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Author Topic: 302 DZ Valve adjustment  (Read 3008 times)
jdv69z
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« on: April 08, 2013, 02:03:19 PM »

I have read John Z's article on cold valve adjustment for the 302 with the 30/30 cam. Want to try this, but I have Competition Cam roller tipped rockers. Not sure if these are true 1.5:1 ratio. If so, I should set the clearance at .030 if I understand correctly. what would happen if I set it to the .026 clearance with a true 1.5:1 ratio rocker? Would this cause excessive cam wear? Thanks.
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Jimmy V.
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« Reply #1 on: April 08, 2013, 08:01:10 PM »

Probably the Comp rockers are a lot closer to the 1.5 ratio than the OEM ones. They are cast and not stamped so I would imagine they are almost as good as a machined true roller rocker in fact.
They should work good at the .030" settings that John recommends in his procedure for a rocker with an accurate ratio, and I would imagine that with .026" clearances they might not hurt the cam or lifters unless you got into a coil bind situation (if your springs weren't ideal).
But almost certainly with a setting that is too tight you could end up with valves open too early and still open too late and/or possibly not have them close completely or long enough to trap all of the compression you need for a good flame front and efficient burn over the top of the piston. all of that could lead to a lot of lost compression and maybe even reversion causing a poor running engine..
Or maybe I'm just 'all full of it' - Ha!
I'll leave a lot of the higher theory to John, and like you, hope that he sees your question and chooses to respond to initial your question.
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JohnZ
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« Reply #2 on: April 09, 2013, 08:52:37 AM »

See reply #4 in this recent thread:

http://www.camaros.org/forum/index.php?topic=10464.0
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'69 Z/28
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jdv69z
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« Reply #3 on: April 09, 2013, 09:47:30 AM »

I Think I've got this. So with the engine hot, I rotate to TDC #1 and set #8 exhaust and #2 intake to .030. Then let the engine cool. When cold, I measure the clearance on the two I set to .030 "hot", and can set all the valves to this whatever this "cold" clearance is using the method in John's article.
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Jimmy V.
JohnZ
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« Reply #4 on: April 10, 2013, 10:29:34 AM »

<<So with the engine hot, I rotate to TDC #1 and set #8 exhaust and #2 intake to .030.>>

That's correct - when you set the engine at #1 TDC, make sure it's on the compression stroke, with both valves closed on #1 cylinder; if both rocker arms on #1 aren't even/parallel, you're at #6 TDC and need to go around once more.
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jdv69z
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« Reply #5 on: April 10, 2013, 01:40:24 PM »

Yup, I was thinking of checking the distributor rotor position to verify it was located at #1. Or you could remove spark plug and check for compression. Thanks, I'm looking forward to seeing how much improvement I can get.
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Jimmy V.
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« Reply #6 on: April 10, 2013, 02:33:29 PM »

Hey Jimmy V. if you happen to do a compression test or vacuum ck. I would love to know what #s you get. I have those rockers and I only have 7.5 inches of vacuum. I would like to eliminate them being the culprit. Everything else has been done! Thanks, Gary (myty)
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69Z28-RS
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« Reply #7 on: April 10, 2013, 04:57:06 PM »

I don't see how the lifters can cause loss of compression, UNLESS you have them lashed so tightly that the valves aren't fully closing.   ie.  If you have non zero lash at TDC, the lifters can't be the problem...
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Gary W.  /  69Z28-RS, 72 B 720 cowl console rosewood all tint
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jdv69z
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« Reply #8 on: April 16, 2013, 01:57:33 PM »

So at what point was this adjustment done in the assembly process? after coming off the line? With the engine hot and running? Or was is done cold at Flint before running? Engine was run at Flint for only short period, right?
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Jimmy V.
JohnZ
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« Reply #9 on: April 17, 2013, 11:28:04 AM »

So at what point was this adjustment done in the assembly process? after coming off the line? With the engine hot and running? Or was is done cold at Flint before running? Engine was run at Flint for only short period, right?

Valve lash was set at Flint V-8, cold, prior to hot-test; the engine ran for less than 30 seconds at hot-test - just long enough to set the timing and check for leaks and abnormal noises.
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jdv69z
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« Reply #10 on: May 28, 2013, 01:58:15 PM »

Update on this topic: Using John Z's cold recommendations, I set valves #8E and #2I to .030 with the engine at TDC and hot. After letting it cool, I re-checked these 2 valves and measured .035 with my Competition Cams Roller tipped rockers. Set all valves to .035 cold per the procedure. Idle is now much more stable. Performance seems to be improved as well, although "seat of the pants" feel is only a subjective  measurement. Anyone who has not tried this should give it a shot. Thanks again  John for your help. Thought you might appreciate a success story.
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Jimmy V.
jdv69z
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« Reply #11 on: May 31, 2013, 03:24:33 PM »

Hey Jimmy V. if you happen to do a compression test or vacuum ck. I would love to know what #s you get. I have those rockers and I only have 7.5 inches of vacuum. I would like to eliminate them being the culprit. Everything else has been done! Thanks, Gary (myty)

Gary, my vacuum @ 900 RPM = 7-8 ins-hg  just like yours. It is inches of Mercury I think.
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Jimmy V.
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« Reply #12 on: June 03, 2013, 09:05:12 PM »

Thanks Jimmy, I am currently lashed at .030.
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