This effect has been mentioned on here before, and for the life of me I could never figure out what the heck is going on. None of us ever came up with an explanation of why the blade could not be tightened. There's something we don't know, and the people who are doing it don't know enough to tell us.
If the blade is not secured to the shaft, the engine will give the very symptoms you described. The blade acts as the major part of the flywheel effect and smooths out the starting pull. Without it the engine could darn near break your arm. Most mowers these days use a stiffener that fits over the blade center portion before the bolt goes in. The blade also must be right-side-up. Good luck and let us know what happens.

I'm going to have to get a flywheel removal tool to check the flywheel key, the blade is on as tight as it would go without stripping the threads.

What kind of tool are you using to tighten the blade? There's a world of difference in how tight a bolt will get from a crescent wrench vs. a socket on the end of a breaker bar or torque wrench.

When I install the blade bolt, I use a ratchet wrench. The mower is on its side with the blade horizontal. The box end goes on the bolt and the open end is about 2 inches higher than the blade. That way I can hold and push down the blade with my left hand and push down with full body weight on the wrench and hold the blade at the same time with my right hand. I'd say the torque is about 40-60 ft. lbs. Many repeat customers and never a loose blade.

I've never cranked down on them with ultimate force. I use a 1/2" drive ratchet - I guess its about 12". I usually block the blade with my work shoe, bend over and let some weight go onto the nut/bolt - probably a good 50#. I have no trouble getting 90# to 100# on lug nuts with a long torque wrench. I guess my point is, even with 35# on the blade bolt, it's just not coming loose. Something strange is going on that we can't understand because we're not there to see it. The correct blade with the correct hardware in the correct orientation will tighten up and stay tight until you loosen the bolt.

Since I posted, I put a blade on as above and then checked it with the torque wrench. It was 45#. So, that's how tight I make all blades which are held on with a bolt.

Ok, got the flywheel off and sure enough the key was sheared completely off, will be getting that fixed within a week or so. Thanks for the tip baymee.

My Toro mower was starting and then dieing. I read a fix by someone here that i found on a google search. there were photos of the bolt that hold the cup on. I couldnt beleive how easy the fix was. I was ready to throw the mower out. I could not even see the little jet hole prior to seeing your photos. (thank you who ever you are) i used tie wrap wire to clean it and washed it with alcohol and blew it out with compressed air. It now works like a charm. Thanks a million.

Pictures like this? I'll have to increase my collection someday.

Glad I could help lb. If your key was completely sheared off, are you sure the blade didn't hit something that bent the crankshaft?

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If the flywheel key is sheared off the spark timing can be advanced (because the flywheel has spun ahead of intended position held by the key when slammed to a stop)the advanced spark will will tear the handle out of your hand when it fires early as the piston is comming up and the advanced ign, fires the spark way too early if bad enougth it will kick the engine backwards posably causing the blade to kick loose can also happen if the valve timing or adjustment is not proper or if compression releaf is not working (not all small motors have this)

We may well have the definitive answer to the several 'blade won't stay tight' complaints, first posted by baymee, and Brian's succinct statement of it definitely passes the 'is it possible' test in my book. Obviously, the flywheel key must be sheared to throw the timing off that much, and it's possible that some people will not realize they have this condition.

I know this posting is old but to add to the blade coming off issue I thought I would throw in my experience that I just experienced. I was having the blade bolt unscrew every time I would get the mower started or every 2 to 3 pulls. I went out and replaced the lock washer multiple times thinking it was the issue to trying to torque down the bolt to an extreme. My issue ended up being the drive assy. that slid over the crank shaft and had a pulley for the belt and that the blade lined up and rested to. The key within the drive assy that lined up with the groove on the crank shaft broke off and would cause the drive assy to spin freely and back the bolt out with the momentum of the blade spinning around.

Wow. Another cause for the blade coming loose. This easily-replaceable blade driver comes on many 4-cycle Lawn-Boy Insights and some Toro mowers too. Thanks to Brian and rhaas for these tips. I had never seen this effect of the blade kicking back and coming loose.
If rhaas's blade driver is the Toro type that slips on and off easily after blade removal (makes belt replacement easier), the problem could be that the slip fit allows a small movement of the key in the keyway which over time could fatique the key and make it snap off. But more likely the key was over-stressed by hitting something with the blade, just like a flywheel key.

I replaced belt on toro 22” recycler and it started right up but was very noisy looked underneath an new drive bolt loosens. Now I can’t get drive blade off when I had no problem before

Try explaining your issue again please ! Cutting blade vs drive wheel ?

It sounds like the blade was tightened and not flat on the adaptor. Then it broke free

Hey , it's baymee! Where you been?

Well, first of all, they changed the website and I didn't have time to learn it cuz I'm working full time and running a small engine business at the same time. I was getting an occasional email from the site. I also began to notice years ago that a question could be answered and the poster would never respond and it seemed like they posted in desparation and when an answer didn't come within one minute, they went to another site. I suppose the info we give does help when people research. Ethanol is the repair shop's best friend; it creates 99% of the business and is probably the first cause of a person junking their mower. If you drain the gas at the end of the season from the tank and carb, 99% of repair shops would be out of business and manufacturers would have to close their doors. lol. Nice seeing you Tom, you've helped me in the past.

My major source mowers for repair was sending throwaway 2 stroke stuff from Home Depot and Lowes. If you change the fuel and spark plug and it wouldn't start, then you were into the carburetor rebuild or replace. How can you repair them and it costs more than the $79 they paid for it new? So, after spending an hour a day working on this junk and making no money because you want to keep the customer for their other equipment, I told my source that I no longer wanted to take in any junk. He said if I wanted to repair their big stuff, I had to repair their junk too. Since I make more than enough money with my full time job and my own customers, I said "See you later, I'm not doing it". We split up from around 2013 to 2016 and he contacted me again and begged me to come back. The guy that he was using was right next to his business and he left all the customers equipment outside, uncovered, in the rain and the snow. His customers would shop at the store and see their equipment outside in the weather when they left. It would take weeks for a simple repair. Well, he had 1000 customers on the list when we split and only a handful in 2016. I went back on my own terms and it's been good since then. So, I've been busy. I'll be retiring soon and this is a nice supplement. What I noticed when i came back in 2016 is that there are few Tecumseh engines, more Briggs and a new one, Kohler, and the carbs have changed. In 3 years, we now have many automatic choke carbs, plastic bodies and they aren't too hard to remove from the engine.

Is Rusty still with us?

Hey Bay long time no hear Bud ! No Rusty has not been on in a few yrs , last time was on the Tractor forum i believe ., Complaining about his last snow storm in Pennsylvania ! lol. Yeah between the auto start carbs with thermostat chokes and the e fuel issues , hard to get a spare moment to fish !

Good word. The evolution continues!

Ok I posted earlier. I initially had belt problems and replaced belt. I have a toro 22” recycler mower and when I put the drive blade on I forgot to put spacer inside. It started up but the blade bolt kept loosening and then I had to get the drive blade off with a hammer. Bought a new drive blade but still had to force it on. Did I do something to the crankshaft?

jack, what model # is that.

20332

Model313058436

That was serial number

No everything is good with crankshaft ensure to tighten with a 3/4 drive ratchet . Ensure new blade is put on correctly use old blade as reference clean side towards the crankshaft .

He might be talking about the spacer that goes inside the blade adaptor. It drops inside and it has to be flat. I tightened a blade once without the spacer and it ruined the adaptor and the blade loosened up while rumming

Running. The mower wasn't drunk lol.

No all the problems started after I didn’t put the spacer in. Then I had the drive blade stuck and forced it off and had to force the new drive blade on

I guess what I’m asking is why the drive blade doesn’t easily go on and off like before

can you post a pic of this "drive blade"

take it apart and try and thread the blade bolt into the crankshaft, if it theads in (you hope) , some thing else might have been tweaked.

https://www.toro.com/parts/partdetails/?id=40320

Drive blade

It threads in now the pull cord pulls but doesn’t turn over. New gas oil spark plug

I’ve been through the toro parts manual already but thanks

what do you mean by the pull cord pulls but doesn't turn over.

It started originally. Then I did all the work on it. When I went to pull start it it wouldn’t move. Now it does but doesn’t turn over

when you had the mower tipped on it's side, could you have tipped it so the carb was on the low side?

No I made sure of that brand new air filter too

sorry jack, without seeing whats going on it's hard to say.

look at the bottom of the blade adaptor, is there a 1/4" thick spacer in the bottom? It will be round with a flat spot on the side. Maybe your cylinder has oil in it. take the plug out and pull the cord and see if anything comes out the hole. don't let the coil lead get near metal cuz if it's gas, it will ignite. I've done it.

Is the cylinder full of oil or fuel? Remove the spark plug and turn it slowly- don't let the spark ignite the fuel...

x2 on the above. could the belt have fallen off the pulley on the trans?