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This B&S 900 problem with backfiring and jerking starter rope out of hand.

With only limited "smarts" for this engine, thought timing off so looked at flywheel key and it was sheared in two. Checked valve clearance and appeared to be ok. New shear pin, reassembled but same problem.. hard to start and when it fired, backfired only. Looked and key was sheared again.

Thinking this is a camshaft issue, but don't know how to check if that is the problem without tearing the engine apart.

Any help or guidance for this beginner?

I'll bet the second time it sheared was caused by improper torquing of the flywheel nut. Get anew key and make sure you torque it properly.

Thanks, that may be the problem.

Do you think not enough torque?

The aluminum key purchased at a B&S dealer was tight when slid in the crank keyway, but there was some slop when the flywheel was slipped on (prior to tightening the nut). Didn't like the slop but figured it was my ignorance at that point.

What torque is advised?

Slop is normal, torque is 60 foot pounds.

Thanks Rivets.

Found in the Briggs Service Manual graciously forwarded to me by a member, that the flywheel is to be torqued to 100 lb-ft. That's a bit more than 60.

Also, if it comes to replacing the camshaft, the part # 693404 appears to only be the nylon plastic one.

A basic question.. but is counter-clockwise rotation of the crank to position TDC looking at the engine from the flywheel end of the crank?

Hopefully tomorrow we'll know more about what might be the problem of the serious compression buildup when rope starting, and then only a backfire. Seems that would be more than just the valve clearance out of tolerance.

That seems high, here's where I got my info.

http://www.mymowerparts.com/pdf/Bri...N ALL SINGLE CYLINDER INTEK ENGINE MODELS.pdf

Removed camshaft... and learned the small spring on the compression release is twisted out of shape... contemplating next move.

Any thoughts... other than to buy new camshaft?

Have a new camshaft, seal, plastic push rod guides, and gasket ordered.

Learned that before this engine had the backfire problem, that it had been over-filled with oil (to the brim in the dipstick plug hole). Am thinking this extra oil caused the real fine hair spring on the compression release to rip off making rope start a problem and the backfire.
Will see if we can get it put back together and the valves set right, and hope we will have a running engine.

Will report back, and thanks for the help. Not comfortable with the two different torque values to contemplate. Will have to decide on the 60 or the 100 ft-lb soon.

Talk about confusing. I checks several different briggs torque charts and found the 12xxxx vertical uses 60 ft/lb the 12xxxx horizontal uses 100 ft/lb and the 12xxxx professional engine uses 60 ft/lb

Thanks ILENGINE

This being horizontal, will go with the 100 and stick to the "book". Keep our fingers crossed.

Proper torque is very important. When you over torque you are starching what ever you have just tighten and have weaken it.:thumbdown:

reynold.. so you suggest we undertorque the 100 lb-ft per the torque sheet for this horizontal 12xxxx ?
Are we better off to undertorque than risk the 100 lb-ft spec is overtorque?

Also, there is a slight bit of slack in the key/keyway... should that slack be taken out one direction or the other... say either CW or CCW before torquing the flywheel nut?
I'm thinking rotate the flywheel in CW direction against the crank.

Thanks

Update on the Intek 900.
Today we put the engine back together with the new camshaft and it fired off and ran fine.
Thanks to all who contributed to this thread.