Maurice

I see everyone "breaking in" their new cams. I am sure that this is a conditioning process that must happen to make the cam run correctly, but why isn't it already done? It seems like this could be done in mass quantities at the factory and save every 20-30 minutes and an oil change when they get it. Just wondering what exactly this process is doing to the cam that modern technology couldn't do already. I am getting ready to replace all my lifters and I have been told that I need to break them in also.

Thanks in advance for what I am about to learn. :D

soundguy

You are breaking in the outside edge of the cam lobe and a circular section of the lifter face. Cam lobes are ground at an angle. (one side is 'fatter' than the other by a couple of thousanths) Half of them are ground with the 'fat' edge towards the front of the engine and half towards the back. (this arrangement allows the valve train pressure to keep the cam stationary from front to back - i.e. 'floating') Each lifter sees a unique contact area because no two blocks are machined absolutely the same. Each lifter bore is ever-so-slightly misaligned with it's neighbor and with it's counterpart in any other block. (we're talking a few thousanths here, but it's an important few)

The lifter rides on the outside edge of the cam lobe which causes it (and it's associated pushrod) to spin. This creates a circular wear pattern that is unique to each lifter & lobe. Since the area of contact is so incredibly small, the valve spring pressure translates to thousands of pounds per square inch. That's why it's a bad idea to swap lifters around after break-in. Once the parts establish a wear pattern, they stop wearing as fast. Mix them up and they have to break in again, only this time you're working with two existing wear patterns that don't match. In some circumstances, that can strip a camlobe flat in just a few seconds.

That's essentially why cams can't be 'pre-broken-in'. No two blocks are the same, so it's much better to mate 'virgin' surfaces and break them in where they are going to live for the rest of their lives.

daniel77350

I think breaking in the cam gets the lifters seated on the lobes. This couldn't be done at the factory, because when you put the cam and lifters in(assuming you got the exact same lifters and cam that was broken in at the factory), you'd still have to make sure the correct lifter was on the correct lobe, and "spun" so it lines up correctly...it just makes more since for you to do it at home IMO. Not to mention rods...that'd be the same deal I think.

Daniel

Techno

Breaking in an engine means the surfaces that touch each other, wear away to mate properly. You can't pre-machine any of this since its such a small amount. Which ever part is being 'broke in' is just wearing slightly to mate as perfectly as possible. A high degree of accuracy is .00001" even this is very loose when you consider a contact area. To compound all of this the entire engine changes shape and size when it heats up. The pistons and bores increase in size. Rods increase in length. Things that impose a stress can change the shape of a part-like the heads torqued on.
So the heavily loaded cam and lifter faces break in very fast, the lightly loaded rings and walls more time.


Read on another site that lapping in the rings before installation reduces cylinder wear and ring wear. I forgot the tool, a sunnen lap tool? The ring is put on a piston and stroked in a bore(the tool), this finishes the ring perfectly. It only takes a few strokes but removes any sharp edges that the rings have that scratch the new crosshatched bores. When installed in the engine the rings still wear in to mate with the cylinders but don't cause any damage. And end up sealing better. He mentioned that new rings weren't flat or round and you could see the shiny surfaces that were out of spec. after lapping. :crazy:

tnt76vette

Ditto all of the above.....and certainly all of that cam lube that you liberally smear on everything new should be flushed out right away w/an oil change after your 1/2 hr. breakin anyway, so you cant get around that either...... :nono:

Maurice

Thanks for all the info! Now for my next question. Why do I have to use that "break-in lube". Shouldn't regular oil be good enough?

tnt76vette

Believe ALL cam makers recommend and/or furnish cam lube....why would you want to go against their wishes? :nonod: :seeya :flag

Maurice

Not trying to go against anyones wishes. Just trying to understand what the thick red sticky gunk does that nice smooth slick oil wouldn't do. :D I did the break-in by the book, again. I replaced one lifter last week, broke it in, realized that another lifter was also bad, so I replaced all of them today and did the break in proceedure again.