Why at the value stem and not at the cam?

[Joe911]

OK – at risk of looking foolish – why not adjust the valve lash at the cam? There must be some obvious reason that escapes me. Certainly if the rocker shaft is offset the clearance would be different by a small amount. BUT all the discussion about how difficult it is to get the feeler gauge between the end of the valve stem and the rocker arm adjusting screw – the other end of the rocker is so much easier to access. I just checked them at the cam and they were all right around the required .004” and most of them were right on. To me this suggests this method should be accurate. What am I missing?? Also would anyone care to speculate on the approximate torque for the adjusting locking nut – to me firm would be about 12-15 lbs. Similar to a spark plug.

[Tyson Schmidt]

It won't be accurate. The rocker ratio is not 1/1. I think it's 1.5 /1.

So I guess you should divide the .004 by 1.5 to get the cam-side spec.

[Wayne 962]

Joe, a very original and unique thought. I think that the rockers are 1:1 or close, but I can't recall exactly. One quick way to check would be to set the valve clearance under the screw to be .004, and then check the clearance under the cam lobe. If it's the same, then the ratio is 1:1.

Either way, you could adjust one valve with the clearance under the valve, and then adjust all of the others with the value that you determine from that first valve you adjusted.

Not too shabby - pretty clever in fact...

-Wayne

[KTL]

I too wonder what the torque value for the jam nut would be. Kinda hard to torque it to spec. though because you have to counterhold the adj. screw. You'd need a special open torque wrench or a crows foot, right? Whatever the case may be, i've found it easy to overtighten the jam nut so I use a stubby 13mm wrench on that nut.

The jam nut is a fine thread M8. M8x1 to be exact. Not sure of the property class, but i'm thinking it's a 8.8 fastener.

Since it's lubricated (by engine oil) when tightened I would think the torque spec. would be something a little less than that value listed below in the Electrically Zinc Plated fine thread chart.

Thanks Metric & Multistandard Components Corp. for the information!

[sammyg2]

Very good question.
What are the chances of sctatching the surface of the cam or cam follower with a feeler gauge? I'd like to think they are very small but if there is a chance that these sliding surfaces could be scratched that would be a good reason why not to try it. maybe just me showing my paranoia. Anyone?

[JWest]

What are the chances of sctatching the surface of the cam or cam follower with a feeler gauge?

There are overhead cam engines that do not use rockers (VW rabbit, Jaguar XJ, I'm sure you can think of many more) that are checked with a feeler on the cam lobe. So this may not be an issue?

[Joe911]

Looking at the picture in the PP tech article on valve adjustment - it looks like the rocker ratio is close to 1-1. I will check for the differences on my spare engine. When I checked/adjusted them at the cam - I could do it without lifting the car so it is can be rolled in gear to turn the engine over.

Damage - My method is to set it at .004 and then confirm that a .005 fill not fit with light pressure. I always lightly wipe a thin layer of oil on the gauge so that it is not dry and both surfaces are lubed.

Regarding the torque specs - not that I was thinking about using a torque wrench - just was wondering how tight so I don't worry that one will back off. Although I see that the spec sheet shows 17.7-19 ft/lbs for an 8mm fastener. I don't think I typically do them that tight.

[Tyson Schmidt]

The rocker ratio is most definitely NOT 1/1.

If it were, then the cam measurements would equal the valve lift, which they don't. It's either 1.5/1 or 1.6/1, I can't remember which.

[Zeke]

It does't make any difference what the rocker ratio is. If there is .005 clearance at the stem, there will be .005 clearance at the lobe. It's a wider area to measure, so the small area at the stem is ideal. But, if the rocker will tip back .005, it will tip forward .005.

[Tyson Schmidt]

Milt, I think you should think about this a bit longer.

[82SC]

hmmm...I think Milt would be right if the pivot point/fulcrum of the rocker was dead center....

I think it isn't...therfore if at the valve end the movement is 0.004
if the other side is FURTHER from the pivot as the valve side you get >004

it the other side is EQUAL in dist from pivot you get =0.004

and if the other arm is LESS in dist from pivot point you get <004

do I get a prize tyson???

[Tyson Schmidt]

Sorry MJ, but no prize. You almost got one, but lost it due to lack of capitalization.



Seriously though, yes you are correct. It's easier to visualize if you exaggerate the distances. Like a teeter-totter that has a pivot moved way over to one end. The movement is very great at the long end and very short at the short end.

BTW, I'm pretty sure the rocker ratio is 1.5/1

When I measured my lobe heights on my cams, I multiplied them by 1.5 and it worked out to the correct valve lift spec for my cams.

[Joe911]

I have been playing around and with 0.004 at the valve - 0.003 will go and 0.0025 will not but it is close However as I am using the Porsche feeler gauge "tool" as the standard, I don't have an .005 to check my work and I suspect I am less consistent setting the lash at the valve vs. cam.

To convince oneself that the ratio would make a difference just move a pencil holding the middle vs. 3/4 towards one end and move the pencil 1" up or down.

There are actually some valves that were easier to get at with the L-shaped tool checking at the valve but some were much easier using a flat blade feeler gauge checking at the cam & setting them to a tight .003.

Thanks for the comments. Possibly someone with a dial indicator and the engine on a stand could verify the correct values.

[Zeke]

Originally posted by Tyson Schmidt
Milt, I think you should think about this a bit longer.

I did and you're right. Man, I'm glad Wayne is in Montery. I don't even want to think about his wrath.

So, now that I'm on the right side of this, you should adjust at the point of the larger of the 2 measurements, right? Seems more acurate.