CRG Discussion Forum
Camaro Research Group Discussion => Maintenance => Topic started by: 68 z28 RS on October 21, 2018, 07:33:47 PM
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Hello everyone,
I would like to ask about adjusting the valve lash on my 68 302. I have rebuilt the engine and now have it back in the car and running. While the engine was still on the engine stand I adjusted the valves using the John Hinckley and Duke Williams method as found on this website. (start on TDC and turn the engine 90 degrees 7 times adjusting 2 valves at each 90 degree position at .027). Now that the engine is running and somewhat broke in (there are a couple valves that are a little noisy) I am going to adjust the valves again. The cam I installed is the Federal Mogul Speed Pro 30/30 grind part # 53059 12002 and the rocker arms I used are the Comp Cam 1.5 ratio roller tip stamped steel rockers.
Here is my question......Is the Speed Pro 30/30 cam Identical to the original cam where this adjustment method would still work, and are the Comp Cam rockers different in some way that this adjustment method would still work? I think the method is fine but would it change the .027 clearance?
Thanks in advance to everyone who replies.
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Best method is EOIC - Exhaust opening - adjust intake; Intake closing - adjust exhaust.
This method has the lifter on base corcle of lobe. Start with firing order and follow through.
You're welcome.
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What clearance does the cam manufacture recommend? It should have come with the cam along with specs on lift and duration.
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Speed Pro says .030 just like the original cam. If you read the John Hinckley and Duke Williams method at the link below they state that the stock rocker arms which GM advertised as a 1.5 ratio are actually a 1.37 ratio and that's why they recommend .026 to .027. So I am wondering if the Comp Cam 1.5 ratio rockers changes this.
http://www.camaros.org/302valves.shtml
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I prefer the one at a time method, by rotating each valve to peak lift, then one full crank revolution so I can be certain the camshaft is exactly on the base circle. Takes longer, but is dead nuts accurate. The method on this site will also work very similar if you don't want to rotate the engine as much.
The reason for this is to make absolutely sure the cam is on the base circle. With so many lobe profiles these days and differences in lash ramps etc... it's just good practice.
As far as the rockers, I don't see where that would make much difference in your lash adjustment. However the stock rockers are in fact notorious for varied ratios. The aftermarket stuff like Comp and Harland tend to be a bit over their advertised ratio. Depending on the spring pressure you run you may find the "running ratio" changes due to flex at the rocker and the pushrod. I always check with a dial indicator. I'd bet you'll find those comp roller tips to be in the 1.55 range.
I'd simply go back through your lash adjustments and recheck, you may find you simply have a couple you didn't lash the same. Roller tip rockers are tricky. I make a conscious effort to pull the feeler gauge sideways because the roller can give you a false sense pulling perpendicular.
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Thanks X33RS,
I think I will stick at the .030 like you all are suggesting.
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X33RS gave great advice but I would add if you are going to adjust the valves with a cold engine then you need to add 0.002" (0.032") to your lash if it is stock cast iron head and block.
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Not sure how much run time you have on this new cam, but before I would touch the 1st adjusting nut I would make note of which valves are noisy. This can be done when re-adjusting and noting the loosest valves, ie most clearance. You can also do this with a section of hose, like a couple of feet of rubber fuel line or similar. Start engine with v covers off. Put one end of hose to your ear and other to each valve. It will be easily apparent the culprit(s). Regardless of method mentioned, the reason to note which valves is after you re-adjust, I would set up a dial indicator on those valves and note full lift. You may want to record this and if there is significant (.050) change from stated lift on cam card, I would want to determine if you are wiping out a lobe, having premature cam failure from break in.
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Good idea ko-lek-tor,
I will check to see which valves has the most lash. I think there are 2 that are just a little noisy.
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The actual rocker arm ratio can be different than the advertised ratio.
The GM original cam grind has a .020 high clearance ramp (that is very long). If you have a dial indicator you can determine the exact lash for your particular non-original rocker arms.
Remove one rocker arm - Set up dial indicator to read cam lobe lift on that pushrod tip - Rotate the engine until the cam lifts the pushrod .020" - Remove dial indicator and reinstall your rocker arm with zero lash - rotate the engine so that cam lobe is back all the way down to the base circle - Measure the lash at that rocker arm tip to valve now. That lash dimension you measured is your hot lash spec for your particular rocker arms.
Good idea to recheck and record all the valve clearances after cam run-in. If the dimensions are opening up on one or more valves, you could have wiped out those lobe(s).
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Or be pushing a rocker stud if they are not screw in studs.
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Thanks everyone, all good advice.
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Thanks everyone for the help. I readjusted the valves over the weekend and it now runs and sounds great. For some reason number 1 and number 4 valves were a little loose. I originally used the EOIC method when the engine was on the engine stand. This time I used the 90 degree method which I think is the best method to make sure the cam is on its base circle.
I chased this car for about 30 years which my ex father in law bought new at Harry Mann Chevrolet in Los Angeles (68 Z28 RS). Its been sitting for about 25 years and has 67000 original miles, original paint and interior, all #s matching and extremely well documented. He told me he used to adjust the valves with the engine running. He would use cardboard to deflect the oil to keep from making a mess.
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That is one good looking camaro .... I am glad you were able to finally purchase it.
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I agree! A great looking Z28, AND a *returned* family member in a super color~ :)
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Thanks everyone for the help. I readjusted the valves over the weekend and it now runs and sounds great. For some reason number 1 and number 4 valves were a little loose. I originally used the EOIC method when the engine was on the engine stand. This time I used the 90 degree method which I think is the best method to make sure the cam is on its base circle.
I chased this car for about 30 years which my ex father in law bought new at Harry Mann Chevrolet in Los Angeles (68 Z28 RS). Its been sitting for about 25 years and has 67000 original miles, original paint and interior, all #s matching and extremely well documented. He told me he used to adjust the valves with the engine running. He would use cardboard to deflect the oil to keep from making a mess.
Nice car!
Hot and running is how I was taught to adjust valve lash. :)
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Thanks everyone for the help. I readjusted the valves over the weekend and it now runs and sounds great. For some reason number 1 and number 4 valves were a little loose. I originally used the EOIC method when the engine was on the engine stand. This time I used the 90 degree method which I think is the best method to make sure the cam is on its base circle.
Just as some of us were trying to explain, that was just the product of a few lobes not being exactly on the base circle and why the EOIC method isn't always accurate. With the lobe designs of these cams, new and old, it's just best to make sure you're on base circle for lash settings. Glad to hear it's running fine. Great looking Z.
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You were right X33RS, I learned a lesson from this. :)
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btw, it should be a chrome shifter ball since the pattern is already on the console. :)
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Copy that KurtS, I already corrected that. It should also be a Muncie shifter, not a Hurst.
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I'd leave the shifter.
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"I'd leave the shifter."
I'll second that. I had a car in high school with an original Muncie shifter. It was notorious for hanging up between gears when pushing the car hard. A new competition plus from the local Ramchargers speed shop cured the problem.
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I agree Z10Mike,
I was considering modifying the stock Muncie shifter handle to work on the Hurst shifter so it looks original.
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I think they make a Muncie handle to bolt on the hurst. I have one on my 64 vette.
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I will have to look into that Kelly.
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I think I'm liking that car. Thanks for showing us.
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Thanks maroman :)
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If I am not mistaken Duke and John have an updated lash spec.
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Thanks firstgenaddict, I will have to look that up. Do you know what they changed it to?
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Very nice 68Z. Maybe we can convince you to submit the history of the car, and your story to Bryon.
(I would love to read more about it, and see more pics)
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I could do that Bullitt65. Let me know what I need to do.