View single post by Esprit2
 Posted: 09-14-2017 04:52 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 282
A full 4-stroke cycle involves two full revolutions of the crankshaft. If the crank is at TDC, and the cam pulley timing marks are on far opposite sides of the pulleys, then #1 is at BDC (Bottom Dead Center). Turn the crank through one more full revolution and back to TDC. The cam pulley timing marks should now align on the imaginary centerline between the cams. If not, then at least you get a real idea of how far off they are.

With your crank timing mark at 9:00 o'clock, the crank is not at TDC, so the cam timing marks as they are at the moment do not reflect how the cams are timed. Carefully rotate the crank to TDC, with the cam pulleys timing marks adjacent to one another. That will tell you how the cams are currently timed... right or wrong.

Setting the crank to 90 degrees before or after TDC puts the pistons half way down their bores. That's the safest position (all pistons farthest from the valves) for working on the engine with the timing belt off. It keeps you from having an Oops moment that damages valves.

The stock cams have a valve lift of just 0.340", so having the pistons half way down is a large, overkill clearance margin. There's nothing magic about 90 degrees/ half way down, just a very unscientific way of giving yourself the largest possible margin for error. Simply get the pistons well away from the valves. Half way/ 90 degrees works without thinking about it too much.

Tim Engel

Last edited on 09-15-2017 02:14 am by Esprit2