ARP Studs/MBSP-2001
 

What the hell? Building my motor, I put on main bearing support plate only to find it doesn't clear the arp studs! UHG! Has anyone seen this before?

Odd everything clears on my motor. Didn't notice if anything was clearenced or not though.

Can you just cut down the studs a couple tenths?

You don't want to modify the studs in any way!

Instead, grind/cut the MBSP to allow for proper fit.

Do you have photos of where the issue lies?

Actually, you can grind down the top of the studs. Machinist did it for my car with the MBSP, and even MiataRoadster.com mentions having to do so.

Why not? Its not going to affect the studs strength or anything.

That doesn't mean it's the right way of doing it. You spend a lot of money on top fasteners to then mess with their metallurgy?

If a lot of grinding is necessary, excess heat is generated and could/will affect the heat treating.

Well if you use a hacksaw or porta-band or a zip disc you should be fine heat wise.

If you use a grinding disc you might get it hot enough to affect the metallurgy, but I really doubt it would be significant.

We're not building 1000hp motors round here.

I don't know how it applies to this case, but the biggest reason to leave a certain length of stud (or bolt) sticking out of the nut is stress distribution in the stud/nut joint. If the thread abruptly ends at the nut, the end of the thread has a higher stess concentration and won't take the same load before rupture.

Like I said, dunno if it matters in this case or not. I'd call ARP.

I had the same issue, and I ground the studs down, and clearanced the MBSP some. Grind slowly, uses lots of oil and it will be fine.

:werd: That is a standard rule of thumb in bolted joint design. At least two threads protruding past the nut, to help with stress distribution.

There was some talk about this at miata.net as well. Go there and do a search on MBSP and you'll find it. I think a solution was IIRC to drill clearance holes in the MBSP for the ARP studs. I do not have a MBSP myself (I do have ARP), but I remember reading about it when researching MBSPs during my engine build.

Here's the m.net thread.

APR Studs / MBSP??? - MX-5 Miata Forum

uh huh - a little protrusion isn't bad, but these are too much. Some are slightly worse that others, and some holes tapped further than others. Actually, I'd be more tempted to cut off the backs, and let them since in further.

I'll check out the M.net link you posted... Still, it's odd ARP didn't take care of this. Even so, thinner washers might be needed.

I'd place a call to ARP, tell them you want to cut the studs back to 1/2 bolt diameter protrusion (will this clear w/ holes cut in the baffle plate?), cut w/ a hacksaw, not an abrasive wheel and keep the heat down.

See if ARP agrees w/ that. It's strange that the holes in the block are tapped to different depths, did you run a cleanup tap through them? Use tapping oil if you do, use a bottoming tap. DON'T BREAK THE TAP.

ARP would probably just redesign them and send you new ones if they knew what's good for em.

Not breaking the tap is a good suggestion! I did clean them up till I was worried of just that.

I will just have to call arp - tell them it's a common problem, see what they say.

Few things in this world that are more frustrating than breaking a tap in an otherwise perfect part. Always happens flush w/ the hole too. :vash:

Funny you should mention that.

https://www.miataturbo.net/forum/t39274/ (for anyone following)

The short answer is "no." I've put in probably 6 months of my time on this. More than ready to just put the motor together and weld my wastegate shut.