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Valve clearance adjustment question


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I followed the procedure in the Haynes manual -- set #1 to TDC (pointer on timing cover to mark on pulley) and adjust #1 intake and ex to 0.006 to 0.008. At this position the cam lobes are not exactly 180deg from the sliders on the follower. #1 was at 0.006 in and ex at this position

If I rotate it so that the IN lobe is closer to 180de from the follower slider, the clearane opens up by 0.002-3".

Is this ok? Or should I ignore the Haynes procedure and check every valve only when lobe is 180deg from follower?

PO told me he had a perf cam in there but it was not clear which cam. Could this play a role? (Cam has 2' marked on it between #1 lobes and front bearing).



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The factory manual says adjust clearance at TDC. At TDC the valve lobes are not 180deg away from the rocker. The lobes point downward (but there a range of positions which could be called downward).

So I'm confused -- it either is at TDC per manual or when lobe points away (i.e. 180 deg from rocker) which is what many posts in the FAQ state -- but not what is in the manual or in Haynes.

And setting clearance at one of the above positions results in a different reading when measured at the other position -- at least this is the case on my cam which is stock, but possibly reground.



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You are over thinking this. TDC can refer to the individual position of a single cylinder or the position of all the cylinders.

Put some masking tape on your fender.

Mark it



Remove spark plug wires and valve cover.

Look at the cylinders and see which lobes are pointing directly down. Set the valve lash on only those valves. Cross them out on the masking tape map. Crank over engine using key (It wont fire since we removed the spark plug wires).

Now look and see which lobes are pointing down. Set those valves and mark them off the masking tape map. Repeat until all valves have been set.

Also use 2 feeler gauges. A 0.007 and a 0.006. Set the lash with the 0.006 and then try insert the 0.007. If you can, your lash is NOT set right. Redo.

1976 BMW 2002 Chamonix. My first love.

1972 BMW 2002tii Polaris. My new side piece.

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The best way to tell if the cam lobes for a cylinder are truly pointing down is to look at the cam lobes for the "paired" cylinder and see if the lobes are up. When #1 is at top dead center and its cam lobes are pointing down, the lobes for cylinder #4 are pointing straight up. This can be visualized by looking at the rocker arms for #4 and seeing if they are overlapped -- if the rocker arms are equally on the intake and exhaust lobes. If they are, then #1 lobes are truly pointing straight down. Same thing with #2 and #3 -- when #2 is up, #3 is down.

The new book The Best Of The Hack Mechanic available at https://www.amazon.com/gp/product/0998950742, inscribed copies of all books available at www.robsiegel.com

1972 tii (Louie), 1973 2002 (Hampton), 1975 ti tribute (Bertha), 1972 Bavaria, 1973 3.0CSi, 1979 Euro 635CSi, 1999 Z3, 1999 M Coupe, 2003 530i sport, 1974 Lotus Europa Twin Cam Special (I know, I know...)

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The cam flange has TDC markings, so I used that as a more precise guide.

"Pointing down" confused me if I interpret that to mean vertically straight down -- as only one lobe at a time can be made to point exactly down -- plus the engine is tilted... But I get it now.

Adjusting valves on a Fiat I used to own required the clearance to be measured when the valve lobes were pointing away 180 deg from the follower/rocker.

My questions is that on the '02 when I set clearance at TDC (lobes pointing down) and then rotate till (say) IN lobe is 180deg from its follower, the clearance opens up by 0.002-3".

I was wondering if that was normal or was an indication of a reground cam.


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"pointing down" in this case is not gravitationally plumb. remember the engine is offset at an angle. "pointing down" or "straight up" is in reference to the lobe/rocker arm position and travel. Mainly, if you are consistent with your positioning you will get a cosistent result in valve timing. Once you become familiar with the engine response to your valve lash you might subtly notice that you may need to have more or less lash than spec. If you do have a reground cam, it might be worth while to remove the gear and see if there are millers inscriptions. I know that the reground cams I have had, use the .006" - .008" as a reference point. The Schneider cam I have now has a recommendation for differing lash for intake and exhaust.

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Byas. see note 3 at bottom of the page for valve lash specification which is measured between rocker eccentric and valve stem. the table you are looking at is showing example of the drag of valve timing with two different measurements. These two examples are measuring the gap between the rocker pad and the cam base circle, which is not used for adjusting the lash. These two tables show the different timing that would occur with the lash adjusted differently. Quite a remarkable difference for a few thou. I would say. Think of it this way. with a tighter lash the rocker will ride more of the lobe opening and the valve sooner following the cam profile more acurately and deliver the expected machined curve of the cam. with a larger lash gap, the rocker will follow the cam and open the valve later and more loosely delivering a more peaky opening and closing of the valve. making ignition timing more critical I would think. With proper valve timing you will be able to get a stronger sense of distributor curve on acceleration because you can dial in the ignition timing to use more of the dynamic area of the cam. At least that makes sense to me.

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  • 4 months later...

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