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tolerances for cam gear alignment (timing belt change)

 
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Old 14 Dec 2015, 10:38 pm
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Default tolerances for cam gear alignment (timing belt change)

Hi everyone, I couldn't find a clear answer to this elsewhere...does anyone know what the tolerances for aligning the cam gears is?

As I understand it, when properly aligned, all four alignment notches on the cam gears should line up perfectly. However, when I got my timing belt on, I found that the middle two marks were 2-3mm higher than the right and left marks.

cam gear overview

closeup

I tried rotating the left cam clockwise one notch to try to get them to align better, but that just threw it completely off. Which didn't really surprise me, since the amount the cams are off seems to be a good bit less less than the length between two teeth.

For those that have done this before, is this within the normal tolerances? Or do I still need to adjust it in some way?
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Old 14 Dec 2015, 11:05 pm
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Default Re: tolerances for cam gear alignment (timing belt change)

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Originally Posted by ushumgal View Post
Hi everyone, I couldn't find a clear answer to this elsewhere...does anyone know what the tolerances for aligning the cam gears is?

As I understand it, when properly aligned, all four alignment notches on the cam gears should line up perfectly. However, when I got my timing belt on, I found that the middle two marks were 2-3mm higher than the right and left marks.

cam gear overview

closeup

I tried rotating the left cam clockwise one notch to try to get them to align better, but that just threw it completely off. Which didn't really surprise me, since the amount the cams are off seems to be a good bit less less than the length between two teeth.

For those that have done this before, is this within the normal tolerances? Or do I still need to adjust it in some way?
Pay no attention to the outer marks. Just the inner ones. They should line up to each other through the center line of the cam bolts. Use a straight edge.
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Old 15 Dec 2015, 09:15 am
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Default Re: tolerances for cam gear alignment (timing belt change)

start the car and make sure it idles, then make sure it revs, and then you know it's right.

i did this, as i was instructed to by an ASE certified friend. no coolant, no belts, no mounts, just a quick test.
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Old 15 Dec 2015, 10:23 pm
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Default Re: tolerances for cam gear alignment (timing belt change)

Thanks Rob! I gave it a try, let it run for just a few seconds - seems to work! Now putting it all back together...
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Old 16 Dec 2015, 08:36 am
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Default Re: tolerances for cam gear alignment (timing belt change)

While it looks like the OP has got this alignment thing figured out, I thought I'd go ahead and post of photo of what's been talked about.

It's very easy to end up with these sprockets one tooth off. And when this happens, the sprockets can still be turned in a way that the two inside timing marks align but the outer marks will be either higher or lower than the inside marks.

In the photo below, you can see what proper alignment looks like. All four marks roughly align, but as the OP described, the two inside marks will be slightly higher.

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Old 16 Dec 2015, 01:49 pm
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Default Re: tolerances for cam gear alignment (timing belt change)

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Originally Posted by Handy_Cruiser View Post
While it looks like the OP has got this alignment thing figured out, I thought I'd go ahead and post of photo of what's been talked about.

It's very easy to end up with these sprockets one tooth off. And when this happens, the sprockets can still be turned in a way that the two inside timing marks align but the outer marks will be either higher or lower than the inside marks.

In the photo below, you can see what proper alignment looks like. All four marks roughly align, but as the OP described, the two inside marks will be slightly higher.

Actually if you notice the picture. The outward are out in the low side. The inner marks line up directly through the center of the sprocket. That's why you disregard the outer marks.
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Old 17 Dec 2015, 11:19 am
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Default Re: tolerances for cam gear alignment (timing belt change)

Thanks for the image, Handy_Cruiser - that explains it perfectly!
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Old 17 Dec 2015, 08:33 pm
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Default Re: tolerances for cam gear alignment (timing belt change)

Seeing that here are camshaft and crankshaft position sensors, has anyone used a scan tool to verify correct positioning. Other than the cam-to-cam alignment, a good tool should be able to read the positioning of cam-to-crank, which might be more of a challenge.
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Old 18 Dec 2015, 11:28 am
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Default Re: tolerances for cam gear alignment (timing belt change)

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Originally Posted by RCSnyder View Post
Seeing that here are camshaft and crankshaft position sensors, has anyone used a scan tool to verify correct positioning. Other than the cam-to-cam alignment, a good tool should be able to read the positioning of cam-to-crank, which might be more of a challenge.
The real issue is that using the OEM style timing components, you can only get the timing within one tooth-width of being correct. So the variance is fairly wide.

To make finer correction, you have to install variable timing gears. After that, you use a tool that locks the cams in place in relationship to each other and then use a dial gauge to get #1 piston at top dead center. And this "floats" the cams in to give you a baseline. After that, small adjustments can be made to the timing of either cam as desired.

I did not add variable timing gears to my performance cams. But I did use a similar setup to take measurements so I could have more precise information and confirm some issues like what I posted about above. Darrell Cox Racing makes a better tool for locking the cams in place. I made my own.

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Old 20 Dec 2015, 08:06 am
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Default Re: tolerances for cam gear alignment (timing belt change)

i wouldnt trust the start-it-up test. with the crank or a cam 1 tooth off, the engine should still start, idle, and run, though it might sound a little odd. i had a 98 2.0 sohc mtx stratus that i finally put a water pump on at 120k. i got it in time before knocking it apart and discovered that the cam was 1 tooth retarded. the timing cover had never been off of the engine and i had no (noticeable) drivability issues and no CEL. upon reassembly, i made an executive decision and timed it properly instead of retarding it 1 tooth like it had been for 120k miles.
first start up gave me a CEL for cam/crank misalignment that stayed on until i sold the car at 150k because i didnt want to tear it back apart or pay for a crank relearn. I noticed no performance, drivability, or fuel mileage effects/issues between the two timing settings.
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