EL7

Just wondering if it's okay to re-use the studs for my DP install. The DP is the one from M2. If not then what specific replacment bolts should I use? I have 4 stainless 10.9 8MM hex bolts but I think they are too long. I tried to test feed one of them into the hole but it seems to stick way to far out, even accounting for the thickness of the flange. Does anyone have a size recommendation for length?

wingsfan

My studs were in such poor shape that I didn't reuse them. Also, I think that there are only a few DPs that you can reuse the studs on, and I don't remember if the M2 is one of them.

Anyhow, I ended up using M10 x 1.50 30mm grade 12.9 bolts. I had to dremel off a little bit of the flange and some of the DP flange weld to get things to fit. I also used split locking washers to make sure things stay tight. You can try using threadlocker, but whatever you put on there is just going to burn itseld off the first 5 minutes that you push your car hard anyways.

wickedrx7

iTrader: (14)

get new stainless bolts to replace the studs, put anti seize on them and split washers. I would get allen head bolts instead of hex head bolts. Do it right, do it once.

Scrub

iTrader: (25)

I just re used 3 of the 4 studs and bolts. there really isn't any need to replace them unless your DP comes with now studs.

the_saint

Question: What percentage of the studs can be reused. I have an incredible ability to destroy the studs while removing the locknuts that Mazda used.

About 50% of the studs (downpipe studs, manifold studs, turbo manifold studs) were completely destroyed while removing the lock nuts.

Those lock nuts are indestructible.

thesaint

Scrub

iTrader: (25)

Most of the studs came out with the nut still attached to it. On both the turbo and the Down pipe. Not really a big deal. Just use some PB blaster to get those suckers out if they are too stuck, or you can heat them up. Sometimes that helps.

chaste94

I re-used my studs when I installed my M2 downpipe. Like scrub said, the nuts were stuck on really well, but with a little coaxing they did come out. The studs were in good shape and I couldn't see any reason to replace them.

EL7

From what I can tell, the studs look alright to me. Three came out and had the nuts stuck to them. I don't see a problem simply bolting them back in. I'll just soak them in PB Blaster in case they need to travel in any to pick up the thread slack.

wickedrx7

iTrader: (14)

the reason you should re-use them is simple. heat expands and contracts metal, the more these bolts expand and ccontract the more brittle they get. once you romove them and then re-torque them they will be more suseptable to breakage. If the entire stud comes out this is more reason to replace them. You will not be able to get them back in tight again. Think about it, the lock not didn't come loose, the stud came out, there is nothing stoping it from working its way out again, no lock washer or nut.

Like I said before, do it right,do it once.

RonKMiller

Just about any fastener that is exposed to constant heat cycling should be replaced after the initial torque is released. It's not so much that they become brittle, (which can happen if the wrong type of fastener is used in this application - like stainless steel) it's that they have elongated. The elasticity in the fastener when it is initially torqued to proper levels is actually what keeps things together. Any kind of washer will dramatically alter the amount of torque that is actually transferred to the fastener from the torque wrench. There are guys running around in lab coats sweating the details on this stuff.

Get new OEM studs and flange nuts. A drop of motor oil on the threads will help the flange nuts to seat evenly. Toss on a little HIGH TEMP anti-sieze on the block end. (yes, there is a difference) You'll never be looking over your shoulder wondering where the exhaust leak came from. Sure, you'll pay a small premium, but do you really want to do this job again?

Don't forget that insanely expensive $46.00 metal gasket that everyone says you can re-use. It's designed for one time use only.

There simply is no substitute for OEM parts in this case.

chaste94

I didn't realize that the studs would be enlongated. I did replace the gasket, but not the studs. I don't currently have an exhaust leak. Do you think it would be worth pulling the downpipe back off and replacing the studs? I'm thinking leave it as is unless a problem develops since I would have to pull it off then anyway(and replace the damn gasket again). Is there any reason why this is not a good plan?
Thanks

rotary-tt

Stock studs on my RX7.com downpipe. Just work them in and out slowly when you first pull them out and you can reuse. You can grab the center part of the stut once out with locking plyers to get the nuts off. The stock nuts are not typical as they are purpose-built to be hard to screw on (high thread friction) so it tightens in the studs before the nuts start to turn. I had difficulty with aftermarket studs as I could not get them to thread in all the way before the nuts turned. And use anti-seize as everyone said when you put them back in.

RonKMiller

Nah, if it ain't broke, don't fix it.

DamonB

But if you need to break it, grab a hammer!

JSpecRZ

I basically just reused my studs.. but went to Napa autoparts and got new locking nuts... the nuts are the most important to replace so they won't back out and get loose...

EL7

Will washers prevent the stud from staying tight?

dgeesaman

iTrader: (7)

Lockwashers certainly may. I wouldn't ever put lockwashers in such a tension critical situation.

Dave