2.5 DOHC timing belt question - Subaru Outback - Subaru Outback Forums
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post #1 of 27 (permalink) Old 12-13-2011, 04:02 PM Thread Starter
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2.5 DOHC timing belt question

This is further to my earlier "help with overheating" thread in which I received
a lot of excellent guidance.

I'm reinstalling my existing belt, meaning the factory markings are worn off.
I've read the TSM instructions on the exact tooth spacing between the
sprockets, but I'm having a problem with them: On the driver's side intake
(upper) cam sprocket, the single (i.e. upper) mark is exactly on the edge of
the tooth, so it's really unclear where belt tooth #51 is supposed to be - to
the right or left of of the sprocket mark. Can anyone clarify this for me?

Thanks much.

Jonathan
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post #2 of 27 (permalink) Old 12-13-2011, 05:30 PM
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If my flawed memory is correct, the main timing mark is in the middle of a thin section of the belt, to match the middle of a tooth on the sprocket. So the 51 segment should also fall on a thin section of the belt, at the middle of a sprocket tooth.

So 54.5 teeth the other way ends up at a thick part of the belt...
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post #3 of 27 (permalink) Old 12-13-2011, 05:38 PM
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I have a different illustration that shows the belt marks, but doesn't give the counts. (And I previously posted it as a GIF file that looked really bad...)
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post #4 of 27 (permalink) Old 12-13-2011, 05:46 PM Thread Starter
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Yeah, I've got all that, but the problem I'm having is with that 51-tooth count from the crank to the "left hand inlet camshaft". Your second drawing shows Z2 spanning from the crank tooth to the cam sprocket tooth. The index mark on the crank is right on top of the tooth, alright, but on the cam sprocket the mark isn't - it's on the right falling edge of the tooth, and that's what's confusing me.
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post #5 of 27 (permalink) Old 12-13-2011, 07:57 PM
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Quote:
Originally Posted by outinthewoods View Post
Yeah, I've got all that, but the problem I'm having is with that 51-tooth count from the crank to the "left hand inlet camshaft". Your second drawing shows Z2 spanning from the crank tooth to the cam sprocket tooth. The index mark on the crank is right on top of the tooth, alright, but on the cam sprocket the mark isn't - it's on the right falling edge of the tooth, and that's what's confusing me.
Yup, gotcha... The tooth that's closest to the molded mark is the correct tooth. Treat the tooth as the real indicator, the mark is just the visual aid. (Unless you think the cam pulleys are on the wrong cams?)
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post #6 of 27 (permalink) Old 12-13-2011, 08:25 PM
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+1 /\ what he said.

but the proof is not there untill you pull the pin on the tensioner. line it up, pull the pin. and then check the alignment hash marks on the cams and the crank sprockets. if they are on the marks , then it is right.

if not, then try again.

happy motoring.
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post #7 of 27 (permalink) Old 12-13-2011, 09:10 PM
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but the proof is not there untill you pull the pin on the tensioner. line it up, pull the pin. and then check the alignment hash marks on the cams and the crank sprockets.
I actually had a lot of fun with this while I was setting mine up... Once the belt and all of the idlers are in-place, leave the tensioner pin inserted. I didn't want to pull the tensioner pin until I was sure it was perfect.

Press (pretty hard) with your finger near the position where the tensioner will press on the belt. This takes up the slack in the belt, and you can see where the timing marks will be when you finally do pull the pin. On my install, I had both of the lower cams one tooth out-of-position. You release the tension on the belt, and with a ratchet you GENTLY turn the out-of-line cam(s) so they skip one tooth on the belt in the desired direction. (Manipulate the belt so it's loose near the cam you're adjusting.) Then tension the belt with your finger and check again. I went through this a few times and triple checked every mark before pulling the pin. Not too difficult once the belt and idlers are all installed...
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post #8 of 27 (permalink) Old 12-13-2011, 09:20 PM
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Quote:
so it's really unclear where belt tooth #51 is supposed to be - to
the right or left of of the sprocket mark. Can anyone clarify this for me?
Based both on my memory and the composite graphic (below) from the FSM, the belt tooth goes to the right of the sprocket mark. As is evident on the top right of the graphic, the mark shown on the belt is slightly off-center to the left side of the tooth, so if the mark on the belt were lined up with the sprocket/cover marks, the tooth would be to the right.

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post #9 of 27 (permalink) Old 12-13-2011, 10:01 PM
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lines on the belt and counting teeth is completely unnecessary - but the mark is usually (i would even say always) a little towards one side - you count by rounding. but of course that's silly since it's hard to look at it from perfectly dead on and distinguish such a small amount without getting into geometry and straight edges...LOL

my method - line the crank and cam marks, ignore the timing belt marks and tooth counting - and it's right 100% of the time. granted i've done a lot but still it's straight forward, easy, and never confusing.

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post #10 of 27 (permalink) Old 12-15-2011, 03:26 PM Thread Starter
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Understood, but since I haven't done it a lot, I'd like to get the tooth-counting right, and I'm finding it difficult. I don't want to sound dense, but every way I look at the instructions they're ambiguous, and I'm really trying to avoid a fencepost error. Here's my problem: I don't know whether a "tooth length" (the phrase used by the TSM) is just the belt tooth, or the tooth and the trough next to it. That is, am I counting cycles or just peaks?

Or to be more specific: I want to count the 51 teeth. If (belt) tooth #1 is the tooth immediately to the right of the 12:00 crank tooth, is #51 in the sprocket trough nearest (and just past) the mark?
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