Now I am confused (more than usual). Most of you say the marks should be at 12 crank and 6 cam at TDC compression stroke. Then another says his car runs fine with them both at 12.

I installed the cam in my Vette, crank @ 12 and cam @ 6. I don't know what stroke it was on at the time of install but it runs correctly. I thought I remember seeing in a previous post on this subject that when installed at 6 & 12 after rotation to TDC they would both be @ 12.

Anyway, I'm gonna yank the cam today and examine it closely for damage. I'm not gonna reuse it because it's one size bigger that I wanted in the first place (COMP XE294HR 242/248@.050). I'm gonna replace it with either an ISKY 282HR 234/246@.050 or a COMP XE288HR 236/242@.050.

 

from haynes

 

OK I am not sure whether it is #6 or #1 cylinder which should be firing in this configuration. I do know if, say, it is #6 and you have the rotor pointing to #1 tower on the distributor then the motor will not fire.

You need to turn the motor over with the balancer attached. When the timing mark is coming up to 0 degrees look at the rockers on #1 and # 6 to determine which ones are in overlap ( exhaust closing and intake opening )

When you determine which cylinder ( 1 or 6 ) is in oeverlap then the other one is TDC and ready to fire so the rotor should be pointing to that tower on the cap.

 

Best answer I have seen yet. This horse has been beat to death on this forum. BTW-when I went through this I verified the above with Crane Cams and they confirmed.

 

i ain't dead yet

 

shes still kickin'!

 

Hold the phone, you stated in the earlier thread that the combination was running then a screech then it doesn't run aymore. Are you now saying you did a cam swap and it wont run? If this is the case line up the crank at 12o'clock and the cam at 6o'clock then point the distrib to #1 terminal on distributor cap then start the car. If I misunderstood about the cam swap, I stick to my original thought of a gear being bad or broke cam.

 

Vettevic,

This was the first time that I saw the Haynes instructions pointing out that #1 is on exhaust stroke when the marks line up as described...

It was my first time when I installed my cam and I was confused with different books giving different advice.... however, if you install it as the book says (points facing each other, #1 on TDCC exhaust stroke) - all you have to do is turn the crank 360 degrees (one full rotation) and the cam turns only 180 degrees (half rotation). Now your marks are both at 12 o clock and #1 is at TDC on comp stroke...

After you've done it once it's easy to understand - as I said it wasn't easy the first time...

 

Right, lots of details get left out due to many thinking it is just common knowledge and I am very bad about that myself

vic

 

I did not say I did a cam swap. I stated I was going to pull the cam today to inspect for damage and I would probably replace it with a smaller one regardless of what I find.

 

The pic clears things up. You install it at 12 and 6. When its rotated to TDC on the COMPRESSION stroke they will be at 12 and 12. If that is the case then my cam was installed correctly.

 

OK, just wanted to make sure, been a lot of discussion about this so wanted to make sure I didn't miss something. Before I pulled the cam I would rotate the engine to line up the dots as described before-crank dot at 12 and cam dot at 6. This will make it easier when reassembling.

 

That alignment will be #1 TDC on exhaust stroke. Not good to point the distributor to the #1 plug.

 

 

All of you may know this but one of you may not and it can be confusing if you haven't thought about it. This is for that one who didn't know.

OK, There are 22 teeth on the crank and 44 teeth on the cam.
The crank must make two revolutions to one rev. of the cam.
If the piston is at top it has either just exhausted or is compressing.
If it is going down it is either intaking or has just fired.
Thus, the four strokes= two revolutions of the crank...two upward strokes and two downward strokes. And one rev of the cam to open and close the valves.
If an intake valve is open the piston is going down sucking in fuel. It's easy to tell which rocker is intake and exhaust. Just look at your intake manifold and header to see which is above or below the rocker. After the intake closes, continued turning of the crank gives you the compression stroke when obviously both valves must be closed. Before the piston reaches top the distributer will cause the plug to fire. This spark fireing can be changed by rotating the dist. ie: advance to fire earlier or retard to fire later. As you can see, the timing of when the spark occurs does not change the relationship of the crank and cam. The crank/cam relation is set when you install the chain and sprockets.
Seem a bit strange to me that you set the explosion to go off before the piston has started down but that's the way it works.

 

How hard can this be to understand. The cam sprocket is twice as big as the crank sprocket so the cam turns one time to the cranks two times. It makes no difference if the marks are aligned at 6/12 or 12/12 when installing the cam. If you align the marks 12/12 oclock and not turn the engine again, you can put in the lifters, pushrods, and rocker arms and drop the distributor in pointing to #1 and expect it to fire.

 

I think the best answer is...



-Mark.

 

What with all this 6/12 v 12/12 stuff ... it seems clear to me that what has gotten lost here is exactly what gdaina said ... you MUST match the type of marks ... and seems nastee's motor has a mismatch.
First, regardless whether 6/12 or 12/12 ... DO match & line up the marks. If you want cam advanced you use two triangles ... straight up, use two circles ... retarded, use two squares.
Next use the 6/12 method ... but it doesn't matter all that much because it'll either be right or wrong ... if it's wrong, simply rotate distributor 180 degrees. If you'll watch to see when BOTH #one valves are closed/lifters are down ... that's when you line up marks ... it'll probably be 6cam/12crank.

 

I don't know what type of timing set is in this motor but it only has a circle on the cam sprocket. There isn't a triangle or a square on the cam sprocket. I don't think I've seen a cam sprocket with triangles or squares on it.

 

The purpose of the marks being FIRST aligned at 6 and 12 is to verify the are lined up directly to one another and to make sure the chain dimension is not off (ie: stretched). that is another reason you MUST turn the engine at least one full turn in the direction of running crank rotation Before tightening everything up to verify that the marks still line up exactly. Without the proper centering alignment tools on the cam and crank bolts (machine shop tools) you cannot EYE the cam gear at the 12 o'clock position with any accuracy, it could be as much as 3 degrees off and be undetectable to the naked eye. This is a problem if you are using a old chain or a defective chain cause the chain may be stretched or have a weak link and possibly break in the future. Just follow the directions as they are there for a reason (align facing each other then rotate crank 360 degrees), this is the ONLY correct way way of installing a timing chain. Doing it any other way, regardless of whether or not it has worked for you in the past, just increased the chances of a piston eating a valve later in life.

vic