Engine; Heavy Duty Connecting Rod Bolts
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- Isuzuperformance Heavy Duty Connecting Rod Bolts
Connecting Rod Bolts
These are the only aftermarket connecting rod bolts made for the Isuzu 4XE1 or 4XC1 engines. These bolts
are made by Isuzuperformance. These bolts are NOT made by ARP.
ARP do not make these bolts and ARP does not make bolts intended for use in the Isuzu 4XE1 or 4XC1 engines.
Justin Phillips, Specialty Products Coordinator for ARP Incorporated confirmed that ARP do not make bolts for
the 4XE1 or 4XC1 engines and that ARP do not have anything that is, in their professional opinion, close
enough to substitute.
Robie Blair of Robie the Robot (aka: BlairCraft internet technology and website consulting of Colorado Springs,
Colorado) do not sell connecting rod bolts made for the Isuzu 4XE1 or 4XC1 engines. Mr. Blair of RTR has been
selling an ARP bolt made for another engine, which ARP has already stated, does not fit and is not recommend
for use with the Isuzu 4XE1 and 4XC1 engines. Mr. Blair of RTR expects the customer to modify the connecting
rod to accept this ARP bolt. Mr. Blair / RTR's unfortunate customers report that the ARP bolts do not fit the
Isuzu connecting rods and spin in the hole they are intended to be pressed into. Such a poor fit prevents
proper installation and inevitably results in engine failure due to bolt failure.
The bolts offered in this item listing are not ARP bolts, are in no way associated with Robie Blair, Robie the
Robot, or ARP Inc., and exhibit none of the installation problems or engine failures associated with those
The bolts offered in this item listing are made by Isuzuperformance and specifically designed for use with the
Isuzu 4XE1 and 4XC1 engines. And they are the only aftermarket connecting rod bolts available which have been
made specifically for these engines.
The Story Behind This Item
Isuzu engines are very durable with the exception of one piece: the connecting rod bolts.
The original connecting rod bolts in the 4XE1 engine were manufactured by a process called cold heading. This
process starts by cutting a length of heavy gauge rod or wire into a slug, which is then cold formed by
hammering it into various forms and dies by use a horizontal reciprocating rams and stationary bolsters. This
process is cheap and fast, producing up to 400 pieces per minute for pennies a piece. But the process also
maximizes the number of imperfections and weak veins within the part, due to cold folding of the metal. In
addition to this, the original connecting rod bolts are not heat treated.
The original connecting rod bolts are torque-to-yield or torque-to-angle. This means that the bolt is installed
and stretched to its tensile capacity. The factory shop manual describes installation as "torque to 11 ft-lb,
then turn 45° to 60°". This is unfortunately past the tensile capacity of the original cold headed connecting
rod bolt. Disassemble an engine to check the rod bearings and several of the original connecting rod bolts will
break at the base of the threads during reassembly.
The original connecting rod bolts were placed on the discontinued parts list by Isuzu, though they are of such
poor quality that they are not desirable as a replacement. There are no aftermarket connecting rod bolts
available for these engines through parts stores or engine rebuild parts suppliers.
After destroying one very expensive engine block, one very expensive crankshaft, and breaking numerous original
connecting rod bolts while reassembling engines, we decided to build a better bolt.
Failed Connecting Rod Bolts Cause Two Things:
There is only one cause for throwing a connecting rod through the engine block, and that is failure of the
connecting rod bolt. The reason is the poor quality of the original connecting rod bolt. Anyone with more
than a few years of experience with these cars, who has not personally experienced throwing a rod through the
front of the block, would almost certainly have seen the results of a rod bolt failure (engine block with a hole
in the front of it) in a salvage yard while shopping for used parts.
- First, a stretched connecting rod bolt will allow the rod bearing to become loose and "spin", for the all
too common "spun rod bearing". This will damage the crank shaft, which should not be re used if the tuftride
or nitride coating is worn through. Eventually, a stretched bolt will allow the nut to fall completely off,
freeing the rod from the crankshaft, at which time the rod will go through the front of the block, destroying
it as it passes through, usually after bouncing off the crank journal a few times and destroying the crank
before the rod exits the engine.
- The second failure is when the bolt fails by breaking in half, dropping the nut and the threaded end of the
bolt into the oil pan, freeing the rod from the crankshaft, at which time the rod will go through the front of
the block, destroying it as it passes through, usually after bouncing off the crank journal a few times and
destroying the crank before the rod exits the engine.
About This Product
Manufacturer is ISO 9001:2008 certified.
Heat treat is Nadcap certified with AC 7004 quality control system.
That tensile strength rating should be familiar to engine builders. This tensile strength is 4.5% above ARP's
rating of 220,000 PSI stated on their website, and 15% above the claimed rating of 200,000 PSI on third party
websites claiming to sell ARP brand connecting rod bolts.
- Precision turned from 1/2 inch diameter, 4340 alloy steel.
- Heat treated, by hardening and tempering, to 230,000 PSI tensile strength. Tests 47 Rockwell hardness.
- After hardening, the shafts of the bolts were hand polished to the upper limit of the factory specification,
for a tight fit in the original connecting rods. The installer may wish to further polish the shaft for an exact
fit in the connecting rod. This can easily be done with fine grit wet/dry sand paper.
- Made in Chicago, Illinois and St. Louis, Missouri, USA.
- 8 mm x 1.00 thread pitch, uses the original connecting rod nuts.
4340 alloy steel is an extremely tough alloy that hardens completely through. It does not become brittle with a
tendency of cracking, like 8740 alloy ChroMoly (ARP) or H-11 Tool Steel (Crower). The hardening goes completely
through the material, unlike case hardening (used with tool steel), which hardens only the surface, leaving a
soft core. This results in a much more durable bolt.
4340 alloy should be familiar to experienced engine builders, because it is the same alloy used in high end
connecting rods made by Pauter, Eagle, Manley, ProComp, Lunati, Scat, and other noted connecting rod manufacturers.
These bolts are made of the same material as the connecting rods used in NHRA top fuel dragsters and NASCAR race
We did not set out to make a bolt for one thousand horsepower engines. The intent was to make a bolt that is better
quality than the original bolt that would not break upon installation like the original bolt, and to prevent con rod
failures due to weak connecting rod bolts. In the development phase, we decided to match or exceed the tensile
strength specs of the popular racing connecting rod bolts. These will probably take more than anyone could possibly
get out of a 4XE1 engine. But if your goal is to build a one thousand horsepower monster engine, then you probably
already picked out a set of custom made rods that will come with their own custom connecting rod bolts.
These heavy duty bolts are legal for use in SCCA Stock, Street Touring, Street Prepared, and Improved Touring classes,
which require the use of stock (or aftermarket stock replacement) engine internals. These bolts are a direct
replacement with no weight reduction or performance advantage, aside from being many times stronger than the original
It is somewhat humorous that people will spend almost $200 on cylinder head studs/bolts to do a stock rebuild for
these engines, when the factory original head bolts are grade 12.9, 12 mm diameter, socket head cap screws, with a
tensile strength around 172,000 PSI. There has never been a documented case of failure of an original head bolt.
But no one ever replaces the connecting rod bolts, despite the overly common shared experiences of spun rod bearings
and thrown connecting rods.
We attempted test the original bolts and these heavy duty bolts by torquing them to failure. Each bolt was pressed
into an OEM connecting rod, and the OEM connecting rod cap placed over the bolt. The assembly was placed into a
bench vice. A Grade 10 hardened 8mm x 1.0 nut was obtained from the local industrial fastenner warehouse, and was
then threaded onto the bolt and torqued down in 5 foot pound increments using an ATD brand model 102 torque wrench.
At just past 30 ft-lb, the original, Isuzu connecting rod bolt failed. It stretched by .011 inches, and the threads
were torn off of the OEM bolt by the nut. This was surprising, we expected the bolt to shear.
The Isuzuperformance heavy duty bolt did not fail in the test. The nut was torqued to 60 ft-lb, stretching the bolt
by a mere .003 inches. At this point, the threads were pulled off the inside of the Grade 10 hardened nut. The
heavy duty bolt was stronger than the Grade 10 hardened nut.
In terms of determining the breaking point of the Isuzuperformance heavy duty bolts, the test was a failure, because
we were unable to break the bolt with the available, sacrificable, Grade 10 hardened nut. However, we did determine
that the Isuzuperformance heavy duty bolt can take more than double the torque of the original bolt.
Appropriate Use Of This Product
- Any build of a performance engine which uses the stock or OEM connecting rods. All applications involving
enhanced performance and requiring increased durability.
- Any stock spec rebuild of an engine. All applications where longevity and durability is desired.
- Any time that a crank shaft mains or connecting rod ends are removed from an engine for the servicing of the main
or connecting rod bearings. Any time where reinstallation and reuse of the OEM bolts will likely result in breaking
- Any time a used engine is to be installed, and it is opened up to check bearing wear. Any time an engine's life
can be lengthened by the installation of more durable bolts.
Installation and Precautions
Use a hydraulic press to install the bolts in the connecting rods.
Never pull the bolt into the connecting rod by tightening a nut onto the threads to pull the bolt into the connecting
rod. Doing this will damage the bolt. Always use a hydraulic press to install connecting rod bolts.
Never exceed 40 ft-lb of torque with these bolts. There is no reason to torque the bolt that tightly and doing so
will probably damage the bearings and/or crankshaft.
Use the OEM connecting rod nuts.
Follow the factory installation instructions in the factory shop manual.
Suggested supplemental installation instructions:
Cut a cardboard torquing template in the shape of an equilateral triangle (three 60 degree angle corners) about 15
inches on each side. Draw a line in marker at 45 degrees from one corner to the opposite side of the triangle,
sloping toward the right. Notch the corner at the base of the marker line to clear the socket. The template now
shows a 45 degree angle marked with a marker line, and a 60 degree line to the outside edge of the template.
Following the factory instructions of torquing each nut to 11 pounds, the template makes it easy to then rotate each
bolt to a consistent 45 to 60 degrees for the final torquing step.
Now, if you use a torque wrench to install the nuts, and measure the torque setting required to rotate the nut to
the 45 degree mark, you might find that the torque setting is 27 ft-lbs. And if then measure the torque setting
required to rotate the nut to the 60 degree mark, and you might find that the torque setting is 31 ft-lbs. Please
verify these numbers for yourself.
Torquing the nuts onto the bolts while using both the angle template and a torque wrench set between these two
measured torque settings allows you visually verify that each nut is rotated to the factory prescribed angle, and
audibly verify that each nut has reached a consistent torque setting and that the bolt has not failed during
4XE1 and 4XC1 Engines
1989-93 1.6 liter 4XE1 engine
Shipping of rod bolt sets is via US Mail Priority and costs are as follows: Please see Ebay
item listing for shipping costs.
1985-1989 1.5 liter 4XC1 engine
- 1990-1991 Isuzu Impulse XS
- 1990-1992 Isuzu Impulse RS AWD Turbo
- 1990-1991 Isuzu Stylus XS
- 1990-1993 Isuzu Stylus S 12 Valve SOHC
- Isuzu Gemini JT191 and JT191S
- 1989-1991 Geo Storm GSi
- 1989-1993 Geo Storm Base 12 Valve SOHC
- 1989 Isuzu I-Mark RS
- Isuzu Gemini JT190
- Lotus Elan M100
- 1985-1989 Isuzu I-Mark
- 1987-1989 Isuzu I-Mark Turbo
- 1985-1989 Chevrolet Geo Spectrum
- 1987-1989 Chevrolet Geo Spectrum Turbo
- 1985-1989 Asuna Sunburst
- Isuzu Gemini JT151
- Isuzu Gemini JT150
This is a direct replacement for Isuzu PN 8-94362-688-0 and GM/Geo PN 94362688, for use with OEM
connecting rods in 4XE1 and 4XC1 engines.
The 1985-89 4XE1 and 4XC1 engines use a different connecting rod bolt: Isuzu PN 8-94107-550-1, GM/Geo
PN 94107550, and Lotus PN A100E6254S. This bolt is identical in shaft diameter, knurl diameter, and
thread, but is .076 inches shorter in length. This replacement connecting rod bolt is interchangable
for the earlier 4XE1 and 4XC1 engines.
Set of 8 Bolts.
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