Which cylinder is at tdc?

[2011dandd]

Hi guys

Had a mag rebuilt last week and forgot to check which cylinder the rotor arm was on when I removed it.

What is the easiest fool proof way without taking the tractor bonnet and rocker cover off to know that I am at tdc and not 180 degrees out?

[rxe]

Not sure what it is, but I’ve never found a case where it matters. If the distributor is 180 out, just re-arrange the leads to suit.

Other than that - you have to see the cam timing on number 1. Pencil through the plug hole to detect the piston coming up (or a dial gauge if you’re posh), and zero pressure on the rockers/lobes whatever means the cylinder is sealed. You’ll probably have to take the rocker cover off to do that - but it probably isn’t hard?

[Limpet]

Finger or some sort of bung over the plug hole as an assistant turns the crank. You'll feel the pressure when the piston is on the compression stroke. Then use a dial gauge or pencil as above to fInd TDC. Or use crank pulley marks if the engine has them.

[Steve_D]

I have a spark plug with a hole drilled down the middle.
When I hand crank it round to TDC on compression stroke it whistles.

Sticking your finger in the hole works just as well.

Steve

[stevieturbo]

Finding tdc...and finding which cylinder is on compression at tdc arent quite the same.

And a little more detail on the tractor ? but assuming you have access to the cylinder and and rotate the crank ok, it's dead easy to establish which one is on compression.

[Motor Surgeons]

With the Spark Plug Removed put a straw or a wooden dowel down the hole. Then turn the Engine until the Piston pushes the straw or Dowel to the highest point. Easy!!
When you find TDC put a Mark on the Crank Pulley and the Block

A couple but's

1. Only ever turn any engine forwards, never backwards
2 TDC will happen Twice. Once at the Top of the Exhaust Stroke & then again at the Top of the Compression Stroke, the latter is near to
where the Plug is fired so Rotor arm will have to be pointing to that Piston at that Piston Position.
3. To Find the compression stroke hold your finger over the Plughole. On the Compression Stroke the Rising Piston will push up on your finger.

Hope that helps

[Coilspring]

Motor Surgeons said:

With the Spark Plug Removed put a straw or a wooden dowel down the hole. Then turn the Engine until the Piston pushes the straw or Dowel to the highest point. Easy!!
When you find TDC put a Mark on the Crank Pulley and the Block

A couple but's

1. Only ever turn any engine forwards, never backwards
2 TDC will happen Twice. Once at the Top of the Exhaust Stroke & then again at the Top of the Compression Stroke, the latter is near to
where the Plug is fired so Rotor arm will have to be pointing to that Piston at that Piston Position.
3. To Find the compression stroke hold your finger over the Plughole. On the Compression Stroke the Rising Piston will push up on your finger.

Hope that helps

Been a while since I worked on an engine with a rotor arm involved.

For the purposes of engine timing, there is only 1 tdc. The firing or exhaust stroke is controlled by the valve timing.

If the valves are not yet timed there will be no compression to feel.

Other than that, ok.

[2011dandd]

Cheers for all your help guys

In the end I took the bonnet and rocker cover off and watched the valves to know the right tdc I wanted.
But some great help, thanks