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Who's torque specs to go by?

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Have some conflicting torque specs to choose from on the bolt that goes through the center of the cam gear into the camshaft.

The factory bolt torque specs are 41 ft/lbs

The cam gears are by Toda and came with their own bolt that has a bigger but shorter head because there are clearance problems with the valve cover when using the factory bolt with these gears. The spec provided by Toda to use with their bolt is 44 ft/lbs

The camshafts are from Skunk2 and they seem to assert strongly in their instructions that they want the bolt torqued to 30 ft/lbs due to their camshafts being made of chill cast iron and something about that means less torque is allowed on the fastener.

So which one do go by? I watched the webinar on how to toque a fastener and that taught me that torque specs are based on the bolt and it's yield strength not the female threads however if the female threads have a very a weaker strength this seems like a contradiction.

Technically, the correct term is lbs.ft, as ft.lbs refers to work done.

A bit surprised by Skunk2's claim that the torque should be reduced because of their camshafts being made from chilled cast iron (that term is usually used as a generic term for high carbon ferrous metals). That is the material and process normally used by camshaft manufacturers, and fitted as OEM, with most 'performance camshafts also using that material, so I would expect the same torque values to be used. As you said, the clamping, and elastic 'stretch', is closely related to the applied torque, and the bolt will be 'lose'. Some performance 'shafts are made from billet steel, but it is uncommon.

Considering the other issues you've mentioned with Skunk2, I'm not sure how much trust I would have in what they say - I would definitely query them and ask for a written assurance that they would cover ALL repairs required if a bolt backed out. As an aside, depending on the specific application, normal practice is to rely on the fastener torque to clamp the pulley and for the keyway, if used, to be used for alignment only - they are prone to instigating fatigue cracking and failure.

Thanks again Gord, it’s been a mystery to me for years if it was lbs/ft or ft/lbs as I’ve seen it both ways but knew only one was correct.

Based on what you said and the fact I’ve ran it thus far torque’d to Toda’s specs I’m just gonna leave it at that. Seems like any of the options are a roll of the dice in one way or the other.

I did ask Skunk2 this one today while I was working on the other issues with them and they stuck to their party line of 30 lbs/ft because that was the only value they said they could assure me of but at the same time they refused to accept any responsibility for it if the bolt backed out. That’s why I asked it here. I do try hard to find answers that seem reasonable to me first before asking here.

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