CRG Discussion Forum
Camaro Research Group Discussion => Maintenance => Topic started by: Shooter69z on February 04, 2013, 08:45:43 PM
-
Hi folks, still finding my way around here. I have a question about valve setting on a 30/30 cam. I read the CRG report on setting valves cold by setting the valves a 90 deg atdc for intakes and 90 deg btdc for exhausts. The report says this method does not work for roller rockers, it's for OEM stamped rockers. Is there a reason this won't work for rollers and is there a modofied method?
-
Welcome, Shooter.
I have always used the EOIC method in adjusting the solid lifters with roller rockers on a Camaro I had.
'E'xhaust valve starting to 'O'pen, adjust intake valve.
'I'ntake valve almost completely 'C'losed, adjust exhaust valve.
You can start at the beginning of the firing order and follow it around all eight cylinders.
-
I believe the reason the 90 degree JohnZ/CRG method only works well when OEM stamped rockers are used and not the cast roller, stamped roller tip (comp-type) or machined roller types, is because the tight lash settings as suggested in this method take into account the traditional inaccuracy of most OEM stamped versions - in that they never prove to be even close to the claimed 1.5 ratio - thus the advised tighter cold lash tolerances are used to somewhat make up for this 'lazy' ratio inaccuracy..
Aftermarket and roller type versions are produced to ratios much closer to what is advertised and therefore the cold lash settings as suggested with CRG method would end up with the valvetrain being much too tight when everything warmed up..
I'm sure JohnZ could probably suggest what he considers would be a more appropriate lash for rockers with a real 1.5 ratio, and if I had to guess I would bet it would be close to the .030" the cam was designed and named for..
Randy
-
Thanks for the replies. Dutch, in case I'm a little dense ??? You are saying you think the cold method would be OK, just set them at .30? Instead of .26? I'm glad I found this forum lots of knowledge here! Even though I have two Camaro's, a 67 convertable and recently, 6 months ago, aquired a 69Z, I'm still learnming about this Z28.
-
Dutch is correct - the .026" (cold) setting accommodates the 1.37 (closed) to 1.44 (open) ratio variation inherent with the stamped factory rocker arms, as they never reach the 1.5:1 ratio that the original .030' lash was specified for (1.5 times the .020" height of the clearance ramps on the cam lobes).
With more accurate aftermarket roller rockers, set them (hot) at .030" using either the progressive method or the EOIC method (to ensure that the lifter is on the cam's base circle); you can set just one cylinder or all of them, let the engine cool down completely, and measure the ones you set hot. That measurement will tell you what the (cold) lash should be set at from then on.
-
Thanks a bunch, that's what I needed to know.
-
Randy/John,
I thought the original rocker arm ratio for the '69 302 was 1.6:1 ? Low Perf at 1.5:1 ? Am I having another senior moment ? I realize that has nothing to do with the lash specs, but I used to think the ratio was changed somewhere along the early years to the 1.6 -
please correct me if I'm wrong.
Regards,
Steve
-
Original was 1.5... 1.6 rockers happened in the aftermarket much much later...
-
Many early cams were single pattern deals and the aftermarketers came out with longer ratio rockers that would to a small degree allow users to add lift and to a small degree more duration to alter the cam characteristics by using them.
They are usually an easy and cost effective 'crutch' to make a cam seem bigger depending on whether you needed more intake flow due to manifold or combustion chamber restrictions or more exhaust timing to assist in getting rid of burnt gasses through poor exhaust setups and are a lot easier to install than changing out the cam itself..
-
Hard thing to reason - either you can't learn everything, or can't remember everything. Must be the latter, 'cause I forgot which is more important.
I went back and looked up the ratio and the rocker part numbers - I agree completely. My parts book says the 302 "0" rockers and the 350 rockers were one in the same, I always thought they were different. I had been thinking about using rollers anyway instead of the stamped 1.6 rockers I bought for the '68; I think this has made my mind up.
Regards,
Steve
-
I adjusted these using JohnZ's method and they really sing. I'm happy so far, haven't got to drive it much, weather has been terrible.