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Old 12-13-2005, 04:20 PM
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Damn Cam!

you're supossed to have #1 piston TDC, top of the compression stroke, both valves closed, timing marks aligned, right? well what are you supossed to do if you've got #1 piston TDC, top of the compression stroke, both valves closed, but both timing marks are 12 o'clock? if i line up the timing marks, i've got #1 piston TDC, top of the EXHAUST stroke, both valves closed. what the hell happened? timing gears came as a set and the crank gear has only 1 key slot.

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Old 12-13-2005, 04:26 PM
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Either way is right. You'll figure out why sooner or later!

tom
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Old 12-13-2005, 04:33 PM
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What problem are you having? What type of engine? If it is a SBC, you put the cam gear at 6 o'clock, crank gear at 12 o'clock. Both valves on #1 closed, #6 rocking (exhaust just closing and intake just beginning to open). Turn the crank 360* (cam dot will now be at 12 o'clock) and drop in the dizzy with the rotor pointing to the #1 lug on the dizzy cap. Not pointing to the #1 plug.
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Old 12-13-2005, 04:53 PM
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Quote:
Originally Posted by wayneair
you're supossed to have #1 piston TDC, top of the compression stroke, both valves closed, timing marks aligned, right? well what are you supossed to do if you've got #1 piston TDC, top of the compression stroke, both valves closed, but both timing marks are 12 o'clock?
This is actually how it's supposed to be done, the magazines and manuals tell you otherwise because it's easier to "eyeball" the marks when they're close together. With the mark on the cam gear at 12 o'clock you're in the correct position to time the distributor.


Quote:
if i line up the timing marks, i've got #1 piston TDC, top of the EXHAUST stroke, both valves closed. what the hell happened?
This is why, 100% of the time, you get a backfire through the carb when you try to start it and have to pull the distributor up and spin the rotor to make it work.

Larry
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Old 12-13-2005, 05:23 PM
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ok, i understand now, if i'm at TDC compression and turn just the cam 180, it would then be TDC exhaust. it just really threw me when i was trying to degree it in. is there a noticeable difference in performance if my cam is only about a degree off? i've got bushings to change the timing but the cam gear bolt holes aren't sloted.
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Old 12-13-2005, 06:58 PM
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Originally Posted by machine shop tom
Either way is right. You'll figure out why sooner or later!

tom
.... ....
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Old 12-14-2005, 07:46 AM
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Quote:
Originally Posted by wayneair
ok, i understand now, if i'm at TDC compression and turn just the cam 180, it would then be TDC exhaust. it just really threw me when i was trying to degree it in. is there a noticeable difference in performance if my cam is only about a degree off? i've got bushings to change the timing but the cam gear bolt holes aren't sloted.
1 degree isn't even measurable on a dyno. It's plenty close enough.
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Old 12-14-2005, 11:38 AM
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The first thing that you are suppose to do is set the engine at TDC compression before removing the old gear and chain.....

Ever seen anybody take the gears off and then crank the engine with the starter with the valves and pushrods installed?

When installing a new cam, be sure and install the gears before hooking up the valve train..
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