Re: question about con rod fasteners...
[Re: dirtybee]
#186852
01/07/09 06:28 PM
01/07/09 06:28 PM
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Joined: Feb 2007
Posts: 5,080 organ
maximum entropy
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master
Joined: Feb 2007
Posts: 5,080
organ
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consider what the bolt is threading into. cast iron? stud is a major improvement. threading into 4340? a bolt will do just fine. and you're not relying on the fastener for alignment of the cap. the rod can also be profiled for more clearance without a notch at the base of the beam.
Last edited by maximum entropy; 01/07/09 06:30 PM.
for what is the good life if not doing things thoughtfully?
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Re: question about con rod fasteners...
[Re: maximum entropy]
#186853
01/07/09 06:43 PM
01/07/09 06:43 PM
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Joined: Jan 2005
Posts: 3,635 Oakland, MI
dizuster
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master
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Oakland, MI
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I'm not a fastener engineer, but I'll take my best guess at it. First of all you need to think about the total length of a rod fastener vs. a main cap fastener. If you use a bolt on the main cap, a large portion of your torque is actually twisting the bolt itself, not threading it in further. So the force is transfered through the large shaft of the bolt, before it can get to threads. Since the main bolts are very long, this creates a twisting problem (think torsion bar). If you put a stud in it, the force is immidiately put on the nut to tighten the fastener. It doesn't have to go down the shaft of the stud to get to apply the energy to tighten it. Rod bolts are obviously much shorter, and don't have to deal with this problem. Also, if you think about putting studs in a rod, the top portion of the stud is actually fairly thin. That thin section is the only thing preventing that stud from pulling through the rod. Also, this creates a very high stress concentration at that loading point. Where as if you put a bolt in it, the threads help distribute the load through the rod more evenly. Lastly as mentioned, the profile of the rod can be trimmed down (lighter, more clearance, etc...) if you use a bolt. Like I said, I'm not a fastener engineer so someone may tell me I'm wrong? But that's how I see it...
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Re: question about con rod fasteners...
[Re: dirtybee]
#186855
01/07/09 07:15 PM
01/07/09 07:15 PM
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Joined: Feb 2007
Posts: 5,080 organ
maximum entropy
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master
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material is removed from the ends, same as i beams. i've only seen very small amounts removed. my guess is that manufacturing methods are much more accurate these days? even overseas? stand by for imbroglio!
for what is the good life if not doing things thoughtfully?
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Re: question about con rod fasteners...
[Re: dirtybee]
#186857
01/07/09 11:10 PM
01/07/09 11:10 PM
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Joined: Nov 2003
Posts: 2,715 closer to Canadian beer!
torkrules
I'm neurotic
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I'm neurotic
Joined: Nov 2003
Posts: 2,715
closer to Canadian beer!
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Quote:
i'm just curious about connecting rods and why all the newer style h beams and fancy i beams all use cap screws instead of a bolt and nut like the oem rods. then look at hi performance engines today and the main caps and heads are all held down with nuts on studs. aren't studs way stronger than bolts? so why the trend to move to bolts on one of the most important components of the engine instead of a nut and bolt?.....winter.....snow......bored....any engine gurus feel like enlightening me?
Rod bolts need to have a broached "notch" for clearance for the bolt head and to register the flat part of the bolt. This leaves a weak spot in the rod. With cap screws this operation is not needed and more material is available around the big end.
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Re: question about con rod fasteners...
[Re: jcc]
#186859
01/08/09 12:50 AM
01/08/09 12:50 AM
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Joined: Jan 2004
Posts: 27,347 Today? Who Knows?
1_WILD_RT
Management Trainee
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Management Trainee
Joined: Jan 2004
Posts: 27,347
Today? Who Knows?
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Quote:
That doesn't sound right to me, most high dollar bolts with partial thread lenght are necked down to the small thread root diameter anyway, to even out stresses anyway, if I understood your comment correctly.
What torkrules is actually refering to is the area on the connecting rod that is broached for clearance for the rod bolt head... It definately creates a weak area
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Re: question about con rod fasteners...
[Re: torkrules]
#186863
01/08/09 10:31 AM
01/08/09 10:31 AM
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Joined: Apr 2007
Posts: 807 Toronto, Canada
dirtybee
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OP
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Joined: Apr 2007
Posts: 807
Toronto, Canada
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Quote:
Rod bolts need to have a broached "notch" for clearance for the bolt head and to register the flat part of the bolt. This leaves a weak spot in the rod. With cap screws this operation is not needed and more material is available around the big end.
ok, now that actually makes alot of sense. thanks
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