What this comes down to is making sure that you have a comfortable cover factor against separation of the joint at TDC-exhaust. A cover factor of 2.0 vs separation at maximum power should be adequate. You can go a little lower than this if you use yield-controlled bolt tightening (instead of torque-controlled).
Be sure to consider bearing crush in your calculation, as well as inertia loads (of course). I like to use the entire thickness and width of the steel backing, plus 1/2 the thickness of the bearing lining, in this part of the calculation. A typical bearing hoop crush stress figure would be in the neighborhood of 215 MPa.
It is also nice to compare the washer face stress to the yield strength of the conrod material, to make sure you aren't going to smoosh it too badly when you torque down your bolts.
A couple more thoughts- Rod big end distortion at TDC exhaust adds a bending load to the bolt that should be considered. A good general reference for bolted joints is J. H. Bickford "An Introduction to the Design and Behavior of Bolted Joints".
I understand the tendency of an engineer to give the most technical answer, perhaps correct, but----Every rod bolt mfgr. lists the torque, yield(stretch), and torque to yield numbers for all the bolts they sell. Why not just use their numbers? ARP sends a nice little spec sheet and a tube of moly assembly lube with each set and STS sends the spec sheet(they cost a bit less, I guess it must be the lube!).
Try giving their tech dept. a call, they would love to help. It keeps the boss of their a** !
I have been trying to get real info on comparitive bolt strength vs size for rod bolts for the Little Giant.
I am makeing a pair of rods for her with much more compact bigends, useing a 4 bolt design, instead of the original hinged design. I am trying to keep the distance from the journal to the outside of the bolt head as close as possible, so I can maximise the stroke. Yes I am makeing a crank and pistons also, and useing a modern oil system and bearings. All hiden inside the crankcase and cam box. Regards
pat
Thanks for all of the replies. I'm actually trying to determine the tensile and hardness to specify for rod bolts that are used in a specific application.
Allen, try giving ARP a buzz and tell them what your after. It's faster as they know everything that I don't.
Pull up their website.
Pat, I just had to do a brake job on the front of my Model A and I am still stuck in the 30's . It may take a week to get back. LOL At least now I can stop without the hand brake!!!
If I had you email I'd send you a photo. Of the CAR, not me!
If you like I can return the favor for several cars and boats, the most interesting being:-
The 1913 Little Giant
A late 70's British Ford Capri with blown, alky, injected SBC, running 9.02 at 154 mph, with a lot of development left.
A 1970 timber, clinker built ski boat. Regards
pat
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