It's a 5/16 bolt.
The L19 is what Saenz uses as their standard bolt for a 6" A-series racing rod. Given that this rod is typically twisted well north of 8 K on a significantly longer, whippier 1275 crank (3.2 v 2.45) with 3 mains, I suspect the forces put upon that combination warrant extra strength and clamping capacity.
Do I need it with a stiffer, balanced billet crank? Maybe not.
But on the other hand, despite my screw up, they didn't let go.
I might be able to save $100.00 by going with the ARP 2000. But I would be kicking myself all the way home if one let loose.
I did look at the Aermet® bolts - so I can rationalize that I'm saving money by not using a bolt that has 20% more tensile strength than what I probably already don't need.
Fordboy's Rod Bolt Rules:1) Just my own opinion, mind you . . . . .
2) Feel completely free to utilize your own "Rod Bolt Rules", at your own peril, and additionally, do not expect me to have a sympathetic ear if you experience a
failure . . . . . .
3) I base my rod bolt selection, both size and material, on the load I calculate for the maximum safe operating rpm I expect the engine to "reasonably encounter" in the
course of operation. I tend to be "Republican" about this, (that is to say "conservative"), simply because it is foolish to be otherwise. I will always choose to use the
next size up, when loads tend to be "marginal" for the fastener's load carrying capability. Fastener designers think I am "too conservative" for using a design spec.
limit of 80% of the yield strength. DO NOT USE "Ultimate Tensile Strength" for your calculations, in spite of what anybody tells you! BAD THINGS happen when rod
bolts yield . . . . . . A "small" weight penalty in terms of big end weight is the cost of "reliability", something I consider to be a performance factor . . . . . . .
4) I ALWAYS discard bolts at a mfg's recommended cycle limit: ie,
x number of hours of operation at
y rpm, etc.
OR, if the maximum safe recommended rpm has been exceeded.
5) I also discard all rod bolts if ANY rod bolt fails ANY inspection process. Such as:
A) Visual
B) Magnaflux, dye penetrant, etc, etc.
C) Micrometer length inspection. Bolts MUST match the mfg's dimension & tolerance. For obvious reasons. Bolts that are long, are "stretched",
AND HAVE YIELDED IN USE! D) If I don't like the current moon phase . . . . . .
The bottom line for me is:
I like to disassemble racing engines at whatever service interval. A lot can be learned in the process. I have done MANY racing engine "post mortems" trying to determine which part failed first. Nobody is ever happy about those . . . . . . The usual culprits are: rod bolts, other tensioned fasteners, valve springs, certain types of valves, steel retainers, and assembly and/or interference errors. Not in any particular order.
A sensible engine builder weighs the cost of a set of new rod bolts ($$) Vs. the repair cost of a rod bolt failure . . . . . .($$$$) A "Big Blast" can destroy "everything" below the head(s) . . . . .
Caveat Emptor . . . . .
Fordboy
edit:
Midget,
The only way to do this properly is with a rod bolt stretch gauge. We can use mine.
rodboltparanoidboy