TDC question

[Member 10617]

Thanks to the Forum, TDC is less a mystery to me, but I have one last question: How does one determine if #1 piston is coming up to TDC on the compression stroke?

 

[Mickey Richaud]

Hey, Ed -

Remove the #1 spark plug; hold your finger over the plug hole in the head. If it's the compression stroke, you'll feel pressure as the piston rises.

Mickey

 

[TR3driver]

On a TR3, another method is to look down the oil filler. If you can see anything moving as the mark comes up to TDC, then #1 is on exhaust stroke, not compression.

Or if the ignition timing is close enough for the engine to run, you can check whether the rotor is pointing towards the #1 plug wire.

 

[Member 10617]

Mickey and Randall,

Many thanks. Feeling the pressure rise seems to be a good method.

Randall: Instead of running the engine, can I just turn it by hand and look to see if the rotor points towards the #1 plug. As you point out, it seems that the rotor aiming at the #1 plug wire is the clue.

I have read the #1 and #4 reach TDC at the same time, but only one -- of course -- would be on a compression stroke.

 

[Geo Hahn]

That's correct -- and worth remembering if you ever use a timing light (I think you sometimes do) as it is easier to get that clamp over the long #4 wire than the short #1. The timing light doesn't care whether you use 1 or 4 (on this engine).

 

[Member 10617]

George,

Many thanks. The mysteries of the TR3 continue to be unravelled, thanks to you guys.

 

[TR3driver]

Randall: Instead of running the engine, can I just turn it by hand and look to see if the rotor points towards the #1 plug.

Sorry, I wasn't clear. What I meant was that if you know the ignition timing is close (ie you aren't trying to find TDC in order to install the distributor gear); then you can turn the engine by hand and look at rotor position.

 

[Member 10617]

Thanks, Randall. That's clear now.