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Garden Tractors Discussion Forum

Valve Adjustment On A 18.5 Briggs

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Author  [Modern View]

03-11-2017 15:31:41

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I know that when the valves are set too loose on the motors ( 18.5 Briggs OHV single cylinder ,verticle shaft ) that it makes it hard for the starter to turn over kinda like the battery is weak . I know all the other things that can cause this problem to like bad battery , bad connections , bad cam , et. , but what if the valves are too tight ? Can it still act this way ? I normally set the valves on .oo4 thousandths and that didn't fix it . I then set them on .003 thousandths and still same problem . I changed the starter and tried two different starters , same problem . I didn't reset the valves back up to .004 thousandths , left them on .003 thousandths when I did this . Neither starter changed anything , same problem . I know battery is good as it is about a year old and is 400 CCA and started my 20 hp dual cylinder OHV vertice shaft Kohler motor . What are the symptoms / problems of valves being too tight in these motors ? How can you definitely tell if the cam is bad ? It's looking like it, but I don't want to tear into motor unless I have too ! Thanks for any and all help !


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Mule Meat

03-11-2017 19:51:52

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 Re: Valve Adjustment On A 18.5 Briggs in reply to whizkidkyus, 03-11-2017 15:31:41  
310000 series engines = .003 Intake .005 Exhaust

All others = .004 Intake .006 Exhaust

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03-11-2017 19:06:41

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 Re: Valve Adjustment On A 18.5 Briggs in reply to whizkidkyus, 03-11-2017 15:31:41  
I'm new to this forum so bear with me. If I do something wrong let me know.I have played with some of these ,and in my experience have found the compression release on the cam is bad when this happens.If I can help on the adjustment feel free to e mail me. wdcuda

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Steve A W

03-11-2017 18:17:41

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 Re: Valve Adjustment On A 18.5 Briggs in reply to whizkidkyus, 03-11-2017 15:31:41  
There's a lot of video's on youtube.
Remember, their not all experts.
You can usually tell who knows what they are doing,
And those that got a video camera for Christmas.

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03-11-2017 17:07:55

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 Re: Valve Adjustment On A 18.5 Briggs in reply to whizkidkyus, 03-11-2017 15:31:41  
By the way it is a 2008 model engine and no oil filter or pump on it !


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03-11-2017 16:49:22

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 Re: Valve Adjustment On A 18.5 Briggs in reply to whizkidkyus, 03-11-2017 15:31:41  
I don't think valves set too tight will cause it to stall on compression. Usually a too tight valve will cause the engine to die when its hot because then its open all the time.

You are adjusting the valves with the piston part way down the cylinder after TDC aren't you? That way you can be sure you aren't adjusting the valves with the tappets on the compression release tab and are definately on the base circle of the cam.

Do you know any history on the engine? I recall one several years ago that would run about a month and then get that 'when cranking it stalls on compression' problem. The third time it was in the shop I realized that: 1: I hadn't screwed up setting the valves. and 2: It had never had an oil change and running it that way they had worn through the hard surfacing on the cam. At that point, the customer was fed up and decided to replace the mower.

There was another that we took apart just to inspect the camshaft and the mechanical compression release was laying in the oil pan. The customer decided to junk that one too. I later put a used camshaft in it and my manager gave it to one of his sons.

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