pitman47

I have a Sears Craftsman rear tine 6HP 14 inch tiller. It's probably got less than ten hours use over five years.
I got it out the other day to till my veggie patch, had to clean the bowl nut orifice out, some dirt from the fuel. Now I cannot start the darn thing, I have a problem I've never encountered with any small engine. It appears to have too much compression!! ie, I cannot pull the starter passed TDC!
I have removed the spark plug and the engine is free to turn, no tight spots, both valves are free. But put the plug back in and it's almost impossible to get it to crank it over.
HELP!! I have never come across a problem like this and have stripped and overhauled many small B&S engines in my time.
John

coleman mobile

How old is this engine? Briggs and Stratton has put a tech bulletin on over head valve engine (if it is) not starting past top dead center on the compression stroke. You may need to check the valve clear clearance. The valve clearance should be .004 to .006 if im not mistaking. I dont have my book in front of me right now. If the valves are ok then you need to replace the cam shaft. There is the mcr (mechancial compression release) on the cam and they stick or fail completly. Before you do that check the timing on the fly wheel. Let me know if this helpful.

NoTicIntek

John,

Are you saying that with the plug out the engine will tun freely **through several cycles,** but with the plug in it will not go past TDC at all? Couple of thoughts here.

Is the compressible volume of the cylinder clean and dry? Meaning it there a bunch of oil or fuel in there. It may be reducing the compression space. Try squirting some WD40 in there then pull it furiously a few times with the plug out. Repeat until no visible mist comes out the plug hole.

Did you change the plug? Maybe you picked up the wrong plug and put it back in and it is too long.

Can you pull slowly on the start rope until it gets to the TDC spot, then keep applying load on the rope and the compressed air/gas should slowly bleed past the rings and allow it to move past TDC. If you can't get it past TDC it sounds to me like the piston is hitting the plug or maybe a stuck open valve.

Can you see any marks on the top of the piston with a flashlight?

Is the plug ground tab bent and touching the electrode?

Dave

pitman47

The tiller was bought in March 2005 brand new from Sears.
It's had approx 10 hours of use.
No, plug is the original, an no, no water or anything else in the cylinder, just end of season maintenance carried out as per book.
It's deffo compression as when I pull to TDC and ease a valve in it frees, so down to auto de-compression problem.
Both valve clearances are to spec, I have removed the exhaust valve and cleaned some carbon from the seatings.
Looks like I'm going to have to check the auto decompression set up on the cam shaft as Coleman mobile suggests, seems the only resort now I've cleared everything else.
John