looks like a fun hobby. If I run into this again I’ll be checking the flywheel key before pulling the engine and dropping the crankcase.

Thanks again, take care and have a blessed weekend!

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Next time you try to diagnose an engine problem remember this KISS keep it simple to start with and them work up to the hard stuff.

hlw49 said:

You said starter and ring gear have been replaced. If the flywheel nut was not torqued to 150 ft pound it very well could be a sheared fw key. I would check it.

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Actually the flywheel was tight but not torqued anywhere close to spec.

hlw49 said:

Next time you try to diagnose an engine problem remember this KISS keep it simple to start with and them work up to the hard stuff.

Click to expand...

I hear that, makes sense!

Hobbesnmina2001 said:

Hi all, new member trying to help a friend. I’m not a small engine expert but worked on cars.
My friend’s John Deere Series 100 125 Automatic with 20 HP Briggs V Twin has a replacement engine with some use. The engine quit and seems out timing. After watching YouTube videos I’ve checked the valve adjustment, fuel delivery and has spark. Engine had a starter and flywheel ring gear replaced. It’s not the fuel solenoid.
The engine was pulled and this model doesn’t have a decompression lever, cam looks okay and timing marks line up.
With spark plugs out and ground to head both have spark. I haven’t pulled the flywheel yet but trying to eliminate any other possibility before pulling it.
Flywheel doesn’t feel loose, owner did hear a loud sound when it quit. I never heard it yet, engine spins fine then every once in a while a backfire. The valves and push rods all go in and out don’t seem bent.
Besides a sheared flywheel key any possibilities? A small engine repair guy doesn’t think it’s the flywheel key. Saw the engine and felt it turn with crank case cover off. Nothing seems damaged inside and saw the camshaft lined up and cam condition and timing.
Cylinder compression was at 140 lbs for #1 (left side facing forward) and 160 for #2 (right side. I thought it was good amount although 20 lbs difference a bit concerning.
Any diagnosing thoughts and ideas would be great. My friend doesn’t have a lot of money and we’re trying to help although small engines admittedly are not my forte.
I don’t mind pulling the flywheel to check for a sheared key but wondering if there’s anything else it could be or to check?
Thanks

Click to expand...

You don't have to pull the flywheel, just take the bolt off, you will be able to see if the key is sheared without pulling the flywheel.