Where do the dots go for TDC
 

So I'm putting my 350 back together with some refreshed heads. I have the timing cover off as I painted and cleaned up while it was out.

I obviously need to find TDC before I put my distributor back in...there is a lot of info on here about the magic dots, but nothing (that I saw) that said definative, this is what you want/have to do. Just talk about it's on compression or exhaust.

So, dot on crank and cam gear both point at 12, means TDC for #1. Is that when I want to stab the distributor back in, or do I need the crank dot at 12 and the cam dot at 6? I think I had them pointed at each other last time I did this, but that was a few beers ago :)

Thanks for any help ya'll have...

Re: Where do the dots go for TDC
 

Yes both are supposed to be at 12 that's TDC for #1. Reason I know is I just finished putting mine back together yesterday. :lol:

Re: Where do the dots go for TDC
 

That is correct but you install the timing chain and gears with the cam dot at 6 and the crank dot at 12 for accuracy. Quite easy to be out a couple teeth if you try to eyeball it the other way. It was designed that way.
Then crank it one turn so you're on #1 tdc.

Re: Where do the dots go for TDC
 

Cool. Gonna take a straight edge and get the dots closer at 12 each. Hopefully it'll fire enough for me to get a timing on it. I do remember last time I did it, backfired through the carb, adjusted the timing and bit and it ran like it was made to.

Thanks for the help fellas!

Re: Where do the dots go for TDC
 

After you set it at 12 and 12 crank it round to 6 and 12 and see how accurate you are!

Re: Where do the dots go for TDC
 

It's far easier to set it a 6 and 12, then just drop the distributor at the number 6 terminal instead of number 1.

Re: Where do the dots go for TDC
 

So it'll be pointing at #6 vs #1? Or it'll be on the right stroke and still point at #1?

Sorry if these seem like rookie questions, but I'm just trying to make sure I have this right with it still on the stand :D

Re: Where do the dots go for TDC
 

When the dots are at 6 on the cam gear and 12 on the crank gear you're on #6 tdc.
You can install the distributor with the rotor pointing at #6 or you can rotate the crank one revolution and install the distributor with the rotor pointing at #1.
Your choice!

Re: Where do the dots go for TDC
 

Attachment 1176705

Cylinder 1 at TDC

Re: Where do the dots go for TDC
 

This is correct.

Re: Where do the dots go for TDC
 

Correction, this is at #6 TDC

Re: Where do the dots go for TDC
 

Could it be #1 at TDC, but exhaust stroke instead of compression?

Re: Where do the dots go for TDC
 

Correct. #6 and #1 are both TDC at the same time. The cam timing will determine where you drop the distributor.

Re: Where do the dots go for TDC
 

Never seen a thread so all over the place, bring number one to TDC, align the cam and crank gear as I posted above, drop in the distributor with the rotor pointing to one.

What is the problem??????

Desert

PS: the OP got way over is own head over analyzing the process anyway, C'MON MAN....

Re: Where do the dots go for TDC
 

Problem is you'll be firing 180* off on #6.

Re: Where do the dots go for TDC
 

Agree.

I think the confusion is coming from simply stating "TDC #1".

There needs to be a distinction between TDC #1 firing vs not firing.

K

Re: Where do the dots go for TDC
 

It doesn't matter if both are at 12 o'clock or cam is at six. Remember TDC is at the end of compression and recheck for that after complete assembly to insure that even though things get moved around you will be spot on

Re: Where do the dots go for TDC
 

It does matter!
So you can put the distributor in correctly with the rotor pointing at #1 so it starts.

Re: Where do the dots go for TDC
 

The problem with both dots at 12, you can be a tooth off and think you're correct if you're not looking at the engine straight on. This can be a problem if you're timing the engine in the engine bay and not on an engine stand. It's much easier to see that you're tooth to tooth at the 6/12 position, then rotate to the 12/12 position or vice versa to double check. Dropping the dizzy is easy at either position, you just have to know if you need it to point to 6 (at the 6/12 position) or number 1 (the 12/12 position). Mistakes can be made, we're just giving ways to double check, which is good, because we're dealing with a not-so-confident engine builder here.

Re: Where do the dots go for TDC
 

Dang it Desert, you weren't supposed to tell anyone :lol:

I started just searching threads, and that led to something else, then I found myself creating my own :D

Good thing is, I still have the intake and timing cover off, so that'll come in handy when I'm putting the rockers back on...

Re: Where do the dots go for TDC
 

Your engine won't start. With cam at 6 and crank at 12, you better drop distributor pointing at number six if you want it to run. Otherwise, turn crank one revolution until both crank and cam dots are at 12, now drop in pointing at number one.

Re: Where do the dots go for TDC
 

this is an interesting post.. i have been doing this for years.... lets keep this simple....
did the original poster even change or remove the timing gears/chain? looks like one could just get #1 cyl at tdc.. and jabb in the distributor..... should be good to go..

Re: Where do the dots go for TDC
 

Remember, there are two TDC to account for. One where the ignition should spark, the other with the valve open. You must make sure you're at the right TDC to drop in the distributor. Just having the harmonic balancer mark lined up is making a 50/50 guess that you have it right. You must have the balancer mark lined up AND compression to assure you have it right.

Re: Where do the dots go for TDC
 

yes, the valves must be closed, hence compression stroke..

Re: Where do the dots go for TDC
 

Post #9 pic is correct your motor is timed.you just have to time the dist ...........................forget all that #6 at tdc crap

Re: Where do the dots go for TDC
 

Bingo, thank you Maliburat

Re: Where do the dots go for TDC
 

Post #9 shows the dots together, which means number 6 should be firing. If you put the dizzy at #1 firing with the shown cam timing, your engine will not run because the cam just finished closing for the exhaust stroke and starting opening for the intake stroke. Firing the plugs 8* before TDC on the exhaust stroke does not make an engine run. The timing dots together at te 6/12 position vs. the 12/12 position is nothing more than a double check on yourself. Treat it as such. Whether you want to stab the dizzy in at #1 TDC or #6 TDC, or any other TDC is up to you, but it HAS to be between the compression and power stroke by referencing the cam.

Re: Where do the dots go for TDC
 

Whatever ,,,,,,,,,, you confused the ones that have never put a motor together line up marks and youre engine is timed correctly... The only issue you have now is timing youre dist and that being said if dots are lined up its either on compression and will fire up and run or pop its 180 out pull cap if its 180 out rotor will be facing opposite of 1 spot restab and youre done....want me to school ya on degreeing a cam now or i can walk you through timing a detroit or cat

Re: Where do the dots go for TDC
 

one other thought... keep in mind the slotted gear drive on the oil pump is easily adjusted with a long screw driver. this way the distributor can be clocked to sit in the ideal position.

Re: Where do the dots go for TDC
 

A PHILLIPS OR FLAT BLADE ......................LOL :mm:

Re: Where do the dots go for TDC
 

No it is not. That is 180º out. It will not run if you drop the distributor at #1 with the dots together. No one knows "why" GM did this?, but that's just the way it is....

Forget the screwdriver thing too... Just drop the distributor where you need it to be, and if it doesn't line-up with the oil pump drive, you just "bump" the starter....it will drop right in.

Re: Where do the dots go for TDC
 

Ive been building motors for 35 + years that is how you time the motor

Re: Where do the dots go for TDC
 

Oh with youre piston at tdc youre camshaft determines the compression both valves closed compression stroke..youre turn

Re: Where do the dots go for TDC
 

The cam gear is huge the crank gear is small line dots up install chain and rotate motor they wont line up till another turn thats why you have a key way and a dowel to install gears ..... Thats were youre getting the 12 and 6 stuff

Re: Where do the dots go for TDC
 

Do you get what we are saying in that cam at 6 o clock, crank at 12 o clock, you're not ready to drop the distributor in for number one firing ?

You either drop distributor in with rotor pointing at number six or you turn the crank a turn until the cam is pointing at 12, then drop distributor in pointing at number one.

But, if you drop distributor in pointing at number one when your timing set is showing 12 on the crank and 6 on the cam, you're 100 percent guaranteed to have a non running engine.

Personally, I don't do the try it to see if it runs then turn the rotor 180 degrees if it doesn't thing. I put it together the first time where it's guaranteed to start.

Re: Where do the dots go for TDC
 

so do i ...but some dont understand tdc dot aligned balancer line 0 on tab motor at tdc both valves closed it starts

Re: Where do the dots go for TDC
 

That is correct. Every time.

I think there's something getting lost in the discussion here though.

That picture of crank at 12 and cam at 6, is TDC, but it's the TDC valve open. You turn the crankshaft one complete turn until the crank dot is again pointing up at 12 o clock. Except now, the cam dot will also be pointing at 12 o clock. Now you're at TDC, compression both valves closed.

The crank sprocket is exactly half the size of the cam sprocket. Every complete turn of the crank only turns the cam half a turn.

To time the engine internally, ie crank to cam relationship, you can do either 12/12 method or 12/6 method. Both are right. Do one and turn the engine a complete turn and you'll have the other. It's only when you want to drop distributor into place that you need to either verify 12/12 positioning or check for compression at the number one hole, or line up balancer and watch both valves closed.

It's just so easy to line up crank and cam at 12/6 orientation and either drop distributor pointing at number 6 wire or turn the engine a complete turn and drop distributor pointing at number 1 wire. That way you don't have to watch valves, stick your thumb in plug hole for compression, or even have the harmonic balancer installed onto the engine yet.

Re: Where do the dots go for TDC
 

you got it haha................ I just look thru the hole to see tdc .big block ftw i know were im at.......

Re: Where do the dots go for TDC
 

That's pretty much what I was trying to Say. There is a good chance he will move engine timing as he's reinstalling everything. And I doesn't matter to the dizzy wich is #1 cylinder. Put it together then check for compression TDC

Re: Where do the dots go for TDC
 

Longhair, we are just trying to help the guy...no need for your negativity