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Engine is a 20HP year ~2000, Opposed Twin. About 7-800hrs. Splash lube.

Always smoked on startup.

It was ok until now except for issues with starter gears and the ignition coil. Decent maintenance, but the oil may have been left a season, but under the hours for a change. Not much use recently.
After this incident there was oil spillage, but the oil was a bit below the low mark. So lets say oil level was in the low range of the crosshairs. I don't believe the case is cracked.

Anyway, after the last starter gear stripped, I tried starting it with a strong impact driver, that may have contributed.
Installed starter.

So it made a terrible noise - smoke- came to a halt. Took off the inspection cover- both rods broken.

upper rod spun on the crank. Crank looks like it has material transfer but in my inexperienced eye salvageable.

Lower rod is still connected to crank, but broken in the middle.

Bores have no scratches.

Camshaft ok

Lots of metal pieces large and small in the engine.

I'm wondering if for about $100 or so it is worth to get used parts, clean up and repair? I have a repair manual.

My neighbor said I would repair it if I were you, even for a few hundred. he said he went thru 2 big box $1500 mowers in the last 6 years. They were professionally serviced too. He feels it would last at least that long repaired.

Before deciding to repair the engine, I suggest that you tear it down and get a good look at the entire engine. Valves, cylinder, piston, rings, etc. condition of the valves and cylinders, plus pistons and rings will dictate whether it is worth repairing. You may need to replace more parts than just two rods. Even with out seeing it, I suspect you will need to stick at least $200 in used and new parts. I wouldn’t stick a dime into it unless I knew exactly what I had. If you have more questions, feel free to post back, but remember to include all engine numbers, so we know exacting which engine you have.

Rivets said:

Before deciding to repair the engine, I suggest that you tear it down and get a good look at the entire engine. Valves, cylinder, piston, rings, etc. condition of the valves and cylinders, plus pistons and rings will dictate whether it is worth repairing. You may need to replace more parts than just two rods. Even with out seeing it, I suspect you will need to stick at least $200 in used and new parts. I wouldn’t stick a dime into it unless I knew exactly what I had. If you have more questions, feel free to post back, but remember to include all engine numbers, so we know exacting which engine you have.

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Yes, I plan on at least tearing it down. Just looked in the inspection hole, there could be more surprises.

When I do I'll probably post pics. I pulled the heads a few years ago and except for some cleanup, it all looked good.

Visually it may look good, but I’ve learned that the eyes will deceive the most experienced mechanic. Measure everything and check for sizing in the manual. Plus try to find the exact cause of the failure, this is where experienced eyes help.

Rivets said:

Visually it may look good, but I’ve learned that the eyes will deceive the most experienced mechanic. Measure everything and check for sizing in the manual. Plus try to find the exact cause of the failure, this is where experienced eyes help.

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How do you determine root cause?
I suspect the impact driver, but many said no way.

Also, if the oil was toward the low mark, I could believe that.

The opposed twins are good engines but they really don't like being low on oil. Especially at startup. Upper rod seizing kinda indicates that. I have fixed a few like that. The crank will cleanup. I would get the proper ball hone and deglaze the cylinders and put rings in it with the new rods. Don't use an impact to try and start an engine. Never a good idea. Use a drill instead.

It is difficult to determine exact cause many times, but an experienced mechanic will look at things like discoloration, material transfer, scoring, measurements and general condition when looking for a cause. Saying the cause is the result of things like using an impact wrench is just an outright guess, and I would never even suggest it. Even saying low oil level is the cause needs to have some sort of physical backing. Remember the saying about “I assume”, it fits any time you try to find a cause. You need a backup.

There was definitely oil around the engine, on the frame. I don't see any cracks on the block. Some on the pulley too. Guess I have to pull it off the tractor and start digging in. I estimate that amount of oil should be enough to push it into the low crosshatch area, which probably isn't optimal.

Probably should have checked the oil before hand. Going to put a check oil level before starting sticker on all my equipment now.

I have some numbers off it:
460707-2278E1-9910225A
Put in service 10/11/2000

It is a 46 series, which is a large engine.

I'll also add I fixed the trans on this tractor. It has a Techemseh hydro trans. A bolt got loose in there.

Failure analysis is a hands on experience thing .
It is not all that difficult but only if the failed item is in your hands.
Cracks will tell you a lot as will the shape of the fracture surface, which side of a conrod has the little neck, weather there is necking or bending.
Then there is metal pick up, the direction of metal pick up and oxide colours where there should be none .

However to do it properly you need to be at one with the engine and understand exactly how each part interacts with other parts .
So for instance with a broken rod you fist look to see if it rotates freely on the big end and if the piston rotates freely on the little end.
Then you look at the oxide colours on the underside of the piston .
Big end is free bit little end is frozen & the piston is blue so you look at the oil slinger / pump .
Teeth missing and the surface is slightly rounded & polished a little then it was a cause, teeth fracture surface clean with no damage, happened during the failure . etc etc etc
And thus it goes on.

In a different life I did occasional overflow work for a tutor who had a contract with the police forensic lab .
Around this time of year you get a lot of car smashes when little Johnny is high as a kite but daddy big time lawyer is busy trying to shift blame anywhere else .
A common trick, before ABS came in was to rev the engine hard then slip your foot across and jump hard on the brake when you had maximum boost on the brake servo.
This will generally pop a seal somewhere in the braking system so little Johnny can claim brake failure

If you get Air Crash Investigations over there binge on a few hours of it and fast forward through all the bull to the bits where they show you how they determined a missing washer caused an engine to self destruct.
It is very accurate, quite a surprise for a TV show.
Even then they ignore the technician who spent hundreds of hours cutting up critical pieces of the wreckage, doing micro analysis of the crystal structure and hardness testing