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Thread: Cam Break In

  1. #1

    Cam Break In

    Box says to only break in with single springs not dual. Is that necessary? would prefer not to take apart the valve train unnecessarily. 306 series cam on gs390.

  2. #2
    4 Cycle Advanced User
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    Only read the instructions as a last resort! ....
    Never saw any instructions like that with any
    Of Dyno's Cam's.
    Several questions come too mind .
    What cam mfg? Welded lobe or reground?
    Flame hardened?

  3. #3
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    Have a separate head with the breakin springs attached.
    Yes, it is a very good idea to seat in a cam in that manner.

  4. #4
    just trying to gauge whether its a legit thing or something people say is a good idea or has merit. My intentions where to idle for maybe 5 minutes then break it in on track full load. with modern machining it seems the best break in is done with the cross hatch fresh and the rings pressed into the cylinder walls as well as possible. thats only done by behind at full load.

  5. #5
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    Yes it has merit.
    Could wipe the lobe off.
    Moly cam Lube could help though it doesn't get mixed well with a splash lube system.

  6. #6
    thanks. i think i will remove the inner spring (i have duals) and idle it while i cut the crank end off (to get clearance with the seat). after that reassemble and run.

    Has anyone done performance studies of a lot of break in idling vs assemble and then run hard?

  7. #7
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    Letting a race engine off any kind idle is almost the worst thing you can do to it . It will gas wash cylinder wipe the lobe off the cam fowl the plugs and glaze the cylinder.

  8. #8
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    Why don't you just polish the cam before you put it in.

  9. #9
    Quote Originally Posted by racerrob66 View Post
    Letting a race engine off any kind idle is almost the worst thing you can do to it . It will gas wash cylinder wipe the lobe off the cam fowl the plugs and glaze the cylinder.
    i can see gas wash and i guess damage the cam by getting gas in the oil (never seen this on my engine, previous engine has at least 25 hours with idling and has perfect cross hatch on it still) but fowling the plug i have never done.

    Anyway you bring up a good point about gas washing. i think i will take it out to the track and putt around at 75% for a good 5-10 minutes then cool off then run it like its a normal engine.

  10. #10
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    http://www.mototuneusa.com/break_in_secrets.htm this is an interesting read I do something similar to this for fresh kart engine's on the Dyno. It has seemed to work.

  11. #11
    What does breaking in a cam do?

    Does it wear in and smooth out the cam and part which rides on the cam?

    Does it heat treat the surface of the cam and what rides on it?

    Why would the stiffer race springs ruin a lobe on the cam?

    I think the most likely cause of the 'race' springs ruining the cam during break in is because the engine was allowed to idle during break in and the oil got thinned out before the rings were able to seat. Unless a cam needs to be additionally heat treated by running it for awhile, I don't see any reason for a cam lobe to rub off other then because of an oil problem. But I don't know and all this is to offer my thoughts on it which ain't necessarily correct.


    ____________________

    Any engine we've ever built kart or car has been: start the thing make sure it ain't leaking anything out of it or out of either end, make sure the timing is ok and it sounds ok in general with good oil pressure, and does it make some heat but not over heat; then shut it down and go racing.
    Last edited by paulkish; 08-15-2017 at 09:42 AM.

  12. #12
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    Breaking in the cam is more important with the increased spring pressures on high lift cams and increased rpm.

    Flat tappet cams are ground with a slight taper to the lobe faces. This taper performs several important functions, not least important of which is to hold the camshaft against the thrust surface. While not critical onn a straight cut gear as a briggs uses, the helical cut gear like honda uses will change valve timing.
    The lifters are also cut with a dome shape. This, with the taper on the cam lobes causes the the lifter to rotate. The rotation moves the pressure point around the lifter, dissipating heat, slowing wear and reducing frictional losses.

    Breaking in the cam with lower spring pressures allows a wear pattern to develop with less damage to lobe surface.

  13. #13
    4 Cycle Advanced User
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    Quote Originally Posted by paulkish View Post
    What does breaking in a cam do?

    Does it wear in and smooth out the cam and part which rides on the cam?

    Does it heat treat the surface of the cam and what rides on it?

    Why would the stiffer race springs ruin a lobe on the cam?

    I think the most likely cause of the 'race' springs ruining the cam during break in is because the engine was allowed to idle during break in and the oil got thinned out before the rings were able to seat. Unless a cam needs to be additionally heat treated by running it for awhile, I don't see any reason for a cam lobe to rub off other then because of an oil problem. But I don't know and all this is to offer my thoughts on it which ain't necessarily correct.


    ____________________

    Any engine we've ever built kart or car has been: start the thing make sure it ain't leaking anything out of it or out of either end, make sure the timing is ok and it sounds ok in general with good oil pressure, and does it make some heat but not over heat; then shut it down and go racing.
    Break in is more about burnishing the Friction Modifiers (ZDDP, Paraffin, Asphalt, Phosphorus, Sulfur ect) into the metals of the machinery, ie cams, rear gears, cylinders, bearings. The old adage ",,,break it in on old paraffin base oil so it'll ware in, then put the synthetic in,," is just not understanding the process. Many of the kart specific oils are glycol based and actually perform better with some of the mineral oil burnished in the metal first.

    Best, WP

  14. #14
    Quote Originally Posted by racerrob66 View Post
    http://www.mototuneusa.com/break_in_secrets.htm this is an interesting read I do something similar to this for fresh kart engine's on the Dyno. It has seemed to work.
    this the article that originally got me thinking.

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