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Cam Timing Question [EDIT: UPDATE - see latest post]

Discussion in 'The Garage' started by jim burke, Apr 11, 2005.

  1. jim burke

    jim burke Registered Member

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    I'm swapping out the cam in my '89 350. Before I started disassembling the engine I put the timing mark on the crank damper to the "0" mark on the timing cover (TDC). The rotor was pointing to the distributor terminal for cylinder number one.

    When I took off the timing cover I noticed that the mark on the crank sprocket was in the 12 o'clock position (where it's supposed to be). The mark on the cam sprocket was also at 12 o'clock. I thought it would have been in the 6 o'clock position. I called tech services at Cloyes. I explained everything to the guy, he seemed to understand me perfectly and know what he's talking about. He said everything is fine and that's the way it's supposed to be (timing mark at 12 o'clock for both sprockets). The GM factory service manual shows that to set to set the cam timing, both marks should be as close as possible to each other (12 o.c. on the crank; 6 o.c. on the cam).

    Question: Is the timing mark made (stamped) 180* off on the aftermarket (Cloyes) cam gear for some reason (vs. the factory part)? If so, why :confused: ??? The engine ran pretty good, so I can't believe the cam was 180* out of synch w/ the crank. The diagram in the factory manual shows the timing mark (on the cam gear) at 6 o.c. and the dowel pin at 9 o.c. On mine (the Cloyes), when the dowel pin is at 9 o.c., the timing mark is at 12 o.c.

    I'm more than a little confused on this one...
     
    Last edited: May 6, 2005
  2. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    hes right, 12 oclock and 12 oclock is TDC for #1 cylinder, 12 on the crank and 6 on the cam is TDC for #6 cylinder(180 out on the dist.)
     
  3. jim burke

    jim burke Registered Member

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    Here's what I'm talking about:

    Dowel pin @ 9 o'clock; timing mark @ 6 o'clock:
    [​IMG]

    Dowel pin @ 9 o'clock; timing mark @ 12 o'clock:
    [​IMG]

    Is the diagram in the manual just wrong :confused: ? I'm not trying to beat this thing to death, I just want to make sure I understand why there's a difference.
     
  4. highrpm

    highrpm Newbie

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    Cam Timing

    The cam rotates at half engine speed, rotate your crank another turn and the marks should be at 6 oclock cam and 12 crank.
     
  5. 1-ton

    1-ton 1/2 ton status Premium Member

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    Yes, the timing marks should be at 12 and 6, when on the number one cylinder compression stroke.

    Does this Cloyes timing gear-set have three marks on it for a choice of Advancing, Retarding, or a Standard timing set up? If it is, then there should be a Triangle (Retarded), Square (advanced), and Circle (standard). Make sure you are lining up the marks, which are on the outside of the Cloyes camshaft timing gear, and not the inside ones where it bolts to the camshaft. The marks on the inside of the camshaft gear are only for selecting if you want it to be cam timing to be retarded, advanced, or standard, but are not the marks used to actually line up the crank and camshaft gears with.

    When the marks are 12 and 12, then the number 6 cylinder should be on the compression stroke? Are you sure the distributor is not pointing to the number 6 cylinder?
     
  6. jim burke

    jim burke Registered Member

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    But that's not going to change where the mark is machined into the cam gear (relative to the dowel pin). My *cam gear* (and all the ones I took a look at on eBay) doesn't match the diagram from the manual. I'm starting to think the manual is wrong.

    If the cam was rotated a half turn (crank rotated a full turn) the timing mark would match what's in the manual, but the dowel pin would not (it'd be at 3 o'clock instead of 9 o'clock like in the picture from the manual).
     
    Last edited: Apr 12, 2005
  7. jim burke

    jim burke Registered Member

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    Isn't that usually done w/ different keyways on the crank gear?

    It's apart now, but I'm 99.9999% positive the rotor was pointing to the #1 (not #6) terminal on the distributor.
     
  8. MTMike

    MTMike 1/2 ton status

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    I suppose it's possible that the cam AND distributor were 180* off and in turn working properly, but I've NEVER heard of the 12:00/12:00 sprocket setup.

    I've always been taught it was 12:00 on the crank and 6:00 on the cam. Logic and experience tells me that if it's 12:12 it that would be #1, TDC on the exhaust stroke, not the compression stroke. If somebody (I.E. a previous owner changed the timing chain) put the sprockets in in the 12/12 pattern, they would have found that when they put it all back together, the distributor was 180* off, and had to flip the rotor to compensate. It then would have ran right, but the marks would be off for the next person who pulled the cover.

    Correct me if I'm wrong...... :thinking:
     
  9. 1-ton

    1-ton 1/2 ton status Premium Member

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    Yes, you are correct. What I was getting at is that, for some reason, Cloyes also stamps the different timing mark symbols towards the center of the camshaft timing gear (where the camshaft timing gear is bolted to the camshaft), and also on the outside edge (where the teeth are). People often make the mistake of lining up the crankshaft timing marks with the timing marks towards the center of the camshaft gear (which are the wrong ones), and not the timing marks on the outside edge (which are the correct ones).

    Yes, I think you are correct. I could not remember if 12 and 12 was number 6 compression or number 1 exhaust.
     
    Last edited: Apr 12, 2005
  10. 79Jimmy

    79Jimmy 1/2 ton status

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    12 o'clock cam gear and 12 o'clock crank gear and 9 o'clock camshaft dowel pin(with any Cloyes timing set that I've ever used) IS TDC compression for the #1 cylinder. 6 o.c. cam and 12 o.c. crank is like you think, TDC compression for the #6 cylinder. I've got a 383 in my living room right now (3/4 built) with a Comp cam and Cloyes True timing set installed and degreed using a degree wheel and a Mitutoyo digital indicator to verify intake and exhaust events and intake centerline. Everything is bang on. Either the picture is wrong or GM timing marks are different :( I've also never seen Cloyes stamp any marks towards the inside of the cam gear only the crank gear.

    Everything you describe sounds normal to me :)

    James
     
  11. Mad-Dog

    Mad-Dog 1/2 ton status

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    If he sets the crank gear mark at 12 and the cam gear mark at 6 then drops the rotor down at #6 then the cam and ignition timing are set correctly.
    Some cam gears have a oversized dowel pin hole that uses advance or retard bushings to adjust the valve timing while other gear sets use 3 different keyways on the crank gear to adjust the valve timing (choose your poison).
    4 degrees advanced, straight up or 4 degrees retarded, most cam grinders say to install their grinds straight up as they have already ground 4 degrees of advance into the cam...
     
  12. jim burke

    jim burke Registered Member

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    Edit: Update

    UPDATE:

    I put the engine back together with both the cam and crank timing marks in the 12 o'clock position. The valves for cylinder #6 were rocking (one had just closed and the other was just about to open) with the timing mark on the damper lined up with 0* on the timing tab. Both valves for cylinder #1 were closed. Dowel pin on the camshaft gear was at 9 o'clock. The ignition rotor was pointed to the terminal for cylinder #1. Everything works fine :saweet: .

    The GM factory manual (see picture above) is WRONG :doah: :screwy: . The way they show the dowel pin and timing mark relative to each other (on the cam gear itself) is not the way it actually is (look at the diagram vs. the cam gear I took a picture of).
     
  13. smalltruckbigcid

    smalltruckbigcid 1/2 ton status

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    The cam is timed 180degrees off if you did 12 and 12. do it 12 and 6 then turn the engine 1 revolution and drop the dizzy in and your good to go.
    George
     
  14. jim burke

    jim burke Registered Member

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    Then why does the engine run so well? I'd have to respectfully disagree. If it was 180* off, the engine would run poorly, if at all. What you're telling me is the exact opposite of what Mad-Dog, 79Jimmy and the Cloyes tech services guy told me. I'm not trying to argue, but I'm pretty sure you're wrong.
     
  15. jim burke

    jim burke Registered Member

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    Maybe I misunderstood you. I re-read this. *IF* you're telling me to:

    A) Put it to 12 and 6 and then
    B) Turn the engine (crank) one revolution

    Then it will be at 12 and 12. If that's the case, I don't know why you'd say 12 and 12 is wrong :confused: .

    In any event, I'm quite confident I've got it correct and I'm not changing a thing. I just wanted to post the end result so if anyone in the future has the same problem they'd be able to figure it out by reading the thread.
     

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