Valve Adjustment Question
- Thread starter l008com
- Start date
Craftsman Garage
Well-Known Member
I always adjust Phillips when the one valve is fully open end of the other is closed and loose. Adjust the loose one, then turn over and adjust the others. When you're all done, crank the engine a few times, and check the gap again, this "breaks in the gap". Adjust again if needed. Pro tip: I gap my valves a little bit tighter for power gains 
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StarTech
Lawn Royalty
The way I found to adjust clearance itself on OHV engines is take the gauge that minimum spec adjust it just slips pas and the next size gauge wont pass. This be condensate for each of each having a different what a good thru is. Most valve clearance are usually across a couple thousandths. So say you are doing a valve that specd at .003-.005 you be very close .003 but not under.
I do this because OHV tends to open the gap as the engine wears and would a longer ime between needed valve clearance adjustments.
I do this because OHV tends to open the gap as the engine wears and would a longer ime between needed valve clearance adjustments.
l008com
Well-Known Member
I don't understand this. Aren't both valves fully closed for the entire compression stroke and then the entire power stroke? Or at least almost all of both of those strokes?
ILENGINE
Lawn Royalty
Correct, but you have to be careful because the ACR at cranking speeds bumps the intake on most engines sligntly BTDC compression stroke. So the piston to be in some position that avoids the ACR action when setting the valves.
StarTech
Lawn Royalty
Depends if the engine is starting or running. The problem is because they use a weaker starter than one that can over the full compression. This is why you can't depend on the compression numbers while cranking as they will be nearly half of the actually engine compression. The leak down test is better at determining cylinder condition.
TDC compression is at the very end of compression stroke just as it enters the power stroke. What Briggs and others are doing is slightly opening either the intake or exhaust valve (depending on design) to lower cranking pressure slightly before TDC compression stroke. Once the engine starts the ACR swings out and the engine goes to full compression. Some older engines actually a camshaft grind that did this via a bump or ramp on one the camshaft lobes but that always had some compression bleeding off.
When the mechanical compression release is used you must be off it in order to adjust the valves; hence, the 1/4" down pass TDC compression method but many of us find it just easier to do it the old way instead finding a measuring stick every time we need to adjust the valves.
ACR = Automatic Compression Release
TDC = Top Dead Center
Hammermechanicman
Lawn Addict
LOLPro tip: I gap my valves a little bit tighter for power gains
How many more hp do you get?
I used to build 5hp B&S engines for WKA stock, stock appearing and outlaw classes. I have degreed and plotted many stock and aftermarket cams and put engines on a dyno. If you can tell a power differece of a couple thousands lash on a fairly low compression 3600 RPM governed engine I'd like to see that on a dyno. The old flat head briggs with the "easy spin" bump on the cam it did make a difference. Opening up the lash to defeat the compression release bump would give more low end torque and minimum lash gave more lift and duration and higher hp. All this at the 4000 to 6500 RPM powerband measured on a dyno and the difference is still small.
StarTech
Lawn Royalty
I only know one case here where I slip the camshaft a tooth on an old 12.5 l-head where there a considerable notice performance that only shifted the power band of the engine to more torque at the working speed. I don't even remember if it was advanced or delayed by one tooth but I do remember doing it but heck that was 40 yrs ago,