Welding a turbo

McMaster Carr has bolts already drilled for safety wire - not expensive.

foxtrapper wrote: While cast iron welding is easy (do it myself), I also wouldn't recommend it. But, if you must, trot on down to your handy welding supply store, and get some 55ni Softweld rods, they are made for this job. I do not think it's a lack of bracing that is causing the problem. Though bracing is normally a very good thing. Don't know the engineered specifics of your application, and your description stays very unclear about what the problem actually is (do the studs break, pull out, just blow gaskets?). However, I would concur with others that it sounds most like mounting. Be it too soft or small studs, wrong nuts, wrong retainers. Since it's a Flying Miata product, and Flying Miata has a pretty good reputation for working with their customers, I would likely be on the phone with them about this issue.

Lincoln Electric recommends the Nickel rods too. Given the difficulty of the job I'm shying away from it now.

The specifics are pretty simple, 8mm x 1.25 studs in a horizontal plane bolting a cast iron turbo onto a cast iron manifold. OEM stuff from FM & Bell was routinley mild steel with distorted nuts for retention. I tried several different lock washer setups, (copper, 2 piece, & now Stage 8) all from FM, none worked because the studs are stretching beyond their yield point. Then they break. Rotation is not the problem. No lock washer or safety wire or fancy nut will change this.

The size of the turbo flange dictates a 10mm max stud size if you drill it out. Clearances around the nuts are very tight, I'm surprised people can get a wrench on the 10mm stuff, but they do. As I mentioned above, others have gone to 10mm and had those fail too. No gaskets is used on the joint - per FM & BEGI.

I know from experience that the exhaust swings forward in heavy braking zones and shears the studs off. I built a brace that clamps the downpipe to the bellhousing to (hopefully) eliminate that load. That brace is the same principal as the recently released FM unit. I ordered an FM unit as a backup.

As I mentioned above, I have spoken to FM. FM & Bell are both aware of the issue from customer feedback, and they're both working on it. In the meantime the small percentage of their customers that work their cars hard get to do their own R&D. Because FM doesn't see enough of it locally, and they don't race regularly, they just don't have enough testing under harsh conditions. Although their customer service is excellent, It's hard to make a business case for heavy R&D in this economy to satisfy a small percentage of their customers.

That's my read anyway.

44Dwarf wrote: Sounds to me like you need a few things. A) get rid of the flat gasket. Machine both flanges for a ring gasket Say 1/4 inch deep in both sides. Use copper ring aka thick wall pipe machined to fit. B) use largest stud you can and use (15-20) bevel washer stack under the nut. Both of theses mods would allow for some movement with out loss of the seal. 44Dwarf

Thanks for the suggestions! Unfortunately the clearance between the stud and casting is super tight on 2 of the studs, probably eliminating the bevel washer option. I could MAYBE squeeze some belleville washers in there, but suspect they would lose their spring properties with the extreme heat cycling. The base of a couple of the studs are exposed to the exhaust gas in the manifold, the others are not. This may create a significant temperature differential between the 4 studs. The belleville washers have been suggested and shot down on other forums but I can't say whether anyone has actually tried it yet.

A) There is no flat gasket and the port is rectangular (so the machining would be expensive) but I like the idea a lot. I always thought it was strange that there was no gasket of any kind for that joint - but that's how they do it. Unfortunately I don't the time available to yank the whole setup, get it machined, and figure out how to do the copper ring gasket. With 2 track days and a TT in the next 2 weeks

B) I'll have to spring for the 10mm inconel studs and set up my backup manifold for the quick change.

Thanks again guys.

I guess this may sound silly, but is there anything Flyin' Miata is doing different to the ones they are installing versus the one you have on your car?

Maybe they have a bolt kit that seems to work better than what you have?

Where and how big is the flex joint in the exhaust? Do you have any idea what peak EGTs are and how long they last?

I don't like Bellvilles for this, if you bottom them out they aren't going to be able to provide the same clamping force as the bolt, which would be the idea. I don't think you'll find bellvilles that will fit and not bottom out.

Another point to make is that IF you can get to the other side of the stud, you can drill the threaded hole out to be a clearance for the next size up bolt. This can likely be done without making the hole too much bigger than it is, just removing the threads. This way you can run a bigger bolt and nut combo without resorting to weakening the flange. This also helps because bolts actually work far better when the clamped distance is larger. This assumes you A) have a flat face which a bolt head can seat upon, or B) can spot face the flange.

Also, the biggest issue I see is that I don't see anywhere on this thread what your torque specs were, and how you torqued the nuts. If heat cycling is responsible for losing 10% of your clamping force, and you only had 20 lb-ft, then you're going to be loose. Likewise, if you yield it when you install it, then you're a goner.

Next up is a copper gasket, maybe?

Paul_VR6 wrote: Where and how big is the flex joint in the exhaust? Do you have any idea what peak EGTs are and how long they last?

Flex joint is 2.5" x 4 or 6" long as I recall. The downpipe clamp takes it out of the equation now. So consider the studs the X axis turbo support, and now the downpipe is the y axis support. I am concerned that the clamp will lead to a cracked downpipe. But that's the trade-off for taking the exhaust system load off the turbo studs.

I don't have a thermocouple installed in the manifold, so I can only guess. 12-1500F? My boost & timing maps are conservative to keep my stock bottom end alive (10-11 PSIG, can't remember max timing advance).

A typical DE or practice session is 20-30 minutes with your foot to the floor 80% of that time. Then the car sits and cools for a while before repeating, so lots of heat cycling.

John Brown wrote: I guess this may sound silly, but is there anything Flyin' Miata is doing different to the ones they are installing versus the one you have on your car? Maybe they have a bolt kit that seems to work better than what you have?

Right from the FM website:

1990-97 2.5" FM exhaust brace

The brace supports the downpipe where it passes by the transmission. Easy bolt-on installation. Fits all FM turbos with the current downpipe design. It may or may not fit other applications. For 1990-97 models with the standard 2.5" downpipe.

The O.P. even mentions that he ordered the brace already.

Shawn

tuna55 wrote: I don't like Bellvilles for this, if you bottom them out they aren't going to be able to provide the same clamping force as the bolt, which would be the idea. I don't think you'll find bellvilles that will fit and not bottom out. Another point to make is that IF you can get to the other side of the stud, you can drill the threaded hole out to be a clearance for the next size up bolt. This can likely be done without making the hole too much bigger than it is, just removing the threads. This way you can run a bigger bolt and nut combo without resorting to weakening the flange. This also helps because bolts actually work far better when the clamped distance is larger. This assumes you A) have a flat face which a bolt head can seat upon, or B) can spot face the flange. Also, the biggest issue I see is that I don't see anywhere on this thread what your torque specs were, and how you torqued the nuts. If heat cycling is responsible for losing 10% of your clamping force, and you only had 20 lb-ft, then you're going to be loose. Likewise, if you yield it when you install it, then you're a goner. Next up is a copper gasket, maybe?

Can't throughbolt, the studs are buried in the mani. I am drilling out my spare mani for the 10mm right now. Can't recall exactly, but the torque spec was somewhere around 26 ft/lbs. I can only get a torque wrench on 2 nuts, the other 2 require an open end and skinned knuckles. Crows foot plus swivel makes the torque wrench pretty useless on those.

The manufacturers do not recommend any gaskets for these joints. At least one of the miataturbo guys has blown a gasket through the turbine and wrecked the wheel, so I'm leery of a sheet gasket. I do like the Dwarf 44 suggestion of a copper O ring style gasket in a machined groove, but that's a bit outside my time, budget, and abilities right now.

OK, thanks for the clarifications.

Couple of things immediately spring to my geeky engineering mind.

Aircraft fittings. As in get hold of the titanium studs and nuts that are used on jets and the like. They are strong, to say the least. Darned expensive too. They handle heat just fine, and aren't prone to stretching or breaking.

Bracing. The less force the joint sees, the less likely it is to break. I'm not talking about simply a support to hold the turbo up. I'm talking about addressing the momentum issues you've already noticed. A few brackets and hose clamps to support the exhaust behind the turbo goes a long ways to reducing the stress and resulting strain on those fasteners. Triumph Spitfires have a dandy example of this. When they came with catalytic converters it was bolted directly onto the iron exhaust manifold. A thin little support clamp rigidly clamps the exhaust pipe below the cat to the transmission bell housing. As long as that thin little clamp is there, the exhaust is fine. As soon as that clamp would rust off, or an owner would remove it, the exhaust manifold would crack at the catalytic converter flange within a few thousand miles.

Band clamping. Haven't looked at the Bell Flying Miata kit, so I don't know how feasible this is. But there are band clamps that surround a joint and clamp it together. They can be had in various custom configurations, as long as you're willing to pay for it, including square cornered box types. These things do a great job of spreading a load out along the entire flange, instead of just localizing it at the normal corner bolts.

A dumb, potentially obvious question, but I don't recall seeing this infor yet: What are you torquing those 8mm bolts to? You're using Stainless now, right?

M8 is really small for this application. My T25 is held on with (4) 12.9 M12's. That's what Mitsubishi did stock. No problems.

Dashpot wrote: but the torque spec was somewhere around 26 ft/lbs. I can only get a torque wrench on 2 nuts, the other 2 require an open end and skinned knuckles. Crows foot plus swivel makes the torque wrench pretty useless on those.

WHOA!

I hope this is for the stainless studs?

Steel should be MUCH higher than this... goes off to check torque charts

Depending on lube, roughly 47 lb-ft for 10.9 and 57 for 12.9. Anything less than this is ASKING for them to loosen up. You've got to get there somehow. You can use a crows foot, just adjust accordingly (geometry, man), but get rid of the studs that say 26 lb-ft, they are crazy, unless they are stainless, and then they are weak. Steel should absolutely be able to do this. Any fastener looses clamping load after torquing, so checking again after a day or two of normal driving is a good idea. Any fastener will loose clamping load under heat cycling too, but if you are only starting with 26 lb-ft, there isn't much room for error!

I don't know anything about titanium studs, but if the torque charts here http://www.mettec.com/tech are any indication, they probably will need to be much larger than the steel studs for the same application. This is the crux of the problem, you can't just go throwing other materials at this thing. It's all about clamping load. 26 lb-ft * 4 studs just isn't enough clamping load. A steel fastener is the way to go, I think. It looks like the titanium stuff I see is typically 120 ksi, whereas grade 8 is 150 ksi. That's a big difference.

tuna55 wrote:

Dashpot wrote: but the torque spec was somewhere around 26 ft/lbs. I can only get a torque wrench on 2 nuts, the other 2 require an open end and skinned knuckles. Crows foot plus swivel makes the torque wrench pretty useless on those.

WHOA! I hope this is for the stainless studs? Steel should be MUCH higher than this... goes off to check torque charts Depending on lube, roughly 47 lb-ft for 10.9 and 57 for 12.9. Anything less than this is ASKING for them to loosen up. You've got to get there somehow. You can use a crows foot, just adjust accordingly (geometry, man), but get rid of the studs that say 26 lb-ft, they are crazy, unless they are stainless, and then they are weak. Steel should absolutely be able to do this. Any fastener looses clamping load after torquing, so checking again after a day or two of normal driving is a good idea. Any fastener will loose clamping load under heat cycling too, but if you are only starting with 26 lb-ft, there isn't much room for error! I don't know anything about titanium studs, but if the torque charts here http://www.mettec.com/tech are any indication, they probably will need to be much larger than the steel studs for the same application. This is the crux of the problem, you can't just go throwing other materials at this thing. It's all about clamping load. 26 lb-ft * 4 studs just isn't enough clamping load. A steel fastener is the way to go, I think. It looks like the titanium stuff I see is typically 120 ksi, whereas grade 8 is 150 ksi. That's a big difference.

That is just my (potentially faulty) memory from last September when I installed them. 8 x 1.25 SS studs on page 75 http://arp-bolts.com/Catalog/Catalog.html. Maybe it was 26, maybe 36, I just don't recall very accurately 6 months down the road.

I'm going to the track Monday and I have a choice between retorque or leave em loose. In my experience with steel studs they failed quickly after retorque, and they were brittle. So I'm not sure whether that's a good move on already stretched, multi heat cycled fasteners. I'm more inclined to leave them where they are and let the manifold grow into tension.

Dashpot wrote:

tuna55 wrote:

Dashpot wrote: but the torque spec was somewhere around 26 ft/lbs. I can only get a torque wrench on 2 nuts, the other 2 require an open end and skinned knuckles. Crows foot plus swivel makes the torque wrench pretty useless on those.

WHOA! I hope this is for the stainless studs? Steel should be MUCH higher than this... goes off to check torque charts Depending on lube, roughly 47 lb-ft for 10.9 and 57 for 12.9. Anything less than this is ASKING for them to loosen up. You've got to get there somehow. You can use a crows foot, just adjust accordingly (geometry, man), but get rid of the studs that say 26 lb-ft, they are crazy, unless they are stainless, and then they are weak. Steel should absolutely be able to do this. Any fastener looses clamping load after torquing, so checking again after a day or two of normal driving is a good idea. Any fastener will loose clamping load under heat cycling too, but if you are only starting with 26 lb-ft, there isn't much room for error! I don't know anything about titanium studs, but if the torque charts here http://www.mettec.com/tech are any indication, they probably will need to be much larger than the steel studs for the same application. This is the crux of the problem, you can't just go throwing other materials at this thing. It's all about clamping load. 26 lb-ft * 4 studs just isn't enough clamping load. A steel fastener is the way to go, I think. It looks like the titanium stuff I see is typically 120 ksi, whereas grade 8 is 150 ksi. That's a big difference.

That is just my (potentially faulty) memory from last September when I installed them. 8 x 1.25 SS studs on page 75 http://arp-bolts.com/Catalog/Catalog.html. Maybe it was 26, maybe 36, I just don't recall very accurately 6 months down the road. I'm going to the track Monday and I have a choice between retorque or leave em loose. In my experience with steel studs they failed quickly after retorque, and they were brittle. So I'm not sure whether that's a good move on already stretched, multi heat cycled fasteners. I'm more inclined to leave them where they are and let the manifold grow into tension.

Unless you get a torque wrench on there we're shooting blindfolded. The choice of stud, size, prep and everything else may not effect the outcome at all because the torque values were scattered about so badly. What I mean is you aren't controlling this variable enough, so you really don't know how any of the other variables you've changed affect the system.

foxtrapper wrote: OK, thanks for the clarifications. Bracing. The less force the joint sees, the less likely it is to break. I'm not talking about simply a support to hold the turbo up. I'm talking about addressing the momentum issues you've already noticed. A few brackets and hose clamps to support the exhaust behind the turbo goes a long ways to reducing the stress and resulting strain on those fasteners. Triumph Spitfires have a dandy example of this. When they came with catalytic converters it was bolted directly onto the iron exhaust manifold. A thin little support clamp rigidly clamps the exhaust pipe below the cat to the transmission bell housing. As long as that thin little clamp is there, the exhaust is fine. As soon as that clamp would rust off, or an owner would remove it, the exhaust manifold would crack at the catalytic converter flange within a few thousand miles. Band clamping. Haven't looked at the Bell Flying Miata kit, so I don't know how feasible this is. But there are band clamps that surround a joint and clamp it together. They can be had in various custom configurations, as long as you're willing to pay for it, including square cornered box types. These things do a great job of spreading a load out along the entire flange, instead of just localizing it at the normal corner bolts.

Did the bracing by clamping the downpipe.

A V band setup would be ideal. That's what MINI uses and I've run the MINI on the track more than the Miata. No problems there. Unfortunately Garrett doesn't off it on this series of turbo.

tuna55 wrote: Unless you get a torque wrench on there we're shooting blindfolded. The choice of stud, size, prep and everything else may not effect the outcome at all because the torque values were scattered about so badly. What I mean is you aren't controlling this variable enough, so you really don't know how any of the other variables you've changed affect the system.

Hey I try. It's tight in there, and the bottom rear stud is all but impossible to access. From an old photo:

I'm just doing the best I can with what I've got.

In reply to Dashpot:

You had mentioned a crowsfoot wrench...in order to torque one of the head bolts on a Volvo 122, I needed to use a crowsfoot wrench. I "calibrated it" by checking the known torque of a non-crows foot torqued bolt with the crowsfoot, and then had a pretty good idea that the crowsfoot-tightened bolt would be right. You should also be able to calculate the difference, but my way was more empiracal. "We know it will work in practise, but will it work in theory?"