nastee383

This is what I found. The builder advanced the cam 4 degrees so the mark on the crank sprocket circled is the triangle and the mark on the cam sprocket circled is the circle. The motor is at TDC on the compression stroke in this picture.

The chain is not slack or loose, however if you look at the cam dowel it looks like it tried to break out of the retainer. I'll probably remove the cam tomorrow to see if it's damaged in any way.

I believe I remember reading in some posts that at TDC, compression stroke both alignment marks should be at the 12 o'clock position which they are. Anyone see anything suspicious?

nastee383

Help me out now. I know the motor isn't in my Vette but it may be one day. Are both marks supposed to be at the 12 o'clock position with the motor at TDC on the compression stroke?

GrandSportC3

I assume that you checked the pressure (compression on all cylinders)
If the pressure is ok, the timing chain is ok and the carb is ok...and the rocker arms move.. and if I remember correctly, you also tried another distributor... then I think that somehow the cam gears (where they meet with the distributor) could be worn down which would also explain that it jumps timing...

mandm1200

I prefer to look at the marks when the cam is at 6 and the crank is at 12. The marks are easier to align and it has no affect on the cam timing.

c3 in hawaii

this is the way I always did it

David Ey

me too

big_G

Me three

VETTEVIC

you have got it on the exhaust stroke according to the marks.
START- marks are (cam at 6 o'clock crank at 12 o'clock) top of compression stroke
Stroke 1- (combustion) crank goes to bottom and cam to 9 o'clock
Stroke 2- (exhaust) crank goes to 12 o'clock and cam to 12 o'clock
Stroke 3- (intake) crank goes to 6 o'clock cam to 3 o'clock
Stroke 4- (compression) crank goes to 12 o'clock cam to 6 o'clock and start over agian 4 strokes per cycle (2 revolutions of crank and 1 on the cam)

vic

VETTEVIC

The cam gear only goes on ONE WAY
the crank gear can (on aftermarket performance timing gear sets) be set at 4 deg before TDC, 0 deg TDC, and 4 deg after TDC
Before TDC gives you more high rpm performance.
TDC gives you neautral torque/HP curve.
After gives you more bottom end (low rpm) torque.

vic

MotorHead

So is the cam at 12 and the crank at 12 like in the picture, firing on number 1 cylinder or is it firing on number 6 cylinder ?

MotorHead

THis is what I thought too, meaning it is firing on ( TDC ) the number 6 cylinder in this configuration

GDaina

The cam sprocket and the crank gear have the triangle, o, and square markings. The crank gear is set on the triangle, the cam sprocket should also be be on the triangle, not the O. I think I mentioned that in an earlier post in this thread.

VETTEVIC

This is true, BUT you can only install the cam gear one way, you just line up the different marks. tha crank has to be installed in a different position for each timing change, ie: keyway in slot that corresponds to the mark you are wantin to line up. Good point though, I was assuming that was understood, sorry.

vic

David Ey

I don't believe this is true for #1 tdc.
Holy molie nastee, I hope you don't have a cam ground for a counter rotating marine engine.

comp

6 and 12 for me also

GDaina

Thanks for the correction...yep lining up the marks. Rotate the assembly so the cam is on the 6 and crank is on the 12 o'clock position.

texaswilkins

Does this mean the engine may have been firing but at the wrong time causing it not to start?

Bill

MYBAD79

I've had this problem, too.

When piston #1 is on comp stroke at TDC the mark on the crank sprocket is at 12 o'clock and the mark on the cam sprocket, too.

I watched the valves opening and closing while turning the crank with a wrench (all spark plugs removed, paper towel in #1 spark plug hole to verify comp stroke).

I was sooo sure that it was wrong, I turned the crank, watched valves opening and closing for hours.... couldn't believe it was correct

I have both marks at 12 o'clock and the engine runs fine

As said above: it works only one way

Maybe it depends on the timing gear manufacturer where they mark the sprockets ???

VETTEVIC

No it doesnt depend on the manufacturer, you always (ALWAYS) line up the marks facing each other (crank 12, cam 6) regardless of what cylinder is at TDC. The marks correctly aling the cam to the crank. Nowhere did I say it was supposed to be #1 at compression, cause it doesnt matter when installing the gears and chain, only that it is at TDC. What matters is that the cam and crank are in sync. Then you set the #1 cyl at TDC on compression stroke to set the distributor timing, these are two completely different processes that need each other to be right to effect a proper cyl fire. If you have the sprockets properly aligned for installation, the #6 cyl should be the one on compression and both 1 & 6 at TDC. It is the TDC part that is important when lining up the marks not which stroke its on. Also when you have it set at 4deg advance or retarded it will not be at TDC, it will be off 4deg. There are whole books on this subject, and many details that many (incl me) leave out cause its something that is seen too often.

VETTEVIC

OOps, just reread the first post, you did ask about #1 being at TDC COMPRESSION. Sorry! Anyway, you have all the info you need to get it right, A Haynes, or Chilton manual should be able to give you all the info you need. If you dont have one ill try to scan a pick of the sproket align in a few and post it.

vic