m20 Valve Adjustment

[PG325]

Can I just ask. When checking the valve clearance, should the lobe be pointing down to the floor or 180 degrees away from the face of the rocker (approx 5 o'clock if looking from the front of the engine)?

[tha881]

I dont think it makes much difference as the valve will be in the same position. There is no difference in the profile of the lobe at both those positions.

[jimf]

180 degres from rocker face.

There is a guide with a diagram in the wiki pages

[Supafly]

When adjusted check by hand moving up and down to see if there is any excessive movement.

I adjusted mine and still couldn't get it to sound right, it turns out that the eccentric lobe had pitted which meant when I used a feeler gauge it was spot on but where it made contact there was a bigger gap. Some new eccentrics and proper adjustment made a huge difference.

[PG325]

I've read a few reports of people adjusting the valves using the cam lobe and rocker face, this is because the eccentric can sometime wear.

Unfortunately I can't get a exact feeler gauge size when doing this as there are comments about it not being a 1:1 ratio.

Has anyone adjusted the valves this way and if so what size when cold are you setting them at?

[clipper]

I've read a few reports of people adjusting the valves using the cam lobe and rocker face, this is because the eccentric can sometime wear.

Unfortunately I can't get a exact feeler gauge size when doing this as there are comments about it not being a 1:1 ratio.

Has anyone adjusted the valves this way and if so what size when cold are you setting them at?

Yes, but it doesn't get around wear to the eccentric adjusters.

The eccentrics usually wear if the same section of the circle has ben operating the valve for excessively long periods of time, creating a flat. Given that the correct ajustment involves rotating the eccentric very slightly, the "flat" worn area will just cause the adjuster to rotate back to its previous position.

The theory with setting the adjustment between the cam lobe and the follower is that any concaved wear on the top of the valve stem would be compensated.

So, in other words, if you replace all the eccentric adjusters, but not the valves, it could be worth doing.

Here is a sketch I did to inlude in a technical write up I posted in another forum on the same subject (it is greatly exagerated for effect, but it shows how measuring at the valve stem / eccentric interface "can" give a false result:

[clipper]

As you correctly say, the gap at the other end of the rocker needs to be factored by the rocker ratio.

By reading as many sources as I could find on internet, it seems that the M20 rocker ratio is either 1:1.56 or 1:1.5.

Either way, the 0.06 difference shouldn't make too much difference if you set them "mid-spec".

I set mine at 0.17mm given that the spec for the gap at the eccentric is 0.25mm

0.25/1.5 = 0.1666 (if you take the other value of 1.56 then the calculation would be 0.25/1.56 = 0.160)

This gave me a gap at the stem / eccentric of around 0.19mm which means that the wear on the valve stem (shown as "X" in the sketch) equates to around 0.04mm which seems reasonably correct.

I did this about 6 years ago and the noise at tickover was noticeably better and the car has been fine ever since.

[Brdjo]

Nice explanation clipper.. Always wondering how much gap can be in worn valve, excenter, cam, atc.. My b20 on 0,25mm is making sewing noise kind a normal after 400 000km xD... in coupe ocasion i was going to set it to 0.23mm just was not sure is that going to make some trouble to engine...

Like some one said if you can hear valve train noise on m20 you have a problem xD

[Brianmoooore]

To go back to the OP's question: You shouldn't be looking at the lobe of the cam you're adjusting at all. You should be looking at the valve which adds up to 9 with the one you're adjusting, and positioning the cam for max. lift on that valve.
For instance, if you are setting clearance on valve 2, then adjust it when 7 is fully open; if setting 6, then 3 should be fully open, and so on.

[Brdjo]

To go back to the OP's question: You shouldn't be looking at the lobe of the cam you're adjusting at all. You should be looking at the valve which adds up to 9 with the one you're adjusting, and positioning the cam for max. lift on that valve.
For instance, if you are setting clearance on valve 2, then adjust it when 7 is fully open; if setting 6, then 3 should be fully open, and so on.

I do not fully understood this, in what order you count valves? valve 7 is?

[BenHar]

1 to 12 counting from the front of the engine.

Ben

[clipper]

1 to 12 counting from the front of the engine.

Ben

1 being the inlet, 2 being the exhaust I presume?

[paultv]

So if your setting valve 12 gap - (cylinder 6 exhaust valve ) how does one calculate using the "adds up to nine" method? or is this system only good for the inlets or do you count the exhaust set as 1 to 6 as well....

I must be a bit dense, I'm not sure I follow Brian's method.




Paul

[pianist]

I have always been adjusting my valves with the cam lobe pointing away 180 degree from the valve I'm working on, and always using feeler between cam and rocker due to it being either the only flat surface or valve stems being a PITA to get to. Never had an issue

[reggid]

the rocker and cam are rounded not flat, regardless you just need to adjust the feeler gauge size to account for rocker ratio but it works fine and is pretty easy. which ever way works for people personally wont matter.

[paultv]

In 1987 I bought a 525i E34 from Cooper Bishops Gate in London, it was 5 months old, had covered 650 miles only, metallic Dove grey, all black leather, sports auto box, Pioneer stereo, heated everything.

At the time this "new shape" BMW looked amazing, at least having seen one on display in Heathrow's arrivals hall, I thought it did.

One thing I distinctly remember - is was absolutely silent at tick-over, no valve train noise at all, and it drove like a rocket - at least in '87 it was probably pretty quick for a saloon car.

I ran it for three years until it got nicked at - you guessed it, Heathrow Terminal 1 business car park - nothing left but a pile of glass - then found totally stripped, dumped in someone's driveway 3 weeks later.

That's why I love my crumbly Cabby I guess!


Paul

[Brdjo]

since I have 24000 km from last valve adjustment, I adjusted my valves now to 0.23mm cold.. and the results are fantastic, rocker noise is almost gone, injectors are louder now

out of curiosity is there a torque spec for excenter holder bolt?

[reggid]

there is 10Nm iirc but i dont have a torque wrench that would fit haha. nip it up but not so much it strips.

[Brdjo]

First 200 km done with new valve setup, I have a feeling that car on lower rpm is lose some of torque.. It's not like a big difference, but definitely on lower rpm it's pulls a bit slower.. and idle is a slightly shaky, like it's revving on idle 50-60 rpm lower than before.. I guess that's the price for silent valve train

Also did notice that time to reach operating temperature is now longer then before.. I have no idea how is that possible, but it;s just like that..

[M3Pete]

Sound like you've gone too tight and your valves are not sealing anymore. I'd sort this straight away as it will burn a valve seat.

[Brdjo]

I was gone through some valve opening diagrams and come to conclusion that 0,23mm clearance can not damage valves whatsoever with stock camshaft.. u have some other experinace? maybe i was missing something? bare in mind that my engine is long from any stock dimension, 400k kilometers on it..

[Brdjo]

Can anyone confirm my conclusion or I make somewhere mistake? Stay on 0,23 or go back to taping 0,25?

[drakesmith]

My mate aways does them to 0.30mm. He used to work at bmw back innthe day and to spec made them not run good.0.30mm was the sweet spot.

[minesapint]

The book says 0.25mm cold (0.30mm hot) There's no more to say as far as I'm concerned.

[drakesmith]

Are we talking m20b25 (only) my mate swears to do it hot only and at 0.35mm.

[minesapint]

I am!

[drakesmith]

He swears by doing them at 0.35mm hot. His done a hell of alot of them.

[Brdjo]

wow 0.35 hot, I just don't wanna do that.. That will put more stress on rockers.. and speed up the wear, just do not make any sense...

[reggid]

yeah dont set them to 0.35mm it is totally wrong the clearance ramp is not long enough to do this on the m20b25 cam, some of he earlier cams it might be ok e.g. b23 had really long ramps

[Brdjo]

Of Course I won't, I will set them back from 0.23mm to 0.25mm just because it is safe bet.. but I am pretty sure that 0.02mm is make same noticeable change in engine work, especially lower rpm power..

[reggid]

you can tell a slight difference in idle and low it drives when you get to 0.20 its a bit more noticeable as well and then at 0.15mm it becomes crap when you are driving around normally because the valves open earlier and close a bit later so the cam acts about 10* larger and you get reversion which is worse at idle and low rpm and low throttle. but you dont gain enough lobe lift area to make it worth while except maybe on a race car might gain peak power but its hard to test such small changes on chassis dyno unless you are setting them on a hot engine.

if you buy an aftermarket cam with 10* more duration you get more lobe area to so the chance for performance gain at topend is much better than trying to cheat and run tighter clearances

[drakesmith]

yeah dont set them to 0.35mm it is totally wrong the clearance ramp is not long enough to do this on the m20b25 cam, some of he earlier cams it might be ok e.g. b23 had really long ramps

0.35mm set it to that on the rockers 325 only

[Brdjo]

you can tell a slight difference in idle and low it drives when you get to 0.20 its a bit more noticeable as well and then at 0.15mm it becomes crap when you are driving around normally because the valves open earlier and close a bit later so the cam acts about 10* larger and you get reversion which is worse at idle and low rpm and low throttle. but you dont gain enough lobe lift area to make it worth while except maybe on a race car might gain peak power but its hard to test such small changes on chassis dyno unless you are setting them on a hot engine.

if you buy an aftermarket cam with 10* more duration you get more lobe area to so the chance for performance gain at topend is much better than trying to cheat and run tighter clearances

So 0.23mm do not have risk burning the valves at all..? with stock cam.. maybe my idle was strange because i did not reset the ecu after adjustment..

[reggid]

its odd that people think you will burn valves. in reality even at 0.15mm the valve will be on the seat long enough to dissipate heat, still much longer infact than some of the cams at the bottom of the catcams catalogue who coincidentally recommend 0.15mm on some of those due to the short clearance ramp they grind onto it....Basically as long as the valve is not adjusted incorrectly such that it does not / can not actually close properly (it must be able to close when both cold and hot as clearancesdo change with temperature a bit) you will be totally fine.

[Brdjo]

thanks for clearing things up, so hot/cold clarens is different in 0.05mm...
when i was gaping valve back from 0.23mm to 0.25mmi found that on 4 valves i could put a 0.25 feeler gauge.. so something went loose or bad gaping at first place...