Flywheel Bolts: Shouldered vs. Non...a bit confused now??

E. Roy Wendell IV erwendell at
Sat Aug 26 17:15:59 EDT 2006

> Thank you so far for your insightful replies.
> I'm, however, a bit confused now and would like to get
> more or less a consensus as to what kind of flywheel
> bolts my VW QSW has.
> I guess the real Q here is what the Bentley really
> means by shouldered vs. non-shoulder bolts.
> The bolts that hold my car's flywheel a just like
> these:
> However, a couple of listers here as well as in the
> QSW list referred to my flywheel's bolts as simply
> "flanged" ones and that shouldered bolts have the
> shank between their head and the threaded part larger
> in diameter than the threaded part and smaller than
> the head.
> ================================================
>> From Rory at QSW list:
> Louis,
> I am not an engineer, and don't want to confuse
> things, but I believe what you have are "flanged" or
> "flange" bolts. What I have always known
> as "shouldered" or "shoulder" bolts have a part of the
> shank a larger diameter than the threaded part, so the
> nut can be tightened against the shoulder, instead of
> the head. A self- contained spacer, so to speak. A
> flange bolt has a self-contained washer, which sounds
> like what you have. The URL of the picture you posted
> would indicate that also.
> For pictures of both kinds of bolt on one page, with
> explanations, see:
> <>
> Not the biggest pictures, but I think you can see the
> important parts in the top two sections. (In the "Hex
> Flange Head Bolts" picture, the top bolt is a
> flange-shoulder bolt. In fact, in the "Shoulder Bolts"
> picture, most of the pieces shown are flange-shoulder
> bolts, but the shoulders are obvious near the threaded
> sections.)
> Why a flywheel would use shoulder bolts I don't know,
> but as I said, I'm not an engineer, I'm not even sure
> I've spelled it right :) But double check your
> Bentley; IIRC, shoulder bolts generally take *less*
> torque than standard bolts, due to a weak spot between
> the threads and the shoulder.
> Good luck, and if you find the definitive answer,
> please post it, my son's QSW definitely needs a new
> clutch, so I'll probably be facing those bolts soon :(
> Rory

I can't see an actual shoulder bolt being used in your application  
because there would be no way to actually clamp the flywheel to the  
crankshaft via stretching of the bolt that normally occurs during  
torquing. A shoulder bolt doesn't torque in the conventional sense  
because the shoulder bottoms on the area around the threaded hole and  
therefore can't be loaded in tension. Your flywheels bolts are indeed  
commonly known as flange bolts and they do have a higher torque value  
because of the extra friction between the flange and whatever it's  
holding down versus a conventional head bolt and washer. I would have  
to say that something was lost in translation and you should use the  
torque value for the "shoulder" bolts.


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