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Old 02-27-2013, 05:08 PM
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Question about camshaft timing

Hey guys just looking to clear something up that isn't quite adding up in my head. I am wondering how a small block chevy timing set with multiple crankshaft keyways results in either retarding or advancing cam timing only 2,4,6, or 8 degrees. When you look at the crankshaft gear there are 18 teeth and the 2 degree increments for either advance or retarding are placed 2 teeth apart. With that in mind, doing the math would reveal that every tooth on the gear is 20 degrees apart, every 2 teeth are 40 degrees apart. The keyways are also staggered in much the same maanner the teeth are. I am assuming that the way the small advance or retard increments are achieved is by changing the distance between the crankshaft keyway and matching tooth, correct? For instance the distance between the keyway and corresponding tooth for 8 degrees advanced (tooth marked 8A) would be a 16 degree difference than the distance between the 8 degreees retarded marks. Just trying to figure this out because its been on my mind lol.

Also as a side note I would like to know the advantages and disadvantages of both installing a camshaft advance and retarded. In what situations would you want to install the camshaft advanced/retarded? Ive always installed straight up at 0 but for my build I would llike to change it up and compare the differences.

Thanks,
Keith

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Old 02-27-2013, 05:17 PM
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Your assumption of the keyways vs. the teeth placement to vary the cam timing, or phasing, is correct.

A couple pages w/some info on cam timing:
http://www.crankshaftcoalition.com/w..._.22phasing.22

http://www.crankshaftcoalition.com/w...g_the_camshaft
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Old 02-27-2013, 05:29 PM
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advancing/retarding the camshaft can effect where the powerband comes in.IE: retard the cam 3 and the peak torque and horse power might be as much as 3-400 rpm higher than before.
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Old 02-27-2013, 05:32 PM
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Do not assume the thing will move the cam 4deg. Degree it in.

Advancing the cam makes the intake valve close sooner.
Tends to enhance low mid range torque. Will not make a big cam into a small cam.

Most hi perf cams are made so that they are in fact 4 to 5deg advanced, from a true "straight up" orientation, when you install on the normal "0" position.

If you want to move it, degree it first to verify the intalled .050" timing events.
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Old 02-28-2013, 12:11 PM
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So if you have 3 keyways and 36 teeth that means each tooth is worth about 10 degrees. Now with your cam you can move the gear one tooth over and then change the key way to get the combos the book says that timing set is capable of. If that make since. So yes you only have 3 choices at striaght up timing but moving the chain a tooth and changing the keyway may only result in a 3 degree change.

Im sure that makes no since to anyone but me. LOL

Use a degree wheel and do what it takes to put it right on the button. Advance or retard are no fun unless its supposed to be installed that way. Usally anything beside zero is adding to the take side of the give and take of engine performance. Much easier to understand on a twin cam engine. Chevy single cam makes you figure a lot more things out before its all laid out in front of you.
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Old 02-28-2013, 12:23 PM
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Quote:
Originally Posted by 383SBC View Post
For instance the distance between the keyway and corresponding tooth for 8 degrees advanced (tooth marked 8A) would be a 16 degree difference than the distance between the 8 degreees retarded marks. Just trying to figure this out because its been on my mind lol.

Just remember that the crank gears spins twice for every turn of the cam gear so 16 degrees on the crank is in fact 8 degrees at the cam.
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Old 02-28-2013, 04:29 PM
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Are you sure they are placed 2 teeth apart. If you look closely they may be slightly off, mine were. And the numbers on the crank gear pertain to the crankshaft degrees [at least in the ford racing and Cloyes timing sets], cut them in half to get the camshaft degrees.
The only thing you should be worried about is what shows on the degree wheel and dial indicator. Don't add any confusion to this straight forward albeit very important procedure. If you end up in between camshaft degrees I went with the higher of the two as chain stretch will slightly retard the camshaft eventually.
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Old 02-28-2013, 09:46 PM
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say i were to degree a cam to verify phasing, how would i change the phasing if the timing gear set is phased as factory? ive always lined up timing marks and had engines run just dandy. i am far from a pro and i would like to understand why degreeing the phasing is so important if it cannot be changed if problems exist in the phaseing of the camshaft. i verify phasing with a little common sense that the tdc #1 piston simulates bolth intake and exhaust valves are closed at that time. if that is the case, i start the engine as if i had not a worry in the world. dont let me be a doofus and elighten me if you would on how to veryify and set the degree withough a degree wheel and degree'able timeing gear set.
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Old 02-28-2013, 09:55 PM
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some gear sets have several options for advancing/retarding cam,also offset keyways.
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Old 02-28-2013, 10:16 PM
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i am familiar with the offset keyways. im curius how one could be picky about phasing whene factory timing gear sets are used. is it just a simple answer stating that if your phasing is off...you need a degreeable timeing set to reset the correct phasing?
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Old 02-28-2013, 11:16 PM
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Quote:
Originally Posted by s-10again! View Post
i am familiar with the offset keyways. im curius how one could be picky about phasing whene factory timing gear sets are used. is it just a simple answer stating that if your phasing is off...you need a degreeable timeing set to reset the correct phasing?
Besides offset woodruff keys, the cam gear of a SBC can be drilled for offset bushings.
http://www.crankshaftcoalition.com/w..._.22phasing.22
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