17.5HP Briggs and Stratton Valve adjustment, what are symptoms of over tightening

I am learning how to adjust the valve space on a briggs and stratton 31C707 type 3346 G6 code 110510ZD

I saw two ways to prep the engine.
ONe was TDC and a 1/4" turn and then set the valves.
The second was to just compress one valve at a time set and then compress the other set and check.

If I do it the second way,but then double check using the first method, the gap is too tight by a shim thickness.
This would then seem to be too tight. Example. If I compress one valve at a time and work on the loose one, intake at .003", And then check it using the TDC 1/4" method, It is very hard to get the .003 feeler between the rocker and the valve when at that position.

Now if I set the clearance using first way but after setting check by taking off the pressure on just one of the valves. I have a feeler thickness difference looser. Example. I might set intake at .003" using the first method of TDC+ 1/4" and then check by rotating around to the exhaust is compressed, the feeler between the valve is .004"

I was just curious how I would know if I was too tight? What are the symptoms?

Also, for that engine, which is the best why to set it since they are not producing the same outcome by one feeler thickness. Is it better to have it a little looser than a little tighter?

Thanks

Take a look at this. It describes the "Exhaust opening; intake closing" method. That's all you have to remember: EOIC.

Keep in mind that automotive cams don't have a compression release, but it guarantees that you will be setting valve lash at a point on the cam lobe that is on the base circle of the cam, directly opposite the highest point of the cam lobe.

http://www.cpgnation.com/forum/threads/how-to-set-valve-lash.4837/

First thing to remember is it is a governed, low reving mower engine, not a Nascar top fueler.

Next thing to remember is if you got 20 mechanics to set a .010" gap you would have 21 different settings.

Now all cams are not created equal and a lot of cams have a slow lift and a slow close.
On a cam these are called quietening ramps because that is exactly what they do they drastically reduce the valve clatter.
On cams with pronounced ramps, you set one valve clearence with the other fully compressed to ensure you are on the base circle and not on one of the lift or lower ramps.

On the Briggs engines, the ramps are quite small and tighter EPA emission regulations cause them to be smaller.
That is why Briggs recommend 1/4" to 1/2" past TDC to set the valve clearences.

On a mower engine too much clearence defeats the decompression so the starter will get to TDC on compression & not be able to get past it.
Too little clearence and the valves will not close when the engine is hot which causes loss of compression and burned exhaust valves

Basically anywhere between these limits is quite fine.

FWIW I set both at .004" because that makes things easy and I buy 0.004" feelers loose so I am not perpetually faffing around looking for the 0.004 in a pack of 35 feelers that I never use.

bertsmobile1 said:

On cams with pronounced ramps, you set one valve clearence with the other fully compressed to ensure you are on the base circle and not on one of the lift or lower ramps.

Click to expand...

I'm struggling with this.

With the exhaust valve at peak lift (fully compressed), the intake lifter is positioned on the side of the intake lobe. That is definitely not the base circle. With the intake valve at peak lift, the same situation as above exists with the exhaust valve. The sides of the lobes are where the acceleration ramps (quieting ramps, down under) are. This method practically guarantees you would be setting the clearance on a ramp, not the base circle.

That doesn't strike me as even a good place to set valve clearance, let alone an ideal one.

Firstly the OP wanted to know why there were different methods of setting the valves, which I tried to explain in a simple way.
Secondly you might want to get the dial indicators & timing wheels out and clock a Briggs OHV engine.
It is not a big block Chevy with a mile of valve overlap.
Briggs engines do not have catalytic converters in the exhaust so have ZERO valve overlap as the EPA mandates NO UNBURNED FUEL is allowed to exit the exhaust.
I think Kohler do have some with after burners but Briggs do not thus the exhaust valve is well & truely closed before the inlet starts to open and by full lift which you will find is about 1/3 stroke the exhaust is on base circle.

If you want to proffer a better easier to understand reply t the OP's question by all means go ahead and do so.

Thanks for the advice

I used the TDC +1/4 turn method and did not encounter any issues. I did not run it for more than 15 minutes but it seems fine.

It did not fix a surging while cold start up issue but I did not really expect it to. It was just in another thread I started someone said valves can be an issue and I was too fixated on the carb being the issue.
When I saw how easy it is to check and set, I figured why not. I bought the machine used and don't think the valves were serviced . It is a late 2011 engine and the RTV gasket seemed to clean to be done by a fix it shop. (I removed the sealant and went to the paper gasket. So far no leaks)

bert--

Well, you didn't explain how that "peak lift" method works.

A camshaft doesn't know (or care) what kind of engine it's in. Cam lobes are cam lobes and there is one, and only one, correct place for the lifter to be when the clearance is set and that is when the lifter is on the BASE CIRCLE of the cam. That is roughly the bottom 180 degrees of a cam lobe and the closer you can get to the middle of that arc, the better off you'll be.

Overlap has little to no effect on choosing the correct place for the crankshaft to be when the valves are set. There isn't that much difference in overlap anyway, from the wildest high-rpm cam to the cam in a 1600 rpm Cat diesel.

cpurvis said:

bert--

Well, you didn't explain how that "peak lift" method works.

A camshaft doesn't know (or care) what kind of engine it's in. Cam lobes are cam lobes and there is one, and only one, correct place for the lifter to be when the clearance is set and that is when the lifter is on the BASE CIRCLE of the cam. That is roughly the bottom 180 degrees of a cam lobe and the closer you can get to the middle of that arc, the better off you'll be.

Overlap has little to no effect on choosing the correct place for the crankshaft to be when the valves are set. There isn't that much difference in overlap anyway, from the wildest high-rpm cam to the cam in a 1600 rpm Cat diesel.

Click to expand...

There is one correct way to set the valves of a B&S engine and that is the way the people who designed and built the engine specify. It never ceases to amaze me the people who think they are wiser. Sure, you may get by using some other method as B&S engines are very forgiving, B&S sets out the correct way. I am fortunate enough to be able to afford two separate leaf type feeler Gage strips. (Last part just a good matured jab Bert)

Walt Conner

Whatever.

Set your valves any way you please, I do not care.

I only posted that link so that someone who *might* want to learn how to find the base circle on *ANY* engine, be it tinker-toy Briggs and Stratton or 14 liter Caterpillar diesel.

It's not me you're arguing with, it's Comp Cams, who I would wager has forgotten more about cams than B&S ever knew.

I have no argument with anyone. I doubt if that outfit you mention has any idea about the positioning of B&S engine piston/cam to obtain proper clearance. B&S based their clearance on the point 1/4"down past TDC.

Walt Conner