The Stovebolt Site Forums The Shop Area Engine Shop timing marks on flywheel

I have searched the site for other posts on markings on the flywheel and use for timing and setting valve lash

There are conflicting answers to whether to use the circle or triangle for setting valves (TDC)and timing ignition (BTDC... 5 degrees?)

with the flywheel turning clockwise the triangle comes into view first.. followed by the circle shortly after. Wouldn't this indicate the triangle is for timing (BTDC).. and the circle is TDC?

I timed the motor (62 261.. original flywheel) by vacuum and its shows with the timing light just before the triangle

Engine runs fine with this timing ...approx. 20" vacuum... smooth idle.. Im just curious as to what each mark is supposed to mean... any insight?

The general consensus is the circle is for timing.. which then brings the question... what is the triangle for?

another question... if using the circle or triangle... if they are within 5 degree's or so wouldn't the cam be on the base circle for this period of revolution and show no lift... and shouldn't either be able to be used for setting valve lash..?

My understanding was the triangle was tdc and the bb was the advance mark for stock timing.

I read the tech article before.. references other valve positions to position valves for adjustment rather than indicating a specific crank position as noted on flywheel.. this is the same method I used on V8's.

my question still stands on what circle and triangle represent... I looked in repair manuals and nothing is explained as to what the marks are for.. is there any reference as to what these marks are for?

Ill try the above method this week and see where the marks line up on flywheel

You should see a mark U|C which is top dead center. Setting it on the BB which is 5 deg advanced (if I remember right) won't make a noticeable difference. Some references say to set to the BB and some say U|C so pick your poison.

here is another post on the subject... sounds like what I am seeing as far as relationship of marks on flywheel.. based on this I should probably check timing again!


I'm refering to 6-8 in Minor service operations-Valve Timing in the 49-53 shop manual. The triangle is to be used to position the engine to do a valve timing and timing gear wear test.

I searched "triangle" in the 49-54 archives and found this from raycow: Topic #71924

"U|C (it's not UIC) is TDC at the line between the U and the C. The ball is 5 degrees BTDC and is normally your timing mark. The triangle is about 20 degrees BTDC and I believe it might have something to do with checking the camshaft timing, but I'm not certain enough to bet any money on that one...."

I think what he say's is correct.

Please have another look at my reasoning and what the manual says and let us know how you see it. It seems important to have this settled, because a too far advanced motor is trouble, and there are some contradicting opinions being advanced.

There are several variations of marks on flywheels depending on the year and what engine it was originally on.
In this link I show some of these.
Originally most engines were timed at the ball or circle, but a few were set at TDC, which is the line before or between UC.
The triangle is only for checking cam spec's.

With today's fuel I find most engines run better with about 5 degrees additional advance over stock timing.

Well crap looks like i was wrong lol. sorry about that.

Great information. When doing a rebuild its nice if you mark TDC for each cylinder pair too. I find it so much easier to do static timing and valve adjustments when I can see those markings too. I explain what I am talking about in the Important Flywheel Information discussion here:

http://devestechnet.com/Home/Project1959235

Maybe it makes more sense to count from the line (between UC) down XX number of teeth instead of using the BB? Or maybe its better to have it 5 degrees BTDC? It's amazing... but someday I may have all the information I need to be most accurate. I was always under the impression you got best results in timing things with the BB. Been doing it that way for years.

The BB is the best place to start when adjusting timing for optimal performance.

Here are some things which can make the BB NOT optimal:

The octane of the fuel in the tank.
The points gap.
Wear in the timing gears.
Altitude.
Tappet clearance (normal vs heavy duty).

All of these will affect performance, and may require more or less timing to provide for best performance.
I am a fan of adjusting to maximum vacuum, then backing off a smidge.
Carl

Carl,

When you say "backing off a smidge", in which direction of rotation of the distributor?

Everything you posted is good information/advice.

One other factor regarding the BB not being optimal: the flywheels often get swapped around over the many years. Since the markings (BB location relative to TDC) were different in many different years, the only good/consistent marking is the TDC marking (not the timing/BB marking).

For us normal hobbyists (normal?), the adjustment of timing to maximum vacuum is no doubt better (and easier to do and uses cheaper equipment) as a general practice, than other traditional techniques (standard or advance timing light), unless and until you know the best setting for your particular engine.

On my mostly still stock 49 216, trial and error has determined that the BB centered on the pointer provides the best performance on that engine. I tried the vacuum method and it was too advanced, i.e. the valves pinged under load. I also played w/the octane adjustment to see if I could tweak alittle more out of it. In the long run that 49 216 starts and runs best timed to the BB.
Just another humble opinion in a sea of opinions

re. the OP's original question, I used the BB to originally setup and adjust my valves and it worked out fine in my case, but then again my engine is the original and mostly stock. Perhaps your answer is somewhere in all these posts

Dave

Good advice, Dave.

The comment about the Octane Selector (adjustment) might confuse some people. It is simply an easy way to fine-tune the timing to adapt to differing driving conditions (such as large changes in altitude) and octane differences (in the good old days). Adjusting the Octane Selector is a timing adjustment (that requires no "timing equipment").

I advance the timing until maximum vacuum reading, then turn the opposite direction, retarding the timing that ultra-scientific smidge. A test drive under load will help one verify if one's smidge is within specs.
Great question BTW!
Carl

Where are you taking the vac reading from?

The big one used for the wiper motor.

The big one used for the PCV valve. LOL! Same same. Good to know. I want to do some tests there as well as the dipstick tube when I get my test engine back. Thanks Carl!

clockwise rotation of distributor - advance?

counter clockwise (anti clockwise) rotation of the distributor - retard?

yes. I had to ask Dave myself because I dont want to get this internal HEI adapter plate backwards.

looking down on distributor

counterclockwise is advance .. and clockwise is retard....

correct?

See, I was not simply stupid for asking.

The shaft turns clockwise.
Turning the housing counter clockwise advances the timing.

Thank you, Dave

Yeah, I was gonna say... turning the distributor means what? Turning the shaft or turning the housing? Nothing stupid about clarification.

Hey 52Carl,

Can you quantify that ultra-scientific smidge for me? Will I see a small drop in the vacuum?

I think I'm going to use the maximum vacuum method.

Thanks,

That works for me; and, it is oh so simple to do, and to explain.

Update

Checked top dead center by valve position method as well as #1 cylinder mechanical stop method and it appears on my 261 that TDC seems to be the circle on the flywheel ( not a bb or ball). Before the circle is a line that is approx 5-6btdc. On a previous post that showed a few varities of timing marks mine looks like the last one