adjusting valves...
alright, my M20 seems to be sounding like a 'diesel' and I was told to adjust the valves. I looked at the valve adjusting DIY and it says that when the valves are fully closed, I should be able to fit a .010 feeler gauge... well whats confusing me is, why would ANYTHING fit there? if the valve is closed, it should be a fully closed seal between the valve and the head?
I guess I need to open it and look at it to get a better idea.
Just wanted to ask this before I tackled this thing... the diesel noise is oh so very annoying. plus I'm sure I could get back a few HP back once they are adjusted.
is .010 right? I saw some people doing .010 intake, .012 exhaust here.
Big, Big Time Poster
Originally Posted by taseal
If you didn't have some type of gap, the valves would always be partially opened. When the valves are off the lobe, there's a gap between the valve and the rocker. I don't know offhand the spec for the m20, but .010 sounds about right.
Sorry, I just read it again, you're not measuring the gap between the valve and the head, you're measuring the gap between the rocker arm and the valve.
I see. rocker arm and valve....
I guess I'll check it out.
m-20 engines are a breeze once you get the feel for the right amount of drag on the feeler guage.start with cylinder #1 and then follow the firing order of 153624 to adjust all cylinders .you are simply rotating the crankshaft clockwise approx 1/3 turn to adjust each cylinder.the specs call for 12 thousandths on intake and exhaust.being out of tolerance either way is not good but loose is better than tight.if you set the valve to tight you can potentially hold the valve open on compression stroke and the burning gases will be forced by the valve and burn the seat and valve to a crisp.you do have a service manual right?. bones
Big, Big Time Poster
the gap is there for heat expansion
As the metal parts in the engine heat up, they tend to expand slightly. If you had absolutely no gap between the end of the valve stem and the tip of the rocker arm, when everything got nice and hot, the valves would be held slightly open. As another has said, the hot gases constantly passing through the slight gap at the exhaust valve seat would eventually do damage to the valve seat. Once that happens, you're essentially screwed until you take it apart and repair the valve seats.
On a related note, if you set the gap a little larger, say by .001-.002, you may have a bit more ticking noise, but you'll also have better idle and low end torque. By setting the gap a little looser, you're closing the exhaust valve slightly sooner and opening the intake slightly later, which smooths out the idle. I have a 535i with the M30 engine and setting my valve lash .001 looser really made a noticeable difference in the idle. It is soooo much smoother now. Something to think about. Also, I don't know about your engine, but increasing the spark plug gap by a few thousands also makes the M30 engine idle smoother as well. Hope this info helps.
Grace and peace,
Robert K
1991 535i
Big, Big Time Poster
When I first got my car running (new engine and everything... engine bay blasted and painted) it wasn't running properly. I tried blowing the gap wide open, but nothing helped. Turned out to be a bad coolant temp switch. Gonna try the wider gap thing again, I'll give it a shot. It's an m30 btw.
Big, Big Time Poster
when u say not running properly... what do u mean? rough idle?
Big, Big Time Poster
I mean it would run as long as you kept your foot in it, but it would die as soon as you got out of it. Ran good at high rpm, decent at mid rpm, anything lower it would want to stall until it heated up, then I could keep it running at around 1k rpm, still died after taking my foot out. New switch solved it. Now it just idles like crap and will stall sometimes at low rpm. Haven't really played with it since. Just driving it and enjoying it.
Major Contributor
Let us know how you get on - those eccentrics are tricky to adjust if you've never done it before. Just take your time and don't set the valves too tight!!
Cheers,
Shaun M
yeah, never adjusted before, but the valvetrain is LOUDDDDDD right now....
I really wish someone who has done them before was aroudn to supervise, so I wouldn't mess anything up. I don't even know where the eccentric is, i'm gonna have to figure it out as I go... the DIY on bmwe34 was not too descriptive.
car right now idles perfect, i have no problems with it idling right now, its just a really really loud valvetrain
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