[kwikt]

Anyone know the torque value for the connecting rod caps. New oil pan gasket, rod bearings and steering rack in progress. Thanks!

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

I don't know if this is a whole lot of help, but according to the manual, the torque spec for the con rod bolts is as follows:



25 Nm (or 18 lb-ft) + 90 degree torque angle



I'm sure there's a logical reason why Porsche uses torque angle (in this case in combination with Nm and lb-ft), as opposed to the nice, easy-to-understand Nm or lb-ft the rest of the automotive world uses, but I don't know what it i, nor do I know where you could find a torque angle wrench (the guy behind the counter at Advance Auto looked at me like I had just grown a third eye on my forehead when I asked him if they carry any). Maybe somebody on the forum can chime in and answer that question. Good luck.

Partial Post: Please Login or Register to read the full post.

[RS Barn]

Porsche uses similar torque angle spec for cylinder head bolts. We were frustrated and thought there was an easier way. We tried to duplicate equal torque and then tested. The stretch of each of the bolts is different and requires a torque angle method-period. You also need to use new rod nuts. They are one time torque only

Pete

Partial Post: Please Login or Register to read the full post.

[kwikt]

Yep, I got the new nuts. 18ft.lb. plus 90* it is. It's funny that my Harley uses this same method on the cylinder heads. Thanks guys <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />

Partial Post: Please Login or Register to read the full post.

[chudson]

I'll go with what Pete says because he's done the Porsche reasearch and I haven't, but in all the import cars we service when there's a torque angle instruction it's because the fastener (that being the BOLT) is what 's referred to as a torque-to-yeild (TTY) fastener. A TTY bolt is one time use only (once stretched) and not the nut, although new nuts are preferred.



I have the factory 968 manuals and will read up on this because now I'm curious. I don't know of anything else that has a re-useable TTY fastener, if this is indeed what Porsche is using. ALL the VW / Audi head and rod bolts are one time use ONLY.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

I still don't understand the reasoning behind the torque-angle method (I know it's also used on the cylinder head bolts). What makes the head bolts and the rod nuts uniquely suited to this method of tightening, and what advantage does it have over the simple torque-only method? Thanks.

Partial Post: Please Login or Register to read the full post.

[DaveN]

Believe it or not, and I didn't for a while, but torquing a bolt and then stretching or deforming the bolt (the torque angle) is more accurate and repeatable than just plain torquing. The only problem is you have to replace the bolts after every use. One might think the manufacturers invented this method to sell more bolts <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />

Partial Post: Please Login or Register to read the full post.

[chudson]

It's a lot of reading, but it's good info and Porsche is actually mentioned in the "fastener quality" paragraph. One should read the ENTIRE article as it covers torque-to-yield (TTY) as well as torque-to-turn (TTT) thghtening procedures and explaines why engineers have gone to this method. Pay special attention the the statement that in the opinion of fastener engineer's, the original bolts used in the crucial areas of engines are good for only 6 torqueing sequences of which the factory uses 4. That leaves two for you and I.



It's probably overkill for the street, but everything I have built for high performance use has had ARP head studs and rod bolts.



Bolts = cheap



Broken rods and / or holes in blocks = not so much



Once at the start of a race I couldn't understand why, since I was driving one of the fastest cars in the field, the car behind me was wearing out my rear bumper. I had missed the 2 to 3 shift and was holding the throttle wide open the entire length of the front straightaway with the car in neutral. I have yet to open that engine, and the son of a friend of mine was still winning races with it a couple of years ago. Stock stuff would have probably scattered crap everywhere.



Please understand this is NOT being posted to counter anything Pete has posted. He is a Porsche expert; I am not. I would consider any and all advice he offers to be sound. I am just offering more general knowledge to the subject that is being discussed.



http://www.enginebuildermag.com/Article/...angle.aspx

Partial Post: Please Login or Register to read the full post.

[DaveN]

Tks for the link, excellent refresher with some good history. He even mentions Porsche so all the more valid <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />

Partial Post: Please Login or Register to read the full post.

[RS Barn]

Porsche use studs with nuts on heads and rods. I use torque angle method without any problem. There are several methods of using a lubricant or paste on nut surface to get consistant torque.

Porsche head studs are interesting. They do not bottom in case. You set the correct height and torque with loctite on threads in case to create tension and bonding. Then to remove studs you must heat block to 300 degrees for 2 hours and try and break them loose.

Partial Post: Please Login or Register to read the full post.

[chudson]

WOW and thanx for that info. Another one of those "what were they thinking" deals. Would love to hear the explanation from the engineer who decided that had to happen. Do the head studs enter coolant passage? Hard to believe that couldn't just machine everything to fit like everybody else does.



Pete - be on the lookout for a PM from me - need some stuff - thanx



Cliff

Partial Post: Please Login or Register to read the full post.