The Stovebolt Site Forums The Shop Area Engine Shop Timing marks?

I am installing the distributor on my 1962 261 ,TDC #1 ,#6 the valves are rocking, there is some different marks on flywheel ,looking through the timing hole. There is a little circle and very close to this there are 2 lines and beside that there is a triangle. What is the timing mark supposed to be?

It sounds like the marks are like the bottom on in this Link.

pre68Dave, The Triangle...BTDC but is it accurate or of any use when timing engine? Also per the top two pictures, it looks like the vertical line then would be at TDC and not the ball,no?

Any of those marks are OK for initial timing - to get your truck started.

If you know that the flywheel you have is the original one - use the ball (the "bb" embedded in the flywheel). Different years/engine had timing marks in different places - flywheels got moved around over the past 50+ years.

In any case the timing ball/marks were set for the gasoline for the day, and an average altitude.

Using a vacuum gauge (adjust to maximum vacuum at idle) is as good, or usually better, than using a timing mark/ball. Attach the vacuum gauge to the vacuum port on the intake manifold.

Timing on our old inline 6 engines is an exercise in old school training. With the changes to fuels over the years the only "good" way to do it is as Tclederman has described. A Vacuum gauge is your friend. The "Ball", "BB" or TDC will get it started(these are not fussy engines to start). The Vacuum gauge will get you real close. A quick trip up a hill will tell you if you are too advanced(it will "ping") You can use a hi-tech timing light to tell how much advance you have. If it matters to you(tuning for performance?) but these run well when set to the Vacuum gauge.One thing to keep in mind, the mark will line up at #1 TDC or # 6 TDC, so it matters to find which one is on compression. I take the valve cover off so I can see and feel the rocker arms. It is also nice to see the oil on the rocker shaft at the same time. Proof that all is well sorta comforts me.

I have been using the Vac gauge to time engines for years and I'm often surprised how many guys don't own one and don't know how best to use it. What I'm trying to learn is what if any value is there in those other factory markings on the flywheel. I'm sure most people mistakenly believe that the 'BB' is the correct timing mark and stop there.
Thanks
Jim

The marks on different year 235/261 are in different locations and there might be types of symbols.

I guess, at a minimum, they would be at least three marks (unless some of the marks in certain years are in the same place on the fluwheel).

1. UDC or TDC - Upper/Top Dead Center
2. The "tune-up" timing mark, which might be different degrees before or after or on TDC/UDC (depending on the engine and year)
3. Valve timing mark (a triangle, as described here in step 4)

I think I recall reading that different kinds of marks might have been used in different years.

The value/meaning of those marks on the flywheel can get even more confusing when a flywheel from a different year/engine is put on your engine.

FWIW I time by ear. I adjust to the best and fastest idle then use the octane selector to fine tune if necessary. It works for me.

I should have added this engine was just rebuilt and is the initial distributor install and start up, I just want to make sure I am timing it to the right spot to get it started.

I also time by ear (that is my wife's ear, since I do not hear pinging any more). I start by advancing for fastest idle then back it off until the RPM's just start to come down. I then take my wife for a ride to be sure it does not ping. Has worked for years.

Sorry to have to ask this again: is advancing a clockwise rotation of the distributor?

Advance is CCW- - - -opposite the rotation of the distributor shaft. It's the same way the vacuum advance rotates the housing when the RPM is raised.
Jerry

Tiny;

"Octane Selecter"?? Where/what is that?

I don't know when Chevy stopped using it. It allows the timing to be advanced or retarded up to 10 deg each way to adjust for the wide swing of gas quality (octane) back then.

Octane selector on my '38.

How to use it.

You can see gas back then had much lower octane than today. You can advance your timing a lot over the manual recommendation and not have pre-ignition. That's why I time by ear, the spec in the manual really doesn't apply with today's fuel.

Jerry, or anyone,

Do you have any comments about "timing by ear by rotating the distributor to obtain the highest RPM at idle" - in a stovebolt 216/235/261 (no need to discuss other/newer engines)? The "back off" described by Dave is necessary.

I remember reading that adjusting to maximum idle (without the "backoff" described by Dave) was not close to optimal, but I cannot find a reference/reason/explanation?

Should there be an adjustment when timing to maximum vacuum, when using a vacuum gauge?

Thanks,

Larry,
1959 6-cylinder octane selector

That might be a car's adapter (they show a car adapter in earlier manuals).

As posted above, this allowed for "temporary" adjustments due to using different brands/grades of gas, and also when driving at different altitudes.

Keep in mind, this is with a stock engine, and distributor.

I like to use a little different method of "timing by ear" which will promptly be attacked as soon as I describe it. That's OK, I keep a sprig of mistletoe attached to my belt for those folks!

Static-time the engine by aligning the BB with the pointer with the engine stopped, then rotate the distributor housing clockwise until the points close, then CCW until they barely open. An ice pick type test light can be used to find the exact opening point if desired. With the ignition switch turned on and the probe touching the connector at the side of the distributor, the light will not burn with the points closed. As soon as they open, the light comes on. Lock the distributor clamp down lightly at that point so the housing can still be turned by hand. Start the engine and warm it up.

Attach a vacuum gauge to the main port below the carburetor on the manifold NOT the vacuum advance port on the carburetor. Disconnect and plug the vacuum line at the distributor. Using the idle speed adjusting screw, raise the engine speed to highway cruise RPM, 1800-2000 RPM, for instance. Turn the distributor housing clockwise until the vacuum starts to drop, then turn it CCW until it reaches a max point. When the vacuum starts to drop again from over-advancing, back off until it's back at maximum. Lock the housing adjustment down. Reconnect the vacuum advance line.

Now take a road test. Find a long hill where the vehicle can be driven 1/4 mile or so at full throttle without gaining any speed (lugging). Listen for detonation- - -it sounds like a bunch of BB's rattling around in a tin can. If the engine detonates, turn the distributor housing a tiny bit clockwise, go to the bottom of the hill, and repeat the test. Eventually you'll find the best compromise between timing advance and detonation. Bear in mind that one degree of over-advanced ignition timing robs as much horsepower as 5 degrees timing retard from the optimum setting, so err on the side of "not enough" if necessary.

Now, those of you who have bothered to read this novella to this point will probably do like my high school students used to do with a multi-point procedure- - - -do the first thing right, get the next one wrong, and ignore the rest! Have fun!
Jerry

Thanks, Jerry,

I will give your technique a try, when I tune my Suburban.

I use Jerry's static procedure to get the timing good enough to start and run, but I differ on my fine tuning procedure.

I learned along time ago to throw out the std timing procedures when dealing with modified engines.
One method I've found to be easy and accurate is to set the timing at the engines max advance rpm and don't sweat the idle timing.

With the vacuum advance disconnected and capped, I run the engine up to 2500-3000 rpm and set the advance to 30 degrees advanced.
The 216 likes 30 degrees BTDC (which is very close to the stock BB setting at 550 rpm). My ACVW 1600 slightly modified engine likes 32 degrees BTDC. The freshly rebuilt 235 that is also modified is setting at 30 on the run stand but I will fine tune it via the "ping" test once I install it.

I've tried the max vacuum at idle procedure but ended up doing alot of "ping" fine tuning. The max advance procedure seems to require less ping testing to fine tune.

One advantage of Hotrods system: Mechanical Advance is accounted for. I have often wondered how much the mechanical advance changed over the years. I have several Distributors from several salvage operations. All will fit. All will work. And other than the height of the cap they all run just fine. In my humble opinion..it just does not matter a lot with the stock 235. It would seem to be happy with a wide range of tuning. Makes sense, it was a "work" engine. Not a performance beast. Perhaps a 261 might be a little fussy? IDK. The last 216 I worked on ran fine with both early and late distributors so it was not fussy either. More issues from carb and oil to the rockers than from the dizzy.

Tiny;

That octane selector is pretty cool. Noting like that on the 250 in my Burb.