High compression -won't crank

[BLES]

Briggs 20hp single Intek #331777-0956-B1

Won't crank over once it comes on compression stroke. Battery is fully charged. Spins fine with plug removed.

Set valves to .004" intake .006 exhaust. Clearances were previously excessive.

Still won't crank over with plug in. What else will cause this?

BLES

[puttinalong]

Pushrods...are they straight and in their proper spots? Thinking that maybe they are either bent or since it was excessively out of spec before they could lost their seating???

[StarTech]

Check for the decompression lift. There was one report here of the ACR coming apart on this particular cam.

[bgsengine]

dont forget to check for bad ground (voltage drop)

[BLES]

Check for the decompression lift. There was one report here of the ACR coming apart on this particular cam.

Can you elaborate on how to do this? It is definitely a compression issue. You can feel it by manually turning the flywheel. A lot more resistance than normal.

Thanks.
BLES

[StarTech]

Can you elaborate on how to do this? It is definitely a compression issue. You can feel it by manually turning the flywheel. A lot more resistance than normal.

Thanks.
BLES

It is the slight openning of either the intake or exhaust valve depending of the setup at the end of the compression stroke near TDC just before the piston starts its power stroke. This is reason why your are to adjust valves with the piston 1/4" pass this point so the ACR doesn't interfere with the adjustment. If you adjust at TDC then your setting will be off as the rocker arm will partial operated causing you to adjust the valve clearance wider than the specs; effectively disabling the decompression system. If after you adjust valves this way and you don't the little lift (or bump as some call it) as you cycle the engine through the compression and power stroke then the ACR isn't working and the cam will need replacing.

Once the engine starts this ACR retracts and the valves operate normally.

[Mek-a-nik]

Check for the decompression lift. There was one report here of the ACR coming apart on this particular cam.

I just ran into one last week. Two years old, no MCR movement.

[bgsengine]

Dont forget also they are known for cam lobes wearing "round" - I have yet to see it myself, but It is not all that uncommon, I suppose it may have some relationship to maintenance..

As mentioned, double check that you are setting clearance properly and then observe rockers (usually have to go by feel, it can be hard to see happen) while cranking engine over by hand, plug out, make sure after the intake valve closes, and before TDC of compression that one of the valves (usually intake) opens just slightly - if the cam is worn though you may just feel a slight "bump" but not enough to get any valve action which may be indicative of a failing ACR .. but from what I have ever seen, usually just 2 things cause a hard crank - High compression (Why not just grab a compression gauge and see what it is actually making in way of compression?) or a bad ground or weak battery. - There's also possibility of it being a bad starter, but I've yet to find one.

[Luffydog]

I had one the same way. Turned out to be a bad starter.

[bobodu]

Gotta set the valves 1/4" past TDC....