Let me say up front, I am an amateur. I like to rebuild small engines strictly as a hobby and I am still learning.
I got my hands on an old Merry Tiller with a 3.5 hp Briggs model 92502. I can't give you anything on the engine code, serial number or date stamp beyond that because someone at sometime removed a portion of the housing just after the model number. It has a pusla jet carb with the front pull out manual slide choke and the small pickup bowl in the tank so it has the two down tubes. I took the carb off and did a complete breakdown and made sure ALL of the ports were clear. I've redone a number of Briggs carbs so I know where all the small holes and ports are, even the two small holes under the needle valve seat. I'm confident I cleared all of the ports. I put in a new diaphragm and replaced all the gaskets. I mounted it back to the tank securely. I connected all the linkages. I set the needle valve at a turn and a half back from closed.
I had replaced the exhaust pipe. I thoroughly cleaned the tank inside and out. I removed the flywheel and removed all the rust from the flywheel and the magneto. I cleaned the contacts on the magneto. I removed the cylinder head. There was a lot of carbon that I cleaned off the valves and cylinder head. I cleaned the valves with a wire brush and some very fine sandpaper. The valves appeared to be in very good condition so I did not lap them. Both valves seemed to close well, the exhaust valve closed tight and I could not move it with my fingers when it was closed. I noticed that although the intake valve appeared to close well and tight, I could turn it with my thumb in the closed position. The cylinder head was in excellent condition once cleaned and the cylinder walls were perfect, no scratches or scoring. I opted not to remove the crankcase cover. I flushed the crankcase and added fresh oil. I replaced the head gasket and closed it up. I replaced the spark plug and checked it for spark before I put it in and it was sparking well when I turn the engine over. So I buttoned everything up and tried to crank it but it's not turning over. I took the carb off and did a second cleaning and inspection but same problem. I tried a little starter fluid in through the carb but nothing. I tried a little gas directly into the spark plug opening but nothing. It has very good compression. When I took the plug out it was not overwhelmed with fuel odor so it does not seem to be flooded and I even considered whether it was getting fuel but since it wouldn't turn over with gas directly into the chamber I thought that probably wasn't the problem.
The only thing that stick out to me is the intake valve needs to be lapped but I didn't think this would completely prevent the engine from turning over. What am I missing? Suggestions, thoughts and ideas would be greatly appreciated!
I can attach pics if need be but I didn't know what would be helpful at this point.
The fact that you can put your thumb on the intake valve and turn it when it is supposed to be in the fully closed position says it is not fully closing, and is also leaking. Compression may not be as good as you think. Just had the same thing on an 8 HP the other day. Compression when cranked over felt good, but in fact I only had 10 psi.
Agreed, and I plan on lapping the valves but would that cause a complete turnover failure or do I have another problem I need to be looking at as well?
Alright, some of you are probably laughing at my lack of knowledge. I've been doing some reading (Dangerous, I know). If the valve is not seating or is loose I guess I should first check the proper clearance and make adjustments if necessary. Again though, I don't know if this would cause a complete non start but it is still something I must address. If the loose valve has insufficient or no clearance, is the only remedy to grind down the end of the valve stem to provide clearance? I may be putting the cart before the horse, perhaps I should check first and see if that's the problem. Lapping or reseating the valve will not do anything to tighten or cause it to close securely, correct?
Also, I have questions about the model number. This is a horizontal shaft engine. Would the "5" in 92502 not indicate a vertical shaft engine? If so it's possible that the cover has been replaced, this is an old flathead engine but the cover appeared stock. I've never seen the model or engine code anywhere else on a Briggs engine, it's not stamped somewhere else that I have overlooked is it?
I'm guessing by the lack of responses (Illinois aside) that you all knew I would eventually figure it out. I check the intake gap, Zero. The gap should be .004 to .006. I pulled the valve, cleaned it up and grinded the stem, a little too much of course. When I reinstalled it and checked it the gap was .009, oh well, it will have to do. It's nice and tight now. I put it all back together and it fired right up, runs strong. A little smoke, I don't know if I put in a little too much oil or if it has something to do with the gap. Thanks anyway slackers!
The valve issue is common on the old briggs flat head engines. And it was not uncommon for people to swap engine blower housing between engines, when starter ropes, or springs broke. Can be a major pain when trying to find parts sometimes, ie, receive wrong carb kit because of incorrect model or type number.
the floating valve issue as you have found can cause big start/run issues.
