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Discussion Starter · #1 ·
MY buddy was setting the lash on his race car yesterday and we all use the traditional IC-EO method but he encountered a perplexing issue. When he set all his lash at the required .020 cold, he would then roll the motor around and when he would encounter say an exhaust valve at max lift he would check the lash on the intake and it would be at .024 lash.

He would do this same thing on other valves and find the exact same issue. Now I know this has to have been addressed by some engine builders in the past but I couldn't find any articles on line so my question is this.

If the valve lash is set at .020 cold and it is done with the lifter on the base cirle then is there any other point in the rotation of the lifter where it would have more than the .020 lash that was set?

We have been setting valve lash for many years so it is not a matter of not knowing what we are doing it is just that we have nevered checked it at any other point in the rotation before.
 

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The way I understand it is it's actually the eoic method. Check the intake when the exhaust starts to open (eo) and set the exhaust when the intake is almost closed (ic).

I found the same thing you did when I checked mine through the whole cycle. Because of that I set my exhaust when the intake is a little earlier in its closing.

It probably has to do with cam timing and late closing intake. Someone that knows more about it can probably explain it. I don't know if what I'm doing is right, maybe someone can comment on why I shouldn't do it that way. I do know if I wait until the intake is almost closed and then check it throughout the valve lift it definately is looser than what I wanted.
 

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Discussion Starter · #3 ·
Yes and that is the point that baffles us. If you set it on the lash on base circle what about the cam makes it change? My convential thinking is that if you set the lash on the base circle that should be the point the lash would be the loosest and as the lifter travels around it would not increase in lash but decrease.
 

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I'd just be guessing but I bet the tolerances on the camshaft might be a little off when it was ground. I know from when I degreed mine in with the dial indicator traveling across the base circle on to the ramp there was some variation where you'd think it should just read steady all the way across. It seems like at the time I did a search and found several people had similar findings and thought it was "okay" as long as it wasn't too drastic.

I know a lot less about it than probably most on this board, I just commented because I'd noticed the same thing. I'll be curious to see what others think.
 

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Is his cam "ASYMMETRICAL" lobe profile?


Remember to move your mouse over pic to make readable!
 

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Discussion Starter · #6 ·
Yes it is symetrical. The lobe ramp was discussed but is not the issue.
 

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Based on your description, I'd say you should check the lash in the same approximate place that the lash was set at. You didn't set the intake lash when the exhaust was full open, so don't check it there. Knowing what you're working with would help also. Maybe the base circle is not concentric or the cam could be bent or the cam could be walking. If you set them cold and check them hot, the lash will grow. It doesn't sound like you did that though.
 

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Discussion Starter · #8 ·
Well yes if we set the lash based on the suggested IC-EO method it will check out each time the same at those points. We are also speaking about the lash being checked cold not cold then hot or vice versa.

The cam is a comp cams part #12-995-9
gross valve lift .630 .630
Duration @.050 .272 .274
LSA 107

Again the question we are trying to answer is why would the lash increase if the IC-EO method has you setting the lash on the base circle then it should not be any greater than the lash that was set on the base circle.
 

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I know that on our race engine there's about .030 difference between setting the lash hot or cold. It's basically at 0 lash cold and ends up at .030 when hot. You might try it hot and see if there's any difference from what you are getting now. From what you said, it doesn't sound like it will make a difference however.
 

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Well yes if we set the lash based on the suggested IC-EO method it will check out each time the same at those points. We are also speaking about the lash being checked cold not cold then hot or vice versa.

The cam is a comp cams part #12-995-9
gross valve lift .630 .630
Duration @.050 .272 .274
LSA 107

Again the question we are trying to answer is why would the lash increase if the IC-EO method has you setting the lash on the base circle then it should not be any greater than the lash that was set on the base circle.
I'd put an indicator on the tip of one pushrod and spin it. The indicator has to be very very close to the same plane as the pushrod. Measure the run out on that lobe. Then, without moving the indicator, loosen all other rockers and measure again. If the run out improves, the cam is flexing from the spring pressure. If it were me, I'd run it.....but I just race brackets these days. The next time I had it apart I'd check it out throughly. Those kinds of issues drive me crazy, so I'd have to know........but for .004, I'd let it eat for now.
Maybe you aren't on the base circle. Maybe you're just starting up the ramp. Call Comp and see what they say. Tim Cole and Chris Padgett are the best techs there. If you don't call the 800 number you can get through to those guys and they'll call you back if you have to leave a voice mail.
 

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intake open then close for me

i like to set it when the intake closes , then rotate the engine over 1/4 turn or so ,,, you have more of a chance to set it on the base circle there. I do one cylinder at a time but i'd rather have them right instead of how some people worry when they can do more than one.
 

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I've always used the split overlap method. I follow the firing order:


1 6

8 5

4 7

3 2

get #1 cyl exh valve to start closing and #1 int valve opening, when they are at there mid point (they should be level with each other) at that point you adjust both valves on the opposing cyl which would be #6. When done just tap the starter button a short couple of times and you should be on the split overlap of #8 (again they should be level with each other) adjust opposing cyl #5.keep following the firing order. When you finish adjusting #2, you then set #6 on split overlap and adjust #1, etc.

Also if you have stud girdles the adjustment can move when you tighten the girdles, need to go back and re-check. Hope this helps.
 

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I've used the EO/IC method. works for me and I can do it quickly. Joe Sherman suggested another method on speed talk which is where I also saw this post. I have had problems in the past were the rocker gets hung up either because the pushrods were rubbing in the head from poor alignment/wrong length and the rocker was hitting the retainer. Also was suggested on speed talk the cam was flexing.
 

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Discussion Starter · #14 ·
Some great replies and I appreciate your input on this.
 

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For those wondering what Joe Sherman suggested in Speedtalk, his fool proof method is as follows:

For each valve, rotate the engine by hand until the valve to be adjusted reaches max lift. Mark the damper, then rotate the engine 360 degrees. Now you are completely 180 degrees opposite of max lift on the base circle. Adjust the valve. Do this for each valve, and you will be certain you are on the absolute base circle. It was also suggested to make a chart that you can refer to to make checking/setting lash quick.

If you would like to refer directly to my post, it is here:
http://www.speedtalk.com/forum/viewtopic.php?t=15419
 

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This is right off Cranes website...

How To Set Valve Lash


When the engine is hot (at operating temperature), remove the valve covers and pick the cylinder you are going to adjust. When your engine is cold (after picking the cylinder you are going to adjust as described above), you will need to add .002” to your hot setting (Iron Block, Iron Heads) or subtract .006” from your hot setting (Iron Block, Aluminum Heads).. For Aluminum Block, Aluminum Heads, subtract .012” from your hot setting.



Hand turn the engine in its normal direction of rotation while watching the exhaust valve on the cylinder you’re working on. When the exhaust valve begins to open, stop and adjust that cylinder’s intake valve. (Why? Because when the exhaust is just beginning to open, the intake lifter will be on the base circle of the cam lobe.)



Place a feeler gauge set to the correct valve lash between the tip of the valve stem and the rocker arm. Adjust until you arrive at the proper setting and lock the adjuster in place.



After the intake valve has been adjusted, continue to rotate the engine, watching that same intake valve. The intake valve will go to full lift and then begin to close. When the intake is almost closed, stop and adjust the exhaust valve on that particular cylinder. Use the feeler gauge and follow the procedure described above. Both valves on this cylinder are now adjusted. Move to the next cylinder and follow the same procedures.


Hope this helps. Dave
 

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For those wondering what Joe Sherman suggested in Speedtalk, his fool proof method is as follows:

For each valve, rotate the engine by hand until the valve to be adjusted reaches max lift. Mark the damper, then rotate the engine 360 degrees. Now you are completely 180 degrees opposite of max lift on the base circle. Adjust the valve. Do this for each valve, and you will be certain you are on the absolute base circle. It was also suggested to make a chart that you can refer to to make checking/setting lash quick.

If you would like to refer directly to my post, it is here:
http://www.speedtalk.com/forum/viewtopic.php?t=15419
As to why it's different I can't explain it either and I just set my valve lash twice a little over a week ago on my new 427 BB I just finished.....but the method that Mr.Sherman talks about is exactly the same way my Grand Dad taught me clear back when I was a pup and working on my very first Big Block Chevy In his Shop...and I have continued to do it this exact way ever since....(wow the old man was pretty sharp it turns out huh ....go figure).....I always thought a new set of Hardened Push rods every year when freshening up a motor over the winter was like insurance.... you hate to pay for it until you need it and don't have it.
Randy.
 

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Yes and that is the point that baffles us. If you set it on the lash on base circle what about the cam makes it change? My convential thinking is that if you set the lash on the base circle that should be the point the lash would be the loosest and as the lifter travels around it would not increase in lash but decrease.
Because you weren't on the absolute base circle when you originally adjusted the lash.
 
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