The Stovebolt Site Forums The Shop Area Engine Shop Timing Marks on Flywheel

Hey all '51 chevy with rebuild 238 motor of some year (yet to be determined as it has a rebuilt tag riveted into the block over the ID numbers). Also not sure if this is the original transmission 4 speed, with shifter on the floor, with compound granny gear. Otherwise, truck seems stock 6V and all

But the lower flywheel/clutch cover is missing over the tranny so I can easily see the marks. Upside down and from Rt to left - 'U/C', then, I see the little BB (flat round circle), a '5' next to it, and then an inch away I see an upside down triangle. See photos. I have a crappy timing light I prob was given that is so dim It doesnt even help at night. So Ive ordered a quality one and it's to arrive this weekend.

Look at the photos but LMK what you all think.
-Clem

You've got a pretty standard flywheel there. The ignition timing should be set with the "Ball" aligned with the pointer in the block window above the starter to fire the #1 cylinder 5 degrees before top dead center. The U/C mark indicates true TDC, and it's used for valve adjusting. You don't really need to have the engine running to set the timing- - - -just align the pointer and ball with the engine stopped, turn the distributor clockwise until the points close, and turn back CCW until they just barely open. Lock the distributor down, and the timing is set. To be really accurate, use an ice pick style test light and turn the ignition switch on. With the points closed and the light touching the terminal on the side of the distributor, the light will not burn. As soon as you turn the dizzy CCW far enough for the points to open, the light will come on. That method is as accurate as using a strobe light.
Jerry

Thanks Jerry, this explains it ot me, and it's the 5 is the 5 degrees BTDC,

Also, I cant move my dist to make the mark line up, #1 plug lead is not to the right of the clip by the block it's to the left. I'll try and rotate all the leads clockwise one spot, to give me room to get my timing right It runs ok but prob is 7-10 degrees BTDC, This is fun, getting this closer to right, thanks for your help.

So what is the Triange mark down the line more advance. ?
-Clem

Once you get a working timing light, try checking the timing with the engine revved up to around 2500 RPM or so and the vacuum advance line disconnected. I'm going to guess the triangle will be somewhere in the vicinity of the pointer, or at least visible in the
timing window somewhere. That indicates the centrifugal spark advance inside the distributor is working. Connecting the vacuum line will add another 10 degrees or so of advance, but only at light-throttle cruise.

Try centering the slot in the distributor hold down bracket, and loosen the pinch clamp that holds the vacuum advance to the distributor housing. You will have plenty of adjustment for timing setting that way. The calibrated slot is called an "Octane selector" and it was used as a quick way to compensate for variations in the anti-knock quality of different fuels half a century ago. Now the gas quality is universally lousy!
LOL!
Jerry

The shop manual says the triangle is used when checking cam timing.

Here is an old post with various timing marks/meanings.

That thread does not address 1952 trucks, but it gives examples that shows the confusion (?) that might result from having different years/models/engines flywheel on another year's 216/235/261 engine?

In that thread there is other discussion about those marks, and about timing.