put new rocker arms on a 64 fuelie this is a recent rebuild and the tops of valves were wearing a depresion in the rocker tips. adjusted the valves to .028 cold at top dead center of each piston . I noticed that while setting the other valves that some rockers seemed loose and a recheck showed any where from .031 to .032 at ramdom spots in the firing order . also tried setting at tdc and 180 . whith similar results .Doesn't the base circle stay the same till the lifter hits the ramp? Am iI adjusting these incorrectly this is a 30/30 cam reproduction by wolverine. any input thanks Steve
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Re: valve lash
You can't adjust the valves on a 30-30 cam (LT-1 cam, too) at TDC because both sides are still on the ramp. You adjust all the inlets at at 90 ATC and all the exhausts at 90 BTC. If you adjust them at TDC they will actually be about thre thou looser than what you set them at, which is apparently what you found.
If you e-mail me I will send a the written procedure, but use .023" for the cold lash spec. This is based on a thorough evaluation of the GM drawing that shows the clearance ramp tops are .017" above the base circle, and the measured lash point rocker ratio is 1.37:1; 1.37 x .017 = ,02325. (Peak rocker ratio is 1.44:1 at max lift)
The .023" setting has been recently, tested, and the owener reports very satisfactory results - good idle stability and very quite valve train with smooth/strong revving to 7000.
The document says .026", which was based on a dial indicator measurement of the 30-30 lobe that indicated the base circle is .020" high, but the drawing is more accurate than any dial indicator measurement.
The specified lash on the drawing is actually .025", which is based on .017 times the "design" rocker ratio of 1.5:1 (.017 x 1.5 = .2550), but all the service literature says .030". Go figure!
Duke -
Re: valve lash
the orignal GM specs i have from back in the 60s state .025 lash BUT i think they loosen them up to .030 to get better low end power,smoother idle and higher engine vacuum from the engineComment
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Re: valve lash
You're probably right. They found out that the 30-30 cam was just too big for the street, but loosening up the lash spec has probably beat up a lot of valves and valve seats more than necessary.
The one person who has tried .023" cold lash reports no loss of idle vacuum, idle quality, or SOTP low end torque, but his valvetrain is sure quiet, and it pulls like gangbusters from 5-7K.
DukeComment
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Common knowledge
And, It kicks you in the butt when it hits.Comment
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