M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: vee030 on March 07, 2017, 04:02:09 PM
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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.
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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 (http://www.realoem.com/bmw/enUS/showparts?id=AJ93-USA-06-1990-E30-BMW-318i&diagId=11_4356). 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 (http://www.realoem.com/bmw/enUS/showparts?id=CC73-USA-08-1995-E36-BMW-318i&diagId=11_6008). 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?
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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.
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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.
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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.