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Help!! on cam timing

R

rpounds

Guest
I feel like an idiot asking this question. But, I'm yanking my well worn hair out here.

Today I helped a neighbor tear down his 350 for a cam change. In the past, I have made it a habit to set the engine to TDC on #1 before yanking the distributor. It makes it easier to get the distributor back in the right orientation when placing it back in the engine.

Anyhow, with the rotor pointing at #1, and the #1 piston at TDC, the cam is 180 degrees out!! Again, this is from in a running engine!!

Is it possible for an engine to run with the cam 180 degrees out??!! Or am I just being stupid and overlooking something?
 

cntrhub

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Joined
Jun 17, 2002
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390
Location
North Hollywood, Ca.
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Miss my '62 & '80 4- Sp. Vettes
I am trying to remember about how many turns of the crank it will take to make the cam timing line up again? I think it's maybe, 62 or 63 full turns until the cam/crank marks line up again, the piston is at TDC Compression, and the rotor arm is pointed at # 1 cylinder (or approx. 11 o'clock). If your good at timing, you could set the gears of the crank and cam out 180 degrees and still be on the money. Remember your 4 strokes... you will be on the stroke where both valves are open, (180 degrees overlap) as opposed to both valves closed (360 degrees at TDC.) I hope I said all this in a logical way, so as not to confuse things.
 
S

Stingray72

Guest
Is that 180 crank degrees or 180 cam degrees? Are you saying that the engine is running fine with the cam 180 degrees out?
 
R

rpounds

Guest
Okay . . . I've got the answer . . . I WAS being stupid . . .

On a Chevy, when the cam is at 6 o'clock and the crank is at 12 o'clock, #6 cylinder is firing.

Man, am I stupid . . . must be the booze . . .
 

cntrhub

Well-known member
Joined
Jun 17, 2002
Messages
390
Location
North Hollywood, Ca.
Corvette
Miss my '62 & '80 4- Sp. Vettes
I am speaking in degrees of "crank rotation." Remember, the cam rotates twice as many times as the crank. I did not mention anything about ign rotor phasing. I wanted to keep it simple, and just discuss the cam/crank timing. Yes, I am saying, eventually the crank will rotate out of phase with the cam (but still will be in time) and you will see the crank and cam out of phase 180 degrees between each other.
You say the engine is running. I am sure the engine starts quick, idles, and you timed the ignition without moving the distributor a lot from where it was before you tore it down. I am willing to bet the distributor is very close to where it was before you disassembled the engine. If what I say is true, and you agree, then I think you helped your friend greatly, and there is nothing to worry about. You did good!
 
Joined
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Messages
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Location
Washington, Michigan
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'67 Marina Blue Convertible
When the dots are aligned (cam at 6, crank at 12), you're at #6 TDC - turn it one full crank revolution, and the cam only turns a half revolution, so with the cam at 12 and the crank at 12, you're at #1 TDC. "Aligning the dots" has always been the standard method for installing the timing set, but you're NOT at #1 TDC at that point - you're at #6 TDC.
 

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