The Stovebolt Site Forums The Shop Area Engine Shop Which Valves Fully Open at TDC?

Which valves should be fully open at TDC? Or which pushrods should be the highest at TDC?

Thanks!!

On the compression stroke, neither valve is open. On the exhaust stroke the exhaust valve is open.

Delbert, Sorry, I was meaning out of the 12 valves, which are open when #1 is TDC.

IT HELPS IF YOU EXSPANED ON YOU QUESTION. ON TDC #1 BOTH VALVES ARE CLOSED. IS IT A6 OR 8 I WOULD FIGURE A 6 BUT SOME PEOPLE HAVE PUT 8 IN. WHAT ARE YOU TRYING TO DO.

I'll be confirming TDC on my rebuilt 261 by checking for compression at #1 spark plug hole. It's now sitting with the bell-housing pointer lined up with the flywheel ball so it is at TDC or 180 deg. off.

But can you also tell if you are at TDC by looking at the full set of push rods (or rockers/valves)? All pushrods are down to the same level except the 4th and 6th ones which are higher in the valve-open position. These are for #2 cylinder exhaust and #3 cylinder intake, respectively. So, do these these facts say I'm sitting TDC or 180 off?

I realize that a compression check is a trusted "experiment" and that what I'm asking for is more like "theory." But I'd still like to know.

Thanks!!

OK, OK. I'm babbling in this thread but I've got it figured out. I mapped out the events in a 4-stroke, 6-cylinder engine with firing order 153624. Sure would have been easier for a 4-stroke, 4-cylinder. I was hoping that someone would know this off the top of their head. I'm focusing on pushrod positions because the engine is being reassembled.

When #1 is at TDC, only #2 exhaust and #3 intake valves are fully open (pushrods up). #4 is in a power stroke, #5 is in compression and #6 is between its exhaust and intake strokes.

If you are 180 deg. out with the flywheel ball also at the pointer, only #4 intake and #5 exhaust valves would be fully open (pushrods up). #1 would be between its exhaust and intake strokes and both pushrods would be down.

Confirmation, anyone?

I don't understand why you want to know which valves are fully open. If you are trying to adjust them you want them fully closed. At firing position, exhaust 1-3-5 and intake 1-2-4 will be closed. At 180 out, exhaust 2-4-6 and intake 3-5-6 will be closed.

Hey, Cletis! How are things out in Parker County?

Everything is loosy-goosy on the rocker arms so I'm only looking at how much the pushrods stick up when the flywheel ball is at the pointer.

If that's the only info I have and if only #2 exhaust and #3 intake pushrods are fully up (those valves fully open) when all of the other pushrods are down at essentially the same level, I think it means you're at #1 TDC.

I just want to view a panorama of the pushrods while my chin is resting on the right fat fender and tell whether I'm at TDC (flywheel ball IS at the pointer). I believe that if #2 exhaust and #3 intake are up higher than the rest, you are indeed at TDC and not 180 out. Case closed!.??????

Wally I think your right . If you turn the engine direction of rotation and intake valve starts to open your 180 out. If both valves stay closed no push rod movement your tdc on time.

jbennett
40 burb