timing gears

[George peterson]

trying to time my f-12 after complete overhaul. I failed to mark cam and crank gears before taking off. Now that I look at them closely, I see there are dots on each gear. Question I have is there is a single dot on crank gear. And there is spot on cam gear that has two dots, one on either side of a tooth. There is also another spot on cam that has a single dot directly on a tooth. Do I go with two dots to one or single dot on cam to singe dot on crank?

 

[used red MN]

To others, do not read my answer and think I have answered his question with certainty, read my entire reply. I am no expert but the manual I gave you the link to shows a single dot on the crank to a single dot on the cam in the diagram IH34 on page 11, but I see it says the diagram applies to the W-40. So we will see if OTHERS CHIME IN TO CONFIRM. I can tell you this, to check if the cam timing is correct on TDC of the compression stroke of cylinder one the number 4 cylinder valves should be in overlap. So this is the point in engine rotation where the exhaust valve has just closed and the intake is just beginning to open. Just keep in mind I do not know if the cam alignment marks are set to align the engine at TDC compression of number one cylinder or not. You have to make sure the DC mark on the flywheel agrees. To help clarify this on a small block Chevy many people set the crank to cam timing by alignment with the dot on the cam at the bottom and the crank sprocket dot at the top. This DOES give you proper cam timing and works, but in actuality they timed the cam to TDC of number 6 which is the cylinder that fires halfway through the firing order. The actual engineered set point to align the camshaft and crank is having the camshaft dot at the 12 oclock position matching the 12 oclock position of the crank gear. That position places the engine at TDC compression of number one cylinder. Just to get off the path a little more in SBC firing order of 18436572 number 6 cylinder is the one you check for overlap when on TDC compression of number 1.

 

[Fritz Maurer]

All kinds of timing marks on the flywheel. Turn the cam until no. 1 cylinder lobes are between intake and exhaust. Now turn the crank until 1-4 TC appears in the timing hole. Engage the gears and turn it a couple revolutions. Now you should be able to see no.1 EO when carefully turning the crank while watching no. 1 exhaust rocker...soon as you see it move, stop. Cleaning out the hole and highlighting the marks, plus a helper to watch, will make it much easier.

 

[Dave BN]

I don't know about your engine but if it's like my C113 in my BN's you line up the one dot gear with the one on the crank gear. The two dots line up with a mark on the gear that drives the magneto.
Dave