New rebuilt engine issue suspect cam timing

Discussion in 'Mech Tech' started by Gooders, Apr 23, 2019.

  1. :( So the rebuilt type 4 went back in the van last week. Set timing static at 7.5 btdc. Bit reluctant to start and coughed a bit, Had to advance timing some more to smooth it out and get it running at 2-3k to bed in cam.
    20min cam bed in run ok decent oil pressure & no leaks.
    Did oil/filter & valve clearences when cold.
    Reset timing correctly at 28-30btdc at 3500rpm. Vac pipe off distributor & plugged.
    Rejetted carbs as recommendations by Wayoutwestie for 2.0.
    Went for a few short runs and it idles rough seems reluctant to rev & pick up.
    Checked for possible vac leak but all ok.
    I was careful to make sure the timing marks were lined up when i was building the engine but fear the cam timing is out. Having to over advance the ignition timing to get it to run smoother is the worrying issue.
     
  2. Did you bolt the cam gear to the cam or was that already done for you?

    I forget what lobe you line the dot on the gear up with, it does say in the Wilson book, could this be the cause I wonder, especially if you are happy with the way you've timed the dizzy.

    Or, what is the dizzy drive gear lined up like, again Im sure you've been thorough in setting that up for #1 tdc.
     
  3. davidoft

    davidoft Sponsor

  4. E1A3577C-F05F-4D56-85EE-F25432A9FD18.jpeg 9E338276-5F4B-41BE-A611-9A016F76D8AD.jpeg I bolted a new cam gear to the cam & aligned it with the dots to the crank gear. Lash seemed ok & Cam didn’t walk out when turned in opposite direction.
    Its a Scat C25 cam I used.
    Dissy timed up ok on cylinder 1.
    Could it be the new Cam gear marked up wrongly. Lobes look to be in correct position when I look at photos I took during the build but 1 tooth out wouldn’t be that noticeable to the eye I suppose.
     
    Last edited: Apr 23, 2019
  5. Did you just bolt the cam gear in any position or align and bolt up.
     
  6. Bolted it up as per Wilson book & as Raby shows in his video. Can only go in one of four positions and would be 45 or 90 degrees out in the other positions with a definate non start.
     
  7. Is this a points dizzy or electronic.
     
  8. Electronic Pertronix module 1. It worked fine in the engine I removed from the van.
     
  9. With a non stock cam and rejetted carbs sometimes you have to "find " the timing as there is no book to go by.
     
    nicktuft likes this.
  10. GARRICK CLARK

    GARRICK CLARK Sponsor

    Just looked at your pic of the open case. I see number 1 con rod is at top dead or there about's. The front nose cone key way looks like its gunna be at the 9 oclock position. I also see that the number 1 inlet and exhaust is showing the heal of the cam, which means at number 1 tdc... both number 1 inlet and exhaust will be closed , so to me the cam is timed ok.
     
    Last edited: Apr 23, 2019
    Razzyh likes this.
  11. Its a Scat C25. Didn’t degree it though. Could it be out due to tolerances in manufacturing of the Cam & aftermarket gear?
     
  12. davidoft

    davidoft Sponsor

    Possibly but it shouldn’t be, hows is Rev drive etc ?
     
  13. Chugging on idle & shaking. Not misfiring though Picks up steadily when driving but i would say down on power. Bogged down & cut out when pulling out of a junction. Did restart ok though. Just feels & sounds retarded. I have compared a video of it at idle with one i took a bit back of the old engine running. Its very uneven in comparison.
     
  14. You may have to advance timing to find sweet spot.
     
  15. I like this idea but worry about preignition and possibly putting a hole in a piston.
    2 or 3 degrees makes little difference. When I checked it after the first cam bed in run i had advanced it to nearly 20btdc at idle to get it to run smoothly. Started thinking the notch in the pulley was wrong but can’t see how it can be as it’s keyed to the crank. It was correct when i had it on the old engine.
     
  16. Like I say once you go away from stock there is no book that tells you,only a dyno will.
     
    Razzyh likes this.
  17. Another thing I forget to mention the snail meter is showing a high intake reading on idle of about 15kg/h when it should be more like 6-7kg/h. Got both carbs balanced Ok but draw is way too high at idle.
     
  18. Are the carb butterflies to far open at idle? what carbs are you running? This might be a fuelling issue.
     
    Faust likes this.
  19. Are your ignition leads on correctly? I’ve had a van come to me (just) before which coughed and spluttered and misfired because the leads were ‘out’.
     
    davidoft likes this.
  20. Yes more than they should be as only way i can get a resonable 850-900rpm idle. This has not got any better after rejetting.
    Leads are on correct & firing on all 4 cylinders.
     
    KarlB likes this.

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