Quote:
Originally Posted by car4jim
Theory 1: I replaced a bad lifter with another bad lifter. What are the chances?? It was a used lifter with no working history??!! Possible??
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From what I understand, lifters "break-in" by developing a unique wear pattern in concert with the camshaft....however, my experience with roller lifters is limited, so if that is not the case with rollers the rest of my post will be just plain wrong....
Before the days of roller lifters, if you took all of your lifters out and didn't keep track of which lifter bore they came from so that you could replace EVERY lifter on the same camshaft lobe from which it came, you ran a risk of wiping the cam lobes out. The lifters don't have to be bad (per your Q about replacing a bad lifter with another bad lifter), they just have to be different USED lifters going onto a lobe for which they were not broken in.
Re-using used lifters is just not a good risk...a friend who did "shade tree" mechanic work in his driveway replaced the cam in a BBC once and against my advice to get new lifters he just put the used lifters back in...wiped all the lobes off in a very short time and had to replace the cam AND the lifters again.
Quote:
Originally Posted by Gaz64
Have you inspected the cam lobes with the suspect lifters out?
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That's where I'd start...get that cam out of there and mic the lobes to see if you've wiped out enough lift that the valve-train has developed enough clearance that the lifter is separating from the cam lobe as the engine runs (the tapping noise may be the lifter's roller regaining contact with the lobe of the cam).
As much as I hate to say it, you might need not only new lifters, but also a new cam...that is, unless roller lifters don't "wear in" to a cam lobe like the older style lifters did...which is a distinct possibility, given the "old school" nature of my mechanical experience.
I'm hoping I'm wrong....
Cheers!
Dugly
