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When To Upgrade To Arp Main And Rod Studs On A 998?


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#1 The_R1_Kid

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Posted 08 November 2019 - 02:29 AM

Hello all, 

I'm restoring my mk4 998. Working on the engine now. I want to  be able to drive hard and rev it with out worry, so my thought is to upgrade all my bottom end hardware to ARP studs and bolts. The catch is all of my engine machine work has already been done with the stock hardware in place. ARP says to re align hone the mains and rods when upgrading to their hardware. 

Is this worth all the effort or am I over thinking it, and new factory hardware will be adequate. 

 

12g295 Head, 266 cam, 10.5:1 compression, fully balanced, STOCK connecting rods, light flat top pistons, light fly wheel ect ect..

 

 

 

 



#2 Moke Spider

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Posted 08 November 2019 - 07:15 AM

The Original Stock Main Cap Bolts you won't have an issue with and I'd find it hard to find any reason to go away from these. If you don't have these, then I wouldn't buy the current new ones as the quality of them varies.

 

In regards to Big End Bolts however, it's always wise as a matter of course to replace them and ARP or traceable Cap Head Bolts are all I would use.

 

If you do go to ARP Fasteners, these do clamp the Caps on much tighter and in doing so, the tunnels will need to be re-honed to shape and size. There is no short cut here, even if you might be tempted to reduce the recommended torquing of these fasteners to 'stock values' thinking that the caps will settle to the orginal sizes, which they likely will, but as the fasteners will still be in the lower end of the Elastic Range in use, they'll still be stretching and increasing bearing clearances and bearing nip. This will result in spun bearing shells.



#3 The_R1_Kid

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Posted 08 November 2019 - 07:37 PM

The Original Stock Main Cap Bolts you won't have an issue with and I'd find it hard to find any reason to go away from these. If you don't have these, then I wouldn't buy the current new ones as the quality of them varies.

 

In regards to Big End Bolts however, it's always wise as a matter of course to replace them and ARP or traceable Cap Head Bolts are all I would use.

 

If you do go to ARP Fasteners, these do clamp the Caps on much tighter and in doing so, the tunnels will need to be re-honed to shape and size. There is no short cut here, even if you might be tempted to reduce the recommended torquing of these fasteners to 'stock values' thinking that the caps will settle to the orginal sizes, which they likely will, but as the fasteners will still be in the lower end of the Elastic Range in use, they'll still be stretching and increasing bearing clearances and bearing nip. This will result in spun bearing shells.

 

Thank you for the perspective. I'll take your advise and it goes back to the machine shop. 






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