Seeking advice

City Garage said:

Its important to address a few misconceptions often circulated online or by those without hands-on experience. Many who suggest practices like head bolt retorque are either following outdated advice or simply echoing what they've heard from others on forums without understanding the engineering behind it.

First off, let's consider modern vehicles—whether cars or motorcycles. When was the last time you had to take a new vehicle back to the dealer for a head retorque after an initial service? Probably never. That's because once the initial torque sequence is complete, there's no way to replicate it without compromising the integrity of the gasket. If you loosen those bolts for a retorque, the gasket won't return to its original state, which is why bolt marking is done. This lets you visually confirm if anything has shifted.

Moreover, every major modern gasket manufacturer will tell you that a retorque is unnecessary. These companies design their gaskets to perform optimally with the initial torque and bolt stretch. Even in a Harley, which is a close comparison to the 961, there’s no factory procedure for loosening and re-torquing head bolts.

Now, in the case of the 961, it's true that the engine components aren't up to the same quality standards as more refined engines. Norton included a TSB head bolt check because the bolts, gaskets, and other components are of lower quality, the motor tends to run extremely hot, and they had issues with build quality. It's essentially a way for the manufacturer and dealers to cover themselves for potential issues arising from subpar parts

Take ARP, for example They will never advise you to back off a bolt that’s already been torqued to spec. Instead, they recommend the use of their Ultra Torque Lube to ensure consistent torque readings and to prevent issues like galling. The emphasis is on consistency, not revisiting bolts that have already been stretched and torqued.

If you're insistent on checking torque, that's fine. But if you decide to start backing off fasteners that have been torqued at the factory, especially when the factory manual advises against it, you're asking for trouble. A quick check with a properly calibrated torque wrench, followed by paint-marking the bolts, is sufficient to monitor for any movement. If you're finding that a bolt has shifted an 1/32 or more, you've likely got bigger problems to address than just the torque. Something else in the system could be failing, misaligned or wasn't done correctly to start with from the factory.

Now if you want to talk pre 1980 engines that's another discussion.

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Fast Eddie said:

Your point about modern vehicles not needing to have fasteners re-torqued is correct. But it’s not very relevant to a discussion about vehicles that do.

I am not ‘insistent on checking torque’ as you put it. In fact I never mentioned checking torque. I mentioned re-torqueing.

Are you seriously telling me that you have never encountered the high static torque of a stuck fastener ?

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City Garage said:

I'm sorry, but could you remind me how many 961s you own? Also, have you torn down any 961 engines to the cases, headwork, or valves? Have you had customers ship them to you from all over the USA for repairs/service? I just want to get an idea of whether you have any practical hands-on experience with these bikes.

When someone is critical of the relevance of the other person's contribution and the overall tone comes across as dismissive or impatient with the current direction of the conversation that's about the time I quit contributing to these forums.

So, if I install a new gasket that is better than OEM quality, would I need to follow the retorque procedure again after that, or is a modern gasket that the manufacturer states requires no retorque ok with you?

My point about modern vehicles is indeed really relevant, as this is more of a late 90s/early 2000s engine that has modern gaskets in it. While not quite as nice as the gaskets Ollie has, they are still serviceable products when installed correctly.

And regarding re-torquing, Ah, my mistake! You're absolutely right—there's a world of difference between 'checking torque' and 're-torqueing.' One simply observes, while the other actually gets the job done. Thanks for clearing that up!

Your statement of" high static torque of a stuck fastener" is a pretty fancy way of describing a simple, everyday problem that many shops face with improperly installed hardware or other issues like corrosion. But it's an impressive word choice for something so basic! But let's talk about that since you brought it up. During installation, the bolt generates tensile force(stretch) while encountering sliding friction(turn) as the head contacts the surface. However, when loosening the bolt, one must overcome static friction, which is inherently more significant than sliding friction due to its higher resistance before motion initiates—typically quantified as a percentage above the coefficient of sliding friction.

But when loosening a bolt, the torque required to loosen (versus breakaway), will be 70-80% lower than the original tightening torque, which leads people to think it was lose. But the real question is, why would you loosen an already properly tightened fastener just to retighten it, especially if you don’t have an accurate measurement of the initial torque? Without knowing the starting point, you're essentially guessing, which could lead to improper force or potential failure.

So, those who are looking for a baseline figure have two options.

Apply torque in the tightening direction to the bolt and note the value just before the bolt starts moving again. This helps estimate the initial torque without loosening the bolt entirely.

Or breakaway routine involves slowly applying torque to the fastener in the loosening direction until it just starts to move (breaks free). The value at which the bolt begins to turn gives you a rough estimate (really rough)of the installed torque. This method is commonly used in the field to determine how tightly the bolt was previously installed without having the known torque table.

I would only do the breakaway if I was removing the head and installing a new gasket.

In a perfect world, for any 961 that someone services, I would( and we have done this many times) disassemble the top end, replace the lifters, rockers, gaskets, and rings, and install better hardware, coat bolts as needed, if they want to minimize issues.

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Stu Bodycote said:

I'm not a metallurgist, so I'm only poking a greasy thumb at the subject....but the mix of high tensile centre bolts and stainless outer studs providing the clamping force, never sat well with me. Most of the slackening of the fixings was put down to the base gasket compressing by all accounts. For my Domi, I went with high tensile across the board.
I did read that Norton have pretty much gone back to the original, or near as damn it, head torque figure but also made it a thing to check at the 1st/500 mile service and then again at the 3rd/18000 mile service. Odd. And apparently not to check the centre fixings....odder. Dont know thereafter because their wank owners manual only goes up to five years.

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Stretch bolts are designed so that they can be elongated beyond their elastic limit intothe plastic region without problems. When a specific tightening torque has been reached, the bolts are turned further through a defined angle, which pre-loads them into the plastic region. Consequently, no re-torquing is necessary - but the bolts cannot be reused!

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Stu Bodycote said:

. For my Domi, I went with high tensile across the board.

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kommando said:

There is a difference in how head bolts work, old school is where you torque the bolts within the elastic deformation of the bolt. Here the bolts stretches as its torqued but never permanently deforms, un-torque the bolt and it returns to its original dimensions. These bolts can loosen off in service initially and need retorquing as the assembly settles.

There we have modern head bolts where you apply an initial torque and then turn a set angle or part of a turn to take the bolt past the elastic deformation. Undo these and you throw them away and use new replacements. They can never be retorqued.

https://www.partinfo.co.uk/files/Head%20bolts.pdf

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