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post #1 of 17 (permalink) Old 05-26-2011, 12:46 AM Thread Starter
 
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Help with timing pls

So I got my engine back from the machine shop and he installed the timing chain when i picked it up. I am kind of a rookie and this and need help understanding how this works. So the cam gear is at 12 and the crank gear has a R at 12. What's the R? Second, cylinder #2 and #5 are at tdc. Can you guys help me understand or did this dude screw up?
When I set #1 at tdc the marks are lined up at about 2 o clock

Thank You
Seol

Last edited by Seol21; 05-26-2011 at 02:20 AM. Reason: added more
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post #2 of 17 (permalink) Old 05-26-2011, 09:03 AM
 
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Originally Posted by Seol21 View Post
So I got my engine back from the machine shop and he installed the timing chain when i picked it up. I am kind of a rookie and this and need help understanding how this works. So the cam gear is at 12 and the crank gear has a R at 12. What's the R? Second, cylinder #2 and #5 are at tdc. Can you guys help me understand or did this dude screw up?
When I set #1 at tdc the marks are lined up at about 2 o clock

Thank You
Seol
put cam at 6
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post #3 of 17 (permalink) Old 05-26-2011, 11:40 AM Thread Starter
 
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If I put cam at 6 , cylinder #2 is at tdc. Is that ok?
Cam is a edelbrock 7157/ ram IV
Pontiac 400. .040 over
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post #4 of 17 (permalink) Old 05-26-2011, 11:52 AM
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Originally Posted by Seol21 View Post
So I got my engine back from the machine shop and he installed the timing chain when i picked it up. I am kind of a rookie and this and need help understanding how this works. So the cam gear is at 12 and the crank gear has a R at 12. What's the R? Second, cylinder #2 and #5 are at tdc. Can you guys help me understand or did this dude screw up?
When I set #1 at tdc the marks are lined up at about 2 o clock

Thank You
Seol
It's ok - relax Remember that the cam makes one revolution for every two of the crankshaft, so you actually have two choices of how to install it. Imagine two clock faces, one on the front of your crank, the other on the front of your cam. Turn the crank so that the timing mark on the gear is at 12 o'clock (straight up). Turn the cam so that the timing mark on the cam gear is either at 12 o'clock (straight up) or 6 o'clock (straight down). Install the chain, making sure you maintain that alignment. You're done.

(I like doing it with the cam gear at 6 o'clock because it's easier for me to "see" that the marks are in alignment, but either way will work.)

Later in the build, when you're installing the distributor, you'll want to make sure that you have the motor at TDC on the compression stroke and install the distributor so that the rotor is pointing to the #1 terminal on the cap.

Bear

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post #5 of 17 (permalink) Old 05-26-2011, 12:34 PM
 
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RED FLAG!!

If there are three keyways in the crank gear, and the "R" keyway is used, the cam will be "retarded" 4 degrees from "straight up". This a cam tming thing, not an ignition timing thing (for clarity). The cam really should be "degreed" when it's installed. It really can make a big difference in performance. Typically, there will be an "0" for "staight up", an "A" for "advanced" and the "R".

What IS the cam?

Jim
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post #6 of 17 (permalink) Old 05-26-2011, 12:42 PM Thread Starter
 
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Its a an edelbrock 7157 / RA IV. So clearly it was installed wrong right. When cylinder 1 is a tdc I should have the dots lined up right. Now should I use the 0 in the crank gear. Or do want to retard or advance it. As of now if I put# 1 at tdc, the cam gear marker is at about 2 o clock and so is the R on the crank gear.
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post #7 of 17 (permalink) Old 05-26-2011, 12:49 PM
 
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Its a an edelbrock 7157 / RA IV. So clearly it was installed wrong right. When cylinder 1 is a tdc I should have the dots lined up right. Now should I use the 0 in the crank gear. Or do want to retard or advance it. As of now if I put# 1 at tdc, the cam gear marker is at about 2 o clock and so is the R on the crank gear.
does your crank gear have more than one slot? even if you use the r crank slot you still use the dot to line up the marks.
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post #8 of 17 (permalink) Old 05-26-2011, 03:15 PM Thread Starter
 
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Ok so no matter what slot the crank gear is in the 0 and the dot on the cam gear need to line up while in tdc. So if the R and the dot keep lining up its already wrong correct? Sorry for the rookie questions guys just trying to learn.
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post #9 of 17 (permalink) Old 05-26-2011, 03:50 PM
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Ok so no matter what slot the crank gear is in the 0 and the dot on the cam gear need to line up while in tdc. So if the R and the dot keep lining up its already wrong correct? Sorry for the rookie questions guys just trying to learn.
Do you happen to know exactly which timing set (gears and chain) you have? That'd help. I missed earlier when you were talking about the 'R' on the gear, glad Mr. P caught that. The "R" and the "A" (if that's what you have) are used if you want to install the cam "retarded" or "advanced". It's not something to do unless you know what you're doing and why --- GENERALLY SPEAKING -- advancing the cam will move the engine's power band lower in the RPM range, retarding it will move it higher --- but those actions also have an effect on dynamic cylinder pressure too and can get you into trouble with detonation - again if you don't know what you're doing. Mr. P-Body also mentioned degreeing the cam --- highly recommend that you do that or have it done, otherwise you'll never really be sure "where it's at".

Fer example, if you've got a RamAir IV grind on that cam then it's already a "higher than normal" RPM cam, retarding it (which is what it's starting to sound like you've got) is going to make it even more so --- unless the rest of your combination (gears, converter, etc.) are all set up for that you're likely to be pretty disappointed in how it performs on the street - it's going to have very little bottom end power set up that way. With the "wrong" gearing, by the time you get your motor up into the sweet spot the guy in the other lane is going to be long gone. How big's the motor? How many cubic inches? What tranny and rear gear are you running?

Manufacturers of both cams and timing sets sometimes make mistakes - just because a mark lines up with another mark doesn't guarantee that's really TDC - the only way to know for sure is to measure everything yourself, starting with using a piston stop to locate actual TDC. I put a nice and not cheap SFI-rated harmonic balancer on the engine for my 69, and when I measured everything I found out that the "TDC" mark on the balancer was actually "wrong" by a few degrees. Had I not checked it (and corrected it with a timing tape) then everything I did after that with trying to tune that motor would have been off and I wouldn't have even known it.

Bear

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Last edited by BearGFR; 05-26-2011 at 04:03 PM.
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post #10 of 17 (permalink) Old 05-26-2011, 05:14 PM
 
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Ok so no matter what slot the crank gear is in the 0 and the dot on the cam gear need to line up while in tdc. So if the R and the dot keep lining up its already wrong correct? Sorry for the rookie questions guys just trying to learn.
a picture of the crank gear would sure help. there should be a dot on the colar of the crank gear. that is what you line up with even if you use the a or r slots
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