Wrong timing?

[gregidea]

I just rebuilt an old 307. I was cranking it by hand and could hear the air escaping from the cylinders into the exhaust on what I believe to be the exhaust stroke. The only reason there is doubt that this is actually the exhaust stroke is I found that I was also getting air coming out in short quick bursts from the carb.

This was a budget build, and these heads were off of a 5yr old 350 gmperformance crate engine. So I'm thinking that I either set up the timing chain wrong, these heads aren't a direct swap (different valve placement, exhaust valve where intake valve should be??) or I've got some sticky valves.

What's the quickest check I can do without having to tear this thing apart again?

 

[CHRIS.O]

What engine are you working with here. You said old 307 so I am assuming an old Chevy 307 or are you talking about an Olds 307?

 

[CHRIS.O]

Hearing air move out of your engine when turning it by hand is normal. How did you install the timing set. They are pretty simple. Bring num 1 cylinder to TDC and line the timing set up dot to dot. If you did that then your timing set was installed properly. What state is the engine in? Is it in the car completely assembled?

 

[gregidea]

I installed it with the dots looking directly at each other, cam down, crank up. And this is a chevy 307 out of a 71. It is just sitting on a cradle right now.

So, air coming out of the carb with a hand crank is fine?

 

[jrm81bu]

Air coming out both the carb and exhaust sounds like you have the valves too tight and they are being help open. How did you go about setting your rockers?

 

[gregidea]

Well, the air either comes out of the exhaust or the carb. But not at the same time, just to make that clear.

To adjust the valves, I made sure the lifter was down and tightened the rocker arm down until the pushrod could no longer spin.

 

[jrm81bu]

Well, the air either comes out of the exhaust or the carb. But not at the same time, just to make that clear.

To adjust the valves, I made sure the lifter was down and tightened the rocker arm down until the pushrod could no longer spin.

Coming out at the same time or not doesn't matter. It shouldn't come out the carb regardless. I'm thinking as the lifter pumps up it's holding the intake valve(s) open. You may want to back off the rockers a tad.

 

[gregidea]

Ok, I readjusted the valves, but the same thing is happening. So, I watched the valve action to see what I could see. Just a fraction after the piston hits top dead center after the intake valve has closed, the exhaust valve begins top open. So, instead of pushing the exhaust out, it would be sucking air in from the exhaust. I'm pretty sure now I just put on the timing chain wrong. Thoughts?

 

[zuma83]

did u line up the cam mark withe the crank gear mark. take some pics

 

[pontiacgp]

if you put the timing chain on incorrectly the wrong cylinder would be your number one, the valves wouldn't be opening backwards if that's what your thinking