new cam install bad timing?

[davenirish]

I am swapping out a 2.8 with a 3.4 I did a rebuild. I am using a comp cams 252 cam. I have everything installed and it seems that air is blowing out of the intake. I pulled the spark plug and the cam timing seems way off. The intake valveless seem to be opening on a compression stroke and the exhaust on a down stroke. Does this sounds like cam timing 180 degrees out?

[Blacktree]

Getting the valve timing 180 degrees off would not cause the problem you described. Because 180 degrees after the compression stroke, you have the exhaust stroke. The intake valves are closed during both the compression and the exhaust stroke.

So if your intake valves are open during the exhaust stroke (and vice versa), your camshaft is more like 90 degrees off... or something like that.

Just out of curiosity, how did you set the valve timing? In other words, what directions were the timing marks on the crank and cam gears facing? The mark on the crank gear MUST be facing straight up. And the mark on the cam gear should either be facing straight up (TDC#1) or straight down (TDC#4). Then you adjust the distributer accordingly.

[geoffinbc]

It does not matter if either dot is up or down. All that matters is that the dots and the centers of both sprockets all line up in a straight line drawn right up through the centers of the sprockets.

The easiest way if to just point the dots right at each other. If you did this you will be fine

The problem may be poorly adjusted valves

[Blacktree]

If the dot on the crank pulley is facing down, then cylinders #1 and #4 are at BDC, not TDC. And if you have the crankshaft turned to BDC while the camshaft is set for TDC when you install the timing chain, then you'll get exactly what the OP described.

Remember that the camshaft turns at half the speed of the crankshaft. So if you turn the crankshaft 180 degrees (i.e. from facing up to facing down), then the camshaft will only turn 90 degrees. So the dot on the camshaft will be facing to the left or the right.

[bszopi]

If the dot on the crank pulley is facing down, then cylinders #1 and #4 are at BDC, not TDC. And if you have the crankshaft turned to BDC while the camshaft is set for TDC when you install the timing chain, then you'll get exactly what the OP described.

Remember that the camshaft turns at half the speed of the crankshaft. So if you turn the crankshaft 180 degrees (i.e. from facing up to facing down), then the camshaft will only turn 90 degrees. So the dot on the camshaft will be facing to the left or the right.

Correct. But what betterthanyou said is correct as well. As long as the dots are aligned when installing, then it is correct. If you install them both at the top, then rotate the engine 360 degrees, then the crank dot will be at the top, and the cam dot will be at the bottom. Rotate is 360 degrees again, and both dots will be back at the top.

Sent from my DROID2 GLOBAL using Tapatalk

[geoffinbc]

Yes I know exactly how fast the cam turns. But it does not matter turn the crank more and eventually it will line up with the crank dot up and the cam dot down. All that matters is that line drawn through the center has the 2 dots lined up on it. All 4 combination of dots up and down will arrive with successive turns of the crank.

If you have a distributor then your going to have to get number one on TDC compression to get the firing order correct. If you have DIS then just plug all the wires in.