have a 11hp briggs and stratton vertical shaft engine that is about 30 years old. In order to check valve clearance does the piston have to be at TDC on compression or 1/4 past TDC. Also, does it matter which way you turn the engine(clockwise or counterclockwise) when you bring the piston to TDC. On the intake valve I get a different valve lash reading if turn the engine counterclockwise or clockwise. However, the exhaust valve reading is the same no matter which way I turn the engine. Could the camshaft lobe be that worn! This flathead on an old craftsman is puzzling. Any help would be appreciated
Setting Valve Lash
- Thread starter kcrego
- Start date
pugaltitude
Lawn Addict
- Joined
- Jan 11, 2012
- Threads
- 7
- Messages
- 1,142
Servicing Engine Valves | Mower & Small Engine Repair | Briggs & Stratton FAQ
Read this 1st which will help.
You need to be 1/4 inch past tdc on the power stroke.
Thanks for the response. Some how is missed the word clockwise when I read this over before. However do you have any idea why the readings on the intake valve would be different when turning the flywheel 1/4 past TDC either way.
The difference is because going from the compression to the power stroke, the correct way, you are on the front side of the cam lobe. Going the other direction power stroke to the compression stroke, the wrong way, you are on the hack side of the lobe. Lobe wear will contribute to the readings also.
pugaltitude
Lawn Addict
- Joined
- Jan 11, 2012
- Threads
- 7
- Messages
- 1,142
Yes if you turn counter clockwise then it is the wrong way.
Look at the 2 valves while turning clockwise.
Now sometimes people get confused as 1 valve opens and closes and then the other valve opens and closes.
The 1st valve opening and closing is the exhaust valve and 2nd is the inlet so the 4 stroke cycle starts just after the exhaust valve shuts.
So piston down is inlet stroke inlet valve open , piston up compression stroke inlet valve shut, piston back down is power stroke valves shut and piston up exhaust valve open is the easiest way to look at it.
The decomp may be on one of the valves and that allows one valve to open ever so slightly so that is why it has to be 1/4 inch past TDC on the power stroke so you get your adjustment right.