Hey Guys
I picked up a Troy Built Lawn Tractor with a B&S 18.5 HP engine.
Model Type Code
31P777 293-E1 04 702ZA
The mower has not been taken care of very well. The guy I got it from stated that he had gotten the mower back from the repair shop at the beginning of spring and they had replaced the Solenoid and put a new battery in the tractor. He told me that he started the mower up the other day and it "almost immediately" ran out of gas. He stated that he filled it up with gas and then tried to turn the key and the tractor would not do anything. In his disgust, he sold me the mower. Im thinking that some type of failure happened and the mower "just happened" to be low on fuel.
I got the mower home and checked the battery with my multi meter, It read 12.63 volts. I turned the key and I could hear the solenoid on the float bowl click, but the Ignition solenoid wont click. I then jumped the solenoid and the starter engaged but would not turn the engine over. So I think "starter, Valves to tight, Engine Hydro Locked etc. So I went to take the spark plug out of the mower and the dang plug was barely in the spark plug hole about 8 turns in. Took the plug out, jumped the solenoid and the engine turns over fine. Take my finger and place it in the spark plug hole to get a "red neck" compression reading and the engine stops turning and the starter starts whining when I put my finger over the hole and let it build compression. Just me covering the spark plug hole with my finger and spinning it over is enough to stall it out.
I decided to check the valve adjustment and with all B&S OHV they were a little out of adjustment so I adjusted the valves to INTAKE .007 and EXHAUST .005. Tried spinning it again and no change. Oh, by the way, the engine was not hydro locked either. So I changed the starter. No Better.
Im at a loss guys!! Has anyone ran into something like this before? I don't know where to go from here.
Thanks in advance
Sounds like the decompressor on the end of the camshaft is broken which is not allowing the engine to turn past the compression stroke.
To check remove rocker cover.
The inlet valve (bottom) valve should open and shut as normal and then bump down.
If no bump then decomp is broken which means camshaft replacement.
I can send you Detailed Adjustment Instructions which include a test for the operation of the Compression Release. IF you want it, address below, put in proper format and remind me engine model number and what you want.
"Take my finger and place it in the spark plug hole to get a "red neck" compression reading and the engine stops turning "
I had one the other day about that bad. Owner had made a habit of holding the ignition key in "Start" position trying to make the engine turn over which over heated the starter winding causing it to lose its' magnetic value. I replaced it with a good used starter.
Gentlemen, thank you for your information on this subject. Over the weekend I search quite a few threads getting lots of good information. I too am having the similar symptons on my Craftsman 21HP Briggs (331877 2371 G5) 540cc single cyllinder. With the plug out the engine turns over fine with plenty of spark but with compression the engine just stops dead. I tried jumping the battery with the same result. I verified the valve gaps were OK. The info I found for my engine was intake (.003"-.005" and exhaust .005"-.007") I set them to .004" and .006" with the piston 1/4" below TDC. I wasn't sure though if it is the intake or exhaust valve which is used for compression release, I assumed it was the exhaust. At any rate, the mower was working normally the night before and the next day it wouldn't start. What is there that would break inside the engine? Should I suspect the starter or solenoid before I break down the engine to inspect/repair? Is there a way to see if the decompression is working or not by looking at the valve movement?
On a side note, I had a 1976 Yamaha XT500 dirt bike with compression release and if you didn't follow the procedure to start that beast, your knee would be slammed into the handle bars from the back pressure...OUCH!
You can watch the valve as you turn the flywheel. It should bump one of the valves off its seat shortly before TDC compression. What you are showing with it working one time and not the next usually can be a sign of a sticky compression release. I have found if you are going to go through the trouble of pulling the engine, and inspecting the camshaft, just replace it while you are in there, then there is not question.
