perimeter studs went "pop"

nilknarf · nilknarf's Garage

First off, I can't thank you guys enough for sharing your wisdom with everyone over the years- I've posted a bit, but mostly lurked as my experience pales compared to y'all.

After having all the usual mag case stuff done (case savers, etc) I bolted the bottom end of my 7R mag case together yesterday- everything went great until I torqued the small nuts (the 22 or so "perimeter" nuts) to the prescribed 18#... three of them went "pop" and lost their torque, so I know it all has to come back apart... my question is this: do I simply time-cert the studs that popped (two of them were the long studs near the breather and the intermediate shaft bearing, and one near the flywheel) or do I need to re-work all of the perimeter stud threads because they're doomed too? There's another complication... in my infinite wisdom, I used prevailing torque nuts instead of nylock nuts- is it possible these caused the studs to strip?

_curt

MBruns · 12-07-2009, 08:45 AM

My experience with those cases that do that under proper torqueing are about timed out, you can fix them with timeserts but honestly I would not start a fresh engine project with a rotten case
Mike Bruns JBRacing.com

BURN-BROS · 12-07-2009, 09:27 AM

Curt,

Use the nylocs and the crush washers on the mag cases. I time cert the 4 studs by the #8main bearing/intermediate cover. Plus the long stud behind the left chain box for the intermediate shaft bearing. I time cert these studs regardless of a failure.

304065 · 12-07-2009, 09:42 AM

I think the use of prevailing torque nuts puts too much friction between the threads and the deforming feature of the nut-- rather than the nut moving on the stud, you're turning the stud in the hole.

If the studs are broken you can use an ez-out, if they are pulled, it means splitting the case again to time-cert.

nilknarf · nilknarf's Garage

Thanks so much for the input guys- I'm thinking that the main reason these things popped was me... so I'm hoping that the general consensus is that my case isn't necessarily trash just yet (especially after spending hours and hours cleaning and hundreds on the prep work)... my machine shop didn't sound too worried about them and agreed that the prevailing torque nuts probably weren't the best choice for the magnesium, and even if the nylon melts, I figure it's what the factory used, and the crush washers should also help there.

I wish the studs themselves had snapped, but alas, no. I think I may cross my fingers here and salvage what I have- most of the studs held fine, even using the wrong nuts.

BTW, how the heck do you accurately torque the nuts near the flywheel seal? Do you guys use a crow's foot or go by feel? Wayne's book didn't cover that one...

_curt

nilknarf · nilknarf's Garage

BTW John, I heard the pop on a couple of other studs, but when I went back to check the final torque, they held 18 ft/lbs of torque just fine, and having the studs suddenly spin would explain the snapping sound I heard... I guess this is how one gains experience, eh?

_curt

jjrowe · 12-07-2009, 12:34 PM

I had the same thing happen on mine, so frustrating. I ended up helicoiling all the perimeter studs to make sure it didn't happen again. In Wayne's rebuild book he does recommend that all those studs are helicoiled on mag cases.

nilknarf · nilknarf's Garage

Dang! just found that mention in Wayne's book... (pg 52)... it's taking me so long to get this motor going that I'm forgetting some of that good advice. I'd better pick up the pace!

_curt

Walt Fricke · 12-13-2009, 05:24 PM

Curt

When first I did a case I, too, wondered how to torque the flywheel end nuts. I suppose you could put a crowfoot onto your torque wrench.

Me, I just use a 13mm wrench and tug hard. Its length pretty much insures against overtorquing by hand. Haven't had an issue with this. I don't think the perimeter studs are torque critical. They don't have to withstand the reciprocating loads, do they? The case throughbolts take care of those.

Look on the bright side - at this point, all you have wasted are the throughbolt seals, and you've got putting a case together down pat. The real cause for tears is a teardown problem discovered after you have the cams in and timed.

Walt

nilknarf · nilknarf's Garage

LOL- Thanks Walt! You're right- the tears would be tough to fight off had I gotten as far as the cam timing! (so would the urge to go out and buy a corvette instead!)

Thanks for the reassurance on the flywheel end nuts- I did use a fairly short box-end wrench wrench on those flywheel end nuts- I think I just need to be a little more careful (and of course, use the correct nuts)... you're right- the loads on those perimeter nuts are pretty constant, and at only 18 ft/lbs (with a freshly calibrated wrench) I was surprised that I had a problem. I think as jjrowe suggested above (as did Wayne in his book) I'll have all those perimeter studs heli-coiled just in case, and I'll have time-serts installed on the two longer "interior" studs I pulled. My hope is that I don't kick myself for "cheaping out" and not sourcing another case as Mike suggested in the second post of this thread.

Looking back, I don't feel quite so bad about doing the bottom end again- I think I'll do a few things differently next time- the through-bolt o-rings were blue (so next time I'll go w/viton) and I'll try the Threebond sealers per Henry's reccomendation from another thread. It's all good practice!

_curt