Craftsman poc

DPittman · Apr 9, 2017

I think this is the forum I need to be in. Friend of mine got a 17.5 one cyl Briggs in a craftsman rider that has gas, spark, compression but won't run. When it's cranking, it almost comes to a stop on compression stroke, like it trying to fire before piston comes all the way up. Don't know year or model but I'm thinking, if it's got a good key in the flywheel, which it does, it's gotta be in time, right? Never had one this big opened up before so not sure how camshaft is driven off crankshaft. I wouldn't think it would jump time internally without coming completely apart. Guys wanting a cheap easy fix I'm afraid he ain't gonna get. Any help will be appreciated. Thanks DP

Bob · Apr 9, 2017

Set the valves following the exact procedure in the service manual. (Typically a rather narrow gap set with the piston 1/4" down following TDC.)

To much valve clearance defeats the compression release and it will act as you describe.

Also, check for a bent/damaged pushrod if so equipped).

jeffcat · Apr 10, 2017

You are usually looking for .004 intake and .006 for exhaust. If this doesn't fix it you may have a messed up comression release and that involves taking the bottom of the engine off. Cam gear replacement. Neighbor has done two of them. They run like a top afterwards. That hard start is very common on these engines. Also you need a good battery .

DPittman · Apr 10, 2017

Thanks guys, a guy at church said something about compression release, I didn't know they had one. Thanks again. DP

old · Apr 10, 2017

The over head valve engines have a compression release build into the exhaust valve if I remember right and if the valves are not set just right the starter does not have enough guts t spin it over all the way

da.bees · Apr 10, 2017

Aaaahh but the piston must be on COMPRESSION stroke when exhust valve clearance is set. If gap is set on exhust stroke the release won't work right. There's a couple of ways to see if compression release is the problem before going through a tear down. Check exhust clearance on both compression and exhust strokes. If they are same,the release is worn,broke or missing altogeather. If gap is too wide,fashion a temporary spacer to see if engine starts. Using a full size battery in place of the garden tractor battery will often spin engine fast enough to start.

T.R.K. · Apr 10, 2017

Actually, the valves need to be set on the POWER stroke, after top dead center. The manual gives a certain distance the piston should be down the cylinder on the power stroke. (But who's going to take the head off just to measure it?)

I usually just turn the engine until the magnet on the flywheel is completely past the ignition module. and then adjust the valves with a .003 feeler gauge. When I tighten the setscrew, it usually opens up to .004 or a bit more. . .

If a valve adjustment won't get it to cranking over, you will have to disassemble it and inspect the compression release. I've seen several break off and fall in the oil sump.

DPittman · Apr 10, 2017

I set the valve lash like jeffcat said, engine cold, started right up, run good. Took it out and mowed about 50 feet, it quit running like someone turned the key off. Still had spark, gas and compression, although didn't put gauge on it. Does lash need to be set on warm engine? I'm thinking that release is probably broke. I'll set it like da said, see what happens. Thanks again. DP

Craftsman poc

DPittman

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Bob

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jeffcat

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DPittman

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old

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da.bees

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T.R.K.

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DPittman

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