Overlap Cam, What does it mean for my car Options

[jdamiano]

I just replaced my pushrod tube seals and when I adjusted the lash I think I discovered my 73 2.0 has an overlap came. I had to put each cylinder at TDC to adjust the lash. No two where at TDC at the same time. Does that mean my cam was replaced? It was converted to Weber carbs right before I purchased it. All the removed parts were in a tub but no cam. I have assumed it hadn’t been changed.

[nathanxnathan]

I just replaced my pushrod tube seals and when I adjusted the lash I think I discovered my 73 2.0 has an overlap came. I had to put each cylinder at TDC to adjust the lash. No two where at TDC at the same time. Does that mean my cam was replaced? It was converted to Weber carbs right before I purchased it. All the removed parts were in a tub but no cam. I have assumed it hadn’t been changed.

I think you're using the term "overlap" cam incorrectly. To be an overlap cam means that the intake and the exhaust valves are open at the same time. I believe in this sense all the stock cams are in fact overlap cams.

Your question though, there shouldn't be 2 cylinders with both valves closed at either tdc.

There's a "shortcut" method of doing valves that illustrates this.

Find TDC for cylinder #1, and adjust both valves on #1, AND the intake on #2 and the exhaust on #4. Rotate the engine 360 degrees (this will be TDC for #3). Now adjust both valves on #3, AND the intake on #4 and the exhaust on #2.

About overlap cams, I've often wondered if adjusting valves with this in mind would be beneficial? I'm not sure if these specs are correct for a 914, but all the cam specs I've seen for vw's have a similar overlap:

IO:12 BTDC
IC: 42 ABDC
EO: 43 BBDC
EC: 4 ATDC

Would you be getting more lift to set the intake at say 13º btdc and the exhaust say 5º atdc? —At tdc you're not on the base circle of either intake or exhaust, right?

[jdamiano]

I just replaced my pushrod tube seals and when I adjusted the lash I think I discovered my 73 2.0 has an overlap came. I had to put each cylinder at TDC to adjust the lash. No two where at TDC at the same time. Does that mean my cam was replaced? It was converted to Weber carbs right before I purchased it. All the removed parts were in a tub but no cam. I have assumed it hadn’t been changed.

I think you're using the term "overlap" cam incorrectly. To be an overlap cam means that the intake and the exhaust valves are open at the same time. I believe in this sense all the stock cams are in fact overlap cams.

Your question though, there shouldn't be 2 cylinders with both valves closed at either tdc.

There's a "shortcut" method of doing valves that illustrates this.

Find TDC for cylinder #1, and adjust both valves on #1, AND the intake on #2 and the exhaust on #4. Rotate the engine 360 degrees (this will be TDC for #3). Now adjust both valves on #3, AND the intake on #4 and the exhaust on #2.

About overlap cams, I've often wondered if adjusting valves with this in mind would be beneficial? I'm not sure if these specs are correct for a 914, but all the cam specs I've seen for vw's have a similar overlap:

IO:12 BTDC
IC: 42 ABDC
EO: 43 BBDC
EC: 4 ATDC

Would you be getting more lift to set the intake at say 13º btdc and the exhaust say 5º atdc? —At tdc you're not on the base circle of either intake or exhaust, right?

I see now. I was reading the Pelican Parts instructions wrong. I was reading it 1 and 3 not 1 or 3 and was expecting two cylinders to be TDC at the same time. Thanks for the explanation. I need to start keeping some readers in the garage.