Craftsman with 21HP BS engine

[mpqualdie]

The tractor is a 2012 Craftsman 42" 21 HP and has been very well maintained since I bought it new. It looks and runs almost new still. Last spring I was mowing. I shut it off for a minute. I kind of double started it when I resumed, meaning turned the key, accidently let go and then turned the key again in one fast motion. It made a weird "ker-blork" noise and from then on the issue that has me stumped. Now the starter can't pull the motor past the compression stroke. To use it i have to hand wind the motor backwards as far as it will go and hit the starter. When it's warm it'll start up no issue, but cold starting i usually have to do this several times. The battery was new already, but I've changed with OEM parts the starter, solenoid and had the battery tested again and changed the battery cables. I'm stumped, it's like there should be some compression release that's malfunctioning or something because the starter can't pull it past the compression stroke. Any ideas?

 

[Tinkerer200]

When asking an engine question it is always helpful to post the engine model number. HP does not identify the engine. Guessing it is an OHV single cylinder engine, check the valve clearance first thing. IF clearance is within spec, .003" - .005" for the Intake clearance is OK. Then remove the spark plug, turn the flywheel clockwise by hand watching the INTAKE valve very closely for a slight additional movement towards closed well into the compression stroke. IF you do not see any movement then likely the compression release on the camshaft has failed, a fairly common problem. Fix - new camshaft.
Walt Conner

 

[StarTech]

Can be as simple as adjusting the valves. The Briggs 330000 series camshafts are prone for ACR failures but first try adjusting the valves which more common to be out of adjustment.

IF the ACR has failed when replacing the camshaft make sure to remove all broken parts of the ACR and check the oil slinger/governor for damage too.

 

[mpqualdie]

Thank you, this makes sense. I figured it was something to do with compression relief because once it starts it runs like new, just can't get the starter past that compression stroke. Thank you so much!

 

[Richie F]

I believe the compression release is for the exhaust valve, not the intake.

 

[ILENGINE]

I believe the compression release is for the exhaust valve, not the intake.

Intake on the single cylinder OHV engines because the compression release is located next to the camshaft gear, and the single cylinder OHV uses a crossflow head so the intake is on the bottom.

 

[tom3]

Dad had an old Gravely that he put an electric starter on when he got too old to pull the strap. He'd turn it forward up on the top of the compression stroke, then hit the button. This would give it two crank rotations to get up to speed for starting. Old machine is still running and gets started that way.

 

[StarTech]

Intake on the single cylinder OHV engines because the compression release is located next to the camshaft gear, and the single cylinder OHV uses a crossflow head so the intake is on the bottom.

2ND that...

 

[Richie F]

Intake on the single cylinder OHV engines because the compression release is located next to the camshaft gear, and the single cylinder OHV uses a crossflow head so the intake is on the bottom.

Thanks for the info on that.