Older Briggs engine jerking my arm off

[sblg43]

I am fixing up an old "stump jumper" for a co-worker. It is a Cub Cadet mower with a Briggs 128802-0627-01 Serial 95061958 engine. It has been sitting for at least a year with a broken starter recoil. So I fixed the recoil, cleaned the carb, re-gapped the ignition, new plug, new air filter, fresh oil, fresh premium gas and an all around clean up of the engine and mower deck. I left the older rusty mower blade on it for now.

When I go to start it, it jerks back like it would if there was no blade on it! So in anticipation of serious pull back, I give it a couple of short pulls and it starts. After coughing and wheezing (the mower not me) for a bit it seems to run smoothly. I shut it down and restart it - still wants to jerk back violently but it will start and run.

Here is my theory - compression release mechanism is not functioning or flywheel key is slightly sheared. Any ideas or advice?

Thanks

[Deere2me]

Ya wanna make sure the blade/adapter is keyed and tight.
Check the flywheel.
Pop the breather cover off and check the valve action when you turn it over by hand with the plug out. Check for the ACR bump on compression. Also check the valve clearance. If excessive on the exh. it's a good bet the cam is wiped/worn.

[motorhead64]

All your listed possibilities are valid ones. I would start with a valve check first. Also, you didn't mention the carburetor. Older stuff generally benefits from attention to the carb...a good clean and tune, and rebuild kit if needed. MH

[KE4AVB]

Probably will find the cam bad as it looks very cheaply made. Looks like its mostly plastic. Considering the cost (MSRP: $169.00) of the replacement engine I wouldn't put too much time and parts in it.

[KE4AVB]

Before someone thinks that I just down on the engine I might need to explain my reason for suggesting just replacing the engine. First it is a 1995 unit. It has sitting over a year which usually means at least a carburetor cleaning and rebuild. It has a possible bad camshaft. These are just the starters. I see already about $60-$75 in parts alone not counting the labor charge vs the replacement of new engine at about $169.00 + shipping and/or taxes. On top that you can buy whole push mower for even less sometimes, pull the engine, and keep the mower body for parts. I got several push mowers here that I can't even sell just the price of the new parts I have in them; writing off the labor costs.

Here when engine repairs exceed 50% including labor most customers opt for a replacement engine or a replacement mower both of which have better warranties then the repaired item. The only time customers seem will to spend more 50% is on a two-cycle engines knowing they are more likely to last after the repairs. Even then they seldom have engines rebuilt due to costs. There are exceptions when someone is wanting an antique piece equipment restored; mostly collectors.

[Deere2me]

All your listed possibilities are valid ones. I would start with a valve check first. Also, you didn't mention the carburetor. Older stuff generally benefits from attention to the carb...a good clean and tune, and rebuild kit if needed. MH

The OP already covered that.

[motorhead64]

Oops. MH

[sblg43]

Got it! The flywheel key was sheared in half. Put in a new key, put it all back together and bada boom!
Anything more and it would have been toast. I have enough mowers laying around that I don't need to dink around too much with the difficult ones. Thanks all for the input.

[KE4AVB]

Thanks for letting know you found your problem.

Here most times a half shear key won't even let a engine start. I have replaced several keys this year on push mowers and none would start because the partially sheared key problem. Probably the flywheels wasn't torqued to spec. I do get problems in batches.

[Deere2me]

Got it! The flywheel key was sheared in half. Put in a new key, put it all back together and bada boom!
Anything more and it would have been toast. I have enough mowers laying around that I don't need to dink around too much with the difficult ones. Thanks all for the input.

Yeah, that's usually the case! Anytime I get even a hint of "arm yankin' " that's generally the first thing I look fer.

NOW...what caused it to shear? Did ya check for a bent crank?