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Generators & Motors General Discussion Antique Generators, Light Plants and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Motors General Discussion

OHV engines - adjusting valves


Its Valve Adjusting Time for me. My Generac 7000EXL has about 50 hours on its clock and my John...

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Old 05-08-2013, 04:45 PM
alfieepstein alfieepstein is offline
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Default OHV engines - adjusting valves

Its Valve Adjusting Time for me. My Generac 7000EXL has about 50 hours on its clock and my John Deere garden tractor has 200. So it dawned on me that I haven't done this in a long time. The last time I can remember was on my 1972 VW camper before I ditched it (literally - black ice is so unforgiving). I still have the custom bent 13mm flare nut wrench I would use while lying under the VW getting a stiff neck. I've read the Generac and JD instructions; loosen this, turn that until you get some specified gap, and so on. But, what about technique. Someone inexperienced can go very wrong or very crazy trying to get it right.

The things I have learned -
1 - Double check the specs. Is the specified clearance in inch or metric dimensions. Using inch feeler gauges when the numbers are in millimetres can make the engine sound like castanets.
2 - Don't completely loosen the jam nuts, do it just enough so that you can turn the adjuster with a bit of effort. This keeps it all taut so the clearance doesn't change when you tighten thing up again.
3 - I use a go-no go method. If I want a .004 gap, I'll take a .003 and a .005 feeler gauge out as well. When I think I've got my .004 I'll try the .005 feeler. If it goes in, the gap is too big. If the .003 drags in the gap, the adjustment is too tight.
4- Have new gaskets available. If you're lucky the old ones are still good, but if not, you will have a mess to clean up if you try to reuse a mangled one and it leaks.

I hope somebody finds this useful and perhaps others can add their experiences here as well.

A flare nut wrench, by the way is used on tubing fittings. Mine has a hex end with a gap so that it can slip around the tubing to tighten the fitting. They also come as 12 point but a hex is a lot better for avoiding rounding jam nuts which is easy with an open-end wrench or a crowsfoot.
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Old 05-08-2013, 05:38 PM
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John Newman, Jr. John Newman, Jr. is offline
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Default Re: OHV engines - adjusting valves

One thing I would add is to beware of compression release mechanisms that can hold a valve open slightly. Be sure you are not on such a device when setting valve clearance.
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Old 05-08-2013, 08:18 PM
alfieepstein alfieepstein is offline
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Default Re: OHV engines - adjusting valves

Good point John. I always go a little past Top Dead Center even if the engine's instructions say TDC, to be sure. Without taking things apart to see the flywheel marks, guessing the engine's TDC from the piston travel has a wide spread. Making certain that the piston is starting the down stroke ensures greater precision. Briggs & Stratton says to go past TDC until the piston drops by ¼". Generac only states to adjust at TDC. Yet, both use the exhaust valve for compression release. Some engines use the intake valve but I'm unfamiliar with those and I don't know how that would affect the AT TDC or AFTER TDC scenario.
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