Flywheel Torque (Degree Wheel)

[MikeWillison]

I am in the process of replacing the rear main seal on my 98 R1100gs. The flywheel bolt torque according to Haynes is 40nm/30ft lbs followed by an angle tighten of 32 degrees. Is there an alternative to applying the 32 degrees or will I need a degree wheel? I do not mind buying an extra tool if I have to. Just wondering if there is a way around this.
Thanks
Mike

[PGlaves]

Unless you can reliably eyeball 32 degrees you need a degree wheel.

You could fashion a template with a protractor and ....

but I'd just get a degree wheel.

[JimVonBaden1]

There really is not alternative, but you do not have to buy one. Just make your own.

http://www.swarfrat.com/images/DegreeWheels_000.jpg


http://www.swarfrat.com/MotorcycleDegreeWheel.htm

Jim :brow

[MikeWillison]

Thanks very much Paul & Jim.
Looks like I will be making my own.
Just curious.
Why is this method superior to a straight torque value?

[MCMXCIVRS]

The main reason for this method is greater accuraccy of the clamping pressure. As torque values increase, the effects of friction on the threads, the bolt head and such begin to increase exponentially to the point that there can be significant differences in the actual clamping pressure between any two fasteners which are torqued to the same value. The condition of the threads and the presence of lubricants or debris will additionally compound this inequality.

By torquing to a small value initially to ensure an equal starting point, then tightening and additional measured rotational value, the clamping loads on each bolt can be maintianed much more accurately. For many applications, this is not a major concern, but for critical components like cylinder head bolts, connecting rod bolts, flywheel bolts etc. it can be quite important to get the right clamping value on each fastener.

[MikeWillison]

Ed
I knew that it had to be better. I just did not know why.
Thanks for that excellent explanation........
Mike

[BubbaZanetti]

FYI, there are degree wheels available at autozone, etc for less than 10 dollars

i'm pretty sure it's the least used tool in my box.:laugh

[Kaltzg]

The main reason for this method is greater accuraccy of the clamping pressure. As torque values increase, the effects of friction on the threads, the bolt head and such begin to increase exponentially to the point that there can be significant differences in the actual clamping pressure between any two fasteners which are torqued to the same value. The condition of the threads and the presence of lubricants or debris will additionally compound this inequality.

By torquing to a small value initially to ensure an equal starting point, then tightening and additional measured rotational value, the clamping loads on each bolt can be maintianed much more accurately. For many applications, this is not a major concern, but for critical components like cylinder head bolts, connecting rod bolts, flywheel bolts etc. it can be quite important to get the right clamping value on each fastener.

MCMXCIVRS:
Yours is the first explanation of the whole torque - degree angle thing that I’ve been able to get my head around. Thank you, Thank you, and Thank you. :brad

[nrpetersen]

Shorter simpler answer - These steel bolts are being tightened such that they are stretched beyond their elastic limit and are being yielded (i. e. into plastic deformation). The yield stress for steel is closely related to the hardness, which is established by the manufacturer's heat treat process. This gives a more consistent preload stress since it is more fully under the control of the manufacturer.

Unfortunately, steel can only be yielded so much. As it gets closer to fracture, the actual stress will once again be more varied. That's why the manufacturers say the bolts should be replaced on each assembly. Of course you can sometimes cheat a little.......:dunno

[MCMXCIVRS]

Shorter simpler answer - These steel bolts are being tightened such that they are stretched beyond their elastic limit and are being yielded (i. e. into plastic deformation). The yield stress for steel is closely related to the hardness, which is established by the manufacturer's heat treat process. This gives a more consistent preload stress since it is more fully under the control of the manufacturer.

Unfortunately, steel can only be yielded so much. As it gets closer to fracture, the actual stress will once again be more varied. That's why the manufacturers say the bolts should be replaced on each assembly. Of course you can sometimes cheat a little.......:dunno

This is true for the flywheel bolts in this discussion, but this method is also used with non-torque-to yield bolts in some cases as well. Torque-to-yield can be done with just a torque value also as in the case of the clutch to flywheel bolts. The torque value is much lower so there is no advantage to using the degree method for them; that method is better for larger higher toque applications like the flywheel. The bolts do however stretch to yeild and are thus one time use. In some cases the prefered method for determining bolt stretch is to actually measure the bolt as it is tightened to achieve a desired length. This method is done on some high performance connecting rod bolts used in racing engines.

The real purpose for this method is still the consistancy of the clamping pressure achieved regardless of the type of fastener used.

[Andy VH]

Ed does an excellant description of the reasoning for "positional tightening" because it is overall much more controllable and accurate. For a number of reasons:

1. Torque wrench accuracy, is only as good as the torque wrench brand, style, calibration, size, length, method of use, etc. ANY torque wrench is only accurate to within 80% at best of its applicable range. So a 150 ft-lb rated wrench (a big one) is only good up to 120 ft-lb for accuracy. A 80 ft-lb rated wrench is only good to 64 ft-lb. So the user, and his torque wrench, can vastly alter the result.

2. If the fastener is connected "dry" or "wet" alters the actual applied load under the head and in the fastener. ANY torque wrench is ONLY a torque sensing device. Anything that alters the friction between the connection will alter when the wrench achieves the set torque. So if the bolt requires 100 ft-lb "dry", but the installer does it "wet" (with oil or Loktite) the torque wrench will click at 100 ft-lb, but the "wet" threads offer less resistance. So by the time the wrench clicks, MORE torque is applied in the connection than intended. This could easily over-torque the connection by 20%.

3. Variation in the manufacture of the threads, and the surfaces, in the connection alter the torque. Thread quality (chatter marks from machining bits) leaves microscopic ridges that the mating parts must "knock down" in the process of assembly. This thread quality variance affects the actual applied load again, because the torque wrench will always "click" at its setting. But, the resistance in the threads can alter when that "click" happens.

So, basically, when accurate pre-load in a threaded connection is required, given all these variables, the real accurate method is positional tightening versus simply using a preset torque value. This same principle applies to threaded connections in hydraulic systems, which is what I do for Parker-Hannifin as a field sales/engineer.

[PGlaves]

2. If the fastener is connected "dry" or "wet" alters the actual applied load under the head and in the fastener. ANY torque wrench is ONLY a torque sensing device. Anything that alters the friction between the connection will alter when the wrench achieves the set torque. So if the bolt requires 100 ft-lb "dry", but the installer does it "wet" (with oil or Loktite) the torque wrench will click at 100 ft-lb, but the "wet" threads offer less resistance. So by the time the wrench clicks, MORE torque is applied in the connection than intended. This could easily over-torque the connection by 20%.



Actually this (underlined above) should say more clamping force is applied.

Otherwise, agreed 100%