When installing a new cam and the cam / crank gears are dot to dot (which should mean # 1 piston is at TDC firing).....BOTH intake & exhaust lifters need to be on the heel of the cam right ? Wanna get my alu timing gear's mounting holes to line up with those of the new cam. Gots me a mental block...duh !! Maybe been sniffing too many thinners fumes all day..... Rat
Kevin, Thanks very much for taking the time and effort to write such a good tech article. Good writing and spelling (like the old Palmer method of cursive writing) is a lost art.
Okay. Reading your post again and and yeah, you are overthinking. The holes on the cam and gear are spaced in such a way that cam gear will only go on the cam one way. ANd there should only be one mark on each gear so pretty fool proof. Doesn't matter where the valves or pistons are at this point line up the marks and start spinning it over to drop in and adjust your valve assemblies. Worry about TDC with both valves closed and whatnot when you're to the point of installing the distributor.
ThKevin, the cam gear I have is a multi holed one so you can advance/retard the timing. I used it in a previous mill and its in goos shape so I want to re use it. The thing is, I can see where the cam gear was mounted b/c the bolts have marked the alum on the gear, but when I fit the gear to the cam and align the timing marks both the intake/exh lobes are NOT on the base circle in fact, the intake lobe /lifter is rising.... Thats what has thrown me - kinda weird really as that is the only way the cam gear will bolt on. With both the cam/crank gears aligned that should equal #1 piston at TDC and BOTH in/exh lobes on the cams base circle. OR have I got this wrong ? Rat
Thanx Kevin, the cam gear I have is a multi holed one so you can advance/retard the timing. I used it in a previous mill and its in good shape so I want to re use it. The thing is, I can see where the cam gear was previouly mounted b/c the bolts have marked the alum on the gear, but when I fit the gear to the cam and align the timing marks both the intake/exh lobes are NOT on the base circle in fact, the intake lobe /lifter is rising.... Thats what has thrown me - kinda weird really as that is the only way the cam gear will bolt on. With both the cam/crank gears aligned that should equal #1 piston at TDC and BOTH in/exh lobes on the cams base circle. OR have I got this wrong ? Rat
Rat, When the crank timing marks line up the #1 is actually 2 degrees TDC and not actually 0 degrees because of the crank/piston centerline DeSaxe principal. Coupled with this most aftermarket cams open the intake valve before TDC. Example Isky 400JR = 18 degrees BTC and the Max1 is 13 degrees BTC. (Crank degrees) As the cam gear and the crank gear ratio is 2:1 the timing BTC's above would be 1/2 the value above on the timing gear. In this case, yes the #1 intake will be partially open at TDC. Try this for setting valves: 1EX & 7IN Open set 8EX,5IN,6EX & 4IN 4Ex & 1IN open set 3EX,8IN,6IN,7EX,3IN & 2EX 3EX & 8IN Open set 1EX,7IN,5EX,2IN,4EX & 1IN Jim
To answer your initial question, with the timing marks lined up, #1 should be at TDC firing. So yes the lifters should be on the base circle.
You are sort of thinking right, but that's not quite the whole pic. Yes, when all is aligned correctly - as a rule of thumb - (not setting up a race motor) when no.1 is at top dead centre, the valves will be rocking, ie the exhaust closing and the inlet opening. This is not the firing point for no1 though, it's for no6. One rev of the crank, though, no1 is at TDC again and at the firing point, and both valves are on the heel of the cam. If you then check no6 cylinder, that will also be at tdc and no6 valves will be "rocking". Handy hint - if trying to get a flathead running, when timing the distributor you can tell if no1 cylinder is at the firing point by removing no6 spark plug and watching the exhaust valve. At the point where the valve is almost closed is the rough point for the spark on no1. - Not saying you can time it from this, just a way to check you don't have the timing 180 deg out. For adjusting the valves I use the method described by blown49 above, only three movements of the crank.. easy peasy. Mart.
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