rod stress vs rpm

grumpyvette

Administrator
Staff member
many guys don,t realize that the rod bolt material and cross sectional area are critical to durrability , especially in a high rpm range combo,while the rods themselfs ocassionally fail, its much more likely that the rod bolts lost thier clamping strength, stretched a bit first and that was a major contributing factor in the bearing failure or the rod failure process.


interesting info from ARP

P1-CHARTS.jpg


FOSTERP2C.jpg


Other Stresses

It must be realized that the direct reciprocating load is not the only source of stresses in bolts. A secondary effect arises because of the flexibility of the journal end of the connecting rod. The reciprocating load causes bending deformation of the bolted joint (yes, even steel deforms under load). This deformation causes bending stresses in the bolt as well as in the rod itself. These bending stresses fluctuate from zero to their maximum level during each revolution of the crankshaft.

Fastener Load

The first step in the process of designing a connecting rod bolt is to determine the load that it must carry. This is accomplished by calculating the dynamic force caused by the oscillating piston and connecting rod. This force is determined from the classical concept that force equals mass times acceleration. The mass includes the mass of the piston plus a portion of the mass of the rod. This mass undergoes oscillating motion as the crankshaft rotates. The resulting acceleration, which is at its maximum value when the piston is at top dead center and bottom dead center, is proportional to the stroke and the square of the engine speed. The oscillating force is sometimes called the reciprocating weight. Its numerical value is proportional to:
It is seen that the design load, the reciprocating weight, depends on the square of the RPM speed. This means that if the speed is doubled, for example, the design load is increased by a factor of 4. This relationship is shown graphically below for one particular rod and piston


http://www.arp-bolts.com/Tech/TechWhy.html

"are all rod stretch gauges created equal "

obviously no more than all girls are equally good looking
but most of the gauges are functional, some just have more features or more precise calibrations, some are adjustable in length ,over a wider range, some have digital read outs, ETC.

sum-900015.jpg

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-900015&N=700+4294854225+115&autoview=sku

http://www.carcraft.com/techarticles/116_0609_using_rod_bolt_stretch_tool/index.html

http://www.chevyhiperformance.com/techarticles/0710ch_proper_engine_fasteners/index.html
 
Last edited by a moderator:
I see rods and rod bolt failures blamed frequently when engines self destruct at high rpms, but its NOT always what it at first might appear to be....are there any detailed pictures of the rods or rod bolts that failed??? in many cases the source of the problem can be seen with a careful detailed exam, if you don,t know the SOURCE of the problem your doomed to repeat the sequence... and keep in mind a good deal of what might appear to be rod/rodbolt failures, are ACTUALLY the result of over reving the valve train,and loss of valve train control, OR detonation, theres no way to compress a bent valve or broken piston ring land without potentially damaging the rods
rods may fail due to spun bearings, lack of oil flow, etc, but the most comon failures I see blamed on rods are usually valve control issues that resulted in the rod/pistons bending a valve, then trying to compress the broken valve, its hardly a rods fault if the valve fails to retract in time to get out of the way due to valve control issues at high rpms

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why0.html


http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why1.html

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why2.html


http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why3.html



http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why4.html



http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why5.html


http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why6.html

seven words

arp-100-9942_w.jpg



USE A STRETCH GAUGE and ARP BOLTS

http://store.summitracing.com/partde...5&autoview=sku


or at a MINIMUM, READ THE INSTRUCTIONS CAREFULLY,at least tighten then loosen and re-tighten to spec EACH BOLT ,THREE SEPERATE TIMES with a QUALITY torque wrench


great
http://www.nationaltoolwarehouse.com...qx/product.htm

ok

http://www.nationaltoolwarehouse.com...qx/product.htm



http://www.hotrodshack.com/torque_settings.htm

http://www.arp-bolts.com/Tech/TechTorque.html
 
Back
Top