Cold lash after 500 miles, yikes!

[Belgian1979]

Checking lash at tdc will not give accurate results.
Try .018" cold , done right. IO EC

?

at TDC (beginning of power stroke) both valves are closed. Why wouldn't you be able to adjust them at that point ?

[Warp Speed]

Checking lash at tdc will not give accurate results.
Try .018" cold , done right. IO EC

?

at TDC (beginning of power stroke) both valves are closed. Why wouldn't you be able to adjust them at that point ?

We adjust our valves when the exhaust is almost fully open, and when the intake is almost fully shut.
The difference in lash between a tdc base circle type measurement, the way I mentioned, and even differing places on the base circle, is typically caused by how the spring pressure from other cylinders are effecting cam position in block. This is aggravated by higher rocker ratios.
When running, all bets are off! Hahaha

[F-BIRD'88]

Checking lash at tdc will not give accurate results.
Try .018" cold , done right. IO EC

?

at TDC (beginning of power stroke) both valves are closed. Why wouldn't you be able to adjust them at that point ?

Because the lifter is not on the cams base circle.
The EO IC method ensures that the lifter is in fact on the cams base circle at that point and near 180 degrees away of as if at peak lift.

The tdc method CA may well work OK for very short duration stock cams but not racey cams at all.

[F-BIRD'88]

When you do it the right way, instead of all the incorrect alternative methods. It is quick easy and accurate and pain free. (And your lifters live too.)

[randy331]

When you do it the right way, instead of all the incorrect alternative methods. It is quick easy and accurate and pain free. (And your lifters live too.)

I can't believe my lifters survive cause I set them at TDC.

Well,.. just maybe my cams aren't "racey" enough !!

Randy

[rustbucket79]

While I do use eoic method on all but the mildest camshaft since you can do all 16 valves in 15 minutes or so and only need to rotate the crank twice.

That being said, set the valves that way, then check the lash at TDC ready to fire, you might find the lash varies by a couple of thousands.

[fdicrasto]

I am always amazed at this discussion. Harvey Crane had it right 40 + years ago. If you are actually worried about how much time it takes you to adjust valves and want to cut corners to save one or two or even four extra revolutions of your engine then just consider the damage valve train failures cause. Not to mention money and time lost after any valve train issue which, IMO, are predominately caused by sloppy valve lash practices. An extra ten minutes to save yourself $100's-$1000's ? Really?

[gmrocket]

Checking lash at tdc will not give accurate results.
Try .018" cold , done right. IO EC

?

at TDC (beginning of power stroke) both valves are closed. Why wouldn't you be able to adjust them at that point ?

Because the lifter is not on the cams base circle.
The EO IC method ensures that the lifter is in fact on the cams base circle at that point and near 180 degrees away of as if at peak lift.

The tdc method CA may well work OK for very short duration stock cams but not racey cams at all.

im setting some lash at TDC on a racey solid roller tonight ...with a digital indicator on the adjuster nut i can rotate the degree wheel to 75deg BTDC before any movement on indicator and way more after TDC on intake..for ex i can rotate wheel 85 deg atdc before any movement and even more btdc. all through that movement indicator shows zero..so why cant i set both int and ex lash? i also did it the long way and lash did not change at tdc

252/261 @.050 .432"/.413" lobe lift...its kinda racey

[fdicrasto]

So let me suggest this. You have set your lash at TDC with a feeler gauge at say .020" or whatever setting you have chosen. Nice snug setting on both int. and ex. Now go do your rotation and find a position where ex. is opening (EO) and check with the feeler and then rotate to intake closing(IC) and check the lash. Do you find any variation from your initial lash settings ? I say you will.

[randy331]

So let me suggest this. You have set your lash at TDC with a feeler gauge at say .020" or whatever setting you have chosen. Nice snug setting on both int. and ex. Now go do your rotation and find a position where ex. is opening (EO) and check with the feeler and then rotate to intake closing(IC) and check the lash. Do you find any variation from your initial lash settings ? I say you will.

And if you found .001" or .002" difference then what? Is it gonna make any difference ?

Randy

[MadBill]

Right! Given that, as per Warp Speed, much of the apparent variation in base circle runout can be due to unpredictable (static; who knows about dynamic?) camshaft deflection, it can't be stated authoritatively that any one of several methods yields "correct" lash, but for sure TDC is easy to pinpoint from the damper and duplicate, thus better highlighting any changes.

[Stan Weiss]

This a based on an S96 file of a Chevy 30 30 that someone shared with me. How far off would the lash be if set @ TDC?

Stan

Code: Select all

       I  N  T  A  K  E
Rocker Arm Ratio = 1.500         Valve Lash = 0.03000        Valve Angle = 23.0

VALVE     Lift      Opens   Closes  Duration
                 Deg BTDC  Deg ABDC             Area
         0.00000    39.41 | 107.91 | 327.31 |  38.97
         0.00050    38.34 | 105.99 | 324.33 |  38.97
         0.00100    37.32 | 104.24 | 321.56 |  38.97
         0.00600    30.24 |  91.66 | 301.91 |  38.93
         0.01000    26.63 |  85.42 | 292.05 |  38.89
         0.02000    20.52 |  76.85 | 277.37 |  38.75
         0.04000    12.37 |  66.90 | 259.27 |  38.45
         0.05000     9.08 |  63.12 | 252.19 |  38.36
         0.10000    -3.83 |  48.62 | 224.80 |  37.21
         0.15000   -14.29 |  37.63 | 203.35 |  35.92
         0.20000   -24.23 |  27.62 | 183.39 |  34.14
         0.25000   -34.41 |  17.44 | 163.03 |  31.86
         0.30000   -45.46 |   6.41 | 140.95 |  28.50
         0.35000   -58.05 |  -6.17 | 115.78 |  24.53
         0.40000   -73.80 | -21.88 |  84.32 |  18.46
         0.45000  -101.00 | -48.82 |  30.18 |   6.83
CAM
         0.00050   142.91 | 248.02 | 570.93 |  30.34
         0.00100   140.22 | 247.04 | 567.26 |  30.34
         0.00600   112.81 | 181.17 | 473.98 |  30.21
         0.01000    90.58 | 160.43 | 431.01 |  30.03
         0.02000    39.41 | 107.91 | 327.31 |  29.26
         0.04000    16.09 |  71.28 | 267.37 |  28.44
         0.05000    10.68 |  64.95 | 255.63 |  28.11
         0.10000    -8.13 |  43.99 | 215.86 |  26.66
         0.15000   -23.24 |  28.62 | 185.38 |  24.60
         0.20000   -38.69 |  13.17 | 154.47 |  22.10
         0.25000   -56.69 |  -4.80 | 118.51 |  18.02
         0.30000   -81.89 | -30.01 |  68.10 |  10.79

[Geoff2]

IO, EC, TDC checking at any of these locations is just as accurate, or inaccurate, as other methods. They are ok for initial adjustment, but no better than other methods, Cams can & do have base circle run out, just part of the manufacturing process & tolerances allowed. If the lash was measured where the run out was at the high point, & then measured elsewhere on the base circle where the run out was at the low point, you get two different lash readings. Which one is 'correct' ? Which one do you use?

I use the 4 position method to adjust initial lash: TDC, 180, TDC, 180. Quick & easy for cams under 290* @ 050.
Subsequent lash checks, I use the random method. I check/adj the lash on any loose valves. I note which ones are checked. Crank engine for a couple of seconds. Check/adj lash any loose valves, note which ones are checked. I repeat the process until all valves have been checked three times. You would be surprised how many valves check out at correct lash on first two checks, but are loose on the third check, probably because on high point of base circle in first two checks......

[zums]

4 pages on lash setting? how many of you guys worrying about .002 lash difference from TDC compared to EO IC method bother to check rocker wheel r/o, i would bet alot of your discrepancy comes from there, as was mentioned earlier, do you really think you could detect a .002 difference in engine performance.
Tom

[gmrocket]

And we are using a feeler gauge and tightening the nut by feel... no way your gonna get it the same way twice anyway

There is a huge error factor in the feeler gauge method just because it's by feel. I bet if you put a very accurate turn gauge on the adjuster nut, you would have a hard time ever finding the same turn spec you did previously..