It's not the cam

Briggs 31N807 0440. Customer insisted that the cam was bad. He'd gotten that from a reputable mower shop in town. Said the ONLY way to get it to turn over enough to start it, was to jump it off his pick up. He said the valves had been adjusted. I know the owner of the other mower shop, and have no reason to doubt their work, at all.
Before I started on it, I did check the battery, and it was weak. But he told me that the other shop used a new battery and it still wouldn't turn over all the way.

So, I took the cam out and found that the compression release was still in tact. THE only difference between that and the new one I had, was the weight on the old compression release wasn't exactly square. It almost look like it has been rubbing on something. But, I didn't see anything that could even come close to touching it. Much less, rub it down that far.

So I called the customer, and he said to put that cam back in it.

Long story short, It acts just like the compression release is bad on the cam. But, the cam is fine. I checked the lobes with a set of calipers. And got 1.23 on both (IIRC) Which was the same on the new cam I had.

Battery is week. Charging it now.

Oh, also, I put on a good used starter. (Easier than changing the gears on the old one. That also did not fix the problem.

Have you check the timing..?

EngineMan said:

Have you check the timing..?

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Yes, the spots were lined up before I took the cam out. And after I put it back in. One thing I did happen to notice, when the spots were lines up, the piston wasn't all the way at the top. The timing gear on the crank was still set in place by it's keeper. So I assume that's normal.

Took it out for a test drive, and the PTO didn't come on. So I can only assume it's the battery.

hrdman2luv said:

Took it out for a test drive, and the PTO didn't come on. So I can only assume it's the battery.

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Could be but the alternator should put out enough to support the PTO.

wALT cONNER

hrdman2luv said:

Took it out for a test drive, and the PTO didn't come on. So I can only assume it's the battery.

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Could be but the alternator should put out enough to support the PTO.

Walt Conner

Still gotta jump start it. The meter, on the battery, while running, showed a little over 13volts.

What did the part sitting in the cam lobe look like. I have seen those wear down and not open the valve long enough. weight return spring too weak to return weight to resting area, weight sticking in the out position if overextended slightly. Probably should of put the new cam in when you had it apart. If the valves are adjusted correctly and there isn't any other mechanical issue then most likely you have a compression release issue. But may want to make sure the electric clutch isn't dragging down the engine as well as possibly something on the drive line causing extra load issues for starting.

ILENGINE said:

What did the part sitting in the cam lobe look like. I have seen those wear down and not open the valve long enough. weight return spring too weak to return weight to resting area, weight sticking in the out position if overextended slightly. Probably should of put the new cam in when you had it apart. If the valves are adjusted correctly and there isn't any other mechanical issue then most likely you have a compression release issue. But may want to make sure the electric clutch isn't dragging down the engine as well as possibly something on the drive line causing extra load issues for starting.

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Like this one in this video. https://www.youtube.com/watch?v=tceKAAViC1c . Pay close attention to the compression release weight. That's the part that looked like it had been rubbing on something. But, because there's nothing for it to rub on, I'm almost positive it's just the way it was designed. Just my first time to see one that's not square on the end.

Upon thinking about this. If the spring is weak, it's gonna open at a lower RPM. Possibly even at a speed that the starter creates when it's engaged. I did pull on both the new cam spring and the old one. And didn't feel any difference in the tensions between the two. And they both returned to their start position when I released them. I seriously didn't see any flaws in the old cam.

The tension pulley on the drive belt was good. The bearings in the PTO was good as well. Also didn't see any frayed wires around it, or anywhere else. Battery was about about 60% this morning. After running it last night for about 20 minutes, I'm guessing it should've been at least 90%.

I hope to god it's not anything electrical, except the battery. I don't like electrical. And it doesn't really like me.

The tension belt that also goes around both the left and right transmissions, stays tight. I'm guessing that's normal for this machine. But as tight as it is, you'd think there would be some sort of clutch to release the tension on the belt.