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Top Dead Center According To Bruce Lancaster

Discussion in 'The Hokey Ass Message Board' started by Ryan, Dec 21, 2010.

  1. Ryan
    Joined: Jan 2, 1995
    Posts: 20,872

    Staff Member

  2. Wow! Bruce is the man.
  3. Lazer5000
    Joined: Dec 7, 2007
    Posts: 729


    I like the "Heads on Method". Now I just have to find an apprentice to hold the thing.

    Great info though.
  4. Simple and to the point. Always read Bruces replies, feel smarter from them!

  5. Slick Willy
    Joined: Aug 3, 2008
    Posts: 3,036

    Slick Willy

    "Mug an eighth grader..." !
    Man, kids must be smarter in PA!...Around here I'd have to beat up a 5th year senior to get his compass and protractor!:D

    As always, Bruce has wonderful information!
    Thanks for posting, Ryan.
  6. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,906

    need louvers ?

    An eighth grader around here had a compass once, but I think he ate it...
  7. choprodinc
    Joined: Feb 22, 2010
    Posts: 141


    Bruce's bulb burns bright! U don't mug anyone in Texas... we're ALL packin'!
  8. Asphalt Outlaw Hero
    Joined: Dec 9, 2006
    Posts: 973

    Asphalt Outlaw Hero
    from Dixie

  9. Adam.Perrault
    Joined: Nov 10, 2009
    Posts: 124

    from Phoenix AZ

    this is fantastic... the 8th grader i tried to mug must of been from Texas! It was only a flesh wound though.
  10. caseyscustoms
    Joined: May 15, 2005
    Posts: 1,031

    from st.joe, MO

    yea down there they all know a shot below the waist isnt attempted murder, less time served. :D
  11. choprodinc
    Joined: Feb 22, 2010
    Posts: 141


    you're right! down here we'll shoot you just for kicks... you gotta really piss us off to make us kill you!
  12. MIKE47
    Joined: Aug 19, 2005
    Posts: 987

    from new jersey

    Join the Bruce Lancaster Fan Club group!
    Joined: Jun 15, 2006
    Posts: 3,419



    Good material for sure AND it would apply to any engine ever made not just the flathead. For a accurate timing of the engine we must know where we are at all the time.
    I would give the small block chevrolet the worse rating here as a typical "hot rod " build is a mixture of parts. IE : Balancer from one engine, timing cover from another etc, short water pump vs long pump etc...
    Last year i put together a complete test stand engine from parts, complete engine with heads was purchased from machine shop ( a 283 customer never came back for) at a deal, timing cover was from the wall just hanging there and the balancer was a new degreed unit from ebay. Fired the engine up and couldnt get close to any of the marks with timing mark.
    Used a piston stop in plug hole and marks were way off from any marks we had. ( 15-20 degrees etc) Made up new pointer for correct mark, set timing and has ran well every since....

    We need to know correct TDC on every build ..:eek:
  14. Steve Hedke
    Joined: Sep 28, 2005
    Posts: 74

    Steve Hedke

    Easier on 59AB: just bolt it up. Old Henry figured it would be too confusing I guess. Besides, timing lights only get you close, because published numbers are for stockers. Every engine is different: fuels, compression ratios, head designs, etc. I always use 'tune by ear' for final adjustment. Warm it up, then lug it down in 2nd: if it pinks, dial it back. If not, dial it up. No rocket science here.
  15. Nads
    Joined: Mar 5, 2001
    Posts: 11,821

    from Hypocrisy

    A poet he is, that Bruce.
  16. learn something new every day..Thanks Bruce !!!
  17. Simple and affective......good job sharing it with the masses.
  18. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,681

    Bruce Lancaster
    Member Emeritus

    On early flatheads, no marks. There are methods using distributor machines, simple fixtures, and just straightedges (I have posted simple timing methods for '32-41 and '42-8 engines and also a simple dwell device built out of Home Depot components) which time the distributor OFF the car, essentially by registering the tab that fits the cam.
    You do not need to add a timing mark to set initial timing pretty accurately to spec if you own a ruler, but you still want timing marks.
    The reasons...first, of course, you can jack around the initial to experiment, but no big deal...the distributor itself has a timing plate to do that, and flathead always seem to end up right around the stock 4 degrees by preference.
    The real reason is being able to check the whole curve, as moving initial moves it all. Especially important with pre-41, which is a bit conservative for 1930's octane, and aftermarket, which frequently has entirely inappropriate curves.
    If decoding the centrifugal on a flathead on a new installation...remember, once the vacuum is added in the compexity gets up around can first rotate the dist cam by hand and try for a rough measurement of total advance (remember to multiply by 2 to get crank degrees!) or maybe trust the spec...maybe not.
    Then revvitup with a tach, timing light, and newly marked pulley. Most flatheads are going to want full advance by around 2,000 or not far from there, so if your full advance isn't coming in (brake backed off on earlies, vac disconnected on conventional systems)) by thenabouts stuff is sticking or springs are too heavy.
    Typically a good curve starts moving right off idle and finishes in the rough neighborhood of 2,000, and you can see what's happening right on the engine. Remember the brake; with brake dragging heavily, curve is much slower at full throttle, ending maybe above 3,000 somewhat, brake released curve peaks around 2,000.
    This gave less full throttle/more part throttle advance with bad antique gas octanes, but on decent modern octane levels most engines seem happy with brake way off. You do need slight drag to stabilize brake disk according to those with proper machines. Start off with brake adjust turned all the way out BY HAND, then screwed in just a turn or so. Crank it down more only if your rig pings.
    Once you know what distributor is doing, hit the road and see how it goes, hook up the vac and see what happens, try experimenting by TEMPORARILY jacking the initial setting to boost or reduce upper ranges of curve. At least you know the basic numbers to think about what is happening.
    Good advance curve is serious stuff...getting it right gives more seat of pants improvement than any finned aluminum stuff, getting it wrong makes car slow, breaks parts, and causes overheating. NEVEREVER assume a new distributor out of the box is doing anything at all right.
  19. JeffreyJames
    Joined: Jun 13, 2007
    Posts: 16,612

    from SUGAR CITY

  20. hotrd32
    Joined: May 16, 2007
    Posts: 3,557

    from WA

    There is NO substitute for experience.....period
  21. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,681

    Bruce Lancaster
    Member Emeritus

    Theoretical TDC issues that hurt my head have been pointed out to me by mathematically sophisticated HAMBers and by my little 1935 Ford engineering text. I only dimly understand this stuff, BUT...
    Engines have offsets to control piston side thrust issues, noise, and things beyond mortal comprehension. Flatheads achieve the offset by having crank offset from cylinder centers slightly...some others do this at the piston pin.
    The simple story is that piston goes UP differently than it goes DOWN!
    An effect that I only dimly grasp is that the measurements detailed in my post are close but not entirely accurate.
    Measuring the distance a ways down the hole will give UP and DOWN distances closer to equal and so more accurate BTC and ATC correlation at same distance!
    I have charts of the movement curves, but they severely hurt my head.
    The differences ar minor...the methods given ar more than sufficiently accurate and almost certainly closer than original punch marks on pulley.
    I do not know the perfect distance down the hole...and I believe it will vary by stroke. Study of the charts continues.
    The distance issue referred to means that using a bolt an inch or two down the hole (head OFF method) is more accurate than the head ON method, but the difference should be slight and not critical. Blown 49 has posted on the offset issues, and can go deeper than I can.
    Both methods are entirely satisfactory, but be aware that they are not perfect.
    You cannot gauge TDC accurately by purely visual methods, INCLUDING use of a dial indicator!
    Long rod engines with offsets have 2-3 degrees of DWELL at TDC with no motion that can be consistently shown even with a high zoot dial indicator. TDC has to be calculated, though finding it with an indicator might be as accurate as factory pulley marks.
    The interference method is bot better ans easier.
    The limit on the head ON method is of course what you can fit through the plug hole and maneuver...which is to say you cannot get piston down much, maybe 1/4".
  22. choprodinc
    Joined: Feb 22, 2010
    Posts: 141


    Screw Bo! Bruce KNOWS!
  23. Mr 42
    Joined: Mar 27, 2003
    Posts: 1,215

    Mr 42
    from Sweden

  24. firingorder1
    Joined: Dec 15, 2006
    Posts: 2,147


    Somewhere in the back of my mind is a 1964 HRM article where Garlits "revealed" his speed secrets by stripping his fueler. In the article he said he never measured TDC but did it by feel. I started trying it on my motorcycles and was surprised as to how accurate you could be.
  25. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,681

    Bruce Lancaster
    Member Emeritus

    In the fifties...the way TDC was measured in HRM tech articles and the Iskenderian book on valve timing was similar to the interference method...but harder!
    A dial indicator was used, but not at TDC because that was recognized as not precise.
    Piston position was measured part way down, towards the limit of the indicator travel. Then engine was turned over so piston was coming up the other side of TDC until it reached the same reading on the indicator. Using a fixed object (bolt through heavy strap) of unchanging length produces the same result without need to read the indicator.
    Thump, thump, split the dif.
  26. Jimmy2car
    Joined: Nov 26, 2003
    Posts: 1,707

    from No. Cal

    On my engine I took the pulley off, found a peice of 5" tubing, had it cut to 1/2" length, had it welded to the back side of the pulley. Thru Jeg's or Speedway, I found timing tape for a Pontiac that used a 5 1/4" diameter pulley. I installed the tape knowing that it would not be perfectly accurate, but is VERY close. Now I can use a light and see exactly what's going on with the distrbutor advance. I can't get a picture of it cuz I can't get the camera in there. This is on a 59 type engine.
  27. vilanar
    Joined: Feb 9, 2009
    Posts: 71

    from Finland

    Bruce knows his stuff !!!
    Once I read somewhere one neat trick for heads on timing as an alternative
    for that zip tie method.
    It went something like this.
    Take an old spark plug and break the porcelain and weld a piece of small
    tubing on it. Put piece of clear plastic tubing on it (10 inch or so)
    Set engine to near TDC and screw your new apparatus in #1 cylinder
    and make a bend on that tube and pour little amount of ATF in it.
    Now when you turn engine that ATF moves up and down and when it moves
    direction from upward to downward there is your TDC.
    I believe you gearheads get the idea altough my explanation was what it was.

  28. Petejoe
    Joined: Nov 27, 2002
    Posts: 11,608

    from Zoar, Ohio

    Thanks Bruce and Ryan for sharing. If it wasn't for Bruce and another good Friend here, there wouldnt be any running flatheads in Zoar Ohio and it would probably go for alot on the Hamb too. "Discarded 8th grader" cracks me up. Bruce you have single handedly resurrected alot of flatties not just because of your knowledge but because you are so willing to help us backyard mechanics here and on the Fordbarn. Hope to meet you someday. PJ
  29. firingorder1
    Joined: Dec 15, 2006
    Posts: 2,147


    In an effort to be more accurate I have been using a degree wheel and dial indicator. I set the piston at approx. TDC. Then turn it back 30 deg. or so. Move it back to TDC watching the dial indicator. When the dial indicator stops moving, note the point on the degree wheel. Keep moving until the dial indicator starts moving again and note to point on the degree wheel. Divide the degrees by two and that gives me TDC. So far thats as accurate as I can get. The cam on my engine has no marks and the valve timing is set off of the inlet valve fully open. I guess it works. With two records at Bonneville and two at El Mirage I must be doing something right.
  30. Red Ryder
    Joined: Jan 23, 2008
    Posts: 174

    Red Ryder

    You can't beat accurate information, and that's just one of the things I like about the H.A.M.B.

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