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Old 04-23-2011, 11:26 PM
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timing marks

this could easily be a nonsense question. when pulling the cam out of my car today i noticed the timing mark on the cam and crank were both pointing straight up and not toward each other. when installing i followed the same procedure. but i notice in the past and on slides it shows the timing marks pointing at each other.......any thoughts?

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Old 04-24-2011, 12:00 AM
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Both pointing at 12 o clock means you are at true top dead center. When you install a cam dot to dot your actually at tdc on cylinder 6. This is fine. You have to turn the motor one turn before you put the distributor in so your not 180 off.

Last edited by cjoform; 04-24-2011 at 12:08 AM.
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Old 04-24-2011, 12:23 AM
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If you've never thought about it, it can be confusing. In order for all 8 cylinders to fire in a cycle, the crank must turn two complete turns ( 360 degrees + 360 degrees = 720 degrees). Since the cam gear is twice the diameter of the crank gear, it turns only half as fast as the crank, so it makes one revolution (360 degrees) while the crank goes 720 degrees.

As cjoform said, when you assemble the motor, you line up the dots with the cam gear dot at 6 PM and the crank gear dot at NOON. Nobody knows why the GM engineers set it up like that, but when you install the gears on the dots, you are on TDC firing for #6 cylinder, not #1. Once you get the gears all buttoned up, you must then turn the crank one revolution (360 degrees), to where both the crank gear and the cam gear are at 6 PM. This puts the #1 cylinder at TDC on the firing stroke and you are ready to install the distributor.
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Old 04-24-2011, 05:01 AM
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Quote:
Originally Posted by techinspector1
As cjoform said, when you assemble the motor, you line up the dots with the cam gear dot at 6 PM and the crank gear dot at NOON. Nobody knows why the GM engineers set it up like that,
Hey Tech, I was told by a GM mech. that it was done that way because it's easier to line up the dot's at 6 and 12 than it is at 12 and 12. It seems that some mechanics can't see a straight line and 1 tooth mistakes were made trying to line them up at 12 and 12.

And then, there's always the one eyed mechanics.
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Old 04-24-2011, 05:56 AM
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You guys keep talking about the 12 and 12 position. My last engne,which I built ,installed and wired myself last summer was set with the gears at the 6 and 12 position as usual. I installed the balancer and moved it to the 12* position and dropped the dizzy in facing the #1 position. Moral of the story-it started right up just like my last 3 engines( 2-350s & 1-454) I and I alone build my engines-with no help-so I don't understand why they fire up when you guys say its not supposed to.

Last edited by TroyBoy; 04-24-2011 at 06:18 AM.
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Old 04-24-2011, 06:22 AM
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timing

u just explained why.. u can do it 2 ways.. 6 and noon and drop dizzy in pointing to #6 or rotate crank one full turn and put dizzy in pointing to #1... if u didn't rotate it and droped it in pointing to #1 it will not start.. or if it did it's running really bad..
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Old 04-24-2011, 08:47 AM
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Quote:
Originally Posted by delawarebill
u just explained why.. u can do it 2 ways.. 6 and noon and drop dizzy in pointing to #6 or rotate crank one full turn and put dizzy in pointing to #1... if u didn't rotate it and droped it in pointing to #1 it will not start.. or if it did it's running really bad..
Actually, it's all about getting the cam in sync with the crank than getting the dizzy in at tdc. You can start the firing order anywhere the rotor is pointing at tdc. There is no absolute position chiseled in stone as to the orientation of the dizzy, only the rotor to where you start the firing order.

Having the vacuum can pointing around 8 o'clock on the pass. side is like being politically correct.
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Old 04-24-2011, 12:27 PM
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yeah thought about it after posting (im clearly an idiot) thank you guys for your responses
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Old 04-24-2011, 12:37 PM
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Quote:
Originally Posted by badknuckles
this could easily be a nonsense question. when pulling the cam out of my car today i noticed the timing mark on the cam and crank were both pointing straight up and not toward each other. when installing i followed the same procedure. but i notice in the past and on slides it shows the timing marks pointing at each other.......any thoughts?
The way I see it, you saved yourself some work not having to turn over the engine 1 turn by hand. Nothing idiot about that.
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Old 04-24-2011, 03:23 PM
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Quote:
Originally Posted by sqzbox
Hey Tech, I was told by a GM mech. that it was done that way because it's easier to line up the dot's at 6 and 12 than it is at 12 and 12. It seems that some mechanics can't see a straight line and 1 tooth mistakes were made trying to line them up at 12 and 12.
And then, there's always the one eyed mechanics.
Yeah, I understand that, but what I'm saying is, why didn't the engineers punch the timing gear 180 degrees from where they did from the git-go, when they designed the motor? That way, when you put the gears in at 6 and Noon, you'd be on #1 firing and wouldn't have to turn the crank to drop the dizzy in for the politically-correct 8 O'Clock vacuum can orientation.

It just seems to me like somebody either dropped the ball or they did it that way to generate more business for the Chevy dealer service department.
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Old 04-24-2011, 09:29 PM
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Quote:
Originally Posted by techinspector1
Yeah, I understand that,
It just seems to me like somebody either dropped the ball or they did it that way to generate more business for the Chevy dealer service department.
I think it was the latter and not just the Chevy dealers. A lot of dealer mechanics were complaining about low pay and decreased business in the garages. Somewhere around the middle 70's the mechanics (tired of the name grease monkey's) real started to make more money and increased business working on cars with the newer tech. and smog related engines.
I had a good friend from high school on, who started working at a mopar dealer and I told him he should try something better than a mech. but he stuck with it. over time he went to school for mopar, and attended several training seminar's annually to keep up with technology. He ended up working for the same dealer for years, got good ins., and put two kids through college.
Anyone that grew up hopping up and repairing cars up to that period knows what I'm talking about. the driveway mech. started loosing ground on home repair not understanding what was happening compared to slapping parts on an engine. And then there was the start of smog inspections in several states. I can do or fix anything on my 76 350 truck, but when it comes to my 03 GP, it goes to the dealer.
I worked in several garages over the years and I drew the line the day my boss handed me a turbo Trans Am to change the valve cover gaskets on.

That's when I started driving big trucks.
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Old 04-25-2011, 05:32 AM
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Quote:
Originally Posted by delawarebill
u just explained why.. u can do it 2 ways.. 6 and noon and drop dizzy in pointing to #6 or rotate crank one full turn and put dizzy in pointing to #1... if u didn't rotate it and droped it in pointing to #1 it will not start.. or if it did it's running really bad..
My last engine is in my DD truck and I haven't touched the timing since I dropped the dizzy in because it will simply fry a tire with ease from a dead stop if I'm not carefull(this is a 4200 lbs,2.73 geared truck) the same as all the engines I've built. Like I said-I don't get it
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Old 04-25-2011, 05:54 AM
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Some people get it and some people don't. Whats easy for some is difficult for others to grasp. Things such as valve adj. finding TDC, and dialing in a carburetor that some of us take for granted, boggle the mind of first timers or ones with little exp. Most of us started out the same way until either we figured it out or someone else enlightened us on how easy it is with a little practice.
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Old 04-25-2011, 06:04 AM
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Quote:
Originally Posted by TroyBoy
My last engine is in my DD truck and I haven't touched the timing since I dropped the dizzy in because it will simply fry a tire with ease from a dead stop if I'm not carefull(this is a 4200 lbs,2.73 geared truck) the same as all the engines I've built. Like I said-I don't get it
IF you installed the distributor w/the rotor pointing to #1 w/the #6 cylinder @ TDC compression stroke, it will be 180 out of phase. That much is sure.

So, either you installed the dots at 12 and 6 then rotated the crank one revolution before installing the distributor pointing to #1, or you installed the distributor pointing at #6, or you installed the timing set at 12 and 12 and rotor pointing to #1. Or all your timing sets were manufactured differently than all others I've ever seen. Ain't no other way to do it- not and have the engine run correctly.
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Old 04-25-2011, 06:14 AM
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I understand why most push rod engines have the the timing marks where they are - but.....ever work on a Ford Y block where you have to set the marks at 3. Or even figure out why the Ford 'brain trust' in that era decided to do it that way. The opposite noted above (one crank turn) would then be the crank at 3 and the cam at 9.

Just some food for breakfast.

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