valves

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  #1  
Old 07-12-03, 10:14 PM
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valves

i have a 3.5 hp briggs that quits running after about 10 mis. if i put a cold plug in it it will run for about 30 seconds before it loses rpms and stalls. i put 2 good coils and 2 good carbs on it with same result. i took out the exhaust valve. the stem had a lot of carbon on it which may explain why the clearances varied on it. i cleaned it, ground it, and set the clearnce to .010. problem is i cant get the clip back on. what kind of valve spring compressor so i need. i have seen a lot of variations and i need a tool to fit. also i am new to valve repair. am i on the right track?
 
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  #2  
Old 07-13-03, 12:03 AM
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Hello l.mitchell!

Briggs has a special valve spring compressor, made to use in briggs engines. They work well, but a pair of flat head screwdrivers will work too. (insert the valve with the spring and clip already in the valve chamber, and pry the spring and clip back and on). You might be on the right track, but it also sounds like you might have a partially sheared flywheel key.
 
  #3  
Old 07-13-03, 07:30 AM
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Hello l.mitchell. Welcome to our Do-It-Yourself Web Site and our Small Engine forum.

Another possibility is vapor lock caused by a clogged vent hole in the fuel tanks cap. Remove the fuel tanks cap and run the engine.

If the engine continues to run well for a reasonable time span, the vent hole in the fuel cap is restricted and or plugged. Clear it or replace the cap.

Another method would be to remove the fuel hose at the carb and allow fuel to flow freely for a minute with the fuel cap on the tank. Flow should flow freely for at least one minute.

If fuel does not, slows down in the flow rate or stops, remove the cap and continue the test. doing so will determine if the cap is the cause of the problem.

Based on the problem description it apears to be but may not be a fuel related problem. Fuel not getting into the carb or flowing to the carb from the fuel tank.

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  #4  
Old 07-13-03, 11:12 PM
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thank you cheese for your quick response. i put the valve spring back in and mowed the front yard for about 30 mins. when i got to the high grass in the back it would die under load but restart. iwould have to wait for compression and rpms to pick up though. the flywheel key is ok but there was a little play in camshaft as tappet woud not moveimmediately as crank turned. i did not service intake valve as it looked ok. do you think it may need looked at also? the exhaust valve i tested seat by squirting wd 40 into exhaust port. there was a little leakage but not like it was before i cleaned it and ground it. is the loss of compression due to the intake valve(i did not test it or repair it just checked clearancealthough it looked high when i had it at tdc) or the exhaust valve or both? at least it runs now but i would like to improve the compression. any suggestions?
 
  #5  
Old 07-13-03, 11:17 PM
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Was the clearance on the intake valve within specs? Sounds like it could be too tight.
 
  #6  
Old 07-14-03, 09:52 PM
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cheese: i pulled the intake valve today. i lapped and ground both valves. clearances are .005 intake and .0105-.011 exhaust by feeler gauge. when i went to put intake back in ced valve spring was flimsy. so i pulled an intake valve spring from a 3hp briggs that ate flywheel keys when you pulled starter cord. ifound this intake spring to be stronger and measure 1and 3/16in. the other [spring weak one] measured 1and 2/16in. so i put the longer, stronger spring in. the metal head gasket was leaky so ibought some copper gasket sealer from the guy at napa who said that is what to do. i have valves in but am awaiting your opinion before i reassemble it again. the valve heads on the other engine are the full 1/64 but the valves that i have been grinding appear to be just over1/32. would it be a good idea to interchange these? the ones i been working on appear to be seating. what would cause the other engine to be hard to pull with plug in {easy w/o plug} and eat flywheel keys? it did not not have a head gasket. wiil the copper stuff seal the headgasket? which would be the better engine to repair the 3.5 hp with low compression or the 3hp with too much compression? thanks...
 
  #7  
Old 07-15-03, 11:58 PM
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Sounds like both need head gaskets. I would replace the head gasket instead of using the spray copper. The gaskets are cheap, and you may find that the leaky gasket is the entire cause of your problem. The other engine that is kicking back, are you trying to run it without a head gasket? If so, that is why. Another reason could be that the blade is loose or not installed.
 
  #8  
Old 07-18-03, 08:45 PM
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you were right once again cheese. thanks for giving me the incentive to persevere. the 3hp engine had a head gasket but it was cracked a little. the valve clearances were non existent . i lapped the valves ground the intake stem to a close.005 and the exhaust to a tight .010. i bought a new headgasket. you were right it was cheap. i carefully tightened the head bolts in correct sequence guessing the right torque. it started on the third pull. i let it run for 10 mins. no leaks. it then started on the first pull. i took it town and mowed 2 yards with thick wet grass running about 3 tanks of gas out. it starts first pull every time. i dont have enough parts for 3.5 horse right now. it needs a coil but i know now that the leaking headgasket was the problem. thanks again for helping me with my first valve repair!!!
 
  #9  
Old 07-19-03, 12:38 AM
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Great!!! Chalk another one up for the doityourselfer!

Glad we could help, and come back anytime!
 
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