.014 valve adjustment equals M30 smoother idle...

[Robert K]

I just got done adjusting the valves on my 1991 535i. The spec for adjusting the valves cold is .012 in the Bentley. I'd read elsewhere that opening up the gap a bit would smooth the idle, which makes sense since it decreases the valve overlap between the intake and exhaust valves. While I was at it, I regapped the plugs a bit wider to .035 per www.bmwe34.net, which stated that this would also have the effect of smoothing out the idle a bit. After doing these two things, I can say that my M30 does certainly idle much smoother than before. Of course I also had the battery disconnected for a couple of hours while doing this and some other work, so it may have also "unlearned" the ECM, which seems to make the cars run a bit better while the system relearns the engine. Anyway, when all is said and done, the engine seems to idle much smoother and doesn't shake the car at idle near as much as it used to. Just thought I'd share the results of my experiment with all the other 535i owners on the board.

Grace and peace,

Robert K
1991 535i

[Qube]

Thanks for your input

[Hector]

with the engine cold worked great for me. For the first time the engine idles as smooth as silk. The difference is huge. I turned the engine 2 revs 3 times to re-adjust valves between each set of turns which might be an overkill for some but for me it gave that extra reassurance that the gap is adjusted correctly.

[BigKriss]

After I put th eclyinder head back on the car idles like crap now, really rough. The shop that prepared the head adjusted the valves, but I may have to look into it again. I cannot see any vacum leaks anywhere.

[Martin in Bellevue]

Kris, you need to adjust the valves after running in the head re-install. The clearances change when the head is torqued down.

[Hector]

the valves with the engine cold as ice. I used to do it with the engine at temperature and was never happy with the valve chatter. Martin has an excellent point. I did this very same thing after I had burned-in the head re-installation, and after bolts were retorqued. I think I also did another readjustment at the first oil change after head reinstallation.

[BigKriss]

Thanks Martin and Hector. I didn't know that I had to adjust the valves again. I will do both at .014 cold. I had a snap-on modius scanner on the car and everything looked okay with no vacum leaks that I could notice.

[BigKriss]

I adjusted them to 0.014" tonight. The car idled extremely well, but they engine seemed too noisy. It seemed very noisy and when driving the car it's very noisy also. I did the adjustment with the engine dead cold. I checked them twice. I probably adjusted them a bit more than 0.014". Will this cause and engine damage or increased wear?

[632 Regal]

a minimal amount but YES

Will this cause and engine damage or increased wear?

[BFEINZIMER]

im bumping kriss's last question