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Thread: Timing Question

  1. #1
    diggler
    Ok, Here's what I have that I'm basing my questions on.
    511c.i. BBC
    13:1 compression (110 octane, leaded fuel only)
    MSD 7AL with crank trigger
    tunnel ram with duel 650? 850? carbs
    Here's my questions.....
    First question... the timing is currently set at 43degrees advance. The fella I bought the boat from told me when I purchased it that the timing was set conservatively. It runs fine, and idles fine, but I'm concerned about how far it's advanced. Should I retard it to something like 34 - 36 degrees?
    Second question... I adjusted the valves after talking with Comp Cams and followed their instruction when adjusting the valve lash when cold. I had to add .004" to the values given on the cam card. Prior to this, per the specs, I would have adjusted the valves to .028 (intake) and .030 (exhaust). My initial findings prior to adjustment was less than .020 for both intake and exhaust. (not good I know). Anyways, after I did the valve adjustment, I lost 500 rpms. I expected to lose some because of the roller rockers depressing the valves a little less, but is this normal? I went from 6000rpm max to 5500rpm max. (It is a b/c impeller in the berkeley style jet).
    Third question.... what would you recommend for a good girdle on the roller rocker studs. The one currently in there is fine, but it is a five(?) piece girdle and it sucks to make valve adjustments because everytime you tighten the girdle, it would knock the lash out of adjustment. I have Brodix aluminum heads.
    Fourth question... I have a mechanical and electrical oil pressure gauge. The mechanical one fluctuates about 10psi running at 3500 rpms. Once I let off the gas, the oil pressure shoots up. Is it possible I have air in the line feeding the mechanical gauge? If so, how should I bleed it out?
    That's about it... I'm learning here, and getting more concerned the farther I get into this engine. I did all of this today under the supervision of a very good mechanic, but he still suggested I post this to see what others thought..
    Thanks for the input!

  2. #2
    Hotcrusader76
    Ok, Here's what I have that I'm basing my questions on.
    511c.i. BBC
    13:1 compression (110 octane, leaded fuel only)
    MSD 7AL with crank trigger
    tunnel ram with duel 650? 850? carbs
    Here's my questions.....
    First question... the timing is currently set at 43degrees advance. The fella I bought the boat from told me when I purchased it that the timing was set conservatively. It runs fine, and idles fine, but I'm concerned about how far it's advanced. Should I retard it to something like 34 - 36 degrees?
    That's a little high for my blood. I've heard of folks running up to 40 degrees but I think one of two things...
    A. They were experimenting with different burn rates and successfully pulled it off. :idea:
    or B. They didn't know what the hell they were doing but the motor loved it
    I would imagine your motor survived at 43 degrees with a carefull process of perfectly dialing it in, since you claim it has run perfect for ya. It's gotta be hell on that starter if she's locked out...
    Now, since you've adjusted the valves, I would seariously consider taking the timing back down for good measure since the initial settings were part of the 43 timing package he had tuned into it. What prompted you to reset the valves? Just routine maintenance?
    Just make sure you run good gas.
    ~Ty

  3. #3
    GofastRacer
    1 43degrees is way off, start at 36 and go from there!..
    2 There's only one way to adjust valves, E/O-I/C. When the exhaust just starts to open adjust the intake, when the intake is almost closed adjust the exhaust!..
    3 There are good and bad girdles out there, I use Webster they are the shit, I do believe they are like Darts?, adjust the valves clamp em done deal, adjustment don't change. What ever you use don't use the Jomar u-bolt type, they got to be the worst POS there is!...
    4 The mechanical guage is telling you right, sounds like you have a problem in the oiling system, maybe a leak in the pick up, cavitation in the pump??? Do you have a good pump? Did you blueprint it before you installed it???...Do you have the right pan for your application????....
    I will not comment on your "very good mechanic".. :smile:

  4. #4
    diggler
    I decided the adjust the valves because I was told after 10hours of run time to do so. It took a long ass time to do it because of the crappy girdle and it was my first time (supervised at that too!), but we finally pulled it off. Rolled it a few times and triple checked with the feelers every 90degrees starting with cylinder 1 at TDC, and then 8, 4, 3, 6, 5, 7, 2..... I did both exhaust and intake at the same time.
    If I retard the timing to 36 degrees, should I see an increase in the rpms? A loss of 500 rpms after adjustment just seems like too much to me. weird...
    As to the mechanical oil pressure gauge, I don't plan on tearing into it until the winter. I'll likley replace the rod bearings and main bearings, and then replace the oil pump as a safety measure. The pan is a Miloden 10qt pan with a full windage tray, and little doors in the bottom (sorry can't remember the correct word)
    Whew.... oh, no u-bolt girdle here. I know they're not the greatest thing to use.

  5. #5
    Fiat48
    Once again GofastRacer takes the bait like a hungry trout. And I cannot disagree. I see the secret is out on how to adjust valves.
    The pressure shoots UP when coming out of the throttle???
    But 43 degrees is conservative.........if you run nitro.
    Generally I found big high compression motors like less timing. 36 to start.

  6. #6
    78Eliminator
    Well, thanks for the advice. I am going to go ahead and run 50 advance anyway. Thanks. <---------joke

  7. #7
    GofastRacer
    Well, thanks for the advice. I am going to go ahead and run 50 advance anyway. Thanks. <---------joke
    Go for it dude!..

  8. #8
    GofastRacer
    Once again GofastRacer takes the bait like a hungry trout. And I cannot disagree. I see the secret is out on how to adjust valves.
    The pressure shoots UP when coming out of the throttle???
    But 43 degrees is conservative.........if you run nitro.
    Generally I found big high compression motors like less timing. 36 to start.
    LMAO, just figured I'd try and beat you to it!...

  9. #9
    GofastRacer
    I decided the adjust the valves because I was told after 10hours of run time to do so. It took a long ass time to do it because of the crappy girdle and it was my first time (supervised at that too!), but we finally pulled it off. Rolled it a few times and triple checked with the feelers every 90degrees starting with cylinder 1 at TDC, and then 8, 4, 3, 6, 5, 7, 2..... I did both exhaust and intake at the same time.
    If I retard the timing to 36 degrees, should I see an increase in the rpms? A loss of 500 rpms after adjustment just seems like too much to me. weird...
    As to the mechanical oil pressure gauge, I don't plan on tearing into it until the winter. I'll likley replace the rod bearings and main bearings, and then replace the oil pump as a safety measure. The pan is a Miloden 10qt pan with a full windage tray, and little doors in the bottom (sorry can't remember the correct word)
    Whew.... oh, no u-bolt girdle here. I know they're not the greatest thing to use.
    I think you need to start over on the tune up right from the beginning!..

  10. #10
    Moneypitt
    .032 & .034 cold is where your 500 rpm s went....I've never seen a valve grow .004 from cold to hot. Try the real #s cold and see if the r s don't come back up for you....Loose valves give you more bottom, tighter valves give you more top, I think you're losing valve timing with that much lash. Also, once the motor is in it's happy mode/power range, you don't need all that timing, 36-38 should be plenty, and as Art said, use good gas........MP

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