Intake manifold question

rick_rawker said

Thanks !
Now for something completly different... we changed-out the timing chain this weekend as the vacuum was reading low, 13-17 lbs. When we took the old chain off, the marks were at the top of both the crank and cam gears. So, we put it back the same way. ( one keyway ) I am being told now that the marks are supposed to be together. Wouldn't it not be running AT ALL if the cam/crank gears were 180 degrees off ? Or, did we do the same stupid mistake as the last one to work on this timing chain, and THAT is why the motor has low vacuum ! ( I just can't get it in my head that it could be 180 off and still start and run )

Click to expand...

Rick did you notice how the cam gear is twice the size of the crank gear? What happens when you have 2 gears and one is twice the size as the other? The big gear turns at half the speed of the little gear, Right? That means if you align them up at 12 O'clock on the crank gear and 6 O'clock on the cam gear and turn the crank exactly one revolution the cam gear (since it turns half the crank speed) is now at 12 O'clock also. When both gears are at 12 O'clock that's when cylinder #1 is on compression stroke. When their at 12 and 6 O'clock #1 is on exhaust stroke.

All this said it doesn't matter if you align them at 12 and 6 or 12 and 12 O'clock cause next revolution their the opposite. One more revolution and their back to what you set them at. Hope I explained that ok.

BTW: low manifold vacuum can be from retarded ignition timing, mis-adjusted carb, intake vacuum leak, etc...