Inliners International Forums General Discussion Engines Timing marks - help

I’m sorry if this is all over the place... I’m a little frustrated and my head isn’t working quite right.

I’m installing my timing cover and notice the timing marks don’t line up... rotate the engine, following the valves through their cycles, watch the intake valve close and the piston hit TDC... cam mark is 180* out.

Am I daft the have assumed that when assembled, and the marks lined up, it should have been cyl 1 TDC compression? Thus, every time 1 hits TDC compression, the marks line up!

I cannot follow my builders logic and I’m 100% standstill until this is confirmed.

Nope. The cam gear marks are not TDC. They are only to align the cam and crank.

TDC must be established by using a piston at TDC.

My observation on chevy sixes and eights is the same. Align the marks, then turn the crank one revolution will get you to #1 tdc firing. I don't know how universal this is, just what I have seen.

Perfect!
Thank you for clearing that up for me!
Now, I can button up the covers and such and install the engine!

Top Dead Center is a reference to piston position. An individual piston reaches TDC at both the top of the compression stroke and the top of the exhaust stroke on a "four stroke" engine. Some cam timing marks line up once every two revolutions, some I've seen only line up once every 44 revolutions!! Granted, most of these are associated with complicated timing systems that include "idler gears" and other crankshaft driven "appliances", but it helps to remember that the "timing marks" are used for assuring a correct alignment of parts at the time of original assembly or for proper replacement of timing critical parts.

Ignition timing requires the establishment of a TDC combined with the compression stroke which is created by the position of the piston and the proper timing of the valves for that particular cylinder. Theoretically, you can time your ignition off of ANY cylinder in the engine, so long as you know the proper firing order.

tlowe . . . I beg to differ. Degree Wheels and Offset Keys aside (on a blueprinted engine) when the factory assembled these engines they did it 'straight-up' off the timing marks (based on design intention of the crank key-way placement):

Every time the key-way on the crank points at 12 O'clock the #1 and #6 crank throws are both at TDC. By drawing a line through the center of the Crank and Camshaft we can spot the timing the marks and determine whether #6 or #1 is firing. In the photo above the timing mark on the cam-gear is 180 degrees away from the mark on the crank-gear - meaning cylinder #6 has both valves closed and is one gear tooth away from compression stroke TDC . . .


As we all know the assembly instructions call for these marks to align with this centering line running through the crank and the cam when the marks are directly adjacent to each other.

But I get your point that the key-way placement in the cam and crank and the gears may not be perfect for one's blue-printed build . . .