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Discussion Starter #1
I’m changing Testastretta cam belts for the first time. I’ve watched the CCW videos in preparation, and some others. Oddly enough, the marks from the previous cam belt change lined up almost, but not quite, perfectly. I marked the old belts to show precisely where they lined up on top of the u shaped mark the last mechanic drew on the belts, so in essence 2 of the 4 marks were 1/2 tooth off when the other side was spot on. Cycle Works belts were on it and that’s also what I bought. I counted the Belt teeth between the drive gear mark and the first cam mark , and marked the new belt. When I put on the vertical belt there was slack in the belt between the two gears which caused the cam mark to move CW off the mark when I attempted to tighten the belt. . Moving the belt back CCW one tooth on the drive lines up both the cam marks, with 19 tooth count from cam to cam. Of course then my count is off 1 tooth less less between the drive gear than last time. I left the vertical cylinder that way and went to the horizontal. I counted and duplicated the marks on the new belt. There were 20 teeth between cam marks. When I tried this with the new belt I had to go to 19 teeth between cams to get both sets of gears to line up at the same time. I assume this is a result of belt wear. Am I doing the right thing here ? I read that it’s always 19 teeth between cams, true or false ? At any rate, it is now. Comments , witty remarks , scathing criticism ?
 

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Discussion Starter #2
I guess you guys aren’t as smart as I thought.
 

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I haven't piped in because I can't tell you if 19 or 20 is the right answer. And I don't really feel like stripping down my 749 to find out.

It should be exactly what it was before. Did you make your own markings on the belts and rollers to use?
 

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Discussion Starter #5
Yes , I made precise marks because the old one were the U shape I’ve seen in the videos, but I was just on one side of the old mark. I read in a couple of posts 19 teeth between cams on both cylinders, but the PO or mechanic had 20 teeth between cams on the horizontal cylinder. Moving back one tooth to 19 caused the marks to align perfectly. On the vertical cylinder moving the tooth from the drive gear to the exhaust cam one less tooth caused those marks to line up perfectly, but now the count is different than it was with the old belts. Logic tells me the tooth count thing is blown out of proportion and if all the marks line up I’m good to go. I would like confirmation of this from someone who is sure, then I’ll adjust tension and rotate the motor a few times to check for interference
 

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Discussion Starter #8
Thank you, Mr. Black.
 

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Yes, I never counted the teeth when I did mine, I just removed the old belt, and made sure the cams were in the correct position according to the workshop manual when I put the new belts on...

But you're probably correct, I'm probably not as smart as you thought...
 

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Discussion Starter #10
Not many people are.
 

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I know that you know, and you know that I know that you know.:wink2:
No really, I'm stupid and lazy.

If I am replacing on a properly running engine, I get busy with two Sharpies before I take the old ones off, transfer the marks to the new belts and put them back on lined up with the sprocket Sharpie marks I made. If it's already apart, I use the marks on the case and timing gears. If the marks are missing or ambiguous, I degree the cam(s). Because I am so lazy, I'm likely to use a box knife to cut an old belt in half longitudinally. Slip the new belt on half way and then cut the rest of the old one off. Of course, I 'm prevented from being that lazy on the outside belt when they are stacked.

So, no, I don't count the teeth. I've seen a count in the manuals on cam chain engines because it is more difficult to position with a chain that stretches some soon after installation. Otherwise, if you have to go back in later, it can be challenging. I know people on the site claim the belts stretch but I have never seen it. Dayco says their belts "delivers precise length stability to keep the engine running smoothly over the life of the belt".
 

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mistake even only 1 teeth inevitably lead to the meeting of the piston and the valve, so with the procedure you must be very careful. After belts change will not start engine at once, you should to turn by hand the crankshaft and to make sure that everything is fine
 

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Discussion Starter #15
Yes, I made my own marks which were not quite perfectly aligned with the old marks , then I went by my marks on the gears and cases. The new belts now line up perfectly with all marks, but the “ tooth count “ is not the same as the belts I removed, it’s one less. When I tried to line up the gear marks I made that were exact using the tooth count from the old belt things were off a hair.
 

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Discussion Starter #17
Thanks, Brad. I’ll check those pics vs. my cam locations . I notice the paint marks on the cams don’t line up perfectly with the valve cover gaskets, just as I was referring to on mine.
 

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The valve cover gaskets aren't marks for lining up the cams. Depending on the engine, some don't have any. Yours look to be in that group. My 749 is also in that group. Maybe all Testastrettas?

Anyway, that's why we use dots. It doesn't matter where things are as long as it goes back exactly the way it was. Match up the dots you make and there you have it. Now you can rotate the engine where you want it for tensioning.
 

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Discussion Starter #20
I put my own marks on each gear aligning with the gasket. Those marks are now in alignment with the new belts. I think my explanation of the odd tooth count only confused the issue. So now if things are correct I should be able to turn the motor over by hand and have the marks line back up every other revolution, right ?
 
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