[Ducati] Which 900 engines had the bad studs

Tue May 2 18:05:51 EDT 2006

Rich, I think this technology dates back to early aircraft powerplants where 
weight and reliability are real issues.

Peace...Ron"Desmohead"Betts 95 900 SP
I've learned that I don't suffer from insanity, I enjoy it!

>From: Rich Roberts <bigredxrunner at yahoo.com>
>Reply-To: Ducati Owners Group <ducati at ducati.net>
>To: Ducati Owners Group <ducati at ducati.net>
>Subject: RE: [Ducati] Which 900 engines had the bad studs
>Date: Tue, 2 May 2006 09:02:46 -0700 (PDT)
>
>Good info. I was not so familiar with fasteners designed to be used once, 
>well everyone knows about locknuts being designed in many cases for single 
>use but not bolts. In automobiles one would guess weight savings is not so 
>much an issue. Do you think waisted bolts make for better torque to yield 
>fasteners, meaning by design they can be made to work effectively easier 
>than non waisted?  You would think stress and strain would be different in 
>waisted. In motorcycles where gram conscious engineers brag about every 
>gram saved and the aggregate of all parts can be pounds...maybe waisted is 
>critical. I look at Honda fasteners for example and trimmed down fasteners 
>are commonplace, contrasted to say Suzuki which seems to focus less on 
>fastenrs and more elsewhere.   Clearly Honda looks at fasteners differently 
>than the competition and has for some time. they are generally higher 
>quality and have been for decades. I thikn they clearly waist in some cases 
>to save weight and in
>  others for torque.
>
>Scott Cloninger <scloninger at astecinc.com> wrote:  Actually, many automotive 
>companies routinely use "torque-to-yield" fasteners to secure heads and 
>other critical connections as far back as the 1980s (the first ones I saw 
>were Ford Escort head bolts). They don't have to be "waisted".
>
>I believe the use of such fasteners is strictly done to save money (smaller 
>fasteners = less cost), but that doesn't diminish the fact that they work. 
>I could imagine some geometric arrangements where smaller fasteners would 
>be advantageous, but I don't believe that's why they're used in most 
>situations. Also in aircraft or racing engines they are lighter than their 
>non torque-to-yield brothers.
>
>Without going too much into detail, the stress-strain curve of steel 
>materials (that is applied stress versus deformation) is relatively linear 
>to a point called the yield point. Once the material is stressed beyond the 
>yield point permanent deformation in the material occurs, if the stress is 
>removed the deformation beyond yield remains.
>
>Generally, engineers design to remain well below this yield point. However, 
>by designing to take fullest advantage of the material's loading properties 
>(by approaching or even slightly exceeding the yield point), a fastener can 
>be depended upon to carry a greater load. Smaller fasteners can take the 
>place of larger ones and money can be saved.
>
>Now for the bad news. Torque-to-yield fasteners are NEVER to be reused. 
>Once disassembled, they must be replaced. Often when these fasteners are 
>reused they will break upon tightening or, worse yet, will fail in service.
>
>More bad news....the tightening process is critical when using these 
>fasteners. The threads should be lightly oiled and a CALIBRATED torque 
>wrench should be used. I don't believe the type of oil is critical, but I 
>generally use a light air tool oil in my service efforts. Also, these 
>assemblies should use a hearty flat washer between the nut (or the head of 
>the bolt if it's not a stud) and the fastened member to avoid frictional 
>losses at that interface. Tightening order is also critical. Most manuals 
>will give a stepped tightening procedure with multiple torque wrench 
>settings and an explicit tightening pattern.
>
>Hope this helps clarify the situation.
>
>Cloner
>User of a CALIBRATED torque wrench.
>
>-----Original Message-----
>From: Rich Roberts [mailto:bigredxrunner at yahoo.com]
>Sent: Monday, May 01, 2006 7:08 PM
>To: Ducati Owners Group
>Subject: RE: [Ducati] Which 900 engines had the bad studs
>
>
>Uh okay...what does that mean, fastener is designed to stretch to give you 
>the torque? Interesting, since threads are a big part of that torque as 
>well as the amount at head, the thing that always scares me about such 
>things is exactly how do you standardize the procedure of torquing, how 
>much lube on threads, what kind of lube etc etc. As we all know lubrication 
>changes things in a big way. Use too much or the wrong kind and torquing 
>becomes an exercise in futility until that waisted section breaks. Do you 
>work in the aviation mechanics field? Where do you see such fasteners 
>routinely?
>
>frugalyankee-cycles at yahoo.com wrote: Some of the 'waisted' fasteners I've 
>worked with over the years are the 'stretch' type (torque to yield).....
>
>Brad
>CT.
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