Heymow - Lawnmower Racing Forum
Engine Help => Briggs OHV & Vanguard => Topic started by: eddiehenjr on January 08, 2007, 09:15:50 am
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Can anyone give me some advice on how to adjust valve lash on my 17.5 horse OHV? Mr Herrin advised me to get a service manual, but I can't find one. George said I could reduce the valve lash from stock .006" to .003" using a stock cam to give a little better performance and RPM. I've adjusted valve lash on a V8 and with those you gotta run em and warm em up cause the valves expand as they get hot so I need to know if it's the same procedure with a Briggs. And do I have to have the piston at TDC when I adjust the valves? Any information or links are much appreciated :D Thanks
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I said you could adjust down to .003 but I also said you probably would never feel the difference that .003 would give you. But to do so yes warm the motor up. Once adjusted and run a time or two readjust. But as I stated I doubt you will ever feel the .003 differance.
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oh and valve adjustments are nade with piston 1/4 past top dead center.
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Thanks! Thats enough to get me started right there. But uh, how do you find a quarter past TDC with the piston?
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You don't actually take off the head and measure it do you?
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no you can use a plastic straw stuck thru the plug hole to feel the piston.
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How do you know how far to push the piston down? With the piston at 1/4 turn down, does that close the gap between the valve stem and the rocker arm or leave it as wide open as possible?
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On the Hondas that we were running if you set the lash at .003 cold and then measured it when the engine was hot it was .005 because the block expands.One guy that races karts here says that he sets them at .000 cold and says it is noticable on his dyno,but the kart engines are really restricted so every little bit helps them.
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Well I don't wanna try gettin brave with .000 yet untill I know how the motor reacts when it heats up. I might set it at .000 and the valves won't seat right, then I got real problems like burnt valves and low compression.
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Yeah you have to find out for yourself the briggs engine may react different.
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I never thought about the block expanding like that... since it's OHV maybe just the head would expand.
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they are different than car engines so I try to just try things and see what happens,and check things for myself.Like those clearances set, them,run the engine untill the engine warms up and check them again.If you are worried try setting them at .001 so that you know the valves are closing and run the engine,then check them again when the engine is hot.Let us know what happens when you find out,so we can all learn.
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I'll do that. But I need to know how you adjust valve lash on my particular engine. I know on a V8 you just turn the pedistal bolt holding the rocker arm on untill you get the measurement you want. I have no clue how to do it on my OHV.
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im in the same boat, i guess well have to buy a shop manuel onthe engine.
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I wonder if there's a downloadable shop manual on the internet here... I'll have to try finding one.
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let me know if you have any luck, ive found some on briggs website you can order. i think ill go that route
later and goodluck