Toro Tecumseh Lost Compression; found a screw

[windeye]

Am mowing today, and toward the end of it, the mower lost compression completely. Now this mower has been with me for 24 years since new, never had a compression problem. Just oil changes and spark plugs etc. I am thinking to junk it simply because it has been so long. But then curiosity got the best of me, and I started to take it apart based on what I think might be wrong.

I first suspected valve springs, so took the valve cover off, and found the intake valve does not return properly. See video [here]of the bottom valve. When the push rod retracts, the valve seat does not follow all the way, leaving a gap. The exhaust valve is good. The spring on the intake seems to be OK.

Then I thought I had to take the head off, and I did, and saw the intake valve hang. What the heck?! Upon close inspection, I found a screw stuck in between valve and the seat. Picture below.

It's getting dark, and I am being attacked by the mosquitos, so I'll check further tomorrow. But where could the screw be possibly come from? Any thoughts, anyone? Thanks.

 

[Hirev]

Ouch I would look at your carburetor butterfly screws. At least it did not go into cylinder it might be fixable.

 

[spasm3]

Ouch I would look at your carburetor butterfly screws. At least it did not go into cylinder it might be fixable.

This! check the butterfly, if one is missing, get another, threadlock both.

 

[windeye]

That's what I'll look. Thanks for your quick note.

 

[jhellwig]

Could be the picture but it looks like that isn't its only problem. The cylinder looks gone.

 

[TomYoung]

I would say that pulling the engine apart was a solid move. You have your answer, but based on the cylinder bore and valve seat area, I would call it a day at 25 years.

 

[50yr Street Mech]

Something fell into, or out from the carb, no doubt there. But, I do believe you're on borrowed time with this engine. Get the screw out, de-carbonize what you can with a soft wire wheel on a drill. De-carbonize the head ( I've even re-used the OE head gasket using grey RTV gasket maker ). Chase the threads in the block with head bolts. Smear some anti-seize on the threads. Put the head back on. Don't bother torquing it. You can feel it when their tight. Check the carb good, even if you have to take it off ( same deal with the RTV if you tear a gasket by accident ). Replace any missing bolts with threadlocker. You got life in her yet. I just dumped a 1972 Briggs 3 hp lawn mower in 2024. Piston rap, oil blow by like crazy, burned oil as it idled, then burned more oil when you throttle up, leaking lower main seal, had a little hot dog muffler that was noisy as all hell. My neighbors HATED it LOL....Got a no name from WM on sale. Not the same. No fun anymore

 

[SammyChevelleTypeS3]

... does appear to be a carb screw but really looks too big for application?

 

[50yr Street Mech]

Camera adds 10 lbs LOL !!!!!!

 

[Lubener]

I had a screw come loose on an old cast iron Tecumseh from the carb's throttle shaft about 20 years ago.. The screw got past the valve and got beaten into the top of the piston. It was on a 1973 Bolens garden tractor. I rebuilt the engine, had it bored and it's still in use today.

 

[50yr Street Mech]

Ahhh, Tecumseh...they were a GREAT engine manufacturer. I have just 1 left. A 1996 Lawn Boy 2 stage snow thrower. I am the the original owner. Replaced just 1 carb and a starter re-coil. 5 hp. Doesn't burn a drop of oil, or leak oil, no annoying " Briggs" piston rap. Pretty good for just shy of 30 years ! Glad you rebuilt it Best of luck with it, it will keep going and going. Briggs put them out of business, now China is coming for Briggs !!!!! That's karma.

 

[fantastic]

Carb butterfly screw or another screw from the carburetor. It looks like the cylinder bore is severely scored. Can you wipe it clean & post a pic? Since you already have it torn down this far, might as well rebuild it & run it for another decade or more.

 

[Lubener]

Carb butterfly screw or another screw from the carburetor. It looks like the cylinder bore is severely scored. Can you wipe it clean & post a pic? Since you already have it torn down this far, might as well rebuild it & run it for another decade or more.

If the cylinder is aluminum, it is spent.

 

[repairman54]

I'd take the screw out, put it back together and see if it runs out of curiosity. After 24 years goodbye old friend.
Put it on the curb for one of our BITOG curb pirates

 

[fantastic]

If the cylinder is aluminum, it is spent.

Looks like it's beyond a light hone.
Wonder if OP can mention what engine is on it to see. I know B&S used a lot of Al crankcases but I don't know much about Tecumseh.

 

[nbpt100]

I would run it until it does not function to your needs. You can put straight 40 weight in the engine and it may slow down any oil burn and give a bit more compression. You seem to indicate it was fine (or good enough) until this abruptly happened. If you have or can borrow a leak down tester you can get an idea of where the engine compression stands. Those Tecumseh's used on Toro's were pretty well made. Like an LEV115 or 120? They have an oil pump system that lubes the cams. Good Luck.

 

[50yr Street Mech]

Oh just keep it. Put it back together, and see how it runs. If it burns some oil, thicken it up a bit. Then, at the end of the season, go to Lowes or Home Depot. That's when you get you're leftovers slated for " Misfit Island". 50-60% off

 

[windeye]

Thanks for all the ideas and suggestions. The screw was indeed on the butterfly. The plate fell off and got stuck in the intake. Put it back with loctite. De-carboned the piston top and the intake valve with brush and throttle cleaner. The intake valve still sit a bit cockeyed; can't adjust it to be 100% anways, so did not test it for leaks. I also can't find head gasket, my local Toro dealer does not have it, their suppliers don't have it. I smeared some Permatex Ultra Black on the old gasket, and torqued the head back on per the procedure and spec in service manual. Rotating the fly wheel by hand, there is some resistance but not much, thinking this is the end of it. Later on, when I put everything together, and pulled the string to start, the compression resistance felt OK, and it actually started. So I finished mowing the rest of the yard. No idea how long the Ultra Black will last. Before I go buy a head gasket, question: how much resistance of compression should be when turning the flywheel by hand? Oh, there was some scoring on the top end of the cylinder wall, but nothing major.

 

[jhellwig]

The less you mess with it the better. Run it till it dies.

 

[spasm3]

Thanks for all the ideas and suggestions. The screw was indeed on the butterfly. The plate fell off and got stuck in the intake. Put it back with loctite. De-carboned the piston top and the intake valve with brush and throttle cleaner. The intake valve still sit a bit cockeyed; can't adjust it to be 100% anways, so did not test it for leaks. I also can't find head gasket, my local Toro dealer does not have it, their suppliers don't have it. I smeared some Permatex Ultra Black on the old gasket, and torqued the head back on per the procedure and spec in service manual. Rotating the fly wheel by hand, there is some resistance but not much, thinking this is the end of it. Later on, when I put everything together, and pulled the string to start, the compression resistance felt OK, and it actually started. So I finished mowing the rest of the yard. No idea how long the Ultra Black will last. Before I go buy a head gasket, question: how much resistance of compression should be when turning the flywheel by hand? Oh, there was some scoring on the top end of the cylinder wall, but nothing major.

I'm worried that if the valve is cocked and does not make good contact with the seat, that it will burn there.