IML: different lifter reasons
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IML: different lifter reasons



Back when these engines were new, there was a running change in the lifter dimension for either the height overall or the plunger, I dont remember exactly what and when it was. When I was in the parts arena we always showed two different lifters and two different push rods for the RB engines, I think it was 67 and earlier for one, 68 and later for the other. Since you are installing a new cam you will of course get new lifters. IF .. and this is an IF.....the lifter length is radically different from what was in the engine before, then the pushrod length may or may not be right for the combination. This has nothing to do with the cam lift and duration specs, its purely a function of the pushrod and lifter combination being used.

You have to think of it this way, a hydraulic lifter is just basically a little oil pressure fed hydraulic cylinder that has the ability to automatically and exactly compensate for whatever valve lash is needed, no excessive clearance and no tight valves. The little plunger in the lifter has only a certain amount of range it can travel thru, as I recall its somewhere around maybe 1/4 to 3/8 of an inch...I havent had to take a lifter apart in years and its something you seldom have to deal with. The problem results if the pushrod being used with a particular lifter is too short and the little plunger isnt being pushed down in the lifter bore OR if the pushrod is way too long and the little plunger is pushed down and bottomed in the lifter. IDEALLY the plunger should be about halfway down the lifter.

Most of the time this is never an issue, and seldom during a normal cam and lifter swap is it a problem. The only real world practical thing one can do is after the cam and lifters are installed, check one pushrod by installing a rocker arm and shaft on one side and see how much the lifter plunger goes down into the bore, then manually turn it thru a rotation and see what its doing. By the way, it is extremely easy to drop a lifter or a pushrod down the engine gallery after the cam is in place...and no, Im not going into detail about how I know this. Magnets generally wont get them back out either.

A couple other things...some people pre oil their lifters to get oil into the plungers, some just let the engine oil pressure do it during the first second or two of running and they will clatter a little bit. I prefer to use a drill and a oil pump shaft extension and actually get oil under pressure to everything before I fire it up the first time, but thats just me. Some people will just pull the plugs and crank the engine a bit until they see some oil pressure on the gauge. Whatever you do, when the engine runs BE SURE to follow the cam makers directions on break in, if you let it idle before that cam is broken in youre not doing it any favors. Make sure you put whatever break in lube they specify on all the cam lobes and lifters.

Another new thing, apparently from some info on Allpar and other sources, the new modern ultra high tech oils out there have exhibited a tendancy to not provide proper anti wear properties on cams and lifters such as the aftermarket cams or cams with higher than stock spring rates. This has been discussed on the MML as well, the reason appears to be the amount of zinc additives in the oil are rather low for emissions purposes. Several people have posted to Allpar and the MML about using break in lubes such as the one GM offers, or just using oils such as the Delo 400 or Rotella multi weights that many current diesels use. Just food for thought.

Mikey
62 Crown Coupe

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