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Strengthen the crankshaft

Discussion in 'Rootes Racing' started by Kristian Jonsson, Aug 2, 2021.

  1. husky drvr

    husky drvr Platinum Level Sponsor

    Now you've got it! :D With hemi and cross flow, we should be able to go to a three valve design to keep everything in the chamber over the piston.

    While developing the custom OD trans bell housing, do you think we should lean the engine a few degrees so we can get those DCOE carbs mounted a bit easier? ;)
  2. Gordon Holsinger

    Gordon Holsinger Diamond Level Sponsor

    Shim the motor and trans mounts and adjust the pinion angle
  3. alpine_64

    alpine_64 Donation Time

    Well the hunter motor is a 10deg slant....
  4. husky drvr

    husky drvr Platinum Level Sponsor


    I found the reference I thought I recalled about 1725 main bearing caps. Pinned caps might be enough ...

    This is this the first page of an article in issue #11 "The Alpine Marque" by Carl Christiansen (page 23)


    The building block of any race engine begins with a sound engine
    block. Begin by "hot tanking" the block to remove the accumulated
    oil and grease. This should be done with all the "freeze plugs"
    removed as well as the oil gallery plugs. By the way...before assembling
    any parts that flow oil, especially to the rocker shafts, if it has an oil hole
    blow it clean with compressed air and/or run a "pipe cleaner" thru it to be
    sure it's not plugged. Next have the block pressure tested to be sure the
    block is not cracked anywhere. Then have your machine shop "deck the
    block" to be sure the surface that mates with the head is flat. Before you
    go any further "stone" the surface of the block to insure an absolute
    smooth surface and also stone the main bearing cap registers, just to take
    off any burrs that might exist.
    The number 2 and 4 main caps in the Alpine engine are subject to breaking
    under race conditions(I broke a #2 main cap) so it is very important to have
    replacement steel billeted main caps made for those two positions. If a
    main cap were to break it would "whip" the crankshaft around and could
    destroy the engine. The number 1, 3 and 5 main caps are very sturdy and
    do not need to be replaced.
    Next thing is to have your machine shop
    align(line) bore the main caps to ensure the crankshaft journals have a nice
    straight surface to ride on when the bearings are installed. I also have rear
    main seal housings machined to accommodate FORD "lip-type" rear main
    crankshaft seals to stop/slow down oil leaks from that area. Note: the
    crankshaft must be machined smooth also. And at the front of the
    crankshaft I install a Chevy lip seal in the timing chain cover.
    Next have your machine shop check the alignment of the cam bearing
    registers. If necessary, have them line-bored as you did with the
    crankshaft main bearing caps and install larger cam bearings, if necessary.
    Another item to replace with a steel billeted part is the camshaft retainer.
    Two tabs with 1/4-28 bolts hold the retainer in place and the tabs can, and
    will break off, allowing significant movement of the camshaft. That will
    effect the ignition timing as well as cause undue wear on the camshaft/oil
    pump gear.
    hartmandm and RootesRacer like this.
  5. RootesRacer

    RootesRacer Platinum Level Sponsor

    Ive never seen a 1725 break a main cap, I have seen them break cranks.
    I think if you can keep the caps from walking by pinning them, the likelihood of breakage falls off a cliff.
    Billet caps seem overkill to me when its the caps walking thats the real problem.
  6. Shannon Boal

    Shannon Boal Bronze Level Sponsor

    Roller camshafts make more power. GM's 2.5 four cylinder OHV in 1985, went from 90 hp to 98 hp in 1986 with roller cam....same induction, compresssion,etc. You could really feel the difference.... I was a drivability tech at an Oldsmobile dealership, and it made an impression on me. More torque/BMEP at same RPM.
  7. RootesRacer

    RootesRacer Platinum Level Sponsor

    Thats a very general statement. Roller cams came out to reduce the friction of the follower to the cam.
    The actual cam duration and lift (and lobe center angle) is what defines engine power.
    Due to the limited cam lobe contact patch with roller followers, a flat or convex tappet follower will produce a higher duration for a given lobe than a roller follower.
    In order to take advantage of having roller followers, you will need both the roller followers and a purpose ground cam for the roller follower. Just using roller followers with a flat tapper cam will yield lower duration cam specs.
  8. husky drvr

    husky drvr Platinum Level Sponsor


    IIRC, part of that difference is the roller followers don't require the "quieting ramps" which flat tappets require for longevity. Therefore, the lobe lift curve can begin sooner and faster within the same cam timing parameters, allowing a bit more area under the lift timing curve.

    The major issue is flat tappet cams are a type of cast iron. Roller lifters require a hardened surface to roll against. I think most roller cams are made of a hardenable steel. The steel pump drive gear then requires a different oil pump drive gear for durability. It's a system, not just a single part change.

    IIRC, an "Old School" trick before affordable roller cam sets for drag racers, was to machine Ford and Chevy v8 blocks to use a larger diameter Chrysler flat tappet lifter. This gives a small improvement in how the lifter reacts to the cam profile. I don't have any idea if this is possible on a Rootes engine, I don't know any of the needed measurements for comparison. I doubt it to be cost effective for anything short of a 10/10ths engine build. I've also never heard or seen any discussion involving the idea. Just a possibility.

    Have fun,
  9. alpine_64

    alpine_64 Donation Time

    Jarrid, iirc Brian holmes made a roller cam setup for his turbo 1725 alpine ( along with many other mods) do you still have contact with him? Admittedly he ran boost... But what kind of cam spec did he use?
  10. RootesRacer

    RootesRacer Platinum Level Sponsor

    His cam was custom built, it was gear drive instead of chain drive so it spins in reverse compared to the factory cam.
    Brian has access to some nice CNC machines.
    I have his email address if you want it.
  11. Shannon Boal

    Shannon Boal Bronze Level Sponsor

    IIR, Crane Cams did some of his work
  12. Bill Blue

    Bill Blue Platinum Level Sponsor

    So a low friction motor will not produce more power than a high friction motor! Interesting concept. Perhaps you should show us how increased friction is not only aa power robber, but actually increases power output.
  13. Shannon Boal

    Shannon Boal Bronze Level Sponsor

    Don has command of the nuts and bolts here. He comments about the "area under the curve"explaining what makes roller cams rock. Area under the curve is a function of lift and duration; (there are two types of duration). Duration is measured at valve lifts of: 0.005", and 0.050". The first is "advertised duration" and the second, effective duration (significant flow is judged to commence at this lift). Alpine V cams have an advertised duration of 273 or so. If we had both types of cams, both with 270 degrees of valve lift at 0.005", but differing lift at 0.050" ...... the one with greater effective lift would have more area under the 'effective" curve, and produce more power. The roller lifter/cam setup opens and closes the valves faster, hence "roller cams make more power". It gets even better when we look at overlap, and that role in fuel efficiency/emissions....
  14. alpine_64

    alpine_64 Donation Time

    The holbay cam actually has quite a bit of overlap with extended exhaust opening to help scavenging
  15. spmdr

    spmdr Donation Time

    I've been rethinking crankshaft hardness lately.

    One of the main reasons a crankshaft is hardened is for bearing surface durability.

    A hard crank is also a brittle crank.

    Cranks flex from controlling the reciprocal mass.

    And that flex also flexes the engine block.

    Cranks also flex from torsional flex.

    The strongest block can not stop torsional flex.

    I'm wondering how much torsional flex is a thing with a 4 cylinder engine.

    V8s typical have crankshaft dampers, but I have seen several Hi-Fi 4s with ZERO, as in no

    crank dampener.

    And, how much does flywheel mass fit into the equation?

    YUP, I NEED to talk Alpine cranks with the Crank people!
  16. RootesRacer

    RootesRacer Platinum Level Sponsor

  17. Shannon Boal

    Shannon Boal Bronze Level Sponsor


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