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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 28890
Experience:  Service manager and technician for all brands of engines with 40 + years of experience.
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Ok, here we go again. I replaced the counter balances (front

Resolved Question:

Ok, here we go again. I replaced the counter balances (front and rear) and now it won't start. Piston fires once and dies with a definite thud. I opened the crankcase again this morning and rechecked the timing gear alignment, watched the valves open/close as I turned the crankshaft. Everything looks good. It fires once and no more. With pull start the compression stroke can be very hard after several pulls. Checked compression, it's around 50. Carb bowl is filling with gas, float is not stuck. Choke works ok. Please help, very tired of working and paying for parts and not having this mower work.
Submitted: 1 year ago.
Category: Small Engine
Expert:  Curtis B. replied 1 year ago.

You are sure the timing is correct and the balance shaft is in time? Engine turns free and nothing touching in the crankcase? If all ok, have you checked the timing key between the flywheel and the crankshaft.

Customer: replied 1 year ago.
good.
Customer: replied 1 year ago.
Rechecked again, timing key is in place. What next?
Customer: replied 1 year ago.
What next?
Expert:  Curtis B. replied 1 year ago.

Compression is on the low side, did you check the valve lash on the engine when you had the head off?

Customer: replied 1 year ago.
No, please explain more detail.
Customer: replied 1 year ago.
Do you mean clearance? It was running fine before, never touched the valves.
Expert:  Curtis B. replied 1 year ago.

Yes, clearance is lash. Valves may not be seating. Easy enough to check, by removing the vent cover.

Customer: replied 1 year ago.
My torque chart from BS states flywheel nut should be torqued to 85 ft lbs but I don't have a nut, I have a starter clutch or clutch starter instead. How do you torque it?
Expert:  Curtis B. replied 1 year ago.

There is an adapter for the starter pawl, but usually hammer and punch is used to tighten the nut.

Customer: replied 1 year ago.
snugged the starter pawl with a hammer and wood block. I removed the vent cover this morning to watch the springs and valves. The clearance (gap) is checked between the intake/exhaust valves and their associated tappet valves (lifters)? If there is no gap, the valves would not seat properly? Where are they adjusted?
Expert:  Curtis B. replied 1 year ago.

clearance is checked between the valve stem end, ad the tappet, with the valves fully closed. Adjustment is done by removing the valve and grinding of the end of the stem in very small amounts. .006 is perfect. But as long as you have something close, it will work. But zero will not work, or if there is a large gap, the valves is likely not seating in the block.

Customer: replied 1 year ago.
There's a small gap, definitely not large (need to convert sae to mm) so the valves are seating. Chart states .005–.007 for intake and .009–.011 for exhaust. Vent (breather) cover gasket tore and I don't have a new one, is that ok?
Expert:  Curtis B. replied 1 year ago.

Will leak oil, but it won't keep engine from running.

Customer: replied 1 year ago.
Ok, valve clearance is good. Retorqued the connector rod after noting on chart that small bolt is torqued first, can't image that would cause a problem if I torqued in wrong order but at this point I will do anything to get this mower running. What next?
Expert:  Curtis B. replied 1 year ago.

Timing has to be correct, crankshaft and camshaft marks. and the flywheel key; Then it has to have spark , compression , and fuel and air to run. Do you have spark? Will it run for a few seconds, if you put a teaspoon of fuel direct into the cylinder?

Customer: replied 1 year ago.
timing marks are good, fly wheel key in place. I never found anything I did wrong or omitted. Crankcase back together, will remount to mower and re-attempt to start.
Expert:  Curtis B. replied 1 year ago.

OK>

Customer: replied 1 year ago.
Will not start. How do you squirt gas directly into cylinder? Brake cleaner work?
Expert:  Curtis B. replied 1 year ago.

I remove the spark plug and put it direct into the spark plug hole, re-install the spark plug and try it.

Customer: replied 1 year ago.
Got a surrenge from the kitchen and injected gas directly into cylinder, nothing. To test for spark I will remove plug still attached to cord and turn the engine over and look for spark at spark plug gap?
Customer: replied 1 year ago.
It's got spark, checking the gap now but suspect it's ok.
Customer: replied 1 year ago.
Gap is good, looking for electrical skematic now. Cylinder not firing at all.
Expert:  Curtis B. replied 1 year ago.

Spark ok, no run at all. And you say compression was 60 psi? valves ok, was flywheel tight before the first attempt? If not the flywheel key can be sheared.

Customer: replied 1 year ago.
I didn't look too close and without my glasses, my son was holding it and he said around 50, it could have been near 60 and come back down? Yes, flywheel is tight. This Snapper rider has 3 interlocks, brake, seat and gear shifter. On the magneto shorting block there are 3 wires, one goes to the magneto, I'm guessing the other two are interlock grounds.
Expert:  Curtis B. replied 1 year ago.

If you have spark, it is not a safety switch problem.

Customer: replied 1 year ago.
Ok, then what is left, carb? Why wouldn't it fire when I squirted gas directly into cylinder?
Expert:  Curtis B. replied 1 year ago.

Low compression or the timing is off.

Customer: replied 1 year ago.
Ok, will try again tomorrow.
Expert:  Curtis B. replied 1 year ago.

Good night!

Customer: replied 1 year ago.
Fresh gas this morning, getting it to fire occasionally. Tried removing the air cleaner and choking the carb with my two fingers and placing other hand over exhaust. Seems to be back-firing through the card with a little exhaust. Which sounds like timing but I swear the timing marks on the crank and cam shaft are aligned. I put the timing key in the flywheel after it fell out and rechecked it yesterday and it is still installed and doesn't appear to be damaged to the point where it would not be aligned, besides I never hit a stump with the blade. Battery charging and will try again. I put the throttle on full choke while starting and them move back to idle after a few tries in case it is flooded.
Expert:  Curtis B. replied 1 year ago.

!! Timing key for flywheel has to be perfect. Not any damage!

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Customer: replied 1 year ago.
On first appearance it looked fine, but I removed the flywheel cover anyway, and it still looked fine, but then I realized that the slot on the crank was not aligned with the key, the key is sheared off in half. So, going to the store to get a new one. Be back soon!!!
Customer: replied 1 year ago.
Finally, got it started, runs great, however I have other issues with the rider I need to work on. It doesn't like going up hill, drive disk may need to be replaced. Gas was leaking from the air cleaner when mower was on an incline. May need new fuel lines and lube rear end, all wheel bearings should be lubed. Other than that I think it will be ok. Thanks for all your help and the next time I'm in the UK, I'll buy you a beer or more. I'm retired US Navy and we flew our P-3s out of Keflavik into an RAF base outside of Cambridge once, another trip, well I'll have to check the map. Stopped in London for two days on the way back from Karachi in 2006. Cheers!