How To: Timing belts and TDC (long writeup)

I've read so many posts on timing belts etc. I don't understand the mistakes. I thought I would share some of my thoughts.

What is mechanical timing? The valves must open and close at a certain position RELATIVE to the position of the crank. The cams are machined to accomplish exactly that IF and ONLY IF the belt is lined up properly.

So, the cams are following the movement of the crank basically.

I see so many people worry about the cam timing marks but the crank is two teeth off. So is the crank off or are the cams off? Well in my opinion the cams are off as they are relative to the crank. However you choose to define it, it's still wrong.

Now in my opinion the easiest way to start is to line up all the marks first and then take the belt off in preparation to put a new one on. For the sake of argument, I'm going to point out a few things in case you did not do that.

You might be putting on a new head and it's also not completely possible to do what I just suggested. Now then.

The crank has no exhaust or compression stroke, which is a term used to describe the RELATIVE position of the cams. If the head is off it doesn't matter. Top dead center is top dead center every 360 degrees. If the timing belt is off the same holds true, you would just have to make sure the cams are in position once the belt is on.

Okay now, let's say you took the belt off randomly, now what?
Is it possible to bend valves just by turning the crank by hand? Not likely in my opinion but just for the sake of argument let's say it is and you want to avoid that. You still know the position of the crank, obviously, there is a mark for that. What you may not know is the 4g63 has two pistons at TDC while two are at BDC. So when the mark is lined up on the crank at least two pistons are at TDC. If you rotate the crank 90 degrees away from the mark all 4 pistons will be in the middle. Then you can rotate the cams to your heart's content. In this case, simply turn them both to dowels up, turn the crank back to the mark and then start installing the belt and getting all the marks lined up.

The only gotcha, in this case, is the position of the rear balance shaft. It's difficult to know its phase if you took the belt off without having the marks in position (assuming you have shafts). The only 100% positive way is to put the screwdriver in the hole through the block to test whether the weight is at the bottom or not. I have also used the following trick with success. If you rotate the balance/oil pump shaft you will notice that when you let go it will try and return to some resting state. You can experiment without risk if you had all the marks lined up and you try and move it away from center. You'll notice it tries to return to the mark. Turn the shaft 360 (remember which way as you will have to return it by turning the other way 360). You'll notice the gear wants to turn away from the mark instead of returning to it. Makes sense because when the shaft is out of phase (but mark is lined up) the weight is not at the bottom. The bottom is the best resting place so the gear tends to turn in that direction. This does not work well if seals are new.
Why do we do this in the first place? Behind the oil pump sprocket are two gears. Every turn of the oil pump sprocket turns the balance shaft 1/3rd of a turn. That's why it only lines up every so often. The front balance shaft you can see when it lines up.

So what's the big deal with dowels up, dowels down etc etc. Remember it's all about relative position. It's theoretically possible to install a belt with no marks lined up at all. Isn't the belt in a position like that somewhere during its running cycle? The marks are there so you can have a starting point.

One thing is for certain, if the belt is on correctly, once every six revolutions the crank will be on the mark and the cams will be dowels up and on their marks.

Now the balance shafts need to be right also but nothing will blow up if you get those wrong. It will just piss you off because the car will vibrate and you'll have to do the whole job over again.

Lastly, there is the hydraulic tensioner. There is zero subjectivity here. It's either in spec, or it isn't. Once the belt is on and you rotate it around and line up all the marks again you must measure it. If it's not right you retension. You do NOT have to take the belt off again if it's still in time but you may have to install the tools again. If you're using the tension screw tool I don't completely remove it until I'm done. It's enough to just back it off a few threads while you're setting tension. If you need it again just screw it back in.

There is my 2 cents on TDC and timing belts. Hope this helps someone

 

[cliffkemp]

Basically, you are saying that if you just take your belt off and not have anything in time when you do so, all you have to do is line up the crank with its mark, the BS with its mark (oil pump one) and timing gears with their marks (timing gears first so no valves are bent) and then, put belt on, tension it correctly, turn the motor over 6 revs, check pin and if still loose after 10 mins, pull and your are done?

This is what you seem to be saying to me.

 

[pauleyman]

Essentially yes. I did mention the rear balance shaft issue. Thing is people worry about TDC pull spark plugs etc. That is not necessary. It's easiest to line up the belt before you take it off. My point was to describe relative position and keep people from over analyzing this job.

 

[19BLACKGST98]

Hey pauleyman. What if your marks never line up 100% correctly? When Graham, Heath and I installed my valve springs we noticed this and were concerned that it may be the reason the car is flowing over 52lbs/min and running a 2.8 sec 70-90 mph time, and no I dont have an elephant in the car

Edit: that was on 93 oct

 

[GST with PSI]

Good info. Just a few things:

It is indeed very easy to bend valves while rotating the crankshaft by hand. For this reason, you should always position the crankshaft far enough from TDC to allow unobstructed valve movement before ever altering the position of either camshaft. When initially checking your timing and rotating the engine over by hand, go slowly with the least amount of force possible. As soon as you get a full 360 degrees with no clunks, you can freely rotate the crank.

You remove the spark plugs so that you aren't fighting the force of compression on whatever cylinders the valves are closed on. You do this so you can do what I said above, and rotate the crank freely with very little force. If you are fighting compression and your timing is off, you will surely bend a valve rotating the crank with the force required to overcome compression. Additionally, without the spark plugs removed, you are making the job of lining up timing marks more difficult, and I couldn't imagine a reason not to take 5 min and remove 4 plugs.

One thing you didn't elaborate on; The most important thing IMO is proper timing belt tension. The belt tension is where 99% of people end up making mistakes. Setting mechanical timing is the easy part. However, a timing belt that is not properly tensioned could be misleading, and an improperly torqued fastener here will always lead to a belt failure. People with questions about belt tension should read here: http://www.dsmtuners.com/forums/art...5-timing-belt-tensioning-tips-4g63-turbo.html

Or look at one of the million resources or threads here: https://www.google.com/search?sugex...ie=UTF-8&q=proper+timing+belt+tension+on+4g63

 

[pauleyman]

I wouldn't want to hit valves regardless. This is why I mentioned rotating the crank out of the way with the explanation that at 90 degrees from the mark all 4 pistons will be in the middle. Removing the spark plugs isn't necessary but it doesn't hurt anything, I merely mentioned that it isn't necessary and yes it is easier to rotate the crank that way. There is no reason I can see to put anything in the cylinder to check for TDC.

I did mention the hydraulic tensioner. It is either in spec or it is not in spec. I would hope anybody doing this job at least has these specs available.

This was not meant to be a tutorial, but merely a collection of thoughts I've had after watching people attempt this job in real life and talking about it in forums for the last 20 years. It has to be the most over analyzed job on these cars and for the life of me I don't know why. I wasn't a seasoned mechanic when I did one for the first time. Forums didn't exist at the time. What I did have was the factory manual and a good set of tools and time. It was very straightforward to follow the manual. It's even better now with the many writeups and videos available. I haven't really opened the manual for much other than specs in many years. Sometimes that's the most important part.

Hope this helps somebody.

 

[GST with PSI]

It seems like you are defending yourself and I'm not sure why? I just wanted to add some extra info to what you said. Please man, don't get the wrong idea. I'm not trying to nit pick at you or prove anything. I realize this isn't a how to, but I do feel like some points need to be addressed:

Removing the spark plugs isn't necessary but it doesn't hurt anything, I merely mentioned that it isn't necessary and yes it is easier to rotate the crank that way. There is no reason I can see to put anything in the cylinder to check for TDC.

It looks like you removed what you said about not removing the spark plugs entirely from what you originally wrote, meaning to me you probably agree with what I said, or realize the error in not removing them. No, you absolutely do not have to remove them, but it would be dumb not to. I totally agree it is poor practice to stick stuff into the cylinder via the spark plug hole in an attempt to verify piston position. That is what timing marks are for after all.

Okay now lets say you took the belt off randomly, now what? Is it possible to bend valves just by turning the crank by hand? Not likely in my opinion but just for the sake of argument lets say it is and you want to avoid that.

You said that in your opinion it's "Not likely" that you could end valves by hand. It is VERY likely that you could bend valves rotating the crankshaft by hand, and I would not want someone reading this to think anything else. Although it is your opinion, it is misleading to tell others this. The weight of the crankshaft spinning, combined with the force one would use to rotate the crankshaft, would very easily bend a valve if you were rotating it carelessly under the assumption it's unlikely to bend valves just because you are turning the crank by hand.

Lastly there is the hydraulic tensioner. There is zero subjectivity here. It's either in spec, or it isn't. Once the belt is on and you rotate it around and line up all the marks again you must measure it. If it's not right you retension. You do NOT have to take the belt off again if it's still in time but you may have to install the tools again...... I did mention the hydraulic tensioner. It is either in spec or it is not in spec. I would hope anybody doing this job at least has these specs available.

Yes you did mention the hydraulic auto tensioner, but I'm talking about the pulley tensioner, which you never mentioned at all. The pulley tensioner is the part you left out, and that I wanted to point out is most important. This doesn't adjust itself as the hydraulic tensioner does, and is where most people make their mistakes. The correct procedure to properly adjust the pulley tensioner to get the proper belt tension is outlined in all of the sources I cited, and should be paid close attention to.

 

[pauleyman]

Good points.
I've never removed the spark plugs for a timing job. Others may do as they wish, it won't hurt anything.

I still think it's not likely to bend a valve merely from simply rotating the crank but either way it's not a good idea to touch them. Now if you bumped up against them and then kept wailing on the crank trying to get it to turn then yes. Good points still and I won't argue about it. It would be better to never even approach that possible scenario and make sure the pistons are out of the way and never touch the valves.

On the tension pulley, also a good point but I don't think it's possible to get the hydraulic tensioner correctly without also having the pulley correctly set. Actually, I know it isn't as you don't actually set anything on the hydraulic. It's position is as a result of where you set the eccentric (good point there). If you set the eccentric improperly the protrusion of the hydraulic will be outside it's range. They kind of go hand in hand. I didn't want to beat a dead horse on how to do the job in that case, merely point out that in the end the protrusion must be correct.

We see so many botched timing jobs and stories of belts skipping right after the job it's obvious to me the general population still do not understand this. That was really my point.

This job isn't an easy one but I always thought it was fairly straight forward.
Hope this helps someone.

 

[GST with PSI]

Yeah I see what you are saying with the hydraulic tensioner now. Basically when the belt is tensioned and all said and done, the hydraulic tensioner will be the tell tale sign at the end no matter what if the belt isnt tensioned properly. The only way this wouldn't apply is if like I mentioned, you improperly torque the pulley tensioner bolt and it loosens up later on. It that case, you would be screwed, even though your belt tension was good to begin with.

I can definitely agree the general population still does not understand this, which is why so many belt failures occur prematurely. I have no doubts that the thoughts you shared will lead others to a more clear understanding of how this process is simply broken down though.

 

[pauleyman]

A slight addendum to this. I still don't take out the spark plugs. The only reason I would is to make the motor easier to turn over. Those that think you have to do so in order to find TDC aren't reading the instructions. All you have to do is line up the crank mark. You line that up you ARE at TDC on cylinders 1 and 4.

If you want a quick and dirty method to do this here is what I've done for years. If the car is all good right now line up all 5 marks. Then you make a small soap stone mark (or similar) on the timing belt and gears at both cams, the crank and the oil pump sprocket and make a mark on the belt between the cams. Any mark will do. I use a T for "top" or something. YOU MUST LINE UP ALL ENGINE MARKS FIRST. Have cams dowels up also. Transfer the marks from the old belt to your new belt. Now it's easy to get the belt on and have all marks lined up exactly. The only thing left to do would be to get the tension set correctly.

 

[luv2rallye]

Some more tips: http://www.dsmtuners.com/threads/need-timing-help-4g63t.493341/#post-153518654

 

[pauleyman]

Time for another addendum. I won't say 1g vs 2g as this may not apply anymore. Find out what engine you have and use the procedures for the tensioner pulley. Not all 4g63 tension clockwise. Some are counterclockwise. You will read tutorials that say the dots go up on the tension pulley. This is NOT true for all 4g63. I would have to consult the manuals but I want to say all 1g are dots up and all 2g are dots down. Again consult your manuals. I can say for sure 6 bolt are dots up and my 97 is dots down (original 7 bolt 2gb motor).
If anybody has multiple years of factory manuals please chime in.

 

[1990TSIAWDTALON]

You have it right Paul. 1g - dots up. 2g - dots down.

 

[19Eclipse90]

92-94 Manual

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95 Manual

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[pauleyman]

I don't know about you but the 92-94 manual wasn't clear. I say counterclockwise. It could tell once on the car but still that book wasn't good. And it shows a 6 bolt tensioner. The 2g manual is very clear which way to turn.

 

[19Eclipse90]

I agree the 2G is nice and concise!

In the 1G, it may be so due to the fact that the procedure is the same on all 1Gs. Note that it shows the different timing marks between 6-bolt and 7-bolt in the same diagram. If they’ve done that, why make a whole other diagram just to show the 7-bolt hydraulic tensioner? In retrospect, yeah, it probably could be clearer.

But let’s also consider that 1Gs all use the same tensioner arm. So pivot point is the same, arm is the same, hydraulic tensioner is different. Why would it be rotated differently just because the tensioner is different? I understand the 2Gs do, but we’re looking at this many years later. Remember, this manual was published before the 2G existed. That goes without mentioning the 2G used a different arm.

Further, I feel if they went as far to show the timing marks different between the ‘92 and ‘93 that there would be a different illustration here unless, as above, it’s the same process.

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Adjustment turns the tensioner pulley clockwise. Just some things to think about.

 

[pauleyman]

I think because the water pump gets in the way. That may be 2g only. I don't remember.

 

[19Eclipse90]

All 1Gs with the 4G63 use the same water pump kit (MD972052) and, as an example, all AWD models use the same engine mount bracket (MD195094) that the tensioner arm bolts to and pivots on.

 

[pauleyman]

Time for another addendum. I talk alot about setting pistons at TDC when starting. This will only apply if you took off the belt at TDC. It's much wiser to not approach the valves with a piston. This is even more true if you are installing a new head as you can't have a belt laid across the cam gears. You could install a tool to put the cams dowels up but much better to just put the pistons down bore and install a head. After a new head is installed you can set the gears cams up and proceed to put number 1 at TDC. I made this mistake and accidently had 2 and 3 at TDC when putting a new head on. I think the only reason I didn't bend a valve is because I had freshly bled new lifters in it. I did remove the head and have it checked to be sure. Learn from my mistake.