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:idea: About distributor gear wear (UPDATED!!)
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Thread: :idea: About distributor gear wear (UPDATED!!)

  1. #1
    Thank you from BT ULTIMUS MAXIMUS STATUS jeepsr4ever's Avatar
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    :idea: About distributor gear wear (UPDATED!!)

    Here is a list of things that can cause distributor and cam gear wear.



    1. Oiling holes throught the large timing gear, the groove for the oiling hole must be at 2:00 from the keyway, also all passages must be clear.

    2. Cam bearing at the front of the block must have a groove in it, this sends oil through the cam at all orientation and rotation of the camshaft.

    3. The cam must have a 90 degree oiling hole setup to feed the timing gear and must be free from casting obstruction.

    4. Cam gear must be matched to the distributor gear. Their are 2 types of cam gears out there and at least 3 types of distributor gears, they CANNOT be mismatched, replacing just the cam gear will cause big problems.

    5. The timing cover: The oil pump drive gear's shaft that connects to the distributor goes through a hole in the timing cover, this is a precision hole and if tapered can cause distributor gear wear through chatter.

    6. Oil pump gears: Using longer than stock or poorly made after market gears can cause chatter, binding or premature wear of the oil pump drive gear's shaft hole. When you install a aftermarket kit that comes with new gears the idler gear pin MUST be longer. The cam and distributor gears are only rated at a certain torqueload. Some of the new gears available as of 4-22-05 are now hardened (both gears) and can withstand greater pressures

    7. Oil filter.......Yes oil filters can cause premature dizzy and cam gear wear. If you run the wrong oil (too heavy) or a filter that gets clogged early or a filter that isnt a high flow you open up your oil filter bypass and not only send dirty oil through your motor, you also exerpt a high amount of pressure on the oil pump and that alone can cause gear wear, this happens mostly on start up. In late 87 chrysler got rid of the oil filter bypass on the oil filter adaptor, after market oil filter adaptors also have this cast in. Beware that if you use a high pressure oil pump spring without a oil filter bypass you run the risk of ballooning your filter.

    8. Cam walk: Cam walk can be attributed to a cocked or poorly place cam plug (large freeze plug that hold the cam from leaving the rear of the block. Also cam walk can be caused by bad lifters, worn cam bearings, cam bearings installed improperly, or a poorly ground cam and in some cases a new cam that gets flattened on startup

    9. Cam walk can also be attributed to lack of relief holes in the back of the cam, you see pressure can increase between the end of cam and cam plug, most of these cam must be checked, we have 3 in here with no relief holes...............dang summit

    10. The retainer washer for the front of the cam that holds the distributor gear must also provide a positive seal for proper oiling. Off the shelf washers can sometimes have nicks or be convex or concave which to factory torque specs can lead to a loss of oil in front of the camshaft.

    11. The installation of the timing cover without locator pins or worn location holes will cause a mis-orientation of the thrust on the distributor gear and eventually may result in a broken or heavily worn set.

    12. Early Crown timing covers that were not checked for proper dimensional tolerance can attribute to up to 100% of the fast gear wear. Even today vendors should check for proper alingment.


    I have seen a AMC V8 go 210,000mls without any cam walk and very little gear wear. I have also seen a AMC V8 go 2 miles and eat the gears. The factory engineers knew all this and they put these motors together accordingly. Building a AMC V8 can be a expensive build and its a dirty dirty shame to have something like a cam or distributor gear go out, this can cause Major scoring on the oil pump cavity and also can cause the oil filter bypass to open and voila, roached bearings. Hope these hints help anyone out who is building a AMCV8.

    -MC

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  2. #2
    Thank you from BT Tech Master Bulltear Forum
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    there must be a slight indentation on the back of the timeing cam gear

    best ever 11.669 @ 112.33 mph in 1/4 mile on 33 x 10.50 slicks and 4" lift / 7.358 @ 93.03 mph in the 1/8 mile

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    Nice write-up, very nice. From what else I've read, incorrectly ground cams have at least two issues: 1) wrong journal dimensions and 2) lack of lobe taper that keeps the cam back in the block. I wouldn't rule out the possiblity that some will go flat due to incorrect sintering process or simply loss of tempering during a faulty grind.
    '65 J200 401

  4. #4
    Thank you from BT Tech Master Bulltear Forum
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    cast timming cam gear


    old style roll master cam gear



    new style roll master with bearing cam gear

    best ever 11.669 @ 112.33 mph in 1/4 mile on 33 x 10.50 slicks and 4" lift / 7.358 @ 93.03 mph in the 1/8 mile

  5. #5
    Thank you from BT ULTIMUS MAXIMUS STATUS
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    does this apply to the I-6 258?
    83 eagle (r.i.p.)
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  6. #6
    Thank you from BT ULTIMUS MAXIMUS STATUS jeepsr4ever's Avatar
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    nope the rules change dramatically for the sixes

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  7. #7
    I recently got a "Proform" HEI type distributor for my 73 CJ5 w/304 and have heard you shouldnt match a new drive gear with a old cam gear and vis versa. I was thinking of removing the old drive gear and putting it on the new distibutor rather than rebuilding the block. Is this and option I have? If so, is there anything I should be particularly weary about?

  8. #8
    Thank you from BT ULTIMUS MAXIMUS STATUS jeepsr4ever's Avatar
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    Welcome aboard!

    Its true their are 2 different profiles on the dizzy gears these days. One is from the oem gear the other is from the import dizzy gear (the superior one) believe it or not. you may or may not be able to get away with doing that. You cant even take your old one and install it on your new dizzy as their are 13 teeth on each gear and MUST be matched. But lots of guys have just nstalled a new dizzy gear with success...I have had moderate success.

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  9. #9
    Thank you from BT Tech Master Bulltear Forum
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    found this on the amc forum
    More cam/distributor gear issues
    From: Randy Guynn <amx69@swbell.net>
    Date: Wednesday, February 18, 2004 08:23

    This old bugaboo is rearing it's ugly head yet again. The latest
    casualty comes from mis-matched parts. The cam did not have a groove in
    the front journal, and the front cam bearing was not a grooved type.
    This shuts off all oil to the front of the engine which in turn burns
    the gears up.

    Anyone & everyone in the AMC hobby needs to be fully aware of how the
    gears recieve oil. They also need to understasnd the entire system of
    parts , what is correct, what is not, in order the be sure they are not
    going to have troubles in this area.

    When the engines starts and oil pressure develops, the very first part
    of the engine to recieve oil is the front cam journal. The oil splits
    the path at that point and part goes thru the timing gears, the
    remainder goes to the rest of the engine. The oil continues thru each
    cam journal where it splits and oils the upper end and the lower end.

    Back to the very first spot that sees the oil, the front cam journal.
    #1, the cam, & or Bearing MUST have a 360 degree groove. No groove, then
    the only time oil will get to the gears is once every 360 degrees, when
    the oil holes line up, the gear will get a small squirt of oil and that
    is it.
    #2,The cam has a hole in the side of the front journal and it also has a
    hole in the face of the journal. These two holes MUST intersect. If
    these two holes do not join, then NO OIL ever gets to the timing gears.
    #3,The upper timing gear has a pocket machined or cast into the rear of
    the sprocket. This pocket MUST line up with the hole in the face of the
    cam journal. If the pocket does not line up, no oil will go to the gears.
    #4. The upper timing gear needs a heavy chamfer completely around the
    I.D. of the hole where is slides on the camshaft. This chamfer is not
    there to aid in fitting the cam easier, it is there to supply a route
    for the oil to go. No chamfer, no oil gets to the gears.
    #5, The upper timing gear also has two slots. One slot is for the keyway
    that holds it to the cam, the other slot is for oil transfer. The oil
    transfer slot MUST be free and open, no casting flash to block oil.
    #6 Next the fuel pump eccentric comes into play. It will also have two
    slots. One for the keyway, one fore the oil transfer slot.
    #7, finally we come to the cam gear which drives the distributor. This
    gear too has two slots. Again one for the keyway, the other for oil
    transfer. The transfer slot must be open and lined up with all the other
    oil transfers so there is an open groove which will supply the oil to
    the gears.
    #8, the Cam gear MUST have 4 small holes around the outside diameter of
    the gears. 3 of these small holes are on the smae plane, lined up with
    each other. The one hole will be offset. If this one hole is not offset,
    then the keyway will block the oil going to it.

    There are other issues at play here such as mis-machined parts, cam
    walk, bad gears, etc. However, no matter how good of quality parts used,
    if the oil cannot get to the gears then the gears will be burned/eaten up.

    Maybe you are just freshing up your engine and think everything is just
    fine, and it might be. But, just change ONE part in the ''oil circuit''
    and that part could block oil from getting to the gears. This oiling
    issue is VERY, VERY important. Everytime you assemble am AMC V8 you
    should look EVERY piece over that makes up the oil delivery to the
    gears. If you slack off here you are just asking for trouble when it
    comes to AMC V8 engines.

    best ever 11.669 @ 112.33 mph in 1/4 mile on 33 x 10.50 slicks and 4" lift / 7.358 @ 93.03 mph in the 1/8 mile

  10. #10
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    best ever 11.669 @ 112.33 mph in 1/4 mile on 33 x 10.50 slicks and 4" lift / 7.358 @ 93.03 mph in the 1/8 mile

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