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ARP Main studs - crank bore distortion ? (VQ35DE/350z)

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Hey guys, I shall start a build thread in the coming days, it's my first full rebuild (last Christmas I did cams/timing chain/stem seals). And note, I may not be using the correct terminology just yet, bare with me.

However I thought I'd ask this specific question separately just in case it gets lost in that thread itself.

I've just recently stripped my engine down and taken all of the parts to my chosen machinists. Whilst I was there we of course went through all of my new parts, and inspected my old bits and pieces too. My crank did get some scoring from FM, so it's due to have a polish and balance of course but whilst we were talking about these parts, he mentioned to me that these ARP main studs (not the heads at least), could cause crank bore distortion:


So that would involve even more work, and it could just be easier to use the OEM main bolts rather than these ARP studs. He said when I make the initial assembly that I will know for sure if they are an issue. I've tried searching the usual forums for info on this but most of the builds using ARP studs are FI, and I'm staying NA.

I just wondered if anyone has had this happen to them ?

(I did watch the webinar #197 too)

On the Subarus' , the use of the ARP main case bolts always causes bore distortion. One needs to re bore to get them back to spec.

Thank you for replying, much appreciated!

I also got a message back from JWT (I use their cams), saying that they do experience distortion, and recommend the oem bolts, or gtr bolts (both tty) for an upgrade but still to check for distortion as the gtr ones can too.

I thought I'd give a little update on this.

I ended up buying a lightly used 350z crankshaft, and it was very clean indeed (even the oil passage ways seemed very clean!), they gave me the block back and said to dummy build it with either crankshaft (I did it with both), to see if the ARP studs caused any drag initially. And then to use some plastiguage to see what that read like.

Well the reading seemed fine, and no change with how it turned with the ARP studs either.

I'm just about to order a set of micrometers and a bore dial gauge too, so I shall of course check it thoroughly once I have the bottom end back (hopefully next week).

Would be very interested in the results. I have a VQ30 with ARP studs, albeit the block is a different spec material and my dry sump pan also forms the bearing cap cradle.

And another update !

Everything is obviously going very slowly at the moment but the bottom end came back and I am mid measuring again.

Using King XP standard bearings, I got some readings on the looser side, that I'm not sure is ok or not.







Standard : 0.034 - 0.059 mm (0.0013 - 0.0023 in)

Limit : 0.070 mm (0.0028 in)

And the crank mains (after mic'ing per journal) - IGNORE main 1, there was a problem with the cap dowels, waiting for new ones:

1 = 0.0014"

2 = 0.0024"

3 = 0.0022"

4 = 0.0018"

Standard : 0.035 - 0.045 mm (0.0014 - 0.0018 in)

Limit : 0.065 mm (0.0026 in)

(bore is now 96mm)

Aside from the little issue with the 1st main cap, what do you guys think about the clearances ?

I was using 10w50 Millers oil, as I know this plays a big part with clearances, so I'm happy to go with any grade oil required.

There's another chap from the Netherlands that has gone with .0026" on his mains, similar NA DE build. And another friend with a 3.7HR (different to my block) that has gone for a tighter (plastigauge'd) .00175" (cold environment back in Nov).

Brief notes on my build.

2004 3.5ltr 350z


Cylinder heads to come (basic stuff, nothing crazy)

JWT C8 cams

Boundary billet oil pump gears

Cosworth 11.1 96mm pistons/rings

PPE Long tube headers

Kinetix Velocity Intake (really helps extend the power curve)

We'll increase the RPM pending power currently it's at 7100 from 6800, likely to go up to 7600.

(edit, actually I start a build thread sorry hah)

Big ends look fine.

Mains, if on a standard oil pump and a road car I would consider 1 thou tighter bearings. If a race car and on an uprated oil pump and considering the oil upgrade I would probably be happy as is...just watch the oil temperature.

Hi !

Many thanks for your reply.

She's used as a track day car, and weekend fun now. Yes the oil pump is the 06 Rev up but with Boundary billet gears.

Glad to hear about the big ends, I'm happy to try a 1 thou tighter set for the mains.

I presume that's the set sold as .025 in their naming ?

Usually, yes. I would double check because it MIGHT mean 1 thou LOOSER clearance.

The billet gears are a good idea for reliability but won't help pressure. Fit a decent oil cooler!

Yep, I have a 19 row cooler and spacer on the pan too (near 2lt extra capacity), and smaller one for power steering.

Temps were acceptable the last time I was out on track in the summer.

King Sizes

Sounds like a nice bit of extra insurance.

Yeah, .001" is the one. Between those and your current shells you should be spot on!

Fantastic, glad you could confirm that (you know whats it's like when you have a tiny seed of doubt!).

I've ordered that set for the mains :)

And just to confirm, I used one of the dowels that wasn't damaged to see if the main cap would sit correctly with a bearing, it does.

Now the main 1 is reading what I'd expect, which is around 0.0018".

I'll update this thread in due course, and I really should start a build thread too !

Little update !

I removed the old main cap dowels with an inner bearing puller/slide hammer (very easy, no damaging and about 15 seconds), and replaced them with new ones from Nissan. That solved, and then the extra bearings arrived too:

1 = 0.0018"

2 = 0.0018"

3 = 0.0018"

4 = 0.0020"

I tried a half/half on the last one but it somehow made it too tight (within spec @.0014).

So I think I'm happy to go with what I have now, and maybe one last plastigauge check before continuing with the rest of the build ?

I too am curious on this subject. I agree there is a proper method, but ive also found that not everything with assembling engines is black and white.

I assembled an VQ35 last week with arp mains. No line boring was done. The bearing clearances were all in spec and the crank spun freely. I also compared something that may or may not be of value: the oem bolts were torque to 30ftlbs and then 90 degrees. Obviously a TTY bolt. Then i checked the arp studs, I torqued to 30ftlbs and then to arp spec, which did not take an extra 90 degrees to achieve. Now i am aware of the differences between a TTY bolt stretching and the ARP stud stretching, but i felt comfortable with my results. The bearing clearances were in spec, the crank rotated freely, and the applied torque (by feel) to achieve the desired bolt strech did not seem vastly different. So far the engine has started up and been through the first heat cycle. I am now waiting on some other parts to road test it however.

I am currently assembling a VG30 (iron block) that the machinist did have the arp hardware and checked the main line bore. It appears he did not need to machine the main bores (no fresh hone pattern) and everything checked out on that engine as well. I imagine however there is more distortion with aluminum blocks than iron.

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