[RESOLVED] Cam Gear Timing Mark Clarification

[DarthBulk]

I just finished doing another timing job on a 6 bolt 4g63, and there is something about doing it that has always bothered me. I have never seen all 4 timing marks on the cam gears line up in a straight line with the top of the engine block, even though there are numerous threads on this site that say they should all 4 line up. Even the tech article by blcknspo0ln says this (No offense blcknspo0ln, that is really a helpful article!). I am not alone in noticing this, since a quick search of DSMTuners shows numerous threads where people notice this exact same thing, and chase their tails trying to figure out what they did wrong. Well, let me say they are not wrong. Let me explain.
I have the factory service manuals for the 1G DSMs. In the section about installing a new timing belt (page 9-104) it clearly says:

The same camshaft sprocket is used for the intake and exhaust camshafts, and is provided with two timing marks. When the sprocket is mounted on the exhaust camshaft, use the timing mark on the right with the dowel pin hole on top. For the intake camshaft sprocket, use the one on the left with the dowel pin hole on top.

This means that you only use 2 of the timing marks, not all four. Why is that? Because the two marks on a single cam gear are NOT 180 degrees apart. They are (90 degrees) + (86 degrees 55 minutes) apart. Anyone can verify this for themselves. Just start at the marked tooth on one of the cam gears, and count teeth in one direction until you get to the marked valley on the opposite side. In one direction, you will get 23 teeth. In the other direction, you will get 24 teeth. Directly opposite the marked tooth is another tooth, not the marked valley.

What does this mean? It means that you will never get all four marks to line up perfectly with the bottom edge of the cylinder head. That is only possible when the two marks on a cam gear are 180 degrees apart. It is clearly shown on page 9-104 of the factory service manuals that they are not. Well, they actually have a slight error in their diagram, but the spacing I pointed out is true.

When you line up the two center timing marks on the cam gears, the ones facing each other, the two outer timing marks will be slightly above the edge of the cylinder head...they will be rotated about 3 degrees up, in fact.

I would like to see this information put into a tech article on timing on this site, to clear up any confusion. Maybe some of the timing threads can even be cleaned up a little, too. I actually saw someone give the advice that the timing was "half a tooth off" which makes no sense at all. I think this information would certainly help those doing a timing job for the first time.

[Defiant]

Finding tdc and balancer mark.

[DarthBulk]

I'll admit I didn't look back quite that far in my search results. Can this information be added to the timing belt tech articles, since that is where most people will look first? Then they won't have to search back to a thread from 2005 to find it.

[snowborder714]

[RESOLVED] Is My Timing Off?

[DarthBulk]

Yes, Steve is the only one I have seen in the threads who mentions this information. I think it should be put in the tech articles, though. The reason I say this, is because the tech article still says to line up all 4 marks, which is wrong.

[blcknspo0ln]

No offense taken. It actually just occurred to me that the entire time that my (and others) tech article is not necessarily wrong, but a little bit misleading. It's tough because I've done dozens of these timing jobs and generally have a really good feel for them nowadays and tend to forget that some people take articles verbatim. the most important thing to note while timing this cars (mainly the gears side) is to have the middle line up [although the outer marks will ALWAYS line up semi-straight, give or take a few degrees] and to count the 39 teeth. I will edit my article to be more clear.

[DarthBulk]

Thanks! That is all I was looking for, just clarification. I know the first timing job I did, I spent a lot of time messing with it, thinking I was wrong, trying to line up all 4 marks.

[blcknspo0ln]

Originally Posted by DarthBulk

Thanks! That is all I was looking for, just clarification. I know the first timing job I did, I spent a lot of time messing with it, thinking I was wrong, trying to line up all 4 marks.

ok updated it, I think it's on the money now

[1992awdlaser]

When I mention it I mean that if you put a straight edge on the bottom of the outer marks then the middle of the inner marks will also be on the straight edge. To me this means they are all lined up. I'm sure that is the same thing Tom was talking about also.

[blcknspo0ln]

Originally Posted by 1992awdlaser

When I mention it I mean that if you put a straight edge on the bottom of the outer marks then the middle of the inner marks will also be on the straight edge. To me this means they are all lined up. I'm sure that is the same thing Tom was talking about also.

Yes, that's exactly what I mean, but sometimes what we say can be left for interpretation.

[DarthBulk]

Originally Posted by blcknspo0ln

Yes, that's exactly what I mean, but sometimes what we say can be left for interpretation.

Well, I can tell you how many people will interpret it. Since the marks on the cam gears are "lines", then for them to be "lined up" the straight edge would travel along the LENGTH of ALL the lines. It would not go at an angle across any of the lines. I think this is what was confusing about it.

Maybe it is just the engineer in me, but there is only one definition of lines "lining up" to me Maybe if the marks were dots instead of lines, it would be another story.

[sicawd]

i would like to chime in on this too...since i've ran into that problem also.
but i've noticed that only 2 of the timing marks on the cams gears will only line up with the top of the head cylinder with the dowel pins pointed up.

my .01