B&S wont turn over

[backyard bob]

Working on a poulan pro lawn tractor for a friend. Has a B&S 18 hp els engine. He said it was smoking ,running rough and lacking power Then quit. Taking the head off found the exhaust valve seal wejed under the valve holding it open. Everything looks fine in the cylinder.We installed a head kit from B&S,adj the rockers/valves,turned it over by hand and all seems fine, Hooked up a known good battery and it wont turn over past the compression stroke. Pulled the starter and had it bench tested at a shop,its good. hooked the battery direct to starter bypassing the solenoid and same thing. Gets to compression stroke and stops. I can turn it over by hand with the spark plug in and its a little difficult but not crazy. With the spark plug out the battery turns it over fine of course. Help pls

 

[OzRanga]

Hi there....
Sounds like the valve clearance is too big.
The way to check it is, take the piston 1/4" down past TDC on the power stroke, then check both valves have 0.003" to 0.005" clearance.
If clearance is excessive, then the decompressor on the camshaft will not work correctly causing the issue your having

 

[backyard bob]

:ashamed: I dont get this very well. How do I find the power stroke and 1/4 " past TDC? Thnx

 

[twinfords]

OzRanga is 100 % correct 1/4 past TDC, take plug out turn engine until piston comes up and then turn engine 1/4 turn check clearance.

 

[backyard bob]

Set the piston 1/4 turn past tdc on the compression stroke, both valves closed. I set both valves to .004.
Still seems abnormally high compression, but dont know enough to say its too much. How can I check that compression release? Ive checked and cleaned allo connections. I have hooked up a known good battery direct to starter and still wont spin with plug in. I put a voltmeter on starter and turned switch to start and battery went to zero on voltmeter. So the starter or too much compression. I had the starter bench tested but they couldnt put it under load so unsure. Really appreciate your help on this.

 

[pugaltitude]

The decompressor is easy to check.
Rocker cover off, turn engine watching both valves working.
Now keep looking at intake valve(should be the bottom). Does it move back down and up ever so slightly?
If it does the decomp is working.
if it doesnt either valves still arent right clearance (too much) or engine needs stripped and a new camshaft.
Hope you understand this.

 

[backyard bob]

Thnx for info on decompressor check. I tightened up both rocker adjusters to better see any movement in the pushrods,rockers and valves. turned it over slowly by hand and see no movement for either valve.
I also read you should hear a little click there...nothing. I guess ive gone this far, new head kit and starter check ,I will tear engine down. Anybody know where i can access an enGine breakdown,repair manual.? How much for a new cam and related parts? I assume I have to remove engine from tractor.I really appreciate your help on this> The model # is 31m777-0234-e1 single cylinder. thnx again

 

[pugaltitude]

Thnx for info on decompressor check. I tightened up both rocker adjusters to better see any movement in the pushrods,rockers and valves. turned it over slowly by hand and see no movement for either valve.
I also read you should hear a little click there...nothing. I guess ive gone this far, new head kit and starter check ,I will tear engine down. Anybody know where i can access an enGine breakdown,repair manual.? How much for a new cam and related parts? I assume I have to remove engine from tractor.I really appreciate your help on this> The model # is 31m777-0234-e1 single cylinder. thnx again

Yes you will have to remove the engine.
The decompressor breaking is quite common on that model of engine.
Iv even had a brand new tractor at pdi and the decomp is broken.

 

[OzRanga]

Backyard Bob is right.... Decompressor not working on the cam is very common in a certain year range....
If you remove the engine it is a relatively easy job to change the cam

Replace the cam, refit the engine, set valve clearances with the new cam and all your starting issues will be solved

 

[backyard bob]

Thanks, got the engine out ok but not sure where to go from here. I know I have to remove the pulleys. Got any thoughts on that? And then the sump to get to the Cam? I really appreciate any help on this, Im in uncharted waters. Does the flywheel have to come off?/?