M30 Valve Lash

[JMI]

Does valve lash increase or decrease under normal running conditions between valve adjustments?

TIA

[Jeff N.]

Increases.

[Mr Project]

You know, it doesn't make any sense to me, but a couple of times when I went to do the valve adjustments, I had to increase the gap to get it back up to spec. The clearances got tighter. Not all of them, but most did, and it was 2 out of 3 times.

I'm not sure if it was just an anomaly, or if that is common.

[Ausmpower]

Maybe your engine was at a different temp the last time the lash was adjusted?

I've never seen the clearance reduce between adjustments on any of the M30's I've done (about 2 dozen).

[Mr Project]

Every time I did an adjustment it was dead cold, overnight. Ambient temperature was probably different, though, there are no 2 days the same around here.

[gale]

I have adjusted the valves maybe a dozen times since I've owed mine, and the changes are not always consistant. Lately, only about 50% of them need adjusting & the rest are so close I don't bother them. Of the ones that do need adjusting, about 1/2 are too tight & the others are too loose -- usually only off .001-.002" from where I set them the time before.

There are numerous scenarios at play:

- cam lobe wear -- will make them looser
- rocker arm wear -- will make them looser
- rocker arm shaft wear -- will make them looser
- eccentric wear -- will make them looser
- valve stem wear -- will make them looser

- valve seat wear -- will make them tighter
- valve face wear -- will make them tighter

Temperature:
- warmer will make them looser -- aluminum head will expand more than the steel valve train components, but aluminum rockers will also grow, so who knows?

Other:
- loose eccentric -- who knows?
- worn valve guide -- ???
- human element in not being able to set all of them exact.

The actual variance will be caused by all of the above, with some causal factors participating more than others. As long as there aren't any gaps that are way off, I don't think it's cause for concern. I just reset them & drive it 'til they're due for adjustment again.

[Bill R.]

there is no set pattern, on older cars that don't have stellite seats then they definitely get tighter allways. bmw's seem to go 50/50 as Don noticed.
Honda's are one of the few that i see that remain virtually unchanged for a very long time.

I have adjusted the valves maybe a dozen times since I've owed mine, and the changes are not always consistant. Lately, only about 50% of them need adjusting & the rest are so close I don't bother them. Of the ones that do need adjusting, about 1/2 are too tight & the others are too loose -- usually only off .001-.002" from where I set them the time before.

There are numerous scenarios at play:

- cam lobe wear -- will make them looser
- rocker arm wear -- will make them looser
- rocker arm shaft wear -- will make them looser
- eccentric wear -- will make them looser
- valve stem wear -- will make them looser

- valve seat wear -- will make them tighter
- valve face wear -- will make them tighter

Temperature:
- warmer will make them looser -- aluminum head will expand more than the steel valve train components, but aluminum rockers will also grow, so who knows?

Other:
- loose eccentric -- who knows?
- worn valve guide -- ???
- human element in not being able to set all of them exact.

The actual variance will be caused by all of the above, with some causal factors participating more than others. As long as there aren't any gaps that are way off, I don't think it's cause for concern. I just reset them & drive it 'til they're due for adjustment again.