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post #1 of 17 (permalink) Old 06-11-2018, 09:06 AM Thread Starter
 
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Bad lifter

As I was adjusting valve lash on cylinder number 3 intake the adjusting nut bottoms out before lifter gets hard could this be a bad lifter and if so would this be a source for low vacuum reading.

Last edited by Hotsticker1; 06-11-2018 at 09:35 AM.
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post #2 of 17 (permalink) Old 06-11-2018, 12:52 PM
 
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"the adjusting nut bottoms out before lifter gets hard"

PJ: Huh??? Describe how you are adjusting the lifters and why?
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post #3 of 17 (permalink) Old 06-11-2018, 02:50 PM Thread Starter
 
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Ok I have a low vacuum reading and have changed out all vacuum hoses, blocked off the end carbs checked intake and no leakage there. Running about 12 degrees TDC initial timing, rebuilt carbs. Accelerates ok but still kind of a rough idle. I have receipts saying heads have been milled so it is my understanding that adjustable poly locks shou be installed if heads have been milled. As I was adjusting valve lash while running intake valve on number 3 cylinder would bottom out before 0 lash and I broke the nut so I put the original nut back on and torqued to 20 ft lbs and still could nut get 0 lash.All other valves adjusted fine using poly locks. Carb is running rich and I believe is because of low vacuum around 10.
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post #4 of 17 (permalink) Old 06-11-2018, 04:59 PM
 
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Originally Posted by Hotsticker1 View Post
Ok I have a low vacuum reading and have changed out all vacuum hoses, blocked off the end carbs checked intake and no leakage there. Running about 12 degrees TDC initial timing, rebuilt carbs. Accelerates ok but still kind of a rough idle. I have receipts saying heads have been milled so it is my understanding that adjustable poly locks shou be installed if heads have been milled. As I was adjusting valve lash while running intake valve on number 3 cylinder would bottom out before 0 lash and I broke the nut so I put the original nut back on and torqued to 20 ft lbs and still could nut get 0 lash.All other valves adjusted fine using poly locks. Carb is running rich and I believe is because of low vacuum around 10.
Don't like, nor trust, the method you described. Adjust the valves while the engine is running to get "zero lash" then you will know that all valves are set the same. Different lifter manufacturers recommend different specs when doing it your way - unless you are going by the manufacturers recommendations.

Depending on how much the heads have been milled/surfaced, adjusting valves with poly locks may or may not work. If milled a lot, different pushrod lengths may have been needed. The best way to to check the contact "footprint" that you get from the rocker arm sliding across the top of the valve stem - it should about midway across the stem over its full travel. If you see that the "footprint" is more towards the rear or front on the valve stem, then you may need pushrods to correct this.

Low vacuum can be a by product of the cam specs, worn valves or not seating properly, sticking valve (too tight on the clearances or bent), weak valve springs, incorrect cam timing, worn cam lobe, bad/worn lifters, PCV valve/system no working correctly, bad head gasket, worn/broke rings, cracked intake manifold, cracked head, cracked piston, bad modulator on an automatic trans if using one, exhaust restriction, an ignition/timing problem.

Why 12 degrees BTDC? Have you tried any other positions to see if the vacuum increases? - could be the balancer is off. What is your total timing - 12 degrees initial PLUS mechanical from the distributor? What RPM does total come in at?

Have you done a compression test?
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post #5 of 17 (permalink) Old 06-11-2018, 05:21 PM Thread Starter
 
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I did adjust valve lash while engine running. I got all valves at zero lash except for one and it bottomed out and broke the nut before I could get zero lash. All other symptoms you mentioned have checked good. Heads have new valves and guides. Motor has about 1000 mi on rebuild. I have not done a compression check yet. I will tomorrow and post results. The initial timing is 12 degrees advanced. Accelerates great just seems a little shaky at idle and is running rich. I have turned idle mixture screws in till it starts missing and then back out till it smooths out but still not right on. Thanks for your help
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post #6 of 17 (permalink) Old 06-11-2018, 05:42 PM
 
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How much do you tighten the poly locks after the "ticking" stops? Typically, I go 1/4 turn more, but some will go up to 1 full turn depending on lifter brand recommendation.

If you can, post cam specs, I am curious as to the valve overlap on the cam. Valve overlap increases as the more radical the cam gets and the shaky vacuum/idle could be from the cam selection.

With only 1000 miles on the engine, I would call the guy who rebuilt it and run the situation by him to see if he has any comments or suggestions.

Still, many things to check and you have to do one thing at a time. Sometimes it takes knowing what it isn't in order to narrow it down to what it is.
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post #7 of 17 (permalink) Old 06-11-2018, 06:17 PM
 
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Originally Posted by PontiacJim View Post
How much do you tighten the poly locks after the "ticking" stops? Typically, I go 1/4 turn more, but some will go up to 1 full turn depending on lifter brand recommendation.

If you can, post cam specs, I am curious as to the valve overlap on the cam. Valve overlap increases as the more radical the cam gets and the shaky vacuum/idle could be from the cam selection.

With only 1000 miles on the engine, I would call the guy who rebuilt it and run the situation by him to see if he has any comments or suggestions.

Still, many things to check and you have to do one thing at a time. Sometimes it takes knowing what it isn't in order to narrow it down to what it is.
Hey Jim, I must be missing something here. Is this a Chevy motor you are working on?

I remember the push in studs being a problem as they can work out of the head. We used a tool to check the stud height from the deck when we had a lifter ticking. More often than not we drove the stud to the proper height and the lifter issue went away. (that is if the cam wasn't going flat) Different with the screw in studs as that never happened with them, they just broke.
(I still have a tool I made to remove the push in studs when they broke off clean with the head.) If the stud became loose I remember they had an oversized stud you reamed the hole and drove in the new stud.
I don't ever remember seeing an adjustable stud in a Pontiac I worked on, always ran them down to 20ftlbs and called it good.

Chevys were fully adjustable in that day as I hated doing those...oily mess especially with the big oil pump, squirting oil over the fenders :-)

Cheers!
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post #8 of 17 (permalink) Old 06-11-2018, 09:25 PM
 
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Hey Jim, I must be missing something here. Is this a Chevy motor you are working on?

I remember the push in studs being a problem as they can work out of the head. We used a tool to check the stud height from the deck when we had a lifter ticking. More often than not we drove the stud to the proper height and the lifter issue went away. (that is if the cam wasn't going flat) Different with the screw in studs as that never happened with them, they just broke.
(I still have a tool I made to remove the push in studs when they broke off clean with the head.) If the stud became loose I remember they had an oversized stud you reamed the hole and drove in the new stud.
I don't ever remember seeing an adjustable stud in a Pontiac I worked on, always ran them down to 20ftlbs and called it good.

Chevys were fully adjustable in that day as I hated doing those...oily mess especially with the big oil pump, squirting oil over the fenders :-)

Cheers!

Not my engine, its Hotsticker1 as this is his post.

But to answer your question, and it sounds like you had your share of work on them, the early/low performance Pontiac heads used the pressed-in studs. These can pull up if you start going bigger cam/stronger valve springs or probably revving them way more than they should go on a regular basis.

In 1967, the GTO and high performance heads used screw-in bottle neck rocker studs (7/16" at the base tapering down to a 3/8" threaded top - thus "bottle neck").

Both the press-in and screw-in studs used the torque-down method rocker arm nut where you simply cinched it down to 20-25 ft lbs of torque and were done with it. However, to increase the useable revs available in the engine, the trick was to adjust the lifters to "zero lash" using the poly locks. The "Bobcat" performance package that was available for the Pontiac included a rocker arm nut that was more like a nylock type locking nut where it would not back off like the stock nut would if it were not torqued down.

(I have a set of clips made specifically for snapping right onto the top of the rocker arm covering the oil spurt holes and minimizing all the oily mess. Bought them 35 years ago and still use them. LOL)

By backing off the rocker arm nuts while the engine was running would cause the lifter to start clicking. At that point, you would turn the nut back down until the clicking stopped, then turn the nylon lock not (or the poly lock's) 1/4 turn more. This put the plunger in the lifter at a higher point within its body and prevented lifter pump - kind of like turning the hydraulic lifter into a bit of a solid lifter. This gained more useable RPM's out of the engine so you could spin it more like 6,000 RPM's.

As you pointed out, the bottle neck screw-in studs could break off at the bottle neck where it tapered down. So the fix, and what most do in their rebuild and when going with a bigger cam, is to use an ARP brand Big Block screw-in rocker arm stud which is 7/16" from top to bottom and fits right in. Then you have to use the poly lock's to lock down the rocker arms.

If the heads/block have been milled and the valve train has not been adjusted to compensate, the hydraulic lifters/valves could be adjusted just a tad too tight using the factory nuts which could hold the valve open just enough to create an engine vacuum problem. Same goes with the poly locks when using them to adjust the lifters/valves. Just something to watch for and double check if having low or erratic vacuum readings.

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post #9 of 17 (permalink) Old 06-11-2018, 09:46 PM
 
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This post contains my personal opinion, based on my experience. I have no quarrel with anyone who has a different opinion.


"...Adjust the valves while the engine is running to get "zero lash"..."


That is definitely the "old school" method. Don't think most guys do it that way nowadays.

Makes a big mess & oil smoke, coming off the exhaust manifolds or headers.

I always made the adjustments before cranking the engine. When using poly-locks, putting a slight preload on the lifter plunger, up to 1/4 turn past zero, I never had a problem with any Pontiac engine, street or strip.

I'll add this. In order to insure that the poly-lock won't back off, I tighten the the lock screw at zero, then turn the outer nut a little more. This causes the bottom of the lock screw to dig into the top of the stud, so that it won't back off. If you simply tighten the lock screw AFTER making the final adjustment, the poly-locks have been known to back off.

But, I suppose there are guys who insist on doing things the same way they have done them all their lives.

So, to each his own. I suppose, as the say, "there's more than one way to skin a cat".

PS: I don't personally know anybody that has skinned a cat.

Last edited by bigD; 06-11-2018 at 10:04 PM.
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post #10 of 17 (permalink) Old 06-11-2018, 09:51 PM
 
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Ok, thanks for that. None of the guys in my shop were allowed to really monkey around with the hot rod stuff, you know the old liability thing...and the 70's.

I did work on all stock engines only so those performance mods I did not do either. I just did what ever the manual called for. I believe their thinking at the time was not to put a cam bigger than the 068 :-) and stock valve springs. Those that did rev the old ponchos busted piston skirts, especially that 455 with the cast pistons!

Heck, saw a ton of broken push in and screw in studs, broken springs and engines that still ran with 12-18 degrees slop in the timing chain as well as the cam gears with all the teeth stripped off in the pan! We even tore down lifters, clean 'em and if they passed the leak down re-used them.

Last edited by Bob Young; 06-11-2018 at 10:43 PM.
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