LT1 Valve adjustments

[COPO 70 RS/Z28]

Im going to check my adjustments the rocket arms they seem just a little loud, to me at least. I have looked around on line to find information on clearances but have not found any. Before I go and buy a book does someone have the clearance figures. I have a 70 z28 with an M40.

Thanks http://www.yenko.net/ubbthreads/images/graemlins/smile.gif

[DarrenX33]

Do you know what cam is in the car? Standard I believe is .020/.025 Intake/Exhaust hot. I would check with Marlin as he has done a lot to his LT1 so he is a good reference.

[Mr70]

They should both read no more then .30 when engine is really hot & running @ operating speed.
For peak responsiveness,I would set at .28 @ general idle to allow for some expansion later on while on the road. http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif

[DarrenX33]

30/30 is a 302 cam. LT1 was different I thought. Crane blueprint grinds are different part numbers and specs.

[firstgenaddict]

-70's "LT-1" Solid-Lifter Cam
What about the later early-70's "LT-1" solid-lifter cam? In the case of the LT-1, it's OK to adjust the intakes at TDC (its closing ramp ends about 10 degrees BTDC, so it's off the ramp at TDC), but the exhaust is still on its ramp at TDC, so the exhausts should be set at 90 degrees BTDC using the indexing procedure. Both intake and exhaust recommended clearances should be factored down by the 1.37/1.50 rocker ratio correction here as well, from the factory spec of 0.024-0.030-inch (hot) to a (cold) setting of 0.021-inch for the intakes and 0.026-inch for the exhausts.

CRG Link
http://www.camaros.org/302valves.shtml

[COPO 70 RS/Z28]

Im assuming it is the stock cam. All indications are that it is. I was going to use the method described by Crane cams.

#1 When the engine is hot (at operating temperature) remove the valve covers and pick the cylinder you are going to adjust.

#2 Hand turn the engine in its normal direction of rotation while watching the exhaust valve on that particular cylinder. When the exhaust valve begins to open, stop and adjust that cylinder’s intake valve. (Why? Because when the exhaust is just beginning to open, the intake lifter will be on the base circle of the lobe, so the intake is the one we can now adjust.)


#3 Use a feeler gauge, set to the correct valve lash, and place it between the tip of the valve stem and rocker arm. Adjust until you arrive at the proper setting and lock the adjuster in place.


#4 After the intake valve has been adjusted, continue to rotate the engine, watching that same intake valve. The intake valve will go to full lift and then begin to close. When the intake is almost closed, stop and adjust the exhaust valve on that particular cylinder. (Again, when we see the intake valve almost closed, we are sure that the exhaust lifter is on the base circle of the lobe.) Use the feeler gauge and follow the procedure described before in step 3.

#5 Both valves on this cylinder are now adjusted, so move to your next cylinder and follow the same procedure again. In the future you may find shortcuts to this method, but it still remains the best way to do the job correctly.

I was thinking that in the event that the cam is not original this may help avoid a mistake

Any comments???????

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[firstgenaddict]

If you follow the steps outlined in the CRG report you can not go wrong.
90 deg adjust the stated valves, 90 deg adjust the next pair... etc.

[COPO 70 RS/Z28]

In the event that the cam is not stock if the CRG is used is there a posibility of valve piston contact or are the clearances such that the contact situation would be impossible ??

[firstgenaddict]

While this 8-step indexing procedure for adjusting the lifter on the base circle of the cam can be applied - in principle - to any solid-lifter cam, the actual lash dimension required to implement the procedure varies with the height and length of the cam clearance ramps and the as-measured, functional rocker arm ratio (not the nominal value).

So you can adjust the valves using the indexing procedure for any solid lifter cam... but you need to use the lash settings supplied with the cam... unless you go through the sequence to determine the correct cold lash clearances and actual rocker arm ratio.

[COPO 70 RS/Z28]

Looks like I'm going to have to do a little investigating!

http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif

[70CitrusZ]

Use the "per cylinder" method, it is far mor acurate than the 90 degree method. It takes a long time to do it correctly, but with time you get quicker.The most time is taken up with removing the A.I.R pipes.
I usually warm the engine, do one bank, warm it again and do the other. You can set the lash anywhere you want within a range of settings. The cam doesn't really have a set in stone lash setting, just a recommended lash setting.
Different books and manuals have different settings listed for this cam. You can set lash looser to reduce duration, or tighter to increase duration. Both settings produce different acting engines. Lash settings can affect how convertor stalls, idle settings will be different, emissions,engine temperature among other things.Experiment a little within the range. I have run lashes from .024/.026 to.030/.030 ...I wouldn't go tighter than .024, and much bigger than .030 is tougher on parts. I finally settled on .026 /.028
Mark.

[YENKO DEUCE REGISTRY]

I used a procedure from a Corvette site guru, and set the lash per my cam card. It's stock and runs good, so I'm not messing with mine! http://www.yenko.net/ubbthreads/images/graemlins/naughty.gif