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Author Topic: Adjusting rocker clearance on 30-30 cam.  (Read 5447 times)
69Z28
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« on: April 03, 2009, 08:11:35 PM »

Been reading the info posted here for adjusting the rocker clearance on the 30-30 camshaft and was curious to know if the clearances are the same if using roller tip 1.50 rockers?  Huh

Thanks,
Gary
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GaryC

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« Reply #1 on: April 04, 2009, 08:07:25 AM »

http://www.camaros.org/302valves.shtml.
here is a great post....Thanks Fireman John Roll Eyes
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JohnZ
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« Reply #2 on: April 04, 2009, 09:25:27 AM »

Been reading the info posted here for adjusting the rocker clearance on the 30-30 camshaft and was curious to know if the clearances are the same if using roller tip 1.50 rockers?  Huh

Thanks,
Gary

No, they're not - the stock rockers are only about 1.37:1 at the lash point and about 1.44:1 at full lift. If not using stock rockers, the best way to determine the cold lash setting is to set the intake and exhaust lash on one cylinder's valves "hot and running", let the engine cool down completely, and measure the cold clearance on those two valves - that becomes the "cold" lash setting.
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69Z28
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« Reply #3 on: April 04, 2009, 09:41:16 AM »

I have read the info on adjusting the valves many times to see if I am overlooking something but still not understanding it I guess.
If the 30-30 cam with the stock rockers requires a .026 clearance, what should the clearance be with 1.5 rockers. I'm a bit confused on this. Should it be .030? or .026?

Thanks,
Gary
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GaryC

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« Reply #4 on: April 04, 2009, 11:43:59 AM »

i've ALWAYS thought the name came from the .030/.030 lash. I always set mine at factory spec., .030/.030, COLD.
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69Z28
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« Reply #5 on: April 04, 2009, 11:52:44 AM »

After reading and re-reading the info about valve adjustment on this site the .030 clearance is too wide for the 30-30 cam with the stock rockers. I understand the reason based on the provided info for the 1.37 stock rocker, but I'm not quite convinced that the clearances in the info are good if 1.5 rockers are used. Anybody?


Thanks,
Gary
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GaryC

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« Reply #6 on: April 04, 2009, 06:52:07 PM »

After reading and re-reading the info about valve adjustment on this site the .030 clearance is too wide for the 30-30 cam with the stock rockers. I understand the reason based on the provided info for the 1.37 stock rocker, but I'm not quite convinced that the clearances in the info are good if 1.5 rockers are used. Anybody?


Thanks,
Gary
I would think the theoretical clearance for a 1.5 rocker would be the actual .030 the factory recommends.

Jimmy V.
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Jimmy V.
69Z28
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« Reply #7 on: April 04, 2009, 07:08:27 PM »

Actually, I was thinking the same thing myself. For years I was under the impression that all chevys rockers were 1.5 ratio. So I guess it is safe to say the .030 clearance is true with 1.5 rockers. I'll give it a go and see what happens.


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Gary
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GaryC

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aaronz28
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« Reply #8 on: April 04, 2009, 09:58:35 PM »

here is the deal..
Chevy rockers aer supposed to be 1.5 but in actuality, they are closer to 1.37 as  John said..
the tighter lash is to compensate for the sloppiness in the OE rockers..

if you are using blueprint rockers or aftermarket rockers with true 1.5 or higher ratio... then you want to lash at .030

i've read somewhere that the .030 lash setting was originally supposed to be .026 but the FI 327s wouldn't make enough vaccuum to idle properly... so they opened it to .030..
whether or not this is true.. JohnZ can probably verify..

i've never had good luck lashing at .024 or .026 (or whatever the article reads)

but i've never used sloppy OE rockers either LOL.

they make little torque as it is... why would you want to make the cam feel bigger by tightening the lash??? LOL

A
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JohnZ
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« Reply #9 on: April 05, 2009, 01:44:56 PM »

they make little torque as it is... why would you want to make the cam feel bigger by tightening the lash??? LOL

A

Because with stock stamped rockers the .030" lash puts the lifter off the clearance ramp, onto the acceleration flank of the cam lobe before the rocker contacts the valve stem; beats up the valvetrain. From the article:

<<The factory 0.030-inch/0.030-inch (intake/exhaust) clearances are derived from multiplying the 0.020-inch maximum height of the clearance ramp above the base circle by the theoretical max lift ratio of 1.5. However, the actual as-measured lift ratio for the stamped OEM rocker arm at the lash points is actually about 1.37:1 (not the design ratio of 1.5:1, which is a theoretical max lift measurement, or the actual as-measured max lift with factory stamped rocker arms, which is about 1.44:1). The desired clearances in this procedure are therefore derived by "factoring" the OEM recommended clearances by the ratio 1.37/1.5 to compensate for the actual as-measured rocker arm ratio of 1.37 at the lash point. That number is then rounded down slightly to result in the cold clearance number. The clearance ramp, which is exactly 0.020-inch high on the lobe, is all taken up at 1.37 x 0.020 = 0.0274-inch clearance. Rounding down yields the desired 30-30 cam clearances of 0.026 inch/0.026 inch for this cold procedure.

Using the 0.030-inch clearance with the valve closed is too loose - the ramp ends/begins before the 0.030-inch clearance is taken up, resulting in the valve being lifted off and returned to the seat at greater than ramp velocity. This will contribute to valve seat recession, and can cause valve bounce at the seats at high revs - it will also be noisy.>>

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aaronz28
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« Reply #10 on: April 05, 2009, 09:51:01 PM »

ok John,
so then you are saying to lash at .026 even with true 1.5 rockers?

i have a set of Comp Roller Tips on my car... they are far superior (at least in consistency) to the factory arms.

The other thing I don't understand..... if you tighten the lash from .030 to .026  you notice a difference in the way the car idles, and revs... and it makes slightly less vaccuum.
less rocker noise obviously... but if all you are doing is taking the slop out (before the lifter even moves the valve) ... why then do you notice a difference in idle quality and vaccuum with the tighter lash?

I can't believe that the .004 additional valve lift makes a difference
Thanks

Aaron
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Stingr69
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« Reply #11 on: April 06, 2009, 08:08:26 AM »

Aaron,
I know we will wait for John to post but I thought I would add a little bit here - The clearance ramps we know are there to cushion the valve train when the lash is taken up. The rams on this grind are .020" tall. I have measured them myself with a dial indicator and a degree wheel. You want the lash to taken up very closely to the top of the clearance ramp but not over the ramp at all. If you have a true 1.5 (or 1.52) ratio rocker arm - and you know it is 1.5, you still want to be close to the top of the clearance ramp but not exceed it. The problem with setting the lash anywhere tighter than the top of the ramp is that the LONG ramps on this grind will cause even a slight decrease in the lash setting to INCREASE the duration. Extra duration on this cam is not a great thing especialy on the intake side. Other aftermarket cam grinds have relatively steeper clearance ramps so a small decreases in lash will not have as much impact on increasing the duration. This grind is far different than a typical aftermarket grind when it comes to the change in duration per .001" change in lash setting. This grind will add 3 degrees of crank duration for each .001" tighter lash spec. Tighter is safer for the valvetrain but the increse in duration is often not desired.

P.S. - I ran the Comp 1.52's and set them at .030" when I still had the 30-30 cam. I run a different grind now. Cheesy

-Mark.
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aaronz28
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« Reply #12 on: April 06, 2009, 07:11:58 PM »

I certainly understand "taking the slop out"  but unles i'm doing something wrong... (and i've followed John and Duke's procedure)  you can tell a difference with the .004 taken out of the lash adjustment...

unless I have my cam freakishly advanced to where it is climbing on the clearance ramps when I'm tryin to set the lash... i don't know...

i can tell you that i tried the lash adjustment in both my 69Z and my 64 L84 Fuelly ... and neither motor responded well to the tighter lash...

i'm about to break in a different cam in my Z (probably tomorrow)  it is a tight lash modern shaft... i'll probably go back tot he 30-30 if this expiremnent is a failure, but we'll see.

Thanks

A
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sam
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« Reply #13 on: April 07, 2009, 06:44:46 AM »

We set .026/.026 cold with roller tip rockers and have no problems. I idle the car at about 1000 rpm's and still stop pretty easy.
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glenn64vette
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« Reply #14 on: April 07, 2009, 12:20:06 PM »

We set .026/.026 cold with roller tip rockers and have no problems. I idle the car at about 1000 rpm's and still stop pretty easy.

I 've used the 30 30 in my 64 vette since 72. I've always set it .026 with the Comp cams 1.52 roller tips. It will idle at 850 rpm with 9 to 10 inches of vacuum with the 400-- 6 to 7 inches of vacuum with a 350 and with a 327 about 5 to 6 inches of vacuum. This is with the dual quads. I hope this helps.
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