69 400 - loud tapping - Pontiac GTO Forum
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post #1 of 13 (permalink) Old 05-09-2016, 11:40 AM Thread Starter
 
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69 400 - loud tapping

Just got the engine in the GTO running last week for the first time in about 20 years. I was told it had a tick when it was last drive too.

It's a loud tick/ tap from the passenger side front cylinder. When I pulled the valve cover I noticed the very front most rocker and its pushrod is loose. I can grab the pushrod and spin it as well as lift it maybe 1/16 to 3/32" (rough guess).

Now I'm used to LS engines and the preload is set by torqueing the bolt and the length of the pushrod determines the amount of preload. In this case, I would say I have a collapsed lifter and I should replace probably both for this cylinder.

What do the experts say?
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post #2 of 13 (permalink) Old 05-09-2016, 11:47 AM Thread Starter
 
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Doesn't look adjustable to me...
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post #3 of 13 (permalink) Old 05-09-2016, 02:53 PM
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Originally Posted by xWoodx View Post
Doesn't look adjustable to me...
It's adjustable, I would recommend a set of Polylocks.

You will need a mark on the dampener at 180 degrees from TDC.If yours doesn't have a mark,take a piece of string or straight edge and go from the TDC mark through the crank bolt and make a mark on the other side of dampener.This doesn't have to be perfect.
Number 1 piston at Top Dead Center (TDC) on compression stroke.
Adjust intake valve on #2 and #7 ;exhaust valves #4 and #8 .

Rotate crankshaft 180 degrees clockwise and adjust intake valve on #1 and #8 ;
exhaust valves #3 and #6 .

Rotate crankshaft 180 degrees again (TDC) and adjust intake valves #3 and #4 ;
exhaust valves #5 and #7 .

Rotate crankshaft again 180 degrees and adjust intake valves #5 and #6 ;
exhaust valves #1 and #2 .

Use 7/16 studs with polylocks (locking nuts with a setscrew),turn down
adjuster nut slowly while spinning pushrod back and forth with other hand until
all play is removed WITHOUT pushing lifter cup down into body.You should
JUST feel the pushrod get hard to spin.Then turn an additional 1/2-1 full
turn and lock it.

Rocker Arm Adjusting by Wallace Racing-Home of Pontiac Powered Firebirds,Trans Ams,and Dragsters
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post #4 of 13 (permalink) Old 05-09-2016, 03:09 PM
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Hoo boy --- lots of variations on this one. If it has the original factory style Pontiac valve train (rockers, studs, balls, nuts) then it's not adjustable. The correct installation is to torque the rocker nuts to the specified value (the exact value escapes my feeble memory at the moment). They "bottom" on the bottlenecked part of the rocker studs. That's with everything original, everything in good shape, etc.

However, if anything has been changed fro original (perhaps by a previous owner) or is overly worn (rocker nuts "loose" from having been installed/reinstalled a multitude of times, then that procedure may not work for you.

I'm a big fan of "poly lock" rocker nuts because of their positive adjustment capability. I'm also a big fan of replacing the factory bottleneck studs with the beefier 7/16's ones.

If there's any slack at all in that one pushrod as you've described, then that's going to be the source of your noise. Question is, why? Is it because the rocker is loose, a collapsed lifter, or something more bothersome such as a flattened cam lobe... That's to be figured out.

Also, the adjustment procedure GR described will certainly work - most of the time. If the engine has an aftermarket cam with a lot of extra duration over stock, it may not. If you want to be certain, use a wrench on the balancer bolt to turn the engine over until you see #1 exhaust value just beginning to open - then adjust #1 intake. Turn it a little more until exhaust valve #8 is beginning to open, adjust #8 intake --- and so on in firing order sequence until you've adjusted all the intake valves. Now start over with #1 , turning the engine over by hand until you see #1 intake just starting to *CLOSE*, adjust #1 exhaust... etc. until you're done. It takes longer, and your arm might get a little tired from all the hand cranking, but it guaranteed to be right if you're not sure what kind of cam you're running.

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post #5 of 13 (permalink) Old 05-09-2016, 05:40 PM
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Bring #2 up to TDC on the compression stroke and begin to tighten to torque to spec, if the valve starts to move STOP! or you will bend a valve.
If this is the case go with the zero lash procedure.
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post #6 of 13 (permalink) Old 05-09-2016, 07:50 PM Thread Starter
 
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Ok, so I get what you guys are saying, but the nut on the rocker is tight and there is no pressure on the pushrod, unless I'm on a lift part of the cam lobe (valve opening).

I looked up the instructions for poly lick adjustment yesterday and that makes sense how it is adjustable. I can't see any possible adjustment in this.

Surely this confirms a bad lifter that has collapsed? Or a bent pushrod.
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post #7 of 13 (permalink) Old 05-10-2016, 06:19 PM
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Possibly, pull the rocker and pull the pushrod and check it.
I just pulled the pushrod from the same position today with the same loud tick after driving it and this is what I found.
A new set of Magnum pushrods is on it's way from Comp Cams.
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post #8 of 13 (permalink) Old 05-10-2016, 06:41 PM
 
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I'm no expert but had that problem in my 68. Thirty five years ago. Take valve cover off snd start engine and watch that lifter . This has to be quick or you will have a mess. You will see the problem in ten seconds . I bet you have a collapsed lifter. Easy cheap fix . Replaced all my lifter and never adjusted any but maybe you are suppose to but ran fine . Just soak in oil over night and put back in . Doug
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post #9 of 13 (permalink) Old 05-11-2016, 10:54 PM Thread Starter
 
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Ok, so I decided I'm going to replace the cam and all the lifters as the pushrod looked fine. I'd rather do it all once and not have to redo things so I'm going to pull the engine and clean it up, refresh it and give it a fresh coat of paint.

Here's the parts I'm looking at

Crower cam 60916
Crower Power Beast Performance Level 4 Camshafts 60916 - Free Shipping on Orders Over $99 at Summit Racing

summit brand lifters lifters
Summit Racing® Hydraulic Lifters SUM-HT951 - Free Shipping on Orders Over $99 at Summit Racing

Crower 68404 valve springs
Crower Performance Valve Springs 68404-16 - Free Shipping on Orders Over $99 at Summit Racing

Gaskets
Mr. Gasket Cam Change Gasket Sets 4422 - Free Shipping on Orders Over $99 at Summit Racing

timing chain
http://www.summitracing.com/parts/cc...w/make/pontiac

oil additive
http://www.summitracing.com/parts/cc...FQmRaQod1bMEUg

I'm still very confused on what to do with the rockers, pushrods, studs and poly locks. Any help/links and recommendations are appreciated. If something on my list looks off or I'm missing something else, let me know.

1969 400 w/62 heads -I'm told around 9.8CR...thick head gasket to drop CR? 9.4?
wide ratio m20 4 speed,

1970 GTO 400 ~ 4 Speed
2008 G8 GT
2005 GTO - Gone

Last edited by xWoodx; 05-11-2016 at 11:23 PM.
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post #10 of 13 (permalink) Old 05-12-2016, 10:01 AM
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The actual combustion chamber sizes on even untouched original Pontiac heads can vary somewhat - enough to make a difference, so what I'm about to say here is all based on factory "nominal" measurements on everything. Which are:
#62 chamber volume: 72 cc's
Piston valve reliefs: 6 cc's
Compressed head gasket thickness: 0.045"
Bore size (assuming +0.030 overbore): 4.150
Stroke: 3.75
Piston deck clearance: 0.020

Put all that into a blender and do the math, and it works out to a compression ratio of 10.000:1

Changing any of those measurements changes compression ratio accordingly and it doesn't take much. Adding just 2 cc's of volume somewhere in there drops it to 9.8:1.

I don't recommend using fat head gaskets unless there's just no other solution available - the reason is that adding that additional clearance between the highest point of the piston and the lowest part of the chamber does some pretty awful things to combustion efficiency and also in some cases make it MORE likely that you're going to have detonation problems. The usual solutions are changing pistons to some that have dished tops (make sure they're D-shaped dishes and not round -- for the same reason that fat gaskets are 'bad'), machining the combustion chambers larger (hard to get "enough" additional volume this way and also can be touch to find someone who can do it right), or changing to different heads with larger chambers.

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