Finding TDC from valve close in #1?

[jimesh]

Last week I removed the distributor from an engine that's been running relatively well all season to do a little maintenance (and check the advance mechanism -- top end seemed a little low) but forgot to note the position of the rotor! :-( First mistake.

My A4 has a FWC pulley ahead of the flywheel. The only shaft fastenings visible w/o removing it and the flywheel cover are a woodruff key and 1/4" set screw in its hub holding the pulley to a shaft extension keyed for the woodruff key. The available hub on the outside of the pulley is round so the only wrench it will accept is a pipe wrench. :-(

Turning the engine w/ all plugs out but the FWC pump belt on takes two hands so I have no spare fingers or thumbs (and no assistant -- boat is in the water on a mooring) to detect compression in #1 cy. In fact I have to use the pump belt itself to turn the engine like the alternator belt method others here have mentioned. Transmission is in neutral -- I assume the main resistance is the impeller in the FWC seawater pump.

Not able to see top of piston #1 at all either. :-(

So I assumed that the woodruff key slot was aligned with roll pin on the shaft further in but didn't get the slightest flicker of ignition when trying all four possible positions for dropping in the distributor w/ rotor at 3 o'clock. (Key up and down on each stroke) So I'm assuming at the moment that the relation between the key slot and #1 TDC is totally unknown and have to find it some other way.

I can easily see one of the valves operate (aftmost valve in #1) when I turn it but am not yet sure whether it's the exhaust or intake. If I knew that I think I could approximate TDC in relation to that valve closing and get the engine to start again. Anyone know which it is? Or have other suggestions?

I had been hoping to avoid tearing down the engine anymore (e.g removing the FWC pump & pulley etc.) right before the end of the season, but may be stuck with that at this point. When I pulled the distributor I wasn't even imagining removing the plugs and all the time wasted so far trying to get it going again -- just a quick little tune up. :-(

Appendix: I assume exhaust valve closes near TDC of exhaust up stroke and intake valve closes near bottom DC of the following down stroke. So TDC for ignition (full compression) would be ~1/2 rotation from close of intake and ~1 full rotation from close of exhaust. Close enough?

[hanleyclifford]

Even though you cannot see the #1 piston you might be able to get a small wooden dowel down thru the spark plug hole and as you turn the engine the dowel will move up and down. When you have the stick at it's highest point you will either be on TDC or 180 degrees out. You will have to work the dowel a bit to make sure it doesn't get jammed.

[Administrator]

Our video tech tip download will walk you through the basic steps of setting the ignition timing on your Atomic 4, starting with the critical step of finding #1 top dead center. Motors with improperly set timing will run poorly and may not start at all

You can purchase and download the the Windows version here. The Mac version is here.

Bill

[Dave Neptune]

And ~~~

jimesh, what Hanley said is about it for your situation. I suggest you work on the easiest "cylinder" you can get to and line the rotor with the plug wire for it.

Note, remove the plugs and it will turn a bit easier. You can also use a piece of coat hanger and put a bend in it to reach the piston. While turning slowly and observing the height of the wire you can find TDC of the cylinder your working with.

When the intake valve closes the piston is on the compression stroke. Both valves will be closed and the piston at the top. Also note the accy drive rotates at engine speed so you can mark it.

The water pump(s) don't add enough friction to consider.

Dave Neptune

[edwardc]

Starting from #1 (flywheel end), and moving back towards the output shaft,
the valves are:

#1 Exhaust
#1 Intake

#2 Intake
#2 Exhaust

#3 Exhaust
#3 Intake

#4 Intake
#4 Exhaust

[jimesh]

Thanks all

Thanks to all for the helpful suggestions. Good to know the valve assignments, I found them nearly impossible to deduce from what manuals I have. Great idea to mark the accessory drive! Now I'm really wondering why it's so hard to rotate with all the plugs out if it's not the seawater pump.

[Dave Neptune]

Friction

It's hard to turn because your dragging all of the pistons and moving the valves.

Dave Neptune

[ILikeRust]

I found that with a "tactical" LED flashlight, I could peek in the spark plug hole at an angle and just see the valves and piston in #1 cylinder. I used a short piece of wire shirt hanger, bent into an "L" shape, to help me feel what the piston and valves were doing.