How to long tighten the pitbike headset

335i conversion - diary 05/28/01

Adjust valve clearance:

The engine should have cooled down sufficiently, preferably leave it standing for a whole night. First of all, the air filter box and the air flow meter must be removed from the 735i. Then loosen the 9 fastening nuts and remove the valve cover.

Bring any cylinder to the cam overlap:

With a size 34 socket on the crankshaft flywheel or by shifting the car (with 4th gear engaged) you can persuade the camshaft to rotate slowly. You should watch the rocker arms of each cylinder and pay attention to the cylinder whose cams are just about to overlap. The cams are then fairly symmetrical upwards, a few millimeters are not important. By moving the car further or turning the crankshaft, each cylinder can be brought to overlap.

Small math problem:

With a simple calculation we can now determine which cylinder can be adjusted. That is not the one that overlaps, but the one that results from the following simple calculation:

(7) minus (overlapping cylinder) = (adjustable cylinder)

So if the first cylinder is just overlapping, then you can adjust the sixth cylinder.

Use feeler gauge:

A sensor blank is now inserted between the eccentric on the rocker arm and the tip of the valve stem, thereby checking the distance. In the first photo I enlarged the area of ​​the valve clearance.

Valve clearance

Use of the feeler blank

The real skill lies in developing a feeling for the resistance that the emptiness creates when pulling through. If it is difficult to insert and pull through, then the play is significantly smaller than the value printed on it. The following method offers some certainty as to whether the distance is correct:

Default value for the M30 0.30 mm Valve clearance

  • insert a sensor blank with 0.30 mm
  • Loosen the eccentric retaining nut with a 10 mm ring spanner
  • Turn the eccentric with a small nail or Allen key so that the eccentric presses against the blade
  • Now turn back a very small touch so that the leaf loosens slightly again
  • Tighten the eccentric retaining nut
  • the 0.30 mm sensor blank must now be able to be pulled through relatively easily and without great effort
  • then insert a sensor blank with 0.35 mm as a check
  • it can only be pulled through with increased effort
  • Tighten the eccentric finally
If the check with the 0.35 mm blade was successful, the valve clearance is correctly set to 0.30 mm. There are the following possible errors:

1. The feeler blank with 0.35 mm can no longer be inserted and pulled through - then the 0.30 mm are set too tight, so repeat the procedure from the beginning.

2. The feeler gap with 0.35 mm can be inserted relatively easily, at first 0.40 mm is a little more difficult - then the 0.30 mm play was set too loosely.

The main skill lies in the targeted turning of the eccentric. Here, as described, you can press the eccentric against the sheet and take back a little touch. This is actually quite good for beginners too. It is also possible to press the eccentric just very lightly against the blade from the start, but really only very lightly, then there is a similar contact pressure. Regardless of how you do it, the only thing that matters is the result, i.e. the control with the next larger feeler emptiness, which can only pass with a little effort. I don't mean brute force by that, because then every sensor blank fits down, because the valve can move downwards without any problems.

Another tip: The eccentric retaining nut should not be loosened too much. Only partial loosening has proven effective, then the eccentric is pressed together a little and simplifies the targeted turning. Then the eccentric does not twist by itself when you tighten the retaining nut again.

The values:

At the M20 (320i, 323i, 325e, 325i) it has proven useful to set the valve clearance a little looser contrary to the BMW specifications (0.25 mm). i.e. 0.30 mm on the inlet and outlet sides. That brings a more stable idle (especially with the 320i) and a bit more lively performance. The clicking of the valves is hardly noticeably louder, the measure is worthwhile in any case.

At the M30 (528i, 535i, 735i, 635CSi, 530i, 730i) I found various details. Almost all repair instructions recommend 0.30 mm on the inlet and outlet sides. The new repair instructions for the 730i / 735i / 750i say 0.30 mm on the inlet side and 0.35 mm on the outlet side. That's why I set a loose 0.30 mm on the inlet side of my 735i and a normal 0.35mm on the outlet side. As Ingo Köth reported to me, ALPINA has also set 0.35 mm on the inlet side of the M30 engines and this has resulted in a slight increase in performance (on the engine test bench).

The effect of this small improvement through larger valve clearance can be explained as follows: The rocker arm hits the valve a little later, but much more abruptly than if the rocker arm had followed the cam shape without jerk. This sudden jolt in the valve movement causes the air column to be carried away and leads to a small charging effect.

If all of this seems too adventurous to you, no problem, you don't have to try it out. The entire Berlin community drives around with this attitude and can only report positive things. If you are bothered with sawing idle, then you should definitely test it.

And finally: valve clearance that is too large is much safer than too small. Theoretically, the wear on the camshaft increases somewhat. If the valve clearance is too small, however, the valves no longer seal properly and the exhaust valves can overheat because they no longer fit snugly in the valve seats. Possible consequence: valve rupture.