Won't Spin Past Compression Stroke

[andy spence]

This is something that happens a lot with these Briggs engines. I have repaired several with a way that a lot of the hard core mechanics will disagree with but add a set screw in the spot where the compression release lever rests until it starts. It is just like the camshafts were back in the day when Briggs advertised their Easy spin starting. It is just a small lump on the intake valve to release the compression when starting. Works the same as the existing lever as the set screw is rounded and only protrudes .013 of an inch so that it does not affect the running of the engine but solves the problem with the starting using a 25 cent screw and a little time since the engine has to be removed anyway. Agree or not, just food for the thought but it works for me with no complications.

 

[LMPPLUS]

Model 33R777
Type 0003 G1
Code 190214ZD
Single cylinder.

Will not spin past compression stroke.
Battery measures 12.8 v. Starter is new (and all this was tried with 2 used starters as well, so 3 different starters).
Battery connections cleaned, starter relay connections cleaned.
Battery voltage measures 12.7 all the way to the starter; battery, starter relay input, starter relay output, starter lug.
Remover spark plug, spins like crazy.
Attached car battery. Will not spin past compression stroke. Remove spark plug. Spins like crazy.
Attach compression gauge, struggles with partial spins, but got 100 psi , so it may register more if the engine could spin enough to give a good test.
So, why, if all parameters measure good, will the starter not get past compression?
Thank you,'
J

Sorry if this has already been said, but you have compression issue trying readjusting the valves if that doesn't work you probably have a bad camshaft that's not working the decompression release. Good luck.

 

[RevB]

Why does a compression release exist? For the weak human pulling the cord. No engine equipped with a starter should ever require a compression release.

And no amount of adjustment of the valves will fix a worn compression release cam lobe. Drain your oil and look for sparklies. May be worse than you think.

 

[farmerdave1954]

Will almost guarantee its yiur compression release spring. Simply cover the intake on the air box assembly with a piece of cardboard and try it. Once it fires up remove the cardboard and it will run fine as the spring only comes into play to start it. Shame it requires a teardown to fix a two dollar part.

It's early, and I'm still having my coffee, so I may just be dense this morning, but this doesn't compute. Can you explain the logic between covering the intake and that action letting the starter spin the engine through the compression cycle? Is the idea that you starve the cylinder of air so there's not as much compression with the cardboard over it?

Here's a video that shows how the compression release works, so you know what you need to look for, how to adjust the valves, and how to tell if it's working or not by simply watching the action of the intake valve:

 

[den052]

I found something on the net about a valve release system built into the cam shaft that relieves a bit of pressure so the starter can spin. The failure led to metal pieces in the sump and the need to replace the cam shaft.
Could this be my issue?
J

Yes that is exactly what's happening. You have to remove the engine and remove the bottom cover and remove the camshaft and replace it with a new one. They are not a lot of money from Amazon. It's hard to explain how it works but they use a centrifugal mechanism to open the intake valve slightly to relieve the compression while cranking. Once the engine fires up the centrifugal weight pops out so it works normally.
I had to do mine, it's a 16 horsepower that was on my zero turn. It did the same exact same thing. Also the valve lash adjustment has to be right on spot. You could actually check the valve lash first before you disassemble the engine and remove it. That might be all you need to do maybe would be reset the valve lash. It has a bearing on the compression

I'm a retired MASTER light and heavy truck mechanic for over 40 years. Certified front bumper to back bumper.

 

[bentrim]

The 28, 31 and 33 seris use a compression release to help the small starter spin the engine. If you did not have a release you would need a starter the size of the one on a car, truck, or tractor.
The compression release opens the intake valves on these engines just a few thousansth of an inch so when the valve lash increases too much the is no release. Readjusting the valve will put the relief back to working -- IF the mechanism is not broken on the cam, which is a common occurance on these engines.
To check if the cam is good -- adjust the valves to specs. Now turn engine over with the starter or by hand and observe the rocker arms, the intake will make a small movement as the engine come up on compression. No movement or as one tech called it a double tap Bad cam. It is not a full opening of the valve just a small movement.
Because of the compression release Breaks & Scrapem does not publish specs, they say that they are not accurate with the release, But by spinning the engine backwards if it "bounces" of compression it is good to go.

 

[Doofy]

My 19.5 hp Briggs in my '98 Craftsman rider would not crank either. My problem turned out to be an over filled crankcase from my last oil change. Drained out a pint and back to normal starting. Decided to purchase oil in quarts now instead of 5 quart containers.