Rough idle after adjusting valves!

[Bryan in Coral Springs]

I did my valves and installed new spark plugs, cleaned AFM and TB. I adjusted my valve kind of tight at maybe 11 thousandths so give me your take guys! Thanks in advance.

[Bill R.]

Here
(http://www.koalamotorsport.com/tech/misc/valve_adjustment.htm)






QUOTE=Bryan in Coral Springs]I did my valves and installed new spark plugs, cleaned AFM and TB. I adjusted my valve kind of tight at maybe 11 thousandths so give me your take guys! Thanks in advance.[/QUOTE]

[Bryan in Coral Springs]

Thank you so much!

[califblue]

Just adjusted mine at 9 thou...way better performance and gas mileage. :p my .02

[JonE]

Just adjusted mine at 9 thou...way better performance and gas mileage. :p my .02
Isn't that a little tight on a M30? Probably tight for a M20 as well...

[Mr Project]

Adjusted on a stone-cold motor, I've been most happy at .013. I've tried .011 and .012, and .013 gives the best idle and smoothest running of what I've tried thus far. I would think .009 would barely idle.

[Robin-535im]

I've been running .013 for a while, .012 before that, and recently went to .08 intake and .010 exhaust. Engine about 70F.

Idle is surprisingly good... which I think might have to do with my superb adjusting skill :P .

I check mine every 3000 miles or so because I often just need some time alone with my M30, if you know what I mean.

It might end up biting me in the rear being so tight, but I've got a "+1 upgrade" cam (BEE Performance Upgrade engine) so I may be able to go tighter... depending on how they re-grind it.

[Bill R.]

go tighter because its a performance cam.....









I've been running .013 for a while, .012 before that, and recently went to .08 intake and .010 exhaust. Engine about 70F.

Idle is surprisingly good... which I think might have to do with my superb adjusting skill :P .

I check mine every 3000 miles or so because I often just need some time alone with my M30, if you know what I mean.

It might end up biting me in the rear being so tight, but I've got a "+1 upgrade" cam (BEE Performance Upgrade engine) so I may be able to go tighter... depending on how they re-grind it.

[Robin-535im]

go tighter because its a performance cam.....

For a re-grind, they take the old cam and remove metal, right? So you have a different profile, but also less radius along the cam wherever they removed metal.

If you set the clearance at the heel of the cam, as the cam rotates, your valve lift will be less than before because the cam radius at that point is smaller. So a tighter clearance will lift the valve at a height closer to the original, and keep it open a bit longer as well. I'm going for more air at higher speeds, so I want the valve open longer.

Re: burning a valve because it never closes... that's the downside of having it tight. I'm assuming that .008 intake and .010 exhaust will still not burn, i.e., that the hottest condition of the engine still won't eclipse the .008 / .010 I've given it.

So yeah - the "performance" part doesn't mean I can go tighter - risk of burning a valve should be the same for a stock cam. But the regrind part makes me think a smaller clearance will be necessary to recapture the lift / duration and get more air in.

But then, maybe I'm completely off by my understanding of a regrind cam. That's the cool thing about this board... sometimes you learn stuff you didn't know :)

Robin

[Bill R.]

you won't lose any lift on a reground cam. none. When they regrind they remove more off the heel than off the toe so that when you adjust the rocker and take up the slack that you have at the heel then the toe of the cam or total lift is much higher...if you compare a reground to a stock cam you can visually see how they grind the lobes off center on the regrind.
The heel will be much closer to the centerline of the cam.
However the more important issues you should be concerned with is
1. The valve depends on time being closed to allow it to transfer heat from the valve to the head keeping the valve from burning. A performance cam shortens this time on seat and tightening the lash up too much also shortens this time...Any other performance enhancements such as chip or turbo also raise the amount of heat that this valve has to dissipate.
2. The cam lobes to the rockers aren't pressure fed with oil , they depend on the spray bar to drip or spray oil onto the cam lobe. Since the oil isn't pressure fed the only chance it has to lubricate between the rocker and the lobe is when the lash allows clearance and oil can get in there.. If you run the clearance too tight then you'll end up killing the cam lobe from oil starvation , the same as if the banjo bolts had come loose... Thats what Brett Anderson was talking about on his website about hurting the cam.
Its your choice to run them any way you want to but i dont think I would recommend it to others without them being aware of the chances of harm for no or virtually no gain...








For a re-grind, they take the old cam and remove metal, right? So you have a different profile, but also less radius along the cam wherever they removed metal.

If you set the clearance at the heel of the cam, as the cam rotates, your valve lift will be less than before because the cam radius at that point is smaller. So a tighter clearance will lift the valve at a height closer to the original, and keep it open a bit longer as well. I'm going for more air at higher speeds, so I want the valve open longer.

Re: burning a valve because it never closes... that's the downside of having it tight. I'm assuming that .008 intake and .010 exhaust will still not burn, i.e., that the hottest condition of the engine still won't eclipse the .008 / .010 I've given it.

So yeah - the "performance" part doesn't mean I can go tighter - risk of burning a valve should be the same for a stock cam. But the regrind part makes me think a smaller clearance will be necessary to recapture the lift / duration and get more air in.

But then, maybe I'm completely off by my understanding of a regrind cam. That's the cool thing about this board... sometimes you learn stuff you didn't know :)

Robin

[Robin-535im]

I'll definitely factor that in next time I open her up. Good stuff to know.

As for no gain - the engine has more power at the higher RPMs with the tighter clearance, but how much? My butt ain't no dyno, so it's hard to say. Not tons of it, but enough I notice.

It goes back to the age old question of why tweak something that top-notch engineers spend years perfecting... Mostly because we can't leave well enough alone and will spend absurd amounts of time and money to eek a wee bit of performance, and almost always at the expense of one thing or another. If I were approaching this from a purely logical sense, I would buy an ///M and get the power the correct way, instead of trying to mod a M30 past it's limits.

But how much fun is that? :)