Connecting Rods FAQ

[John]

CONNECTING RODS

The production connecting rods for the I6 are cast iron and have press fit piston pins. All have the same journal width and pin size. Production rods are available in two lengths, 5.875” and 6.125”. After market forged rods from Eagle can be found in a 6.150" length.

The 5.875" length was used in all 258 engines.
The 1971-81 258 motors had the 707 casting number and is the strongest of the factory rods, it weighs 700 grams. The 1982-87 258 motors with the 352 casting number is the more commonly foun

The 6.125" length was used in all 4.0 engines.
The 4.0L motors from 1987 until the end of their production have the 544 casting number, weigh 660 grams and is likely the strongest of the factory rods produced for either motor.
The 6.150" 4.0L Eagle, after market, forged rods are out of production I understand, but are available if you look around . They weigh 660 grams.
More to come
John

Although they can be found in the above lengths, with the exception of the 707 castings , factory 199 or 232 rods should not be used for our builds.

[1bolt]

good stuff, I'd love to see someone step up with a similar piston writeup with specs, pin height, top height and dish volume etc.
I could see this topic being headed by a series of sticky FAQ's which would help people find info if the FAQ's get numberous we can combine them as needed.

[oletshot]

Recently on the yahoo group, someone said that 4.2 and 4.0 use different rod bearings. Specifically it was said the difference was the tab locations between the two rods were different. I don't know if this is true as, the part #'s are the same for a rod bearing set between all years that I checked of the 4.2 & 4.0( I checked '79 4.2, '88 4.2, '89 4.0, '93 4.0, '98 4.0). According to partsamerica.com they all use rod bearing set "63310CPA". The author may have been confusing the rod bearings with the main bearings. I checked part #'s of the main bearings and they changed thru the years. '88 4.2 & '89 4.0 use main bearing set "4289M" and '93 4.0 & '98 4.0 use "7211M" main bearing set. These are all Sealed Power part #s if someone is wondering.

Does anyone know if I am correct with my info? Thought I would post this here to let people know that they may need to know what year rod they have in order to get the correct rod bearings. If it is the main bearings that change thru the years and not the rod, then this post may be more relevant to the crankshaft post in this subforum. Feel free to move this post if it fits better somewhere else.

[John]

You are correct in your parts number research, The basic breaks for the main bearings is before 1990 and after 1990. The rod bearings are the same for a 258 and a 4.0. Some of the older catalogs used to show two different rod bearings, but that was related to bearing composition changes. A safe rule of thumb is to order the bearings for the year block you have and that can be found from the casting numbers
John

[oletshot]

Ok, everything is straight forward and makes sense. That's easy enough. I must have read the yahoo group post wrong.

[John]

Some buy crank kits for the 258 complete with bearings then wonder why the bearings are wrong to put in their 90's block to build a stroker. Possible this individual had gone down this path?
John

[Muad'Dib]

CONNECTING RODS
The production connecting rods for the AMC six come in a variety of flavors. All are cast iron (although tracked by “forging” number) with a press fit piston pin. All are the same journal width and pin size. Rods are available in two lengths, 5.875” and 6.125”.

The 5.875" length was used in short deck (64 thru 66 1/2) 232 engines and all 258 engines. There are three castings:
1) early 232 (forging 154, part #3172341),
2) late 232 and early 258 (forging 707, part #3180444),
3) late 258.
The early 232 variety was replaced with the newer, heavier casting starting with engine date code 710L21, which makes them almost non-existant today.

The 6.125" long rods come in two varieties:
1) 199 engines and 232 tall deck engines (forging 207, part #3173210),
2) 4.0L engines (muliple part numbers, see table below).

The Jeep 4.0L rod is the strongest of the available 6.125" rods, lighter than the 5.875" rods, and probably stronger than the 5.875" rods due to it's design and quality controls not available during production of the AMC rods.

No production 199 or 232 rods should be used for high performance applications. If a 5.875" rod is required, use forging 707 rods. If a 6.125" rod is required, use 4.0L rods.

Code: Select all

  LENGTH   ENGINE      YEAR       PART #      FORGING#     WEIGHT (g)
  5.875”    232      1964-66      3172341       154          660
            232      1966-70      3180444       707          700
            258      1971-81      3180444       707          700
            258      1982-88      3237812    unknown        unknown
  6.125”    199      1964-70      3173210       207          660
            232      1971-79      3173210       207          660
            4.0L     1987-95      53020126      544          660

CONNECTING ROD PREPARATION

Rod preparation should be the same as that used for any production type connecting rod used in a performance application. Beams should be smoothed and polished, balance pads should be minimized, and rods should be shotpeened professionally. Rods should be resized by a competent machine shop, not a rod rebuilder. Rods rebuilt by these mass quantity rebuilders are of the poorest quality and will fail under racing abuse. Angle cutting the cap parting surfaces is not to be allowed - they should be cut flat and parallel prior to big-end resizing. The pin end may be bushed for full floating pins with the addition of a chamfered oil hole on the top of the rod and a radiused chamfer on the bushing itself in the vicinity of the oil hole to aid in spreading the oil across the pin. The bushings typically used in Chevrolet rods may be used (similar pin diameter). Rod bolts should be replaced with high strength units similar to those manufactured by ARP. My race prepped 4.0L rods weigh in at 625 grams after balance pad lightening, beam polishing and shot peening, bushing the pin end, and installing ARP bolts.

[SilverXJ]

There are two additional 4.0L rods not mentioned here.

1996-2001 Casting number 691
1999(?)-2006 Casting number 548

Same dimensions, but the rods do look different.

http://www.jeepstrokers.com/forum/viewt ... ?f=5&t=465 shows the 691 casting compared to a 4.2L rod (which looks similar to a 544 4.0l rod).
http://www.jeepstrokers.com/forum/viewt ... ?f=5&t=468 shows the 548 casting compared to the 544 casting rod.