Won't turn over?

[dart451]

Working on a Craftsman 917.276750, Briggs 31P777-0602E2-050921ZE that has a starting issue. I have also tried a jumper and my automotive jump starter...it will not turn all the way over...it goes to turn over and just won't even spin a full revolution. So, I seem to remember some of these motors have compression releases and if the intake valve isn't adjusted properly, it defeats the compression release function. Does this sound like a logical assumption?

[RoyM]

If the valve clearances are correct you likely have a failed ACR which is quite common on this series. With the spark plug out and valve cover removed rotate the flywheel by hand and watch the exhaust valve, it should bump momentarily. If not you are looking at replacing the camshaft with the new improved version.

[Skywatcher]

Hi Dart

Yes, this is the most common cause of engine not cranking, although I have read fairly often as of recent on this forum that the automatic compression release (ACR) mechanisms on the camshaft of these engine is actually failing as in breaking off the shaft. However, I'd be inclined to start with the simplest things first. Does the engine spin over with the sparkplug removed? If no, then you have other problems. If yes, then precede to the next step.

Park the tractor with the front end slightly higher than the rear end to reduce oil spillage. Remove the hood, sparkplug and rocker cover. Rotate the engine by hand in the normal direction and watch the valves. The exhaust valve will open and close, just as the exhaust valve is closing, the intake valve will start to open. The piston is now near enough to TDC exhaust stroke. Use a paint pen to make a small mark on the rotating screen and a matching mark on the engine cowl. Now rotate the engine one full revolution until the marks line up again and turn the engine to move the mark on the screen about 1" further.

Now check both valves. If memory serves me correctly .004" to .006" is the specification range for these engines (correction required if necessary, thx) Now rotate the engine through 2 full rotations and watch the valve action. The exhaust valve should open and close with the intake valve opening just as the exhaust valve is closing (remember, this is how you found TDC). As you continue to turn the engine, the intake valve will close, now you're at the bottom of the intake stroke. As you turn the engine through the next half turn, one of the valves should open very slightly to dump some compression for easy starting. If the valve does this, put the tractor back together and you should be done. If the valve does not open very slightly part way up the compression stroke, you may have a failed ACR. Please let us know what you find and we'll go from there. All the best,

Sky

PS. Looks like Roy posted as I was typing, pretty much saying the same idea. Have a great weekend both.

[KE4AVB]

If the valve clearances are correct you likely have a failed ACR which is quite common on this series. With the spark plug out and valve cover removed rotate the flywheel by hand and watch the exhaust valve, it should bump momentarily. If not you are looking at replacing the camshaft with the new improved version.

This is a cross flow therefore it is the intake valve that the ACR bumps instead of the exhaust valve.

[dart451]

Thanks guys! I did take out the plug today and the engine turns over fine so, tomorrow or the next day I'll take the valve cover off and check the valve clearance. I seem to remember have one awhile back that the valves were loose and setting them fixed the problem...

[Skywatcher]

Hi Again Dart

Just remembered another thing to check on these engines. The rocker studs have a habit of occasionally coming coming loose, so a 10 mm crowfoot wrench on a ¼ drive extension is a very handy tool for checking these for tightness. All the best,

Sky

[dart451]

Update: I checked the valve clearance and both valves were about .015 clearance. So, I set them according to the manual and now the engine turns over just fine. Thanks everyone for your help!