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Old 06-21-2006, 08:49 PM
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installing a Pete Jackson Gear Drive in a SPC

I am installing a PJ gear drive in 1970 LT1 370 hp and changing mech. cam .484 lift to a mech cam .520 lift. I lost my instructions to gear drive installation need help with the dot alignment thing. I set the dot on the crank @ 12:00 and the dot on the cam @ 12:00 (#1 piston up at max). I installed roller- rocker with .016 set clearance on intake and exhaust at this position. I rotated crank clockwise until max lift was reached for #1 intake and exhaust. At these postions, I over- traveled valve by hand to measure valve to piston clearance (note: I changed out valve spring to a 3 lb spring for this test only) Is this procedure correct??? I thought my piston would have been closer to valve. Am I checking clearance at proper timing?? Help please!


Last edited by tim gleason; 06-22-2006 at 07:33 PM.
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Old 06-22-2006, 06:07 AM Moderator

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Ok well, where to start???

You can align the dots at 12:00 or 6:00 because it is a direct 1/2 speed relationship between the cam and crank. In other words if you put the crank at 12:00 and the cam at 12:00 and then rotate the engine 1 full turn the dots are now at 12:00 and 6:00.... They just need to be aligned,,,, really the cam needs to be degreed. But that another story..

You need to check the piston to valve clearance from 20 deg BTDC to 20deg ATDC.. this is the location where the valve is closest to the piston, not at max valve lift... I personally hate checking springs, all my measurments are done in race ready condition...thats just my opinion... In your case the checking springs will work.

Rotate the engine until your 20 deg BTDC install the dial indicator on the retainer, make sure the plunger travel is parallel to the spring travel. Pull the valve open until it contacts the piston and check you indicator reading, then rotate the engine 2 degrees to 18 BTDC and check again. Do this every 2 deg until you get to 20 deg ATDC....

Don't get suprised if you travel the indicator .250" or more and never touch the piston.....

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Old 06-22-2006, 07:54 PM
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pj gear drive & valve clearance check

thanks Keith for help . i did as you directed the result look good.
closest was @ 4 deg. before tdc valve clearance was .253" on exhaust
and .278" on intake . does this seem correct?? remember 1970 LT-1 was 11:1
comp. ratio , so my piston are trw with .1 high dome (#L2304 TRW piston). also note using EDLELBROCK E-TEC 200 ALUM HEADS. EVERYONE was saying
my valves would probably hit piston. any thougths!?!?

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