Small engine advice needed

[Tractors4u]

I have an old Craftsman riding mower with a 12 hp Briggs in it. It was given to me as a fixer upper and I planned on giving it to my brother in law when I got it fixed. Anyway, the thing acts like it wants to start but it backfires through tthe carb but never starts. I was describing the symptoms to a couple of guys and the first one said stuck exhaust valve. The second one, who had a mower just like this one said that he has a nut come off of the rocker arm for the exhaust valve. Today I pulled the valve cover and the vavle isn't stuck, the nut was still on but there was play in the rocker arm. With the valve cover I turned the engine over and the exhaust side doesn't move at all. Any ideas as to what has happened? I was hoping to avoid going all the way into this enginem but I may have to.

Thanks in advance.

 

[Slamfire]

Lifter collapse, or cam lob worn down.

 

[zenmek]

Some cam gears are nylon, could be broke gear or missing teeth

 

[StoneHeartFarm]

I've got an older 16hp tecumseh that did that. Wanted to start, but mostly just kept backfiring. Turned out the flywheel key had sheared and the flywheel was about 1/4 turn off. Pulled the flywheel, put in a new key and it started right up.

Steve

 

[dummy]

If it is an OHV design, the valve gap has to be correct or it will not start. Have to check, but somewhere around 12 thousandths sounds right.

 

[normde2001]

I have read that, on that type engine there is a mechanism on the cam that keeps the exhaust valve slightly open as a compression release to aid in starting. That could be why you get no valve movement, and you probably have a sheared flywheel key as mentioned before. Run it by these guys they know all about these things.

 

[jrlichina]

Make sure you turn it over at least 4 times to make sure you have made it through the exhaust stroke. Is the intake valve opening? If the valve doesn't move while rotating the engine the exhaust valve tappet could be broken or the exhuast cam lobe could be worm completely round. You'll need to open it up and see what's wrong. As stated earlier, check the flywheel to make sure it's on correctly.

 

[Tractors4u]

I really don't think this is a flywheel issue. As I mentioned earlier, I pulled the valve cover off and watch the rocker arms as I cranked the engine and there was no movement of the exhaust side. As someone mentioned in a couple of posts, I think it may be a cam lobe now. I really didn't want to have to tear into this thing. I may stick it in the corner of the barn until I nothing better to do. That will be the day!

 

[normde2001]

You didn't say whether the valve was open or closed with no movement. Assuming closed, one would have to wonder how it ever ran long enough to wear the cam lobe until no valve opening at all. What kind of valve clearance do you have?

 

[Tractors4u]

The valve is in the closed position. The spring is keeping it closed. A neighbor of mine got this mower last year. I went to pick it up for him. It wasn't running at the time. I found some back connections, it wasn't getting juice to start. I got it running and it ran fine. I took it to him and then this summer he gave it to me and said he never got it to start. Then I started tinkering with it. It ran good for me last year, it sat for a year and now this. I don't know what would have happened from then until now. /forums/images/graemlins/confused.gif