m42 con rod bolts

[vee030]

Has anyone on here used ARP connecting rod bolts in an m42 before?

I have just purchased a set of ARP con rod bolts from VAC motorsports.

The length of the new bolts is 47mm, where as the originals removed from my motor are 53mm.

RealOEM shows a part number for both a 53mm and 47mm connecting rod bolt.

VAC says that they are okay to use, but I am skeptical.

[DesktopDave]

I'm just guessing here, but there were two different rods used during the M42 production run. I'm told the later ones were lighter but I couldn't find any proof. I'm also told that the late M42 & M44 use the same rod.

RealOEM tells me that the early two-part conrod is PN 11241437617. They specifically note that the 47mm rod bolts are suitable, and the 53mm is not suitable.

RealOEM also mentions that the late M42 conrod is also PN 11241437617. They specify that the 44mm rod bolts are suitable after 9/94. They make no mention of the 47mm nor 53mm bolts.

Worst of all, the early M44 also uses the same parts. I'm baffled by this; sorry I can't shed a little light on the matter. Anyone else have ideas?

[colin86325]

The ETK says the 53mm bolts are "not suitable for 2-piece conrods."

A two-piece conrod is made from a two pieces (cap and rod body) that are machined to mate flat.  This is the traditional con rod type.

A one-piece conrod is made from a single piece of sintered metal that is then fractured. Most of the time you can't see the parting line between the cap and rod body.  This is a more modern design and I'd be surprised to find it in an M42 engine.

[vee030]

After going back and fourth with VAC multiple times I finally have the correct set in my hands.

ARP PN 201-6301. I believe this is also the same set for a 2.5L m50.


Although I have now found that that OEM bolts are an equivalent hardness to ARP2000 and are the better option.

[RotCowboy]

I hate to revive such an old post.  But I have been debating this same issue.  My '91 E30 M42 Vert that I am considering refreshing the rod bearings on shows two sizes of bolt as stock everywhere I look... and the 47mm ones are about a quarter of the price of the 53mm bolts.  All the other parts I have been lining up has been easier.  Is this just a case of I have to wait till I pull them out and measure and then order that or should I be going with the "early" 47mm?  I am skeptical like the last poster.