Downpipe fastener threading

vrg3 · Post by **vrg3** » Mon Sep 27, 2004 10:33 pm

I'd like to have some spare fasteners around when I replace my turbo. What size stuff should I get?

On NASIOC there seem to be some people who are sure the hardware is M10x1.0mm. Then there are some people who seem sure it's M10x1.25mm. Then there are some people who say it's "M10x1.75mm -- the really fine-threaded stuff."

From what I understand -- someone correct me if I'm wrong -- the turbo has three studs on it and two unthreaded holes? The unthreaded holes are the two on top? So then aside from the three studs, the mounting hardware consists of two bolts and five nuts?

Maybe some of the people who got the threading wrong were just replacing the nuts and bolts that go through the unthreaded portion.

My up-pipe came with studs in it and they seem to be M10x1.25mm, since they're smaller than the EGT bung but have the same thread pitch (and I understand the EGT bung is M12x1.25mm). But that's the up-pipe.

Does anybody know for sure, or have a turbo lying around they can check on?

BAC5.2 · Post by **BAC5.2** » Mon Sep 27, 2004 10:44 pm

There are 3 studs on the stock turbo. 3 on the uppipe. The ones on your new uppipe will be the same thread pitch as your stock ones, and the turbo bolts will be the same.

Easiest thing to do, take the regular bolts from the turbo to home depot and take an uppipe bolt with you as well. Match them up and voila.

I just got M10 bolts and matching nuts to replace the bolts that take up the unthreaded holes on the Turbo. I used the stock nuts on the studs though.

3 nuts for the uppipe. 5 nuts for the turbo. 2 bolts for the turbo.

vrg3 · Post by **vrg3** » Mon Sep 27, 2004 10:56 pm

My uppipe has five studs on it, one in each threaded hole. I figured it was attached to the turbo and the turbo bracket using five nuts. Is that not how it's supposed to be?

I think the TD04 I have is missing one of the studs... I vaguely remember it having two studs, one threaded hole, and two unthreaded holes.

I'd rather not have to make a trip to the store during the swap; that's why I'm hoping someone on here has the info I need handy.

Thanks for confirming that there are indeed two unthreaded holes on the turbine exit flange.

So are you saying that the downpipe studs and uppipe studs have the same threading?

BAC5.2 · Post by **BAC5.2** » Mon Sep 27, 2004 11:13 pm

Oh yea, the uppipe DOES have 5 studs. I was thinking of the number holding the turbo to the uppipe. 3 studs hold the turbo down, 2 hold the turbo to the block.

There should be 3 studs on your turbo and 2 unthreaded holes. My 16G also was missing a stud. I replaced it with a small bolt and just threaded it into where the stud SHOULD have been. I brought the nut with me to fit it up though, I don't recall what the threading was. It seemed fine, or well enough to hold me over until I can get a new uppipe and can figure out a better solution with the car in the garage rather than at 10:00pm in a gravel driveway at Brent's house.

Ideally, you can remove one of the exhaust turbine nuts off of a stud in the parking lot of a store, and just go in and get the stuff.

There's no reason you'd need to replace the uppipe studs, you can use your stock ones (they will be the same).

Everything SHOULD bolt up properly using all of your stock hardwear.

Yes, the uppipe studs have the same threading as the turbo studs. One of my turbo studs is from the uppipe on Brents 98.

vrg3 · Post by **vrg3** » Mon Sep 27, 2004 11:21 pm

Great, that was just the info I was looking for! Thanks, Phil.

I know all my stock hardware should be fine; I just want to be prepared in case I manage to mangle some of it or something. And if it's cost-effective, it couldn't hurt to use some stainless fasteners, right?

BAC5.2 · Post by **BAC5.2** » Mon Sep 27, 2004 11:40 pm

Glad I could help.

evolutionmovement · Post by **evolutionmovement** » Tue Sep 28, 2004 7:17 am

The nuts on mine are stainless (though not the studs!?). I'd definitely bet they're 1.25 pitch as a lot of the HD hardware Subaru uses is that pitch (the one Home Depot never seems to carry).

Steve

vrg3 · Post by **vrg3** » Tue Sep 28, 2004 7:27 am

Cool, thanks for the confirmation, Steve. Subaru does use 1.0mm pitch on the 10mm brake hardware, and that's a hard-to-find pitch. But those aren't heavy duty hardware.

That's odd that the nuts are stainless but not the studs... I wonder if it's important that the studs be made of a weaker material than the nuts or something. Hmm.

evolutionmovement · Post by **evolutionmovement** » Tue Sep 28, 2004 7:42 am

I don't know, but the threads of the studs were rusted pretty well, but the nuts were perfect (just dirty) and came off undamaged.

Steve

legacy92ej22t · Post by **legacy92ej22t** » Tue Sep 28, 2004 3:44 pm

I had to buy 3 new bolts to go with my 16G because I couldn't get them out of my VF11. I got mine at Advance Auto Parts for about .90 each IIRC. They had a bunch of 'em. I don't remember exactly what they were but I believe they were M10-1.25.

vrg3 · Post by **vrg3** » Tue Sep 28, 2004 4:13 pm

Cool... I trust you guys way more than the sources on NASIOC, and with all the other cues I'm pretty much certain they are indeed 10mm with a 1.25mm pitch.

90 cents ain't bad -- I'll be going over to Advance! So you used bolts instead of studs as well, like Phil did for that one stud? Cool.

Steve - I think you can tell for sure whether or not a fastener is stainless by seeing if a magnet will pick it up. I think there are some kinds of stainless do attract magnets, but the highly corrosion-resistant types don't. I know all the stainless fasteners I have on my car require magic fingers to pick up when they fall; the magnet-on-a-stick doesn't work.

evolutionmovement · Post by **evolutionmovement** » Tue Sep 28, 2004 5:12 pm

Some alloys are slightly magnetic, but I don't know if any will stick to a standard magnet. I don't have my real magnet here.

Steve

vrg3 · Post by **vrg3** » Wed Sep 29, 2004 10:21 pm

'Nother quick question --

BAC5.2 wrote:Yes, the uppipe studs have the same threading as the turbo studs. One of my turbo studs is from the uppipe on Brents 98.

Aside from the threading, are the uppipe and turbo studs actually the same?

I know the uppipe studs aren't just pieces of all-thread; they have that portion in the middle with splines and no threads. So the studs have three dimensions, I suppose -- the lengths of the two threaded portions and the length of that portion in the middle.

Are these dimensions the same on the turbo's studs?

BAC5.2 · Post by **BAC5.2** » Wed Sep 29, 2004 11:49 pm

Yes, both studs are the same. They are interchangeable.

I'm disappointed that the studs arent slotted at the unthreaded spot so you can replace them using a wrench. I'm going to flatten the edge of one of the studs on my Vf11 and see if I can pull it out and replace the missing stud on the turbo.

vrg3 · Post by **vrg3** » Thu Sep 30, 2004 12:15 am

Cool, thanks.

If I remember right the unthreaded portion is splined, isn't it? I think you're supposed to use some kind of special wrench to install/remove it.

You could also thread two M10x1.25 nuts onto the stud and tighten them up against each other. The preload there should keep them from turning around the threads so you can then use a wrench to extract the stud.

BAC5.2 · Post by **BAC5.2** » Thu Sep 30, 2004 12:35 am

Some unthreaded studs are replaceable and are splined.

The stock ones on our uppipe isn't. The ones on Brent's Ej20 uppipe wasnt. The ones on the 16G and my VF11 aren't.

I'm more thinking about installing a stud into the turbo than extracting it.

I'll look at it tomorrow morning.

vrg3 · Post by **vrg3** » Thu Sep 30, 2004 2:00 am

Yeah, I just went back and looked at the ones on the CES uppipe and they're not splined either.

But you should still be able to jam two nuts against each other to give you a grip, right?

dzx · Post by **dzx** » Fri Oct 01, 2004 4:48 am

mine were a 1.25 pitch, still need to get a few to put on.

vrg3 · Post by **vrg3** » Fri Oct 01, 2004 4:52 am

Cool, thanks for backing that up.

My brother says the downpipe studs on a MkIII Toyota Supra are also M10x1.25 and on casual inspection look to be pretty much the same as the Subaru ones.

vrg3 · Post by **vrg3** » Sun Oct 03, 2004 10:14 pm

Hey Steve, do you think it's possible that the nuts are brass and not stainless steel? Apparently some carmakers like to use brass nuts on the exhaust (presumably because it doesn't rust and is cheaper than stainless).

evolutionmovement · Post by **evolutionmovement** » Sun Oct 03, 2004 11:21 pm

If they are they're the toughest and most silver-looking brass I've ever seen.

Steve

vrg3 · Post by **vrg3** » Sun Oct 03, 2004 11:40 pm

'Kay.

dzx · Post by **dzx** » Mon Oct 04, 2004 12:39 am

interesting to know i can find them at advance, i was having a hell of a time finding some at home depot and places.

legacy92ej22t · Post by **legacy92ej22t** » Mon Oct 04, 2004 2:50 am

Yep, when I got them they had a whole bunch of 'em and they were cheap, cheap, cheap!

vrg3 · Post by **vrg3** » Mon Oct 18, 2004 7:42 pm

Thanks for all the help, guys.

Here's what I found:

All the exhaust hardware in the engine bay (except maybe heatshield fasteners -- I wouldn't know thanks to all the rust) is M10x1.25.

The uppipe has five studs on it. Three are used to attach to the turbo, and two are used to attach to the mounting bracket.

The two rearmost uppipe studs should be slightly shorter than the rest in order to clear at least the Mitsubishi turbos. I didn't have shorter studs, but I found it worked well to just flip them over and thread the long side into the uppipe instead of the short side.

The turbo has three studs on it, identical to the uppipe ones. These are used in the lower three holes. The top two use matching nuts and bolts.

Those bolts appear to be identical to the ones used on the crosspipe and lower uppipe connections.

AutoZone had studs that almost exactly matched the stock ones in a drawer behind the counter. I think they were around 90 cents each.

All the nuts are indeed stainless steel. Apparently Subaru used stainless exhaust nuts on turbo models, and on some early 1990 (and maybe 1991) non-turbo models. The bolts and studs aren't stainless, but it works out pretty well anyway. I guess that's a pretty cost-effective compromise between mild and stainless hardware.

If you're buying replacement hardware, try to make sure you're using flange nuts and bolts with flange heads. Washers aren't quite the same.

Dealers should be able to get the nuts; I think the part number is 902370010. They'll cost like 5 bucks though. I think I've found a good alternative source. MMS & Accessories (mmsacc-stainless.com) quoted me a price of 75 cents each for stainless M10x1.25 flange nuts. Almost seems too good to be true, considering how rare metric fine-thread stainless hardware is, especially with a flange, but I'll let you know when I receive my order from them.

You should be able to get brass or non-stainless steel nuts from an auto parts store or maybe a hardware store though.

The shiny Class 10.9 bolts that AutoZone sells in little plastic packages hanging on the rotating rack are coated with something to make them shiny. This coating burns/melts off when subjected to the heat of an exhaust.

Jamming two nuts against each other on a stud does work to give you something to grip when you need to either extract a stud or remove a frozen nut from a stud. An impact wrench helps in that process.

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Downpipe fastener threading

Downpipe fastener threading