1966 Impala 396 She's alive! - Impala Tech
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post #1 of 6 (permalink) Old 05-14-2016, 01:21 PM Thread Starter
 
 
Join Date: Apr 2010
Location: Virginia
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1966 Impala 396 She's alive!


After getting from the previous owner who replaced the cam, replaced the rockers, push rods, guide plates, timing chain, I installed a new fuel pump only because it was included with the car. Double checked his rocker adjustments good thing) one was loose. installed intake, water pump, alt, rad, all new hoses, and a base timing of 5 adv.. she runs great...

fires on first turn and no issues, leaks, just a sweet big block
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post #2 of 6 (permalink) Old 05-14-2016, 01:57 PM
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Humor me and check that formerly loose rocker again in about a week's time to see if it is loose again. If so you have a cam lobe going flat.


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post #3 of 6 (permalink) Old 05-14-2016, 05:27 PM
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If its the original 66 396 the cam has to have a grove cut into it for proper oiling. I had a machine shop do mine.
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post #4 of 6 (permalink) Old 05-14-2016, 07:19 PM
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The 1965 and the '66 396 (and 1966 427 engines) had to have the groove to oil the top end. Without it your oil pressure will be blowing open the by-pass valve and your rockers are rubbing steel on steel without any lubrication or cooling oil for the rockers and the valve springs. 1967 and up the groove was machined into the block behind the cam bearing. Additionally even with a grooved cam it takes special 1965-'66 cam bearings with addition oil feed holes to line up when installing there rear cam bearing to feed both sides properly.





Here is an example of a flat tappet cam that has gone flat. Imagine the missing part of that lobe reduced to metal filings so small it passes through your ten micron oil filter running around in your engine pumped by the oil pump into every nock and cranny in the motor. Most get embed in the bearings and score the crank and cam journals (no lose with the cam as it is junk anyway).





That is why I asked you to check your valve lash again after adjusting them. If it is loose again after driving daily for a week or so it means that missing gap used to be metal that came off the cast iron cam lobe as BBC dose not use pressed in rocker arm studs the way a SBC dose (a stud pulling out is another source for a growing valve adjustment air gap).


Reason I mention it is that sounds like a fairly healthy aftermarket cam, and as such it probably has stiffer valve springs. Stiffer valve springs do a better job of controlling the valves, but that added pressure on the tappet going over the nose combined with the loss of ZDDP in modern motor oils generally results in a flat tappet cam failure.


Not just flat tappets suffer from lack of ZDDP. Modern LS Chevy engines are failing inside of warranty due to cam failures as well; and they use a roller tappet. It just takes longer for the wear to appear.

A pair of cams that failed in service that Chevrolet that were replaced under warranty.




Note the brushed look of the cam bearing journal above. The Crank looks the same as the metal is like sand paper.





ZDDP mkes yor rings and cylinder walls or any metal on metal wear point last longer as well.


Big Dave
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post #5 of 6 (permalink) Old 05-14-2016, 07:25 PM Thread Starter
 
 
Join Date: Apr 2010
Location: Virginia
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It a new Edlebrock cam.. Then engine was never started after the new kit was installed... the original small push rods with the ball tip failed so a new kit was installed... He just did not doube check all static adjustments after installing a new cam kit..
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post #6 of 6 (permalink) Old 05-14-2016, 08:38 PM
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I believe that Elgin grinds the cams to Edelbrock specs (or just pulls a cam out of the catalog as there are a lot of common grinds by spec). As you no doubt know Edelbrock is a foundry casting metal; not a cam grinder. If you have the cam card you may be able to find more info about your cam on Elgin's web site.


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