Big end nut torque
- Thread starter sulzeruk
- Start date
PSH
PCGB Member
I think the phrase ' have to be tightened to stretch and not torque' is a little misleading. There is no doubt that the stretch method is the recognised best way of tightening rod bolts by the professional engine builders out there but it's not the only way which is evident by the responses from ARP , probably the biggest seller of after market fastenings that there is. Torquing down is good enough but you need to take care in doing so and follow the manufactures instructions fully, also you don't just fit the bolt and torque it down. First of all there are the ( usually) 3 steps to follow, iirc raceware bolts for the 944T are 25,45 and finally 55ft/lb to reach the correct setting but before this you need to ensure that the rods are fully seated and that they have minimal resistance to the threads. This is done by torquing to the full setting and then releasing and re-torquing again. This may be done 3-5 times depending on the manufacturer used, also of importance is the lubricating fluid that is recommended to ensure that the thread gives the correct resistance. Again iirc Raceware recommend 40w oil and this needs to be cleaned off for each re-torquing and then reapplied with clean fresh oil.
Follow these steps and you'll have perfectly torqued bolts, note I say torqued , stretch method is more accurate especially when using OEM bolts, after market should be of far better quality so a little more reliable. A good torque wrench is paramount, this I have said elsewhere on this forum and stress it again here, get the best that you can afford and have it calibrated. Torque wrenches can be as far out as 50% in their readings of torque so again get the best that you can, I use my son's digital 3/8 Snap-On which is a very good wrench, it also measures angles but at over £400 pound it's not cheap and even this needs to have regular recalibration's done.
When our cars were built I doubt very much that the factory built their engines using the stretched method, I'm not even sure if they do so today, (although with today's use of robots it's possible) certainly not as far as mass produced engines are concerned, motor-sports however I'd be surprised if they didn't set via stretch.
Pete
Edit: forgot to say this is for fitting new rod bolts, you don't need to go through all of these steps for re-using the rod bolts already on the car as the threads should already be in the correct state.
Posts made and opinions expressed are those of the individual forum members
Use of the Forum is subject to the Terms and Conditions
