RWD - Valve Lash Revelations (really long)

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Valve Lash Revelations (really long) 140-160

I spent a few hours today fondling the valve train on a B20E. I've finally gotten around to getting the head bolted on the ITB race car engine. This provided the opportunity to see if I could learn something about the pros and cons of various methods of setting valve lash on the B20 (as promised in an earlier thread).

The engine used for this exercise is a B20E that has just been freshened for the upcoming racing season. The "D" cam and lifters are used (about 800-1000 race miles) but in very good condition. The head has just had the valves done at a local race shop, including new valve springs.

I used 4 methods to check/adjust valve lash, described below. As you read the descriptions of the methods, please note that in some cases we're talking *valve* number (1 thru 8), and in other cases we're talking *cylinder* number (1 thru 4).

Shop manual method
1 - Roll engine to firing TDC for #1 cylinder and adjust valves 1, 2, 3, 5.
2 - Roll engine to firing TDC for #4 cylinder and adjust valves 4, 6, 7, 8.

Phil S. method
1 - Roll engine (normal rotation) until cylinder #1 exhaust valve just starts to *open*, adjust intake valve on same cylinder. (Repeat for cylinders 3, 4, 2)
2 - Roll engine (normal rotation) until cylinder #1 intake valve just starts to *close*, adjust exhaust valve on same cylinder.
3 - (Repeat for cylinders 3, 4, and 2)

Nines method
1 - Roll engine until #8 valve is fully open, adjust valve #1.
2 - Roll engine until #7 valve is fully open, adjust valve #2.
3 - Roll engine until #6 valve is fully open, adjust valve #3.
4 - Repeat until all 8 have been adjusted. (The # of the open valve plus the # of the adjusted valve always add up to 9.)

Valve Rock method
1 - Roll engine until intake and exhaust valves on #4 cylinder "rock" (exhaust closing, intake opening), adjust both valves on #1 cylinder. Repeat for all "opposing" cylinders - #2 rocks adjust #3, #4 rocks adjust #1, #3 rocks adjust #2.

Okay... All valves were adjusted to .018", using the "Rule of Nines" method (this was an arbitrary choice, but a lucky one, as you'll see later). An .018/.020 go/no-go feeler guage was used as primary tool, with another conventional set of feeler guages used for occasional confidence checks. After all 8 valves were at a "perfect" .018, the other 3 methods were then employed one at a time, to check (NOT adjust) lash on all valves. (BTW, no "hot vs cold" testing was done at this time; we were on the engine buildup stand at 60 degrees ambient.)

Backing up a minute, I also had a .001" dial indicator in use prior to doing the lash adjustments and checks. The dial indicator was set up on the rocker shaft in two different "mid-span" locations to see if adjacent valve opening/closing had any "bowing" effect on the shaft. None noted, no deflection of the shaft was seen in either location. We also set up in two places on the camshaft, midway between the front and center bearings, then midway between the center and rear bearings. In both cases, we put the indicator tip on the base circle of a cam lobe (valve open), then loaded and unloaded the cam by alternately loosening and tightening the rocker assembly hold down bolts (using a "dispensable" rocker assembly, natch!). Again, no appreciable deflection or bowing of the camshaft was seen on the dial indicator. Phil, this means I did not verify your observation that the cam and/or rocker assembly might be "flexing" when a valve adjacent to the one being adjusted is open. Or if they *are* flexing, it's apparently not enough to really affect the lash adjustment process. But keep reading... your adjustment method WILL be vindicated soon! :)

Back to the lash checks. Hmmm.... Houston, we have a problem. While Phil's method agrees with the "Nines" method perfectly (less than .001" difference on all valves), the "Rock" method and the "Shop Manual" method have anomalies. The Rock method shows one valve significantly out of adjustment (more than .002") and another that is not so good (fat .001", skinny .002" sort of discrepancy). And three valves using the Shop Manual method also have shakey numbers, two of them more than .001" and one nearly .002" out, compared to the Nines baseline. At this point, I started looking at the exact position of the cam lobe in "adjustment position" for each of the 4 methods. Bottom line? The Shop Manual and Rock methods both end up with some of the lifters NOT centered on the base circle portion of the cam lobe during adjustment. In fact, the Rock method has NONE of the lifters centered on the base circle.

So... not finding any other cause, I am concluding that at least in my case (and probably many others) not every cam lobe is ground (or worn) exactly the same with respect to where the base circle starts and ends. The Nines method and Phil's method both put the high point of the cam lobe exactly 180 degrees from the lifter, which of course centers the lifter in the base circle while you're adjusting the valve. The other two methods do not, so are probably more vulnerable to a less-than-perfect grind.

The other part of this story is that these are the same parts (valves, cam, lifters, pushrods and rocker assembly) that have been in the engine for the last several hundred race miles. And I've been using the "Rock" method since I can't remember when, so that's how all the valve lash adjustments were done on this engine. No evidence that it did any harm, but in any case, because I'm somewhat anal about these things, I will be using the Nines method henceforth. (Now that I've done them back to back, I find the Nines method a little easier to live with than Phil's.) But I can recommend either of them. I do NOT recommend the Shop Manual method OR the Rock method, for reasons cited above.

All of this just my opinion, of course. :)

Gary L
1971 142E ITB racer, 1973 1800ES, 2002 S60 T5


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New Valve Lash Revelations (really long) [140-160]
posted by  Gary L  on Wed Feb 15 17:55 CST 2006 >

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