Flat tappet lifters, wear patterns, cam lobe taper and other things. Let's swap opinions and ideas.

[BSB67]

Geoff - To your original comment/question regarding less contact mileage between the lifter and lobe on a re-grind/smaller base being potentially better - I don't know.

But for a given lobe profile/lobe area, the smaller the base circle, the harder the lobe whacks the lifter. The contact patch effectively moves further out on the lifter surface, kinda like a faster rate lobe would, but its not a faster rate lobe. I think this would be less beneficial.

 

[Geoff 2]

Thanks for the reply. I do not see a problem with the contact patch moving further out on the lifter surface. The actual contact area is very small because of the lobe taper/crown on the lifter. It is so small that the oil gets squeezed out because of the high, concentrated load; the end result is the wear on the lobes & lifters.....
The benefit I see with a smaller lobe is:
- the lifter is in contact with the lobe over a lesser distance & for a shorter time.
- since the wear comes from contact of the two parts, reducing the time they are in contact should improve component life.
- the speed of the lifter travelling around the lobe will be less with a smaller lobe. This should reduce friction. Friction causes heat. Reducing friction [ heat ] should help the oil film survive between the parts.

 

[Krooser]

Most of us have heard of how engines with flat tappet camshafts have had increased failures in the past 15-20 years. There are a bunch of opinions on what is to blame but so far, I have seen no 100% smoking gun on the exact cause. The potential causes are numerous.
Reduced zinc in oil.
Camshafts and lifters made with softer metal than before.
Lower quality machining from Chinese factories.
Lifters that don't spin in the bores.
Valvesprings too stiff.
Improper break in.
Etc, etc....
While all of those things may be true AND if you have more than one of those situations together, the chances of a failure seem to grow exponentially.
I know that there are several threads on this site covering this topic, I was hoping to expand a bit on what has already been mentioned.
Being one with a curious mind, I wonder about a few things...
We have been told that with flat tappet systems, the lifters mate to the lobes. How? I've read that they establish a pattern to each other and that to swap in another lifter, it must be NEW and that the "break in" starts all over for that lifter.
Why? Has anyone ever published pictures and measurements of the actual wear patterns?
Who remembers Jim LaRoy/IQ52 ? he mentioned before that he has swapped lifters around and even reused them in dyno testing and had no failures. How is this possible?
I remember a buddy going out to the junkyard and pulling a couple lifters from an engine to swap into his engine. He had a couple sticky lifters in an old beater. I don't recall any future troubles that he had.
I did the same to a stock 318 years ago.

Interestingly...in the Cummins 6.7 world the roller lifter failures have created a market for retrofit mushroom flat tappet conversions!!!

Better reliability and less cost!