shiming a distributor

Discussion in 'Ignitions & starters and electrically related comp' started by grumpyvette, Sep 25, 2008.

  1. grumpyvette

    grumpyvette Administrator Staff Member

    big2bird posted some of this , on a different thread but it needs to be here also, and I ADDED STUFF YOU NEED TO KNOW

    For those of you who have one, factory or otherwise, and you have noticed your timing jumps around instead of steady, here is your problem.
    As you accelerate/decelerate, the spiral cut gear causes the shaft to rise and fall, turning in relationship to the cam, and making your timing vary. With the cap off, grasp the rotor and try to move it up and down. It will. Shimming the end play is the answer.
    You can check the shaft/bushing clearance while you do these steps, but they are surprisingly durable, and without points, highly forgiving.
    1)Mark the rotor position on the manifold, and remove it. It will turn as you do.
    2)Chuck it softly but firmly as shown in a vice. Rotor point up. Notice the dimple on the gear. It is on the same side as the rotor point.its always a good idea to call the cam manufacturer and ask what is the correct matching cam gear and distributor gear set,and how its correctly installed.
    READ THIS THREAD TOO
    viewtopic.php?f=54&t=2187
    [​IMG]
    [​IMG]

    [​IMG]
    I suppose you could do these oil feed mods and groove the lower lifter bores and distributor gear oil feed groove,while you used a strong vacuum cleaner and magnets to limit the metallic debris ,on a partially assembled engine, but I've never tried it, I do the minor machine work to a clean bare block even before the cam bearings are installed and carefully clean it, and all the oil passages with a rifle bore brush high pressure air and solvents, several times before installing the cam bearings, I generally prefer to start with the block on an engine stand that I can rotate easily for full access. Crane cams recommends filing or cutting a .030-inch-wide by .030-inch-deep groove in the lower ring of the distributor housing immediately above the distributor gear. This slot is cut into a ring that seals a main oil passage, creating a spray of oil that is directed onto the distributor and cam gears for extra lubrication.
    keep in mind grooving the lower distributor oil band will allow pressurized oil to flow through the lower band to supply oil to the distributor /cam gears contact point but this groove will rotate as the distributor ignition timing is advanced or retarded, timing the ignition advance, grooving the block keeps the oil groove directly over the gears regardless of the change in distributor location

    [​IMG]

    summit and JEGS sell several types of distributor gears, check the shaft diameter, on your distributor its USUALLY either .491 OR .500 and the gears DON,T interchange.
    verify the correct gear to install with your cam manufacturer, a melonized iron gear is usually used with a cast iron cam core and a bronze gear with a steel billet roller cam UNLESS its got a pressed on iron gear, and yes there ARE reverse rotation CAMS for marine applications, so if your salvaging a boat engine be aware
    [​IMG]

    [​IMG]
    [​IMG]

    [​IMG]
    [​IMG]
    [​IMG]

    [​IMG]
    [​IMG]
    3) Place a feeler gauge between the thrust washer and the gear. Try different combination's until the feeler is snug, but not tight. This is your end play. .010" is necessary for expansion from heat, and lubrication.
    if your seeing the timing change a few degrees, back and forth,
    slack in a work timing chain, worn distributor gear or not having the proper shim clearance on the distributor center shaft will provide slop that allows timing to vary several degrees

    [​IMG]
    [​IMG]
    This one shows .031". We will install a .020" shim.
    4)Buy these shims
    [​IMG]
    5)Find a .020" shim in the kit.

    Ive used moly grease for decades as a internal shaft lube
    [​IMG]

    don,t confuse distributor end cam gear clearance (usually set at .007-.010) (how far the distributor gear can move on the distributor shaft and the clearance between the end of the oil pump drive drive shaft and the inside of the gear drive (usually set at .050) set when the distributor seats over the shaft and is clamped in the intake manifold

    [​IMG]
    6)Drive out the roll pin. Support the gear, and drive it out with a pin punch. Use one slightly smaller than the pin.
    [​IMG]
    7)Install the shim.(If you don't have a micrometer, you can still do it. Just try varying thicknesses, temp hold the gear with your pin punch, and re-check the clearance)
    [​IMG]
    8)Re install the gear with the dimple up, as well as the rotor . Just drive it in till flush both sides. I gently start it, then use the vice to press it in.
    [​IMG]
    9)Re-check the end play. Here a .010" gauge is perfect.
    [​IMG]
    [​IMG]

    [​IMG]
    keep in mind the distributor base forms one wall of the lifter gallery oil passage
    [​IMG]
    so grooving the lower oil band helps spray extra oil on the distributor/cam gears contact area
    [​IMG]

    UH, ok, fair question....wass wrong with the procedure....???

    :beer:[/QUOTE]


    [​IMG]

    [​IMG]

    viewtopic.php?f=50&t=9946&p=38325#p38325

    [​IMG]

    BTW while were talking distribs...cutting a shallow grouve in the block passage wall the distrib passes thru to form one wall of the oil passages, or the distributor lower body so pressurized oil squirts directly into the cam gear and distributor contact area adds relieablity over just having splash oiling
    some of the better distributors with o-ring grooves have a small oil hole drilled between the o-rings that allows a steady stream of pressurized oil to enter the lower distributor shaft, the upper bearing is sealed so oil can,t exit into the upper distributor, but oil is routed to lube the lower bearing in the distributor, the oil exits to spray over the cam gear/distributor gear contact area, look closely at yours
    [​IMG]
    billet cams can and do have steel distributor gears that are not compatible with stock cast iron or melonized stock distributor gears, so anytime you change cams get and correctly install the matching distributor gear
    [​IMG]
    keep in mind theres a VAST difference in the QUALITY of bronze distributor gears and alloys vary wildly so its best to both use the cam manufacturers input during selecting components and not to assume all bronze gears are interchangeable
    THERE'S AN EXCELLENT CHANCE of chipping or burring either the distributor or cam gears during the procedure, or bending the oil pump drive shaft as there is by definition is a limited tooth engagement and less than ideal alignment of the component during that procedure
    yes it works most of the time IF your only concern is getting the distributor to drop fully in.....but if you could inspect the tip of the oil pump drive shaft and gears your almost guaranteed to see damage eventually, and if you do enough of the engine tear downs you'll also frequently see the broken connector collars the lower oil pump drive shaft and pump drive connections that can result from the temporary binding and mis-alignment during the procedure.....yeah! I know you don,t think IM correct! but after you have pulled down over a hundred chevys and rebuilt them you see patterns, ask questions and see the results

    "Wear Versus Destruction
    The gear that drives the distributor lives in a very difficult environment. First, in stock form, the only oil that lubricates the spinning cam and distributor gears gets there by the practically random splash effect. Second, in a wet-sump engine, the oil pump is driven off the distributor shaft. That means the resistance that the distributor gear applies as the cam gear tries to turn it comes not only from spinning the distributor shaft, but also the oil pump. If you are running a high-volume oil pump or racing on cold motor oil, this can cause tremendous pressure on the system. Even if you don't run a high-volume pump, the tight bearing tolerances used to increase oil control and high rpm levels seen in modern racing engines still cause the pump to work very hard and put extra resistance on the distributor gear."
    [​IMG]
    look if your only installing a distrib after a manifold swap,
    ITS not complicated, pull the #1 plug and put you thumb over the hole tightly, turn the engine in the normal dirrection of rotation, with a breaker bar and scocket untill you get compression in the #1 cylinder, as the damper TDC line approches the TDC timing tab, drop the distributor in with the rotor facing the #1 cylinder,compensate for the way the distrib gear causes the rotor to rotate as in seats,so its seated pointing where you intended, if it won,t fully seat turn the oil pump drive with a very large flat blade screw driver untill it will,with the distrib removed and try again, once it seats,facing the correct dirrection, install and tighten the distrib clamp so its difficult to spin the distrib easily by hand but still possiable to spin the distrib by hand, re-install the #1 plug and wire, install the cap and all ignition related wires, use your timing light and set the ignition timing,per the shop manuals instructions, tighten the distibutor hold clamp so it can,t move, IF it takes more than 10 minutes your in need of more practice or nearly hopeless as a mechanic.The CLOYES true roller style is vastly superior to the factory link belt design
    ID suggest verifying TDC and the use of timing tape on the damper and a decent timing light rather than guessing.

    once youve located TRUE TDC, you either install timing tape on your current damper, or a marked cover
    [​IMG]
    then graphing your advance curve

    http://garage.grumpysperformance.com/index.php?threads/timing-lights.875/

    http://garage.grumpysperformance.com/index.php?threads/timing-tabs-and-indicators.1015/

    http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

    [​IMG]
    this is usually a good start point
    [​IMG]


    how come its 180 degees out of phase?
    I get this question all the time, well here’s something I see lots of guys don’t understand, ONCE YOU'VE INSTALLED A CAM WITH THE TIMING MARKS YOU MUST ROTATE THE CRANK 360 DEGREES BEFORE DROPPING IN THE DISTRIBUTOR, while its true that if the, timing marks are positioned so the crank is at 12 o,clock and the cam gear is at 6 o,clock that the cam lobes will be in the position that fires #6 cylinder that HAS NO EFFECT AT ALL (on finding TDC,) for aligning the degree wheel with TDC,or THE timing tab pointer, for degreeing in the cam, the piston passes thru TDC TWICE in every firing cycle once on the firing/power stroke and once on the exhaust stroke, the cam rotates at exactly 1/2 the speed of the crank so to make it easy to line up the marks they install it with the marks at the closest point 6/12 for easy indexing, rotate the engine 360 degrees to the #1 TDC power stroke and the crank gear will still be at 12 o'clock 12/12 but the cam will be at 12 o,clock also, rotate another 360 degrees and your back where you started. its simply easier to index the cam at the point where the index marks align closely. look at how the cam lobes themselves open the valves when the cam is just installed the #1 cylinder valves are slightly open and the #6 are closed per "Lunati" ‘’YES YOU ARE RIGHT - WHEN CRANK IS AT TWELVE AND CAM IS AT SIX THEN #6 CYL IS FIRING AFTER YOU LINE UP YOUR MARKS AND INSTALL GEAR THEN ROTATE YOUR CRANK ONE REVOLUTION AND THEN DROP THE DIST. IN - AT THAT POINT

    [​IMG]

    WATCH VIDEO


    [​IMG]

    http://boxwrench.net/specs/chevy_sb.htm
    [​IMG]

    drop the distributor in with the rotor pointing at the #1 cylinder, and YEAH! it physically possible to get the distributors rotor to point at any place you want it too by changing the oil pump drive shaft alignment with a large flat blade screw driver while the distributors out of the engine and that's easily changed, but to do it correctly,you want the rotor to point at the #1 cylinder on the compression stroke, so pull the #1 plug, get a large ratchet/socket on the damper and put your finger over the open plug hole and slowly rotate the engine by hand in its normal rotational direction until you see pressure build under your finger as the rotor approaches #1 cylinder location on the distributor base which you should have marked as its supposed to be in direct alignment between the distributor and the number 1 cylinder on the engine, remember the distributor and cam gears are helical and the rotor turns as it seats so compensate slightly. and the rotor should be just coming into alignment as pressure builds under your finger, once that's done re-install the distributor cap and plug and use a timing light to set the timing, you normally want about 6-12 degrees BTDC at idle and watch it advance to about 37 degrees as the rpms build to about 3000rpmok, then have you checked the distributor to oil pump drive shaft length?,[​IMG]
    IF YOUR DISTRIBUTOR LEAKS OIL AROUND THE BASE GASKET..
    it seems the distributor is not seating fully against the intake ring gasket and the distributor to oil pump drive is suspected of being a bit to long, there should be about .050 slack MINIMUM between the oil pump drive shaft and the distributor gear

    READ THIS

    viewtopic.php?f=54&t=123&p=326#p326

    viewtopic.php?f=70&t=6778&p=21751#p21751

    watch the video

    http://www.youtube.com/watch?v=YdIGZ-tV ... re=related

    [​IMG]

    [​IMG]
     
    Last edited by a moderator: Nov 12, 2017
  2. grumpyvette

    grumpyvette Administrator Staff Member

  3. grumpyvette

    grumpyvette Administrator Staff Member

    if your distributor won,t seat on the manifold and gasket the oil pump drive shaft may need to be shortened (thats the correct route)or theres distributor shim gaskets

    http://www.summersbrothersracing.co...LF-CUT-DRIVE-FLANGE-BIG-BLOCK-CHEVY_p_30.html

    viewtopic.php?f=54&t=123&p=326#p326
    http://www.stockcarracing.com/techartic ... tallation/
    http://www.summitracing.com/parts/mor-26150
    [​IMG]
    [​IMG]

    GOT a distrib that seems to come loose and not hold timing?

    MOST DISTRIB CLAMPS LOOK LIKE THIS

    [​IMG]
    THEY WORK BUT NOT EXCEPTIONALLY WELL,
    step one

    buy & install this
    [​IMG]
    http://www.jegs.com/i/Moroso/710/26215/10002/-1

    the distributor won,t move if its installed correctly

    "Why does it have the bolt hole and the slot?
    John"

    your current distributor can usually be easily modified by a local machine shop with a lathe for an adjustable slip collar by carefully machining off the current one and adding a slip collar, if you need to make distributor gear to cam gear engagement or oil pump drive shaft length changes
    [​IMG]
    http://www.summitracing.com/parts/MOR-26217/?rtype=10
    the clamps firmly tightened to the distributor shaft after the timing is correctly set,locking its location in relation to the block,a STUD gets installed with LOCTITE into the intake manifold, it sticks up about 1.25" and most guys use one of these
    [​IMG]
    and it has to go thru the SLOT, the cap screw is used to tighten the clamp to the intake.
    with practice you can pull and replace the distributor and maintain the correct timing.

    you SHOULD READ THRU THIS LINK ALSO

    viewtopic.php?f=55&t=293&p=358#p358

    viewtopic.php?f=70&t=855&p=8931&hilit=distributor+gear#p8931
     
    Last edited by a moderator: Feb 18, 2016
  4. grumpyvette

    grumpyvette Administrator Staff Member

    non-o-ring distributor base , that relies on tight clearances to limit oil flow from the blocks oil passages


    [​IMG]


    notice the o-rings on these distributor bases used to limit oil loss from the oil passages in the block,

    [​IMG]

    [​IMG]

    [​IMG]
     
  5. Dustytrix

    Dustytrix Active Member

    I am having a problem getting my distributor to go in the engine. It will go in untill the distributor gear clears the lifter gally, then it looks like the shaft is a fraction to large. I can see rub marks on the shaft from the engine block. The distributor gear has not gone deep enough to catch on the cam gear. The dizzy is a new pro comp alum type, do you think I might need some emery cloth and take a little off the shaft? I wish I had tried a fit test before I installed the intake. Thanks Dusty
     
  6. grumpyvette

    grumpyvette Administrator Staff Member

    measure your old distributor with a set of calipers and compare it to your new distributor, but its my guess thats NOT the issue as IVE seen the oil bands be a bit smaller in diam. that ideal but never larger.
    Id suggest , its far more likely to be related too, the oil pump drive shaft not seating into the lower distributor gear, the oil pump drive shaft not seated correctly on the oil pump,the wrong distributor gear or improperly installed distributor gear or the intake manifold alignments a bit off, or possibly, the mistake of use of a BBC oil pump drive shaft in a SBC application, where in some cases its easily mistakenly installed, but careful inspection should show the source of the problem.

    BTW IF it was a 400sbc and you used a standard oil pump drive shaft,
    [​IMG]
    the oil pump shaft must have the reduced diam. mid section due to the 400 sbc larger main bearing diam. to allow clearance

    [​IMG]
     
  7. Dustytrix

    Dustytrix Active Member

    Ok thanks I will look back over this today , I have not put the oil pump shaft on yet , so that,s not the problem I will get back intouch tonite.
     
  8. grumpyvette

    grumpyvette Administrator Staff Member

    the oil pump drive shaft can only be inserted from below, up thru the main cap as it won,t drop in from the lifter gallery side, once its installed , the oil pump is installed after its installed, then the pick-up to oil pan floor clearance is verified and the oil pan installed, per the threads below and their links


    viewtopic.php?f=54&t=2376

    viewtopic.php?f=54&t=1800

    viewtopic.php?f=54&t=1192

    viewtopic.php?f=54&t=64

    viewtopic.php?f=54&t=206&p=1154&hilit=+synthetic+gasket#p1154

    viewtopic.php?f=44&t=700&p=973&hilit=+seal+thick+synthetic#p973
     
  9. Dustytrix

    Dustytrix Active Member

    I got it to go in , I put the dizzy in another block and it was snug fit so then I coated it with some grease and put it in the new motor it fit tight but it went in. I had to replace the oil pump shaft is why its not in. For some reason the oil did not work yesterday on the distributor shaft like the grease did today . Thanks .
     

Share This Page