Timing retarding as rpm goes up. BBC

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by boostedgt500, May 13, 2017.

  1. boostedgt500

    boostedgt500 Member

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    I was helping a friend with his car and I noticed his timing is retarding as the RPMs go up. Timing moved about 5 degrees when I revved the engine up.
    I put zero degree chips in the MSD 7AL3 to make sure he did not have a wiring issue. Distributor is locked out. I've never seen this happen. Maybe cam moving? Just baffled.
    Any suggestions?
     
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  2. Mike Canter

    Mike Canter Top Dragster

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    Are you using a crank trigger?
     
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  3. boostedgt500

    boostedgt500 Member

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    No he is not. MSD distributor only.

    I told him he should have a crank trigger as the timing will be more accurate, but I don't know if that would be the fix for the retarding though.
     
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  4. superpro453

    superpro453 Member

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    Certainly worth checking the camshaft end float first. Too much float, and you'll have real problems keeping the timing set where you need it.
    Have had this problem with excessive float meant the motor would start in the pits after the timing had been set, then refuse to start in the staging lanes as the cam had moved on shutting down the motor... Fitting a crank trigger would solve it, but it would still be a good idea to check the float.
     
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  5. Torment

    Torment Member

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    Timing retarding with RPM with a distributor fired ignition is typical, a crank trigger is the usual fix. The stack of mechanical clearances between the crankshaft and the distributor team up to cause the movement - camshaft end play and distributor shaft end play for example. The greater the total clearances, the more the timing will move.
     
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  6. Bjs344

    Bjs344 Member

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    Are you using a known good timing light with no dials?
     
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  7. boostedgt500

    boostedgt500 Member

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    MSD timing light. No dial. We each have the same timing light and I tried mine and it read the same.
    I had him order a crank trigger so I'll install it this weekend and report back.
     
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  8. vht

    vht Member

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    I've seen the MSD 10 boxes do that, never a 7. Friend of mine had it, and that was with a crank trigger. Sent it back, nothing wrong they said, but when it came back it didn't do it anymore.
     
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  9. boostedgt500

    boostedgt500 Member

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    Installed crank trigger and timing is dead on. Doesn't move at all.
     
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