Can someone give me the correct clearances for adjusting the intake and exhaust valves for my 70 LT-1?
I want to make sure the book I have is correct.
Thanks,
Steve
I want to make sure the book I have is correct.
Thanks,
Steve
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Re: 70 LT-1 Valve Adjustment
The specification is .024"/.030", but you should set them at .021"/026" cold with the engine not running to compensate for the fact that the rocker ratio at the top of the ramp is closer to 1.37 rather than 1.5.
Also, you should use the procedure developed for the 30/30 cam because the exhaust cam is on the ramp at TDC and the inlet is barely off.
The following text is the procedure:
"30-30" SOLID LIFTER CAM VALVE ADJUSTMENT
By John Hinckley and Duke Williams
The traditional method of adjusting valves one or more cylinders at a time with each cylinder at TDC is fine for hydraulics and for most solid-lifter cams, but NOT for the factory "30-30" solid-lifter cam used in '64-'66 L-76 327/365 Corvette engines (and in '67-'69 Camaro 302/290 Z/28 engines); this cam has VERY long clearance ramps that are .020" high, and at TDC for any cylinder, both the intake and exhaust valve for that cylinder are still on their ramps, NOT on the cam's base circle, which is why the Service Manual for all cars so equipped says specifically to set them "hot and running".
There is, however, a better way to adjust the valves with a "30-30" - you can set them "cold and not running" by setting the intakes at 90 degrees ATDC and the exhausts at 90 degrees BTDC - so the lifters are on the base circle, not on the ramps. This has been confirmed with cam lift/crank-angle diagrams, and I've done mine this way - results in a nice mechanical "singing" sound, no "clacking", it runs better, sounds better, idle is more stable, and throttle response is improved. Several other Z/28 owners have followed this procedure as well since we developed it, and all of them have seen the same positive results.
Set them cold at .026"/.026". The actual measured (stamped rocker arm) ratio at the lash points is actually about 1.37:1 (not the design 1.5:1, which is a max lift measurement), so the clearance ramp, which is exactly .020" high on the lobe, is all taken up at .0274" clearance; .030" clearance with the valve closed is too loose - the ramp ends/begins before the .030"clearance is taken up, resulting in the valve being lifted off and returned to the seat at greater than ramp velocity. This will contribute to valve seat recession, and can cause valve bounce at the seats at high revs - it will also be noisy.
You can adjust two valves at each 90-degree rotation point, starting at #1 TDC, turning the crank 90 degrees at a time seven times (measure and mark your balancer first at 90-degree intervals from TDC). Removing the plugs simplifies rotating the crank, but you were going to change them anyway, right? Proceed as follows:
TDC #1 - 8E, 2I
90 deg. - 4E, 1I
180 deg. - 3E, 8I
270 deg. - 6E, 4I
0 - 5E, 3I
90 deg. - 7E, 6I
180 deg. - 2E, 5I
270 deg. - 1E, 7I
Start at TDC #1, then rotate 90 degrees at a time, setting at .026" cold. If you like, you can then go back after you're done to each cylinder's TDC position and check clearance on that cylinder's two valves, and you'll find that they've closed up to .024", indicating that both valves are still on the ramps at TDC, as I pointed out in the beginning.
Trivia - the point of max inlet lift on the "30-30" cam is at 112 degrees, with a lobe separation angle of 114 degrees (angle between points of max lift, not the geometric center of the lobe - the lobes on the "30-30" cam are asymmetrical). -
Re: 70 LT-1 Valve Adjustment
The specification is .024"/.030", but you should set them at .021"/026" cold with the engine not running to compensate for the fact that the rocker ratio at the top of the ramp is closer to 1.37 rather than 1.5.
Also, you should use the procedure developed for the 30/30 cam because the exhaust cam is on the ramp at TDC and the inlet is barely off.
The following text is the procedure:
"30-30" SOLID LIFTER CAM VALVE ADJUSTMENT
By John Hinckley and Duke Williams
The traditional method of adjusting valves one or more cylinders at a time with each cylinder at TDC is fine for hydraulics and for most solid-lifter cams, but NOT for the factory "30-30" solid-lifter cam used in '64-'66 L-76 327/365 Corvette engines (and in '67-'69 Camaro 302/290 Z/28 engines); this cam has VERY long clearance ramps that are .020" high, and at TDC for any cylinder, both the intake and exhaust valve for that cylinder are still on their ramps, NOT on the cam's base circle, which is why the Service Manual for all cars so equipped says specifically to set them "hot and running".
There is, however, a better way to adjust the valves with a "30-30" - you can set them "cold and not running" by setting the intakes at 90 degrees ATDC and the exhausts at 90 degrees BTDC - so the lifters are on the base circle, not on the ramps. This has been confirmed with cam lift/crank-angle diagrams, and I've done mine this way - results in a nice mechanical "singing" sound, no "clacking", it runs better, sounds better, idle is more stable, and throttle response is improved. Several other Z/28 owners have followed this procedure as well since we developed it, and all of them have seen the same positive results.
Set them cold at .026"/.026". The actual measured (stamped rocker arm) ratio at the lash points is actually about 1.37:1 (not the design 1.5:1, which is a max lift measurement), so the clearance ramp, which is exactly .020" high on the lobe, is all taken up at .0274" clearance; .030" clearance with the valve closed is too loose - the ramp ends/begins before the .030"clearance is taken up, resulting in the valve being lifted off and returned to the seat at greater than ramp velocity. This will contribute to valve seat recession, and can cause valve bounce at the seats at high revs - it will also be noisy.
You can adjust two valves at each 90-degree rotation point, starting at #1 TDC, turning the crank 90 degrees at a time seven times (measure and mark your balancer first at 90-degree intervals from TDC). Removing the plugs simplifies rotating the crank, but you were going to change them anyway, right? Proceed as follows:
TDC #1 - 8E, 2I
90 deg. - 4E, 1I
180 deg. - 3E, 8I
270 deg. - 6E, 4I
0 - 5E, 3I
90 deg. - 7E, 6I
180 deg. - 2E, 5I
270 deg. - 1E, 7I
Start at TDC #1, then rotate 90 degrees at a time, setting at .026" cold. If you like, you can then go back after you're done to each cylinder's TDC position and check clearance on that cylinder's two valves, and you'll find that they've closed up to .024", indicating that both valves are still on the ramps at TDC, as I pointed out in the beginning.
Trivia - the point of max inlet lift on the "30-30" cam is at 112 degrees, with a lobe separation angle of 114 degrees (angle between points of max lift, not the geometric center of the lobe - the lobes on the "30-30" cam are asymmetrical).Comment
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Re: 70 LT-1 Valve Adjustment
Steve -
Factory spec is .024"/.030" intake/exhaust (hot) - this spec is effective if it's running, but not if it's static, as the LT-1 exhaust is still on the clearance ramp at TDC, and the intake is just barely off the ramp. Best way is to set the intakes at 90 deg. ATDC and the exhausts at 90 deg. BTDC, and you can do this cold, at .020"/.026", following a 90-degree rotation sequence. I'm e-mailing you the procedure Duke and I developed for the "30-30" cam; follow the same procedure outlined except use the .020"/.026" clearances instead.Comment
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Re: 70 LT-1 Valve Adjustment
Steve -
Factory spec is .024"/.030" intake/exhaust (hot) - this spec is effective if it's running, but not if it's static, as the LT-1 exhaust is still on the clearance ramp at TDC, and the intake is just barely off the ramp. Best way is to set the intakes at 90 deg. ATDC and the exhausts at 90 deg. BTDC, and you can do this cold, at .020"/.026", following a 90-degree rotation sequence. I'm e-mailing you the procedure Duke and I developed for the "30-30" cam; follow the same procedure outlined except use the .020"/.026" clearances instead.Comment
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We disagree by .001"
I figure the inlet clearance as .024" x 1.37/1.5 = .2192", so if a .021" feeler gage slips in and a .022 doesn't, you're somewhere between .021" and .022".
I'm splitting hairs here, but a "snug .021" or a "loose .020" is just fine.
DukeComment
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We disagree by .001"
I figure the inlet clearance as .024" x 1.37/1.5 = .2192", so if a .021" feeler gage slips in and a .022 doesn't, you're somewhere between .021" and .022".
I'm splitting hairs here, but a "snug .021" or a "loose .020" is just fine.
DukeComment
Comment