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Discussion Starter · #1 · (Edited)
I've been reading a lot of people talking about cams being improperly set up during timing belt changes even though the marks line up

It's impossible and here's why

With cams out of the picture for now, If the crank is aligned to the oil pump mark then it's guaranteed that 1 and it's corresponding cylinder are at tdc. Can either be compression or exhaust but since cams are out of the picture we don't know yet

We can turn the crank around and around and as long as we are aligned to the oil pump, pistons will obviously be in their same place. 1 and it's corresponding cylinder will be at tdc

Now put cams into the picture. With cams aligned to their timing cover dots

Think about this

You can rotate a cam 1 full revolution in your hand out of the car and when you get back to the place you started, the lobes will be back to the place THEY started at. No matter what. This is a solid piece of iron and you can rotate it 360 over and over again and the lobes will never move out of their position. It's not a magical piece of iron

You can rotate it 360 in your hand one time and the lobes will still be in the same place or you can do it 34 times and again, still in the same place

So with that being said you might be wondering if they can be 180 off

Well if they are 180 off then the gears will never line up to their dots behind them because they will be facing down instead of up so obviously the timing isn't right

So think about that. There's no possible way for the cams to be aligned wrong as long as the marks line up. It's physically impossible!

Unless you have the wrong cams, the wrong gears, or you no longer have the factory oil pump mark and rear timing cover marks

That's why the manuals don't cover this problem , because it's not a problem but it's actually just a misconception, mistakes must have been made reassembling and then blame was put to cams being 360 or 180 off even though the marks lined up. But it's impossible. There's no point in taking off valve covers to check which valves are opened and which are closed. It WILL ALWAYS be right if the marks line up

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Great point! However, I would add one piece of information to this: on VG engines, the timing marks on the cam sprockets do not perfectly line up with the marks on the rear timing cover when the belt is properly installed and the engine is at TDC #1. The cam and rear cover marks should be used for a general lining up of the cams. Also, many VG engines do not have a timing mark on the oil pump and just have the mark on the timing sprocket. At top dead center, the cam sprocket timing mark should be at the 5:30 clock position.

So, getting the cams 180 out is pretty tough to do if you are paying attention. But, to make sure the cams and crank are properly timed, it's best to rely on the painted marks and arrow on the timing belt. If you don't, it's possible to get the timing a tooth or two off. The factory timing belt and most aftermarket belts will have two solid lines and one dotted line on them, plus an arrow to point out the direction of the belt (the arrow should be pointing forward to the front of the vehicle).

The dotted line should align with the timing mark on the right-bank, cam sprocket (which will be on your left, if you are looking at the front of the engine from the front of the vehicle). Respectively, the left-bank cam sprocket timing mark and the crank sprocket timing mark should align with the solid lines on the belt. Once I install the belt, I'll loosen the the nut on the tensioner pulley and will let the slack pull out. Then, I turn the right-bank, cam sprocket about three teeth counter-clockwise and let the tensioner spring pull out the remaining slack. Torque the tensioner nut to 35 ft/lbs and then turn the right-bank, cam sprocket about three teeth clockwise; this puts the slack on the section of belt between the two cam sprockets. If the belt is adjusted properly, you should be able to take your thumb and forefinger and twist the timing belt 90 degrees in the center of the span between the two cam sprockets. If you can't, the tension is too tight and you will likely end up with a "whining" noise when you get the engine running. If you can twist it more than 90 degrees, there is too much slack. Once the tension is good, I re-check the timing marks on the belt and make sure they correlate to the marks on the sprockets. If they all match, your belt is properly installed!
 

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So riddle me this...

When I started my truck, having aligned all my marks perfectly, I heard what can only be described as an M-60 machine gun going off under my L side valve cover. I did this again for the mobile mechanic who came over to confirm what I had done wrong (I had to know) and he confirmed that it was in fact valves colliding with the Pistons. Now, given that this same mechanic also tried to put the new belt on backwards, as well as failing to align the belt's cam lines to the corresponding cam marks, I'm willing to dismiss his testimony on account of him being a moron. All things being fair I'm equally as stupid for giving him $140 after teaching him how to install and align a timing belt. I did assume that mechanic being his career choice he at least knew (from experience) what a collision sounds like, but this is just an assumption. After he finally left I rotated the L cam 360 degrees and put everything back together.

After getting everything back together I fired up the truck. Not only did it start, it idled smoothly around 2000 rpm (eventually dropped to 750 rpm). I was surprised by this. Having read all the horror stories I expected my Valves/Pistons to be toast. Thinking back to everyone (such as yourself) saying there can be no collision with marks lined up I began to wonder if it was actually misfires that I was hearing (exhaust stroke) and not actual collisions. And that's when I decided to recheck my compression.

I checked the compression on all six cylinders (twice) prior to messing with the timing belt. I got 90PSI (+/- 5) on all cylinders (cold engine). After the timing belt incident I got (cold engine) 90-95 psi on #1, #3, #6 and 53-58 psi on #2, #4, and #6. Now before saying this was caused by incorrect timing, know that I did go back and readjust the L Cam counter-Clockwise by one tooth (which appears to be the norm on these trucks) and my psi numbers remained the same, more or less. I believe I was now getting 60 psi consistently on L side.

So if it's impossible to have a collision on the exhaust stroke, then (a) what did I hear when I started up the truck and (b) why did I lose 30+ psi from the affected side of the engine emediatly after the suspected collision occurred? Bear in mind that I'm not trying to be difficult with these questions, I'm simply trying to substitute an unknown correlation with actual engineering facts.
 

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Discussion Starter · #4 · (Edited)
Great point! However, I would add one piece of information to this: on VG engines, the timing marks on the cam sprockets do not perfectly line up with the marks on the rear timing cover when the belt is properly installed and the engine is at TDC #1. The cam and rear cover marks should be used for a general lining up of the cams. Also, many VG engines do not have a timing mark on the oil pump and just have the mark on the timing sprocket. At top dead center, the cam sprocket timing mark should be at the 5:30 clock position.

So, getting the cams 180 out is pretty tough to do if you are paying attention. But, to make sure the cams and crank are properly timed, it's best to rely on the painted marks and arrow on the timing belt. If you don't, it's possible to get the timing a tooth or two off. The factory timing belt and most aftermarket belts will have two solid lines and one dotted line on them, plus an arrow to point out the direction of the belt (the arrow should be pointing forward to the front of the vehicle).

The dotted line should align with the timing mark on the right-bank, cam sprocket (which will be on your left, if you are looking at the front of the engine from the front of the vehicle). Respectively, the left-bank cam sprocket timing mark and the crank sprocket timing mark should align with the solid lines on the belt. Once I install the belt, I'll loosen the the nut on the tensioner pulley and will let the slack pull out. Then, I turn the right-bank, cam sprocket about three teeth counter-clockwise and let the tensioner spring pull out the remaining slack. Torque the tensioner nut to 35 ft/lbs and then turn the right-bank, cam sprocket about three teeth clockwise; this puts the slack on the section of belt between the two cam sprockets. If the belt is adjusted properly, you should be able to take your thumb and forefinger and twist the timing belt 90 degrees in the center of the span between the two cam sprockets. If you can't, the tension is too tight and you will likely end up with a "whining" noise when you get the engine running. If you can twist it more than 90 degrees, there is too much slack. Once the tension is good, I re-check the timing marks on the belt and make sure they correlate to the marks on the sprockets. If they all match, your belt is properly installed!
Not only is it hard to have the cams 180 off like you say, it's actually nearly impossible. The cam marks would be pointing down to the ground which is the opposite direction of their alignment marks and you would never get the belt marks properly aligned either.

The timing belt can only go on one way as it has an arrow showing it's orientation so you can't go wrong there either

Being able to twist the belt 90 degrees seems a little excessive to me but I'm sure it works , I like mine a little on the tight side rather than the loose side
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Discussion Starter · #5 · (Edited)
So riddle me this...

When I started my truck, having aligned all my marks perfectly, I heard what can only be described as an M-60 machine gun going off under my L side valve cover. I did this again for the mobile mechanic who came over to confirm what I had done wrong (I had to know) and he confirmed that it was in fact valves colliding with the Pistons. Now, given that this same mechanic also tried to put the new belt on backwards, as well as failing to align the belt's cam lines to the corresponding cam marks, I'm willing to dismiss his testimony on account of him being a moron. All things being fair I'm equally as stupid for giving him $140 after teaching him how to install and align a timing belt. I did assume that mechanic being his career choice he at least knew (from experience) what a collision sounds like, but this is just an assumption. After he finally left I rotated the L cam 360 degrees and put everything back together.

After getting everything back together I fired up the truck. Not only did it start, it idled smoothly around 2000 rpm (eventually dropped to 750 rpm). I was surprised by this. Having read all the horror stories I expected my Valves/Pistons to be toast. Thinking back to everyone (such as yourself) saying there can be no collision with marks lined up I began to wonder if it was actually misfires that I was hearing (exhaust stroke) and not actual collisions. And that's when I decided to recheck my compression.

I checked the compression on all six cylinders (twice) prior to messing with the timing belt. I got 90PSI (+/- 5) on all cylinders (cold engine). After the timing belt incident I got (cold engine) 90-95 psi on #1, #3, #6 and 53-58 psi on #2, #4, and #6. Now before saying this was caused by incorrect timing, know that I did go back and readjust the L Cam counter-Clockwise by one tooth (which appears to be the norm on these trucks) and my psi numbers remained the same, more or less. I believe I was now getting 60 psi consistently on L side.

So if it's impossible to have a collision on the exhaust stroke, then (a) what did I hear when I started up the truck and (b) why did I lose 30+ psi from the affected side of the engine emediatly after the suspected collision occurred? Bear in mind that I'm not trying to be difficult with these questions, I'm simply trying to substitute an unknown correlation with actual engineering facts.
What kind of belt did you put on, old or new? What brand?

Did you use the same compression tester and method of testing before taking it apart vs after when you suspected piston valve collision?

Why did you check compression before taking everything apart?

Was the belt and gear marks all aligned properly?
If you don't have an oil pump alignment mark then did you make sure that the method that you used to find TDC #1 was absolutely correct?

If the belt was a new reputable brand belt and you tensioned it properly with the marks lined up properly then I don't know what happened but if it was running good with high compression prior to taking it apart then it could only be these:

1. You thought you had the timing right but you actually didn't

2. The belt jumped teeth due to improper installation or tensioning or something caught in the timing cover/ rubbing

3. If you had anything up top removed you could have dropped something in the intake or valve covers if you had them off, then either the cylinder ate then item and shot it out the exhaust, lodged it in the piston, or if it went down the valve.covers it got moved to the side where it wouldn't interfere with anything

I would say there may have been a problem with the rockers/lifters/valve body/ valvetrain/ cams and that was the last straw until it gave out but that doesn't necessarily make sense because it's running just fine now?

Bottom line is it's impossible for cams to be 180 or 360 out if they are aligned to their respective marks so I just wanted to prove that theory wrong

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No I certainly agree that it's a bit of a mystery. Even if my L Cam was off 360 degrees (exhaust stroke) then the exhaust valves still should have closed as the pistons reached TDC. To which I refer back to my previous comment "I began to wonder if it was actually misfires that I was hearing (exhaust stroke) and not actual collisions." Still, the sudden drop in psi on those cylinders afterwards was too much of a coincidence to ignore. I also considered that perhaps some of the valves were just shot to begin with given the condition that everything else on that truck is in it certainly wouldn't be a stretch. But then the engine idles smooth, and power seems to be good, so ruled that out. To this day I remain annoyed that I didn't get it on video to share with everyone.

To answer some of your questions:

1. New belt. I went with the Gates that you recommended.
2. Same compression gauge all four times.
3. I tested prior to replacing the timing belt (as I recommend) so that I would have a base reading to compare against once the task was complete. If psi is significantly lower after changing the belt, then timing must be off. Also did a head gasket leak test prior to as well.
4. Yes, all alignments were dead on. I'm still at work, but I will provide some images of everything once I get home. If anything it will give folks a point of reference for the conversation.


On a side note: I drove the truck around for 4-5 days a couple weeks ago. It ran great. In fact, on that fifth day I remember thinking I might actually become fond of it. So naturally the engine would start making noises a few hours later(as in potential engine being damaged noises), so it's just been sitting in the driveway collecting rust while I await the UPS man and my shiny new engine stand, hoist, and compressor. It may turn out that the valves actually did collide with the piston for reasons yet unknown. I honestly can't wait to get it apart.
 

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Discussion Starter · #7 ·
No I certainly agree that it's a bit of a mystery. Even if my L Cam was off 360 degrees (exhaust stroke) then the exhaust valves still should have closed as the pistons reached TDC. To which I refer back to my previous comment "I began to wonder if it was actually misfires that I was hearing (exhaust stroke) and not actual collisions." Still, the sudden drop in psi on those cylinders afterwards was too much of a coincidence to ignore. I also considered that perhaps some of the valves were just shot to begin with given the condition that everything else on that truck is in it certainly wouldn't be a stretch. But then the engine idles smooth, and power seems to be good, so ruled that out. To this day I remain annoyed that I didn't get it on video to share with everyone.

To answer some of your questions:

1. New belt. I went with the Gates that you recommended.
2. Same compression gauge all four times.
3. I tested prior to replacing the timing belt (as I recommend) so that I would have a base reading to compare against once the task was complete. If psi is significantly lower after changing the belt, then timing must be off. Also did a head gasket leak test prior to as well.
4. Yes, all alignments were dead on. I'm still at work, but I will provide some images of everything once I get home. If anything it will give folks a point of reference for the conversation.


On a side note: I drove the truck around for 4-5 days a couple weeks ago. It ran great. In fact, on that fifth day I remember thinking I might actually become fond of it. So naturally the engine would start making noises a few hours later(as in potential engine being damaged noises), so it's just been sitting in the driveway collecting rust while I await the UPS man and my shiny new engine stand, hoist, and compressor. It may turn out that the valves actually did collide with the piston for reasons yet unknown. I honestly can't wait to get it apart.
Well if your L cam was 360 off then it would be perfectly timed because 360 off is the same as 360 on which is also perfectly timed

Is the engine noise a knock or a tap? Think bass for the knock and treble for the tap. Tapping would indicate a top end problem and knock would be a bottom end problem

Does the engine noise get faster when you raise the RPM or is it a steady tap? A knock getting faster as rpm raises would indicate a bottom end problem

Before you yank the engine maybe you should pull the oil pan first

If it has no metal that's a good sign that your bottom end is still good

If it has no metal and it's a tap then I would reconsider pulling the engine. Pull the heads and if the piston tops and cylinder walls are good then your problem is probably in the top end. Also make sure the crank rotates free by hand

If you reach that point then take apart the rockers and lifter valve bodies to inspect/clean/replace worn parts, replace all lifters either way, but you can probably re use valve bodies if they are good

Check cam lobes and journals - and if there's no deep scoring they can be re used

Then take your heads to the machine shop and ask for hot tank, pressure test, resurface and valve job. It will be about $400 max

Reassemble and you should be good



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OK, since the crankshaft has to turn twice in relationship to the camshafts, the only mistake would be the crankshaft off one rotation, or am I missing something?
 

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Discussion Starter · #9 ·
OK, since the crankshaft has to turn twice in relationship to the camshafts, the only mistake would be the crankshaft off one rotation, or am I missing something?
That's another one that's impossible to mix up

#1 and it's corresponding cylinder will be up when you're at the oil pump mark, every time you reach the oil pump mark. Just like the camshafts, it will never change.

Imagine yourself with a crankshaft in your hand. Turn it 360 degrees by hand and you'll be in the same place you started. Do it again, same result. Do it 53 more times,.same result

Turn it 180 and you'll be in the opposite position of the alignment mark so that's obviously wrong

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"Being able to twist the belt 90 degrees seems a little excessive to me but I'm sure it works , I like mine a little on the tight side rather than the loose side"

Technically, one is supposed to check the belt tension using a belt tension gauge, but there aren't a lot of mechanics (let alone DIY'ers) that have one. I've seen too many people install VG timing belts too tight, which resulted in a high-pitched "whine," and end up having to pull off the timing covers again to adjust the belt. The "90 degree twist" method really only takes a few seconds and it works; I've easily done over 200 VG timing belt replacements over the years. Just install the belt, loosen the tensioner nut, turn the right bank cam gear a little, counter-clockwise, tighten the nut, turn the cam gear clockwise a little and twist the belt in the middle of the span between the two cam gears. Most of the time, it'll be dead on unless the tensioner spring is really worn out or improperly installed.
 
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Discussion Starter · #11 ·
"Being able to twist the belt 90 degrees seems a little excessive to me but I'm sure it works , I like mine a little on the tight side rather than the loose side"

Technically, one is supposed to check the belt tension using a belt tension gauge, but there aren't a lot of mechanics (let alone DIY'ers) that have one. I've seen too many people install VG timing belts too tight, which resulted in a high-pitched "whine," and end up having to pull off the timing covers again to adjust the belt. The "90 degree twist" method really only takes a few seconds and it works; I've easily done over 200 VG timing belt replacements over the years. Just install the belt, loosen the tensioner nut, turn the right bank cam gear a little, counter-clockwise, tighten the nut, turn the cam gear clockwise a little and twist the belt in the middle of the span between the two cam gears. Most of the time, it'll be dead on unless the tensioner spring is really worn out or improperly installed.
You're right,
My problem is when it doesn't whine it feels too loose for my liking haha. I can't stand loose belts

Hopefully I won't have to take it back apart for a whine when I fire it up for the first time after a valve job and performance cams this weekend. But I probably will

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If you can't twist the belt more than 90 degrees as I described, then it's not too loose.
 

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Discussion Starter · #13 ·
If you can't twist the belt more than 90 degrees as I described, then it's not too loose.
Got it done
I was too tight, whining

I broke in my cams at 2.5k rpm for 30 minutes with the noise then I tore it down and just ran the engine with just the timing belt while I slowly took tension off, started it back up, took tension off, started it back up and so forth until the whine minimized

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Sorry for the late reply- This is the engine noise I'm hearing now. Technically it's a combination of that video and this one, but I think they're the same, just hard to hear the thumping in the first one. Cool thing is if you play both at the same time it matches the sound perfectly. I changed the timing belt and everything again about a week prior. New built, new tensioner, new oil, new seals, etc.. I drove it around for several days and it functioned perfectly. On the way home this noise suddenly appeared out of nowhere. Haven't messed with it since.

- Timing wasn't off when I put the engine back together
- The whine can't be from a tight belt as it would have started long before 3 days of hard driving
- The tensioner could have slipped, but then that would also rule out the tight belt causing the squeal
- All belts are new
- Brand new oil
 

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Discussion Starter · #15 · (Edited)
Unfortunately thats not a top end noise

Almost guaranteed to be a light rod knock, that will get bad fast

But before I condemn your bottom end you need to take off all accessories belts, radiator, fan, crank pulley... Basically just strip it down like you're doing a timing belt job just leave the timing belt on(upper and lower covers removed)

Once you reach that point, hook up the battery charger and start her up for a minute. My guess is the noise will still be there.

But you might get lucky and the noise is gone. If it's gone just put back one part at a time and run the engine after you put back each part, once the noise returns there's your problem.

That's an idiot proof method to give you your answer, can't screw it up and can't go wrong

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After putting my ear to it last night I'm convinced it's the timing belt rubbing against the cover. Sound's only present during high idle (2.5k and up). Still drives and idles perfectly, so not sure what's causing it to rub. I'm sure I'll know soon enough.
 

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Discussion Starter · #17 ·
After putting my ear to it last night I'm convinced it's the timing belt rubbing against the cover. Sound's only present during high idle (2.5k and up). Still drives and idles perfectly, so not sure what's causing it to rub. I'm sure I'll know soon enough.
The only way to know is to do the test that I said

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No I certainly agree that it's a bit of a mystery. Even if my L Cam was off 360 degrees (exhaust stroke) then the exhaust valves still should have closed as the pistons reached TDC. To which I refer back to my previous comment "I began to wonder if it was actually misfires that I was hearing (exhaust stroke) and not actual collisions." Still, the sudden drop in psi on those cylinders afterwards was too much of a coincidence to ignore. I also considered that perhaps some of the valves were just shot to begin with given the condition that everything else on that truck is in it certainly wouldn't be a stretch. But then the engine idles smooth, and power seems to be good, so ruled that out. To this day I remain annoyed that I didn't get it on video to share with everyone.



To answer some of your questions:



1. New belt. I went with the Gates that you recommended.

2. Same compression gauge all four times.

3. I tested prior to replacing the timing belt (as I recommend) so that I would have a base reading to compare against once the task was complete. If psi is significantly lower after changing the belt, then timing must be off. Also did a head gasket leak test prior to as well.

4. Yes, all alignments were dead on. I'm still at work, but I will provide some images of everything once I get home. If anything it will give folks a point of reference for the conversation.





On a side note: I drove the truck around for 4-5 days a couple weeks ago. It ran great. In fact, on that fifth day I remember thinking I might actually become fond of it. So naturally the engine would start making noises a few hours later(as in potential engine being damaged noises), so it's just been sitting in the driveway collecting rust while I await the UPS man and my shiny new engine stand, hoist, and compressor. It may turn out that the valves actually did collide with the piston for reasons yet unknown. I honestly can't wait to get it apart.


Dude, if you take the engine out and replace/refurbish the head like you are suggesting please please take pics and do a write up on it! This is something I would most definitely be interested in!


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