How to : Camshaft & valvetrain setup

Discussion in 'Engines' started by HPR, May 17, 2019.

  1. HPR

    HPR Administrator Admin

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    During the past 10 years ive often advised or helped people with their engine projects...beside other things as suspension, etc

    This tread will cover the cilinderhead and its valvetrain components and all the basic checks that need be done to avoid problems.... as long the components are std or close to std spec there are usually no big issues to expect.... altough the more get changed and when more extreme parts are used… the more things that need attention to avoid problems....

    and if thats not enough, some like to mix as much parts as possible from as much different engines ... and its possible, as long you know what you are doing... and as reading books is something from the stone age ( LOL ) many fire their questions online and the level of advice is all to often questionable.... to say the least

    So here we go :

    Head porting or combustion chambers will not be covered, but mainly focus on components as camshafts, valvesprings, springseats, retainers, valves, valve guides, valve seals, hydro and mechanical lifters / cam followers.... and the setup proces step by step

    Its important to go trough these steps... to avoid to get the cylinderhead fully assembled and find out that something doesnt play ball…. then you do everything a couple times….altough its part of engine building … unless you have build similar before and know exact what and how much needs done...

    Even when there are some good books written that cover more than what im able to cover here.... let me try to cover the basic things …. as simple explained... for as far possible

    Let start from the idea that the bottom end is already partly assembled and fitted with either std or aftermarket forged pistons with larger / deeper valve pockets....

    To allow accurate camshaft (s) setup once the engine build comes in its final stage... first you need to do: Set TDC ( Top Dead Centre ) as accurate as possible

    During engine build the engine will be on an engine stand and for setup cam timing a degree wheel and arrow are fitted….
    But also make a mark to the crank pulley and /or flywheel and in a way you can set tdc reference point when the engine is fitted in the car….just make sure its accurate
    Atleast check if the std markings are correct positioned


    Now place a dial gauge ( clock ) on the piston and determine TDC as close you can, now turn the crank back till the piston is exact 1mm lower ( before TDC ) , now mark that point ( @ x degrees) , now turn forward and now again the same but @ 1 mm after TDC and mark that point ( @ x degrees) .... eventually repeat it a few times to get a constant reading.... the middle point is TDC as accurate as can be.... as thats the reference point to set cam timing

    Now when the cylinderhead its disassembled and cleaned already ....

    Note:
    All meassurments and test fitting need be done with the parts you will use in the final engine build as there are some differences in dimensions between say a std valve and a Supertech valve…. and this apply to many parts...


    To fit a new camshaft with extra lift....first thing to control: take the cam bearing caps off and lay the cam in the head and see if it rotates a full 360 degree in head, without touching anything
    if not it will need some machining to the head casting but dont be to over enthusiastic as the more material is taken away from the lifter bore (s) the less stable the lifter is guided while there are large side forces acting on the lifters due more cam / valve lift and higher spring forces compared to std spring force


    Also fit the valve cover and rotate the camshaft (s) for clearance if not, it will need some tweaking …
    ( only apply to ( very ) high lift cams )


    Check valve to piston clearance
    Fit an inlet and exhaust valve in the head on cyl 1 but without springs and fit the head on the engine block with piston 1 @ TDC ....and use the same head gasket thickness as what you would use and tighten the bolts a bit more than hand tight.... there is no need to torque the head fully down... we only try to get a pretty close idea how much the valve can travel before it hit the piston....


    Also realise that the Inlet valve open faster than the piston move down in those first degrees after TDC, certainly with very wild cams and long rods

    Certainly the first 15 -20 degree can be critical….
    After a little play here : http://www.dansmc.com/mc_software2.htm
    We see with a 92.8 mm stroke and a 159 mm conrod….
    after 2 degree the piston has moved only 0.037 mm down
    @4 > 0.146 mm
    @6 > 0.328 mm
    @8 > 0.583 mm
    @10 > 0.909 mm
    @ 12 > 1.307 mm
    @14 > 1.775 mm
    @ 16 > 2.313 mm



    If a cam specsheet say 3.5 mm @ TDC + a 1 mm clearance to piston , as that is regarded as a strict minimum to be safe...
    So that would mean atleast 4,5 mm as a strict minimum distance ...i tend to take 0,5 to 1mm extra as that allow to advance or retard cam timing and still get the 1 mm minimum clearance, and a bit extra safety margin is not a bad either…

    Now there are some tweaks... that can be done, Its all minimal, but it can allow to gain a few tenths here and there.... and create some extra clearance....
    - machine the valve pockets in pistons deeper ( or wider for bigger valves )
    - lay the valve a bit deeper in head ( cut the valve seat deeper )
    Attention: incase Hydro lifters are used as you need to stay within the working range of the lifters .

    - machine the valve head ( only if there is enough material )

    -------------------

    Lets go from a camshaft that has 12 mm lift ( @ full lift ) , that would mean the valve need a free travel of atleast 13 mm... due minimum a 1 mm safety margin

    Retainer to valve seal distance :

    Fit a retainer with collets to the valve, altough no spring .... and there should be a valve guide seal fitted. if you drop the valve with retainer fitted, it will rest on the valve seal....the valve should be able to move a full 13 mm if pushed back to its closed position

    Depending on the type of engine/ cylinderhead, it might that there is not enough distance between retainer and the valveseals for the extra valvelift… in that case to create some extra clearance the valve guides need pressed a few mm deeper

    PS : There is also variation in height between various valveseals , be aware of that !
    So fit the lowest ones if space is tight ….


    Valvespring lenght @ seat pressure AND @ full lift

    The valvespring compressed in its valve closed position ( @ seat pressure ) has a certain mounted lenght when the valve is closed , and it will need a certain minimum seat pressure… from that position the spring need be able to compress the valvelift ( in this case 12 mm) + minimum 1 mm before the valve come to its bloc lenght ... so a strict minimum of 13 mm, before the spring goes coilbound ( spring fully closed / block lenght )

    Note: Spring force at full lift is mostly more than enough… while the highest accelerations are in the opening / closing fase.... so its matter to have enough spring force in the lower 30 > 60 % of total lift
    to keep the cam / valve motion as stable and controlled.
    This might maybe a bit to much spring force @ seat pressure, but as often its matter to make the wright compromises … one of many to take and make a judgement on what is more important....
     
    Last edited: Dec 4, 2020
  2. HPR

    HPR Administrator Admin

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    Valve guides ….

    When you build a new head, with new valves… then also replace the valve guides
    as the better the valve is guided the better the valve will seal, and the engine will deliver better ….
    As we spoke before about to press valve guides a few mm deeper, infact a pinch closer to the valve dish….or even longer guides fitted, its not a bad thing, but it might be a bit more into the port/air stream, altough the guides can be tapered to reduce drag to a minimum ...only if you look for every last drop of power...
     
    Last edited: May 17, 2019
  3. HPR

    HPR Administrator Admin

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    On camshafts can be said a lot... and its one of those grey & secret areas..much confusion and and different standards to talk numbers apply….. be it measured @ 0 mm or O.1 mm or 1.0 mm or 0.050 inch ( 1.27 mm ) lift....
    While in Europe most cam manufacturers mention cam timing @ 0.1 mm and 1.0 mm valve lift
    and valve lift @ TDC and LSA ( Lobe separation Angle ) or PD ( Peak Distance )
    but sometimes in race engines cam timing is @ 2mm or 3 mm lift... this to make things even more confusing...

    Im not going to to dig deep into camshaft design … leave that to cam designers/companies,
    what we need to know is some basic things …

    O mm or 0.1 mm is often what people talk about when they speak about a 260 > 330 degree cam…
    altough its a bit meaningless figure… as the cam has an opening ramp... as transition from valve lash towards opening the valve at high acceleration towards full lift and back closing towards a closing ramp to set the valve gentle back on its valve seat… if these ramps would not exist or extreme valve lash applied the valves would fail due repeated high impact... and valve seats would be ruined within a short period….

    That said the 1.0 mm lift figures are more real world and better to compare different cams
    in general on flat tappet,also known as inverted bucket lifters......as a rule of tumb..the difference between 0.1 mm and 1 mm figures is about 30 degree on Mechanical profiles and about 40 degrees on Hydro profiles…..
     
    Last edited: Dec 4, 2020

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