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mjslim

Exhaust Header Torque Spec

9 posts in this topic

Went to put my pipe back on the bike ('03 450) and cracked open the manual to look up the torque spec. My header has a stud/nut on one side of the exhaust flange and a socket head cap screw (Yamaha calls it a bolt) on the other. Not sure how to interpret what the manual says:

"First, temporarily tighten the nut (exhaust pipe), then tighten the bolt (exhaust pipe) 20 Nm (14 ft-lb). After that, retighten the nut (exhaust pipe) 13 Nm (9.4 ft-lb) and then the bolt (exhaust pipe) 24 Nm (17 ft-lb)."

I may be no factory trained master mechanic, but a few things here do not appeal to my sense of order. Couple of questions:

1) Is the purpose of the "temporary" tightening to compress and seat a new exhaust gasket? If so, I would be inclined to tighten both the nut and bolt to 14 ft-lb in stages, as opposed to completely tightening the nut first followed by the bolt.

2) When retightening the nut and bolt, why would you want to tighten one to 9.4 ft-lb and the other to 17 ft-lb? Wouldn't you want the same torque value for each?

Can anyone out there can explain Yamaha 's logic? Thanks in advance for any help!

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The engineers I would say have found out what gets the header to seat correctly doing it like that.

Just tighten both sides evenly. I don't know how you going to get a torque wrench in there anyway. :thumbsup:

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Don't worry, I can get a torque wrench in there. At this point, I'm like one of the bad guys in the original Dirty Harry movie, "I just gots to know"

Any Yamaha mechanics out there?

Toyota MDT tech?

Please to enlighten me....................

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I just snug the exhaust up. The heat causes the exhaust and head to expand which seats up the fit nice. I have to take my header off EVERY time I change the oil, because it blocks the filter bolts.

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I have to take my header off EVERY time I change the oil, because it blocks the filter bolts.

Me too! Small price to pay for huge power increase.

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One is a stud and the other is a bolt. They are different in the way they stretch. It has to do with friction and torsional stress but it takes less torque to stretch a stud than a bolt.

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One is a stud and the other is a bolt. They are different in the way they stretch. It has to do with friction and torsional stress but it takes less torque to stretch a stud than a bolt.

Thanks for the insight, now I can sleep peacefully :thumbsup:

So would an alternate way of looking at the spec be to make sure the gap between the cylinder and header flange is equal on both sides after tightening, provided you don't overly exceed the torque spec and crush the sh%&* out of the gasket?

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Me too! Small price to pay for huge power increase.

You guys need new headers, try Power bomb from FMF or any other for that matter, this is not a shameful plug - you should not have to remove an exhuast to change oil!!! BAD design from whose ever engineering dept. :thumbsup:

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You guys need new headers, try Power bomb from FMF or any other for that matter, this is not a shameful plug - you should not have to remove an exhuast to change oil!!! BAD design from whose ever engineering dept. :thumbsup:

You can keep your FMF, I'll stick to Procircuit. As for poor design, tell that to everyone that won an AMA championship.

I don't have to remove it, just loosen it off. I choose to remove it to clean all the crap off it then I get to see the titanium change colours again! :ride:

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