timing belt disaster

[Daedalus]

The ratio of the crank to cam pulley is 2:1. So every 360 deg turn of a cam is 720 deg turn on the crank pulley. I didn't know if this made a difference in the position of the cylinders or not.

I thought you can hypothetically lineup your crank position 360 deg off of the cam pulley so when your cams are at TDC, your crank is infact not....not sure if this is the case. But I wanted to get clarification before putting everything back together.

The first part is correct. But "TDC" only refers to the pistons, not the cams. And by convention we set the #1 piston to TDC when setting timing. The timing marks on the cams align at #1 TDC per the FSM and dictate that #1 is on the compression stroke. The marks do not align at TDC compression for any other piston but #1. If you then rotate the crank 360 degrees, #1 piston will again be at TDC, but the cams will be out 180 degrees from where you set them per the manual. The #1 piston is then at TDC on the exhaust stroke (and #5 is now at TDC on the compression stroke, since #1 and #5 are opposites). The cams determine whether a piston is in compression/exhaust or power/intake.

The common mistake of having the rear exhaust cam off 1 tooth doesn't change any of this, but it does mean that the rear bank exhaust timing is off 1 tooth relative to everything else.

 

[gt_nfr]

The first part is correct. But "TDC" only refers to the pistons, not the cams. And by convention we set the #1 piston to TDC when setting timing. The timing marks on the cams align at #1 TDC per the FSM and dictate that #1 is on the compression stroke. The marks do not align at TDC compression for any other piston but #1. If you then rotate the crank 360 degrees, #1 piston will again be at TDC, but the cams will be out 180 degrees from where you set them per the manual. The #1 piston is then at TDC on the exhaust stroke (and #5 is now at TDC on the compression stroke, since #1 and #5 are opposites). The cams determine whether a piston is in compression/exhaust or power/intake.

The common mistake of having the rear exhaust cam off 1 tooth doesn't change any of this, but it does mean that the rear bank exhaust timing is off 1 tooth relative to everything else.

I see, thanks for the clarification. That was exactly what I was looking for, wanted to make sure that the piston position returned to the same location every 360 deg.