valve setting - Pontiac GTO Forum
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post #1 of 14 (permalink) Old 03-28-2011, 04:39 PM Thread Starter
 
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valve setting

Just installed a new comp thumper cam (flat-tappet) in my 68 GTO. I need to set my valves. Any ideas on were I need to begin and in what order I need to adjust them in, and how to adjust them. I am at TDC right now. My 68 has a 400 stock engine with stock heads, 4 speed, 3:55 rearend, drum brakes, no air, no power steering, weekend driver. I am not sure what my next move is with my adjustments.


Thanks
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post #2 of 14 (permalink) Old 03-28-2011, 05:09 PM
 
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Just installed a new comp thumper cam (flat-tappet) in my 68 GTO. I need to set my valves. Any ideas on were I need to begin and in what order I need to adjust them in, and how to adjust them. I am at TDC right now. My 68 has a 400 stock engine with stock heads, 4 speed, 3:55 rearend, drum brakes, no air, no power steering, weekend driver. I am not sure what my next move is with my adjustments.


Thanks
do you have hydralic or solid lifters? it makes a difference.
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post #3 of 14 (permalink) Old 03-28-2011, 05:57 PM
 
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Comp cams comes with a real good instuctions booklet on how to adjust the valves. You can also go to their website and look up the instructions.
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post #4 of 14 (permalink) Old 03-28-2011, 08:53 PM Thread Starter
 
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valve setting

hydrolic lifters
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post #5 of 14 (permalink) Old 03-28-2011, 09:12 PM
 
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hydrolic lifters
ok. are you using aftermarket locking adjusting nuts or trying to use the stock pontiac nuts? the stock pontiac nuts are non adjustable. you just torque them down to 20 lbs and thats it. the problem is with aftermarket cams you sometimes need to go to aftermarket locking nuts to get the correct setting.
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post #6 of 14 (permalink) Old 03-29-2011, 07:33 AM
 
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This might help:

Pontiac Rocker Arm Adjustment

Rick

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post #7 of 14 (permalink) Old 03-29-2011, 08:06 AM
 
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How much "lift" does that cam "sport"? Anything beyond .470" REQUIRES different valve springs. The stock ones simply won't "do".

Jim
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post #8 of 14 (permalink) Old 03-31-2011, 08:52 AM Thread Starter
 
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camshaft

He guys, I installed a nw comp cam and lifters yesterday. (275 lift) in my 68 GTO 400. I am having trouble with my valve settings. I began at Number 1 at TDC and tightened until push rod had resistance then went 1/2 turn more. I continued the sequence in the correct order. The engined fired right up, but the nuts slowly back off after 5 minutes of running at 2,000 rpm. Do I need to toque them to 25lbs, some instructions say to do that and some say not to. As of right now the nuts will back off because 1/2 turn past tension on the push rods is not very tight. All help is welcomed. Thanks
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post #9 of 14 (permalink) Old 03-31-2011, 09:05 AM
 
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He guys, I installed a nw comp cam and lifters yesterday. (275 lift) in my 68 GTO 400. I am having trouble with my valve settings. I began at Number 1 at TDC and tightened until push rod had resistance then went 1/2 turn more. I continued the sequence in the correct order. The engined fired right up, but the nuts slowly back off after 5 minutes of running at 2,000 rpm. Do I need to toque them to 25lbs, some instructions say to do that and some say not to. As of right now the nuts will back off because 1/2 turn past tension on the push rods is not very tight. All help is welcomed. Thanks
if you are going to adjust that way you need locking nuts. stock pontiac nuts are non adjustable. you just bottom them out on the stud and torque to 20 lbs.

it sounds like your geometry is close enough to use the stock nuts. i would just torque them to 20 lbs and see if it runs. if it runs and there is no slack in the rockers you should be good to go.
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post #10 of 14 (permalink) Old 03-31-2011, 10:56 AM
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Originally Posted by simmons68 View Post
He guys, I installed a nw comp cam and lifters yesterday. (275 lift) in my 68 GTO 400. I am having trouble with my valve settings. I began at Number 1 at TDC and tightened until push rod had resistance then went 1/2 turn more. I continued the sequence in the correct order. The engined fired right up, but the nuts slowly back off after 5 minutes of running at 2,000 rpm. Do I need to toque them to 25lbs, some instructions say to do that and some say not to. As of right now the nuts will back off because 1/2 turn past tension on the push rods is not very tight. All help is welcomed. Thanks
Your procedure was correct as far as initial setup for your current cam and valve train geometry, and the motor liked it, but it wouldn't stay in adjustment. I think that right there is telling you that you need an adjustable valve train with locking nuts instead of the factory arrangement. If you're going to do that, then "if it were me" I'd go ahead and take the next step of replacing the factory 'bottle neck" rocker studs with the beefier 7/16" studs. Those bottleneck studs have been known to break off at the neck, especially with "rowdier than stock" cam and springs. Yeah, it's more expense and hassle, but then so is dealing with the aftermath of a broken rocker stud - which can put metal fragments into your oiling system and take out bearings "and stuff".

Bear

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