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ChevroletSS 05-02-2013 02:02 PM

ARP bolt head/Oil pump issue
Anyone ever had a problem usin ARP studs and not being able to properly seat your oil pump all the way down cause the stud nut is in the way??????

ssmonty 05-02-2013 05:46 PM

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You didn't say what engine your talking about, or what oil pump, or what studs(hex or 12 point).
I hope its a sbc. Got me curious as to what your talking about, so I mocked up some stuff to see for myself.
Glad I did. Found out that I need to drill some holes in my oil baffle, large enough to clear the hex nuts on my studs. Then again drilling holes in the baffle kind of defeats the purpose of a baffle doesn't it? Hmmm
I couldn't cause hex nut interference with a Melling "M55" or a "Select" oil pump.(see pics) Don't know if a high volume pump would be clear or not.
However I found out that I may have to either trim the stud, or clear/grind the neck of the Select pump by about .025". I know that some pumps have had issues with breaking at the neck, but the Select looks beefy enough that just a little sanding/buffing shouldn't do any harm. I don't feel comfortable cutting/grinding an ARP stud as the heat might weaken it? Besides its not exactly easy with ARP stuff as tough as it is.

Richiehd 05-02-2013 07:52 PM

Monty, nice job, and thanks for taking the time to take and post pictures. And you should be using the Melling Select anyway. Many posts concerning the M55 pumps breaking.

496CHEVY3100 05-02-2013 10:00 PM


Originally Posted by Richiehd (Post 1672314)
Monty, nice job, and thanks for taking the time to take and post pictures. And you should be using the Melling Select anyway. Many posts concerning the M55 pumps breaking.

there are 2 m55 pumps 1 with reinforcing ribs (old style )it gives more clearance for bolt ,the non reinforced has a thicker body (new ) ,both pumps carry same part number ,if you know the man at parts counter get him to let you open a few boxes. I have a 77 bbc pump on my sbc with a mileadon pickup and 8 qt pan I had to use a copper gasket that I don't normally use and a metal sleeve didn't trust plastic since I lost a little length in oil pump shaft with gasket, also great display,should help lots of rodders

ChevroletSS 05-03-2013 03:35 PM

Its a SBC, Im using a Jegs standard duty high volume pump and ARP main studs, Dont know the exact size. It looks like ill be able to grind some the stud off and maybe the nut but didnt want to go that route. also thought about getting a single ARP bolt not stud to replace it with. Im trying to get some pics.

ssmonty 05-03-2013 04:36 PM

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Instead of grinding on the nut, you might want to try a 12-point nut with the same threads(7/16-20) as it has a smaller diameter(9/16" socket size vrs 11/16")
A lot less risky than grinding on a stud nut IMO.
They even make one smaller(1/2"socket size), but thats getting awfully colse to the edge of the threads(7/16") IMO.
I've already looked into it and ordered 2ea for myself, so that I won't have to drill as large a hole in my baffle to clear it, and being a 12-point it should fill up more of the hole area to help control oil. At least thats the way I see it.
I'll still have to grind a bit on the pump body, but if I polish it enough there shouldn't be any stress risers to cause a crack IMO.
I must admit that I'm not 100% certain that the torque requirement will be the same for a 9/16" nut vrs. a 11/16" nut. I know that the stud stretch is what determines the clamping force. I also know that the face surface area friction against the washer will affect torque. If the face area is the same between the two, as well as the thread length, would the smaller diameter nut need more torque? Does the larger nut act like a wrench with a longer handle, and not need as much force to create the same stretch?
For instance if the nut had an insane width of 12 inches across the flats, but still had the same threads, and you could get a socket to fit, would it take as much force on the torque wrench to get the same stretch?
Maybe one of the engineering types will chim in? Please! Or anyone else for that matter.
PS I think grinding the stud down a little at a time and letting it cool off naturally(vrs quenching it in water) would work ok, but thats just my opinion, and I'm no pro!

ChevroletSS 05-04-2013 07:11 AM

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I might be able to clear the nut, maybe, I think the top of the stud is the only thing ill have to cut off

MouseFink 05-06-2013 11:13 AM

My machinist said that is a common problem when using main cap studs. The main stud needs to be shortened about .250" and use a 12-point nut. Then the oil pump must be touched up with a grinder, checking the fit until enough clearance is obtained. Those modifications should give the needed clearance. I use OE main cap bolts and ARP washers and this particular problem never occurred.

My engine is equipped with a Melling Select 10552 oil pump and I was more concerned about the clearance between the oil pump and the steel collar on the oil pump drive shaft. The steel collar on the pump shaft is larger in diameter than the OE nylon collar and it has about .015" - .020" eyeballed clearance from the main cap. That is goodenuff.

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