Valve clearance - Snowblower Forum : Snow Blower Forums
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post #1 of 11 Old 12-30-2019, 11:38 AM Thread Starter
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Valve clearance

Why have guys here in the forums sometimes suggested checking for valve clearances to others trying to get a snowblower running? I understand how cam lobe wear along with valve stem wear might cause inadequate valve opening but certainly not an closing problem. Gees, why this suggestion/recommendation to anybody trying to get a small engine running?

I have used many types of small engine powered machinery ............snow blowers, generators, pumps and so forth for years. Never ever had I knowingly had a valve problem. OK, I have had a few burned valves in cars but not many.
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post #2 of 11 Old 12-30-2019, 12:05 PM
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Originally Posted by foggysail View Post
Why have guys here in the forums sometimes suggested checking for valve clearances to others trying to get a snowblower running?
I think the "checking the valves" suggestions have mostly been a last-ditch effort where compression issues have been detected or all other likely causes have been eliminated. I too have very rarely had to deal with OPE valve issues, but I do have a Generac generator that had an intake valve keeper break in half, followed by the valve stem itself breaking. This was likely caused by a low oil situation when the genset was loaned out, but I'll never know for sure.

Last edited by tabora; 12-30-2019 at 12:08 PM.
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post #3 of 11 Old 12-30-2019, 12:20 PM
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Originally Posted by foggysail View Post
might cause inadequate valve opening but certainly not an closing problem.

It is quite common for flat head valves (usually exhaust) to loose all clearance and remain open a few thousandths causing a no or hard to start condition from weak compression. The valve seat gets heated and pounded into the block (head), the valve stem expands from the heat and the valve will not seat and seal.

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Last edited by Grunt; 12-31-2019 at 10:17 AM. Reason: block head
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post #4 of 11 Old 12-30-2019, 12:20 PM
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If the seats wear, then yes, you *CAN* get a case of incomplete closure - fairly common on L heads, and a common reason for pops/backfire through the muffler.
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post #5 of 11 Old 12-30-2019, 12:30 PM
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yup when your muffler starts glowing red on a flat head you usually have an exhaust valve clearance issue. the ohv engines will sometimes not run right if valves are not adjusted right or within spec. had a lawn mower that ran poorly this summer and cleaning carb did nothing. adjusted valve clearance a tiny bit to get it within spec and ran like brand new again.

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post #6 of 11 Old 12-30-2019, 01:50 PM Thread Starter
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THANKS GUYS!!!!

Nice to participate in a forum where so many knowledgeable people contribute/share their valuable experience!!!
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post #7 of 11 Old 12-30-2019, 03:46 PM
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valve face and seat wear with time. when so the gap closes making motor run run among other issues. generac there i have had to replace heads as the pressed in to the casting seat became loose moving up and down banging in the head, only way it was known was that the gap would close up in a very short time and the stem be way higher than the other
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post #8 of 11 Old 12-30-2019, 03:53 PM
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Quote:
Originally Posted by tabora View Post
I think the "checking the valves" suggestions have mostly been a last-ditch effort where compression issues have been detected or all other likely causes have been eliminated. I too have very rarely had to deal with OPE valve issues, but I do have a Generac generator that had an intake valve keeper break in half, followed by the valve stem itself breaking. This was likely caused by a low oil situation when the genset was loaned out, but I'll never know for sure.
here is from a generac forum as to what has been found many times my own unit included

Last edited by 87powershiftx2; 01-04-2020 at 09:36 AM.
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post #9 of 11 Old 12-30-2019, 11:29 PM
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[QUOTE=crazzywolfie;1705583] ....the ohv engines will sometimes not run right if valves are not adjusted right or within spec.... QUOTE]


Common problem on OHV lawn tractor engines is a situation where the valve lash is so excessive the engine can't roll over because the compression release won't actuate.I can't count how many people I know that have bought new electric starters and batteries thinking that was the problem.
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post #10 of 11 Old 12-31-2019, 05:24 AM
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how true mike c

i can't count how many times a machine came in with the owner saying it won't turn over,i have a new battery and starter . adjust the valves and send them home.
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