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Why do you break in a cam?

Discussion in 'The Hokey Ass Message Board' started by EnragedHawk, Jun 12, 2012.

  1. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,109

    EnragedHawk
    Member
    from Waco, TX

    I know I know, this is a super FNG question, but why is it that you have to break in a cam or even an engine? I know that you have to, and I have even read/seen what happens if you don’t. I guess my question could even be, why doesn’t it come from the manufacturer pre-broken in? Or, what actually is breaking in and changing about the cam/engine during this period?

    I did a search but couldn’t find anything. If you know of a thread, please point me in the right direction. Thanks in advance!
     
  2. flatheadpete
    Joined: Oct 29, 2003
    Posts: 10,213

    flatheadpete
    Member
    from Burton, MI

    If ya don't, the cam may break-in the engine. That's bad.
     
  3. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,109

    EnragedHawk
    Member
    from Waco, TX

    Right, I understand that, but what is changing about the cam during the break in period that would cause it to fail otherwise?
     
  4. It's to establish rotation (wear pattern) on the lifters. Engine break-ins do this, as well as "seating" the rings.
     

  5. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,109

    EnragedHawk
    Member
    from Waco, TX

    Ok cool, that makes sense. So is it the cam or the lifters taking on the wear pattern? Or even both?
     
  6. 40FordGuy
    Joined: Mar 24, 2008
    Posts: 2,907

    40FordGuy
    Member

    The main reaso to break in the cam is to mate the cam lobes to the lifter face. The lifters must rotate in order to prevent the cam lobes from wearing a groove into the lifter face. This would also "flatten" the cam lobe(s), which is why the comment about "the cam breaking the engine. The assembly lube that is liberally applied to the cam lobes and lifter faces is somewhat "sticky" (for lack of a better term) in order to make the lifters "spin". Each cam maker has their own instructions for doing this,....but generally, they say to run at 2,000 rpm for 20 minutes. This means that the engine must be in time, fuel in the carb, and no excess cranking. As soon as it fires, and you see oil pressure, throttle it up to the recommended rpm, for the recommended time. Also, be sure to use a zinc additive to your oil, each change after that. There is a good thread about zinc additives and their purpose. A good read.

    4TTRUK
     
  7. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,109

    EnragedHawk
    Member
    from Waco, TX

    Awesome thanks, I think that took care of every bit of my question(s). And yes, I know the thread you're talking about; I read through it a while back. Not being an engine builder, I tend to end my readings on the HAMB with more questions than answers. Thanks again!
     
  8. hotrod40coupe
    Joined: Apr 8, 2007
    Posts: 2,562

    hotrod40coupe
    Member

    What about a roller cam? The lifters don't spin so what am I accomplishing?
     
  9. Pro Shifted
    Joined: May 18, 2010
    Posts: 51

    Pro Shifted
    Member

     
  10. Pro Shifted
    Joined: May 18, 2010
    Posts: 51

    Pro Shifted
    Member

    no break in on a roller cam. install the race springs in the build and hit the strip. the lifters have rollers on the bottom. google "roller lifter"
     
  11. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,109

    EnragedHawk
    Member
    from Waco, TX


    So if I read that right, you send them your cam and lifters and they break it in for you? Would each engine not be a little different depending on rod length and valve spring pressure? Or would you tell them that sort of thing? I'm venturing into an area I know very little about, so bear with me.
     
  12. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,608

    Rusty O'Toole
    Member

    If you examined the parts of an engine under a powerful microscope you would see the surfaces, no matter how carefully made, have a slight rough surface. The purpose of break in is to let these surfaces polish themselves smooth and mate to one another. If you take apart an old engine that has been well maintained the cylinders are polished to a mirror smoothness.

    Pushing a new motor too hard, or running it too hot will cause the oil film to break through and metal on metal contact to occur. This results in the metal getting gouged out and chewed up. In that case the parts will never develop a smooth polish, in fact heavily loaded parts like cam lobes, once the metal is gouged and rutted, will quickly chew away to nothing.

    A new motor with tight clearances will have a lot of friction. Friction causes heat, which causes expansion, which causes even more friction until a critical breakdown occurs. This is why it is necessary to "baby" a new motor until all parts are polished smooth, and friction reduced to a minimum.

    A properly broken in motor will run smoother, cooler, have less friction and develop more power. It will also last much longer before it wears out.

    With today's precision parts and superior lubricants this is not such a big deal as it was say 50 years ago. But flat tappet hot rod cams, with stiff valve springs, still take a real beating. So much so that some guys install stock, soft springs when they build a motor, baby it for a few thousand miles, then install the stiff springs before giving it the works.
     
  13. greg
    Joined: Dec 5, 2006
    Posts: 537

    greg
    Member

    so does it hurt anything to install new lifters on an old cam?
     
  14. 1971BB427
    Joined: Mar 6, 2010
    Posts: 7,090

    1971BB427
    Member
    from Oregon

    Doesn't hurt, but need to break them in.
    Even swapping in just one lifter requires that you go through the cam breakin again, or take the chance of ruining that lifter and adjacent lobe on the cam.
    If you for any reason ever pull lifters you need to be very careful to keep track of what hole they were in and keep them oriented so they go back on the same lobe they came off from. I always make up a box with two rows of 8 holes to keep each lifter in it's place when they go back.
    Another reason I would never put someone else's used cam in an engine without getting a complete set of lifters to go with it. Then I could just do another breakin.
     
  15. RDR
    Joined: May 30, 2009
    Posts: 1,363

    RDR
    Member

    my question would be, when hundreds of thousand of cars were produced ( early engine flat tappets)...were all the engines run to break in the camshafts?...I kind of doubt that.
    I guess they were all started and run at the end of the assy line, but were they run for 20 minutes or so at 2500-3000 RPM ??
    .....Inquiring minds want to know.....
     
  16. swissmike
    Joined: Oct 22, 2003
    Posts: 1,297

    swissmike
    Member

    A crucial aspect of the break in is that the rpm be kept around 2k because below the oil pressure is not sufficient to ensure adequate oil supply to the critical locations.
     
  17. BISHOP
    Joined: Jul 16, 2006
    Posts: 2,571

    BISHOP
    Member

    I have wondered that too.
     
  18. lostn51
    Joined: Jan 24, 2008
    Posts: 1,667

    lostn51
    Member

    My Mom and Dad went to the Ford plant in Dearborn where the were building the Cobra SVT Mustangs and dad told me that when they start the car the thing runs wide open for "X" number of feet 0on the line before they idle it down and drive it off of the line. He said the engineer that was giving the tour told them if it was going to break it would do it then and that they have had a few let go on the line.

    Billy
     
  19. RayJarvis
    Joined: Oct 11, 2010
    Posts: 209

    RayJarvis
    Member

    theres no bad questions just bad answers . this is a good question
     
  20. dreracecar
    Joined: Aug 27, 2009
    Posts: 3,218

    dreracecar
    Member
    from so-cal

    An engine builder down here has a engine run stand with a inline six to rotate the fresh built long block. That way he does not have to worry about fuel or timing, just oil pressure.
     
  21. firingorder1
    Joined: Dec 15, 2006
    Posts: 2,147

    firingorder1
    Member

    All excellent answers. My Dad used to tell me the reason for breaking in an engine was that new parts have to get to know each other. When you think about it that's about what it is.
     
  22. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    It has also been said that if you break in a new car hard it will make more hp. A friend when I was growing up got a new Pontiac every other year (his Dad owned a Cadillac, Pontiac, Olds dealership in town.) He beat the crap out of every car from the moment he got it and his cars always ran a little faster than similar models. He swore it was because he drove them right away like he was going to drive them daily............hard.

    Don't know if there is any truth to it, or if it is an urban legend.

    Don
     
  23. 1971BB427
    Joined: Mar 6, 2010
    Posts: 7,090

    1971BB427
    Member
    from Oregon

    Lot of old hotrodders used to say, "break it in the way you plan to drive it later." I've never run them hard during breakin, but never could wait until they were really totally "broke in" to give them a few little bursts through the gears! :)
     
  24. Nothing. Perhaps you are burnishing the cam lobes if the manufacturer recommends break in.

    One other thing that is accomplished by cam break in is that it burnishes the cam lobes. That is important to cam life on a flat tappet cam.

    Cam break in lube is more than sticky it had really fine grit on it along the same lines as *valve lapping compound. A lot of fellas say you should change the oil @ 500-1000 miles after initial start up, this is a bad idea. Change it as soon as you shut the engine off.

    * Valve lapping compound used for comparison or example only cam break in lube is not valve lapping compound.




    I have always done short blasts of speed and never maintained a constant speed for any length of time. The auto manufacturers used to say keep it below 45 for 500 miles now they don't say a thing just get in it and drive it.

    Funny thing that I have always thought about is that no one breaks a door slammer in and a lot of them don't get rebuilt that often. I have known lo buck guys to run an engine for 5 or 6 seasons.
     
    Last edited: Jun 13, 2012
  25. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,661

    Ebbsspeed
    ALLIANCE MEMBER

     
  26.  
  27. seb fontana
    Joined: Sep 1, 2005
    Posts: 7,208

    seb fontana
    Member
    from ct

    I am surmising that the jig method [because of spring pressure starting light] gets everything "mated" at a less aggressive rate than is possible in an engine so is less chance of a problem..I also am surmising that once everything is mated then putting into an engine an there is slight misalignment [guaranteed] it won't be a problem as long as the lifters all go back on the lobes they "mated" to..
     
    Last edited: Jun 13, 2012
  28. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,661

    Ebbsspeed
    ALLIANCE MEMBER


    Agreed, probably a smaller risk of failure, but I'd guess that there is still that possibility.
     
  29. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,109

    EnragedHawk
    Member
    from Waco, TX

    Thanks for all the responses guys. I feel far more edumahcated now.
     
  30. ugotpk
    Joined: Nov 3, 2008
    Posts: 503

    ugotpk
    Member

    1500 RPM will make them spin to create a wear pattern. IF they don't spin thats when they will start to wear out very quickly. The bottom of the lifter has a slight crown. It sits off to one side of center of the lobe. This creates the roller motion. Making sure the lifter is free in the bore is also just as important.
     

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