[Ducati] Which 900 engines had the bad studs

Tue May 2 17:10:56 EDT 2006

Honda Autos have used rifled head bolts since 78. They were having a problem 
with blown head gaskets. The fix was the stretch head bolt. Use once and 
throw away when rebuilding.

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

>From: Bob Marren <bmarren at bellsouth.net>
>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, 02 May 2006 15:22:20 -0400
>
>GM uses these head bolts now for several years. The Vortec Smallblocks have 
>used them since 1996. A new set of head bolts cost $21.
>All torque wrenches should be calibrated every year if you want to trust 
>the accuracy of your work.
>Bob
>
>Scott Cloninger 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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>>
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>>
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>>the most beautiful products ever for Ducati's.
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>
>Ducati On Line thanks its sponsor and friend, Cycle Cat, maker of  some of 
>the most beautiful products ever for Ducati's.
>Visit http://www.cyclecat.com/
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