.014 valve clearance equals smooooth idle

[Robert K]

This is a followup post to one I made a month or so ago after adjusting my valves. When I adjusted the valves, I set the cold clearance to .014 rather than the .013 that I believe was recommended on BMWE34.net. My car had always had a rather lumpy idle and I wanted to see if the looser valve clearance might help. I could tell right after the adjustment that the idle was much smoother. After pulling it in the garage this afternoon I let her idle a bit and was just amazed at how smooth the idle was. It is much different than it has been in past years.

Although the difference of .002 doesn't seem like much, it is helping to decrease the valve overlap (the time the intake and exhaust valves are simultaneously open at the end of the exhaust stroke). It should also help the low end torque, although I'll admit that I've felt no seat-of-pants difference.

I thought I'd post this followup in case others with the M30 engine had a lumpy idle they wanted to try to smooth out a bit. I'm also running my stock Bosche plugs with a larger gap based on a recommendation from bmwe34.net. Rather than the factory gap of .028-.032, I'm running them at .035. This too seems to help the idle.

Grace and peace,

Robert K
1991 535i

[BigKriss]

Is the idle noticably louder at .014. It was on my car. It was too noisy.

Edit: It did idle really well though at that gap. At 0.11 thats it gapped now, the car idles roughly in park, neutral is better though.

[genphreak]

Is the idle noticably louder at .014. It was on my car. It was too noisy.

Edit: It did idle really well though at that gap. At 0.11 thats it gapped now, the car idles roughly in park, neutral is better though.

Hmmm this is always a debate. AFAIK, noisy valves are just the way of the M30- I;'ve always thought that quiet ones are more a 'cause for concern'. I'm not sure how this translates for you guys but I know its easy to mis-judge (unless you do it all the time) as its very much a feel thing.

[Robin-535im]

Hmmm this is always a debate. AFAIK, noisy valves are just the way of the M30- I;'ve always thought that quiet ones are more a 'cause for concern'. I'm not sure how this translates for you guys but I know its easy to mis-judge (unless you do it all the time) as its very much a feel thing.

Another data point...
Just put in the new cam, new rockers arms, new eccentrics, set at a firm 13 / loose 12 with the engine warm (about 25-30 deg C) which is probably a firm 12 at stone cold. "Very" quiet for an M30... still some sewing machine "chush-chush-chush-chush" but no ticking to speak of.

[Ross]

I could never get one to idle smooth without some noise.

[J.DeFeo]

My valves are a bit more quiet gapped at .012" cold, but there is still audible ticking. Every mechanic I've talked to says that noisy valves are happy valves.

[Ross]

I would set the intakes a little tighter and if I was very careful about cam position when gapping an M30 would almost be quiet.
Just be happy we don't have to deal with the shims as on Jags and Ferraris.