Dropped a valve?

Please post the Briggs model and type numbers from the engine. Remove the spark plug or plugs and take the valve cover (or covers, if twin). Inspect the valve springs and keepers to see if everything appears to be intact. If you find anything amiss, such as loose valve spring, bent pushrod or broken rocker arm, the next step is to remove the cylinder head to inspect and assess the damages in the cylinder. If the valves appear normal, turn the engine by placing your hands on the debris screen on top of the engine. While you turn the engine, observe the movements of the valves. If the engine only turns 330 degrees, you might not be able to observe BOTH valves move between the 2 stopping points the engine now has. If you see both valves move, there is hope that the valves are intact, but no proof, yet. If neither valve moves, the camshaft might be broken.

Another thought maybe an issue on top, such as a very loose starter motor or a magnet coming loose under the flywheel.

Thanks for the help so far. Pat is out in the garage with the lawn tractor and will be back with a follow up post soon.

He just brought in one of the spark plugs that had a damaged end and had me take photos of it for you folks. I'll post the photos now. He's got plenty to do on the lawn tractor without having to figure out how to post photos on garden web.

If you click on the any small photos here it will take you to Flickr where you can large and huge size versions of the photos for detail.

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Lynda

OK - More info.

The Engine number is 286H77 type 0121E1.

Pat says that the lower of the two valves is not moving when he turns the flywheel by hand.

He does not see any obvious visible damage to springs and pistons.

The spark plug was hard to remove and he's concerned about whether there is additional traumatic injury in that area, specifically to the threads.

We're getting the feeling that this is going to be the sort of thing where we'll need to have an experienced mower engine mechanic look at it. Before we arrange for that, is there anything else we should be doing or looking at?

Thanks again for all of the help so far.

Lynda (and Pat too, of course)

I've seen that before. Valve dropped out and broke the piston at the same time.

At the very least, you'll have to pull the head.

Every picture tells a story! I concur with baymee. If you don't plan to tackle the repairs as a DIY project, not much reason for you to remove anything else from the engine. Just take the spark plug with you when you go to your mechanic. Your description, model and type numbers, and the spark plug should be enough to get a ballpark estimate. Brace yourself for the possibility that this engine might be scrap metal now. Catestrophic lock-up like this often bends connecting rods and crankshafts, not to mention the head itself may be unrepairable. See what "they" say and price it both ways (new engine versus new parts and old engine). Considering what has happened, you would be advised to replace rather than repair (my opinion).

Ugh! Not exactly what we hoped to hear, of course.

Thanks a lot for your help on this. Pat and I both appreciate how quick every has been in helping us out.

Just a couple last questions.

What generally causes this type of failure?

If an entire new engine is required, does that start getting close to the cost of replacing the mower? (I realize that's asking for wild guesses, but it will give us something to think about until the repair shop opens tomorrow.)

Lynda (and Pat too)

Look on Tulsa engine warehouse's site. You might be able to get a short block.

When thinking of cost,think of it this way,it could have been a cast iron Kohler engine and that would be much worse.

And, on the next engine, or tractor, install a fuel shut-off valve! Its quite possible a crank-case of gasoline diluted oil could have caused the problem! The gasoline in use today seems to have deleterious effects on the carburetor parts, and could have destroyed the fuel needle in the carb, or the little plastic needle "seat".
All of my powered equipment is getting fuel shut-offs asap.

***"What generally causes this type of failure?"***
The kind of "cascading" damages in a catastrophic failure like this engine suffered are typically due to a "set of circumstances" than from a "single cause" (I am referring to "dropping the exhaust valve")
The valve seats are steel rings, pressed into a machined recess in the aluminum cylinder head. Under "normal operating conditions", the temperature of the engine remains below a critical threshold, and the valve seats stay in place. BUT, whenever "abnormal operating conditions" prevail, the temperature of the engine (especially the exhaust valve sector of the head) may go higher than the design temperature limit. If/when this happens, the exhaust valve seat loosens and jumps out of its recess. Once the seat is out of place, it prevents the exhaust valve from closing, and so the piston comes up and strikes the valve and seat. The impact may stop engine rotation instantly, or the engine may continue to rotate from flywheel inertia a few seconds as it spirals to a stop (the moment the exhaust valve seat came loose, combustion ceased).
A "common cause" of overheating is when mice build nests, or caches of food, inside the sheet metal shrouds that duct cooling air from the flywheel fan over the engine cooling surfaces. An engine running with too little fuel in the mixture (lean burn) can also run hotter than normal, and that will eventually result in loosening of the exhaust valve seat, though that type of loosening may not always result in a sudden, catastrophic failure (but it can). Another way that exhaust valve seats can loosen (in an otherwise "normal" engine) is if valve adjustment is not maintained to the correct specifications. If the valves have too little clearance, the exhaust valve will "leak" a portion of the combustion gases past the valve seat during the part of the combustion process where it is supposed to be completely seated. Cooling of the valve seat and valve are primarily accomplished by having the valve and valve seat in contact with each other for the majority of the time that combustion takes place in the cylinder. This "closed time" allows heat to be conducted away from the valve and seat, into the cylinder head and valve stem, where the heat can then be carried away by both lube oil (inside the valve cover) , and cooling air from the fan. If the "closed time" is reduced because of insufficient valve clearance, the temperature of the valve and seat will increase higher than the design limit of the head, and the valve seat may loosen, or the valve and seat may be "flame cut" by the escaping gases. A good "forensic analysis" of the failed engine is needed to determine the reason for the overheating.

Thanks for the info again. We've taken the lawn tractor into the repair shop and I'll let you all know how things end up working out.

RustyJ, Pat checked and apparently there is a fuel shut off valve on the tractor already.

Once again, a big thank you to all of you for being willing to help. Pat and I appreciate your time spent answering our questions.

Lynda

As the old cooks' saying goes:"Stick a fork in it--its done!"

Just a quick update on our lawn tractor.

We got it back from the shop yesterday. Total cost $132.59.

It had a broken valve and the damaged spark plug. They also replaced a gasket and a bit of gas line.

Parts cost 27.70
Shipping for the parts 12.00
Labor 85.00
Tax 7.89

We got it to the shop right as they were closing on Thursday and got the call that it was done on Tuesday morning. It's home now and running like a dream.

RustyJ, I'm not an expert but I'm not sure I should really go out and poke a fork in the engine! :)

Thanks again for everyone's help -

Lynda (and Pat too)

Glad it was an economical repair. You were lucky!

Oh, my saying is just an old auto mechanics statement, usually used when somebody brought their car in for repairs, after many miles of no oil changes, or filters, etc., and "It just went BANG and stopped!" statements!
good to hear you got away that reasonably! Most of the bigger repair shops here would have trimmed yer wallet a lot more than that!
Bet you'll enjoy yer turkey dinner a lot more, now that you got off that reasonably! Happy Holiday to you all!

I figured you were just poking me with a fork, RustyJ. :)

We try to take good care of our power tools of various sorts. Can't run stuff into the ground if you need to count on it, right?

I'm really pleased with the folks who did the repair. They are also our local Stihl dealer.

Lynda

I'd say you were really lucky on this one.