adjusting valves

[bmwstudent]

i was busting nando's chops for saying that "the lash gets bigger when the engine warms up." I don't think he meant what he wrote, but you never know. He hasn't responded.

[nando]

Some VAFM equipped fuel systems (Toyota for one) run the fuel pump when the AFM flap moves due to engine vacuum. It wouldn't work with the ignition off though so maybe that isnt what he was getting at. I think Motronic runs the fuel pump when it sees a crank position sensor, signal could be wrong though.

E30s (except the 318is) only run the fuel pump when the ECU gets an RPM signal.

[Beach Bum]

Why would you unplug the AFM? That won't prevent the car from starting, idling, or running @ WOT...

I think some of these mooks are talking about adjusting the valves with the car running, but I have no clue how you'd go about adjusting an eccentric-style system while the car is on.

[Sagaris]

Some VAFM equipped fuel systems (Toyota for one) run the fuel pump when the AFM flap moves due to engine vacuum. It wouldn't work with the ignition off though so maybe that isnt what he was getting at. I think Motronic runs the fuel pump when it sees a crank position sensor signal, I could be wrong though.

[u3b3rg33k]

so to adjust valves HOT just take off VC, unplug AFM, use a 10mm and small allen wrench right?

...Sounds like the tried and true method of valve adjusting

What's the best way to adjust valves while COLD (75' F)

Why would you unplug the AFM? That won't prevent the car from starting, idling, or running @ WOT...

[cabriodster87]

Well, I have known this for years, but it was late last night and was confused because i didn't comprehend the meaning of your statement above. when i read:
"the valve lash actually gets bigger as the engine warms up" and "The lash SETTING is larger when hot." simple mistake on my part, then after i posted and read it again i caught the meaning. My bad, didn't mean to step on your toes.

[bmwstudent]

that is correct lash decreases as engine temps rise due to EXPANSION of the parts i.e. the valve actually gets longer and the rocker does too

[cabriodster87]

Doesn't heat expand valve train components? Therefore lash decreases as engine temp rises. I found this write up, also read the first and second sentence in the last paragraph. I hope this will help everyone.....

What Is "Valve Lash"?
Valve lash is the mechanical clearance between the cam lobe and valve stem or transfer rocker when the valve is fully closed. It's usually checked with a feeler gauge and is some non-zero value on with "mechanical" non-self adjusting valve lifter mechanisms.

Differential expansion characteristics cause the cold clearance to be different than the running clearance and margin is built in to make sure their is always some clearance, especially on exhaust valves. An exhaust valve that doesn't close completely doesn't transfer enough heat back to the head and can "burn".

Cam lobes have entry and exit profiles (called ramps) which are designed to limit the opening and closing acceleration of the valve to limit mechanical stress and also noise. Still, the tighter you set the valve lash (less clearance) the more open valve duration you get which tends to boost top end performance slightly. The looser you set the valve lash the more bottom end is boosted and the more valve train noise you get.

If you have all the valves adjusted too tight idle quality and low end performance may suffer slightly with an attendant small gain in top end horsepower. Looser valve lash does the opposite and results in a noisier valve train.

If you have some tight and some loose that might also effect smoothness since different cyclinders will have different power contributions at different RPMs. Some of the above is a little simplified but you get the drift.
Why Does Valve Lash Need Adjusting?

Too much lash can accelerate wear on the rocker arms, cam followers, cam lobes, valve stem tips and valve seats. How much it does depends on the engine and how far out of spec the lash is. Too much lash also tends to make more noise so you're more likely to know it needs adjusting.

Too little lash is more dangerous both because it leads to more serious problems and because it doesn't make any noise. Luckily the NSX valves do not tend to get tighter so unless they are adjusted incorrectly it should not be a problem.

But just for your info, too tight a lash may allow the lash to close up as heat builds up in the engine - especially if the engine begins to run hotter than normal because it's being worked hard. This gets worse as the engine gets hot because valve clearances tend to close up as the parts heat. That's why the NSX shop manual specifies that you should do the gap adjustment when the engine is cold. Some other engine service manuals will specify seperate hot and cold adjustments. The loss of lash can prevent the valves from fully seating which results in loss of compression and valve overheating. Exhaust valves rely on cooling through the valve seats much more than intake valves, so loss of lash in the valvetrain often results in a burned exhaust valve.

[bmwstudent]

"the valve lash actually gets bigger as the engine warms up" NO IT DOES NOT! The valve lash spec is .012" hot .010" cold. The lash SETTING is larger when hot. Metal expands when it gets hot Nando. The reason you have that lash or space between the rocker and valve tip is to allow for expansion when hot. Did you really mean that or was that a mistake?

[Disco Benny]

I got the feeler gauge, nice. Thanks!

[Beach Bum]

so to adjust valves HOT just take off VC, unplug AFM, use a 10mm and small allen wrench right?

...Sounds like the tried and true method of valve adjusting

What's the best way to adjust valves while COLD (75' F)

Same procedure with less hot oil on your hands and you only have to remove the valve cover. It's also nice to have a piece of wire coathanger or an allen wrench to rotate the valve eccentrics.

[Disco Benny]

so to adjust valves HOT just take off VC, unplug AFM, use a 10mm and small allen wrench right?

...Sounds like the tried and true method of valve adjusting

What's the best way to adjust valves while COLD (75' F)

[u3b3rg33k]

Why do people push the car or spin the wheels instead of turning the engine by hand?

Turning it via the wheels requires no tools.

[LagunengrunE36]

Why do people push the car or spin the wheels instead of turning the engine by hand?

[r3d e30]

Values for adjusting valves cold is .010 and warm is .012. BMW recomends setting them cold. In my expierence with setting valves on a m20 the actual setting that worked best for me was .011.