Big Block Valvetrain Issue - Impala Tech
Troubleshooting Diagnosing problems

 
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post #1 of 10 (permalink) Old 05-24-2016, 12:54 AM Thread Starter
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Big Block Valvetrain Issue

Question is on my BBC 402. First one is #6 intake rocker arm adjusting nut set's about 2 threads in on stud when adjusted while the other's are the normal 6 to 8 down. Head's are newly rebuilt by a reputable business.
And second is #3 exhaust and #5 intake rocker arm is dry, pushrod's are turning and valves lift the same as other's. Fortunately the arm's, ball's and pushrods are not burnt or blued. When I pulled the pushrods they did have oil in the bottom half.
These are original arm's and was thinking that is it possible that the pushrod seat at the arm is worn to the point that the passage is blocked traveling through it cycle. A good replacement upgrade set of arm's are fairly inexpensive and thinking I might start there. ??? Any other idea's before I start pulling lifter's. Thanks all!!!!
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post #2 of 10 (permalink) Old 05-24-2016, 08:13 AM
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All 402's use an oil gallery behind the rear cam journal cam bearing to feed oil to the lifters. The holes in the cam bearing have to align with the holes drilled in the block to get oil to the journal. Secondary issue is if you are using an oil restricting lifter that has he oil feed hole drilled higher on the lifter body it will be covered a lot more than one that is drilled into the body lower down. The lifter has a reduced diameter to allow oil to pass on to the next lifter and feeds the hole when the lifter is up.


That being said I suspect the problem is internal to the lifter itself. It needs to be taken apart and cleaned as I suspect a previous owner wasn't as rigorous in changing the oil regularly and it could be gummed up internally with varnish. The lifter has to go back on to the same lobe that it came off of so only clean one lifter at a time. You can see an exploded view of the internal parts inside a hydraulic lifter on line if you search for that info.


As to the one short stud with fewer threads that is just the last piece that was made by a screw machine using a piece of bar stock. That little stub of a rod was a little shorter than what the screw machine would cut off, but still within GM's guidelines for an acceptable quality part. I will wager it isn't flat on top as would be needed if you where to run roller rocker arms with poly-lock nuts on top as it couldn't seat the set screw properly.


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post #3 of 10 (permalink) Old 05-25-2016, 09:27 AM Thread Starter
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Good call on the screw in stud, I'll have to check my pics.
As for the two rocker's, I thought so that I had to pull lifter's. Hopefully I can pull those 2 from the head and save some gaskets LOL.
Thanks Dave as always!
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post #4 of 10 (permalink) Old 05-31-2016, 04:53 PM Thread Starter
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Following up on post with another related question. Is the purpose of oiling through the rockers to lubricate the fulcrums via the grooved balls or also the valve stem on a stock setup? I'm aware it's used to cool valve train too.
I'm getting oil through rockers but only a dribble but it's enough to get through the rocker balls onto the studs. Oiling system is a stock Melling pump, metal coupler on driveshaft, 1 piece pushrods and rocker's. The cam is Comps 268H with Comp's HE lifter's. Lash is 0 +1/4 for best result's. Oil pressure is 50 cold / 25-30 hot. Running HR 15-50 oil due to ring's being on higher tolerance side. Thanks all!
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post #5 of 10 (permalink) Old 05-31-2016, 05:33 PM
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A dribble is all you will get with a hydraulic cam as the rockers are at zero lash all the time. With a mechanical cam the rockers actually squirt oil when the rockers go past zero lash.


All you need is a steady cascade of oil dripping off of the spring retainer at idle; to cool the springs, and lubricate the rocker stud ball.


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post #6 of 10 (permalink) Old 05-31-2016, 06:03 PM Thread Starter
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Go another +1/2 lash for a total of 3/4?
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post #7 of 10 (permalink) Old 05-31-2016, 06:38 PM
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The tighter the lash the less lift the cam can deliver. This is because you re loosing the travel that the plunger would otherwise move during a cycle. Leave them too loose and you get broken valve train because the lifters stay pumped up and mostly solid all the time. Oil can enter the lifter body only when it is on the base circle so oiling is not continuous all the time. Too much oil up top can evacuate an oil pan at high RPM as it takes time to run back down through the engine. The thicker the viscosity the slower it travels down through the engine which is why most engine builders now use 0W5 motor oil if the motor was blueprinted to factory spec. This speeds up oil flow and doesn't add to parasitic drag at the oil pump. (A viscosity of zero is the same as water)


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post #8 of 10 (permalink) Old 05-31-2016, 06:56 PM Thread Starter
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Understood. I pulled the cam card and Comps valve adjustment states intake = .000 and exhaust = 000. Am I understanding correctly that Comp recommends 0 lash with no added turns? On their site they post 3/4-1 turn for full travel lifter's and 1/4 for anti-pump's.
Apologies for a relatively simple procedure.
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post #9 of 10 (permalink) Old 05-31-2016, 07:34 PM
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Quote:
Originally Posted by 68imp View Post
Understood. I pulled the cam card and Comps valve adjustment states intake = .000 and exhaust = 000. Am I understanding correctly that Comp recommends 0 lash with no added turns? On their site they post 3/4-1 turn for full travel lifter's and 1/4 for anti-pump's.
Apologies for a relatively simple procedure.

3/4 is correct for stock Morel lifters (what the factory uses as their OEM supplier). Com Cam also sources their flat hydraulic lifters from Morel. The anti-pump ups are a special design lifter with a faster bleed down rate that have different internals than a stock Morel lifter body. Be sure what you have and follow Comps directions.


I only run roller lifters, and even then generally a solid body, but I still follow the cam car recommendations as to valve adjust despite knowing that tighter gap buys me more lift at the valve. If I wanted to risk valve train I might tighten the lifters more but If I really wanted more lift I would just add it to the lobe as I don't buy off the shelf cams; having mine custom ground to my specs). This is something Harvey Crane talked me into doing about a half century ago when I first showed up on his Daytona Beach, FL door step.

http://www.enginebuildermag.com/2012...d-lifters-101/

Here is an article from an Engine builder magazine I subscribe to that explains the benefits and trade offs between the two different types of lifter and how they work. (it really is basic stuff that makes me wonder why I subscribed in the first place as I haven't learned much reading these articles other than what new machine tools are being developed over the years).


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post #10 of 10 (permalink) Old 05-31-2016, 08:38 PM Thread Starter
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Thanks Dave as always.
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