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I am reassembling my engine after having it rebuilt and stripped the threads out of the lower rear housing stud hole. What’s the best way to repair this?
Ive used helicoil kits on the aluminum head of my turbo protege and it’s held up well, but is that good enough for the 13b-rew? Is there enough aluminum around that hole to drill it out that much? I’m worried if I tap it to a larger size it won’t fit through the manifold, and studs might be hard to find. I’m trying really hard not to ruin my freshly rebuilt engine here.
Im going to go ahead and order new studs and bolts instead of reusing the old ones, and just so I don’t screw this up again, what’s the right way to actually install these studs?
I ran a tap through the hole to clean it up, and I have some thin remnants of threads in the end of the hole. It's enough that the stud catches and holds once I start screwing it in. The back 5 threads or so are intact. Here are some pictures showing this
I have a stud with a longer end which is able to get deeper than the original stud in the hole and grab onto the remaining 5 threads. I think it will still have enough room to get a nut onto the other side of the manifold. I measured it against the original stud and took a picture that I edited below. The blue line is roughly where each meets the housing. The yellow section of the new stud is where it is screwed into good threads, and the red is where it's screwed into the damaged half-threads. Do I have enough threads left here to use the new stud and get a good hold?
I guess I learned never to use a lock washer when torquing down a nut into aluminum.... it just suddenly popped backwards and took all the threads with it once it got tight.
If there are deeper threads that are good, go with a longer stud and use those. Original threads will always trump a Helicoil.
Also, I would use copper locking nuts on all the turbo connections. They don't aggressively bite onto the studs and try and pull them out but will stay secure. Just use them and maybe a flat washer behind, that's it.
From what I’ve read though, only the original studs will hold up to the heat, so my longer stud, which is definitely lower quality, will eventually stretch or break. Unless I can screw an OEM stud in deeper now, which I don’t think I can without more drilling, it’ll only get onto one or two threads at the end. Even if it gets onto all 5, is that really enough to hold better than a helicoil?
Id much rather fix it the right way now while the engine is out of the car than have to add a helicoil with the engine installed, so I want to be 100% sure about what I do.
My bad, just a typo. Let me know if there are some you recommend, otherwise I’ll just check amazon
I’m now thinking about installing a new OEM stud in the block “backwards” so that the longer threaded end is in the block. The tall OEM nut still has almost enough room to screw on, so a non-OEM one should fit without a problem, and I can always use washers if I hit the flat part before it’s tight. Just an idea...
I think no less an authority than Carroll Smith used to helicoil all aluminium/magnesium parts to ensure more reliability than a machined thread. I'd expect what's probably a hewland in DaveW's car, has more than a few!
I'd be amazed if there's not enough meat around the stud, I'd use a 10 x1.5 timesert in preference to a helicoil though.
I think no less an authority than Carroll Smith used to helicoil all aluminium/magnesium parts to ensure more reliability than a machined thread. I'd expect what's probably a hewland in DaveW's car, has more than a few!
I'd be amazed if there's not enough meat around the stud, I'd use a 10 x1.5 timesert in preference to a helicoil though.
It's a Staffs gearbox, but, yes, it has more than a few Helicoils.
It looks like timesert has a flange to stop the insert, and that might interfere with the exhaust manifold gasket. I think I’d use a helicoil just because it would be flush on the outside and so I don’t wind up with an exhaust leak from a manifold that’s not flat.
I think I will go ahead and order a new stud and copper nuts, and try to torque down the stud with the long end inserted into the block. If it holds, great, I’ll leave it. If it strips the threads again, I’ll go to the helicoil. Unless there’s a good chance of the stud stripping the heads out later on down the road I think this approach makes sense - any opinions?
Im still waiting to see if anyone has successfully helicoiled that stud. I don’t have another 13brew housing to look at but my junk 12a housing looks like it has enough aluminum there, but not by a lot. Not sure if the designs are consistent.
I had a buddy with a helicoiled rotor housing that always had problems. May not have been done right, hard to say. It's just a tricky process, you really want the engine out so you can make sure everything is dead straight, see what you're doing, etc.
Yes it was a lower exhaust stud on a s4 T2 block. The kit is a 10mm x 1.5 course thread. And u need a 13/32 drill bit. since the heli coil isn't really long(about as long as the threads u striped off) u don't need to drill all the way down to the bottom. I'd try a longer stud first and use a hell coil as a last resort. Make sure the longer stud gets a good bite into the good deep threads tho.
Yes it was a lower exhaust stud on a s4 T2 block. The kit is a 10mm x 1.5 course thread. And u need a 13/32 drill bit. since the heli coil isn't really long(about as long as the threads u striped off) u don't need to drill all the way down to the bottom. I'd try a longer stud first and use a hell coil as a last resort. Make sure the longer stud gets a good bite into the good deep threads tho.
I don't think I can buy a longer stud that's inconel, so I think I'll try flipping the OEM stud and making sure it gets all the way to the bottom. There's just enough of the top threads left to have a bite, so it might work. The engine is currently out of the car though so helicoil wouldn't be a problem right now, but later on down the road it would be tough.
It looks like timesert has a flange to stop the insert, and that might interfere with the exhaust manifold gasket. I think I’d use a helicoil just because it would be flush on the outside and so I don’t wind up with an exhaust leak from a manifold that’s not flat.
I think I will go ahead and order a new stud and copper nuts, and try to torque down the stud with the long end inserted into the block. If it holds, great, I’ll leave it. If it strips the threads again, I’ll go to the helicoil. Unless there’s a good chance of the stud stripping the heads out later on down the road I think this approach makes sense - any opinions?
Im still waiting to see if anyone has successfully helicoiled that stud. I don’t have another 13brew housing to look at but my junk 12a housing looks like it has enough aluminum there, but not by a lot. Not sure if the designs are consistent.
Timeserts come with something like a counterbore tool so they end up flush. From memory, something like 80~90% of a bolted joints strength comes from the first 2 or 3 threads, which may explain part of the reasoning for the flange. Suppose the obvious thing to say, is to make sure the stud doesn't bottom if you go your method.
There have been pics of sectioned rotor housings to show the attachment of the sheet metal running surface to the aluminium in the past, if you're lucky, might be an image somewhere out there going through the stud area, but I reckon you're over-thinking the potential for something a couple of mm larger than the thread major diameter to cause problems.
I seem to recall the mx5 turbo, back when, had inconel studs on a few bits and pieces, that might get a range of sizes.
use a helicoil, the studs are inconel and you don't want to use inferior stud materials in there. being that they are inconel and metric, there isn't a lot of suppliers for them. you could try another exhaust stud but i don't like leaving threads exposed, it creates a weak point.
I used a helicoil on an exhaust stud. There is a step by step pictorial record of the process in my build thread. Link in my signature.
Bottoming out the stud has more potential for damage in my experience.
I found the images, that’s exactly what I need to do, thank you! How many miles have you made it on that engine now, and have you had any issues with the helicoil?
I found the images, that’s exactly what I need to do, thank you! How many miles have you made it on that engine now, and have you had any issues with the helicoil?
None, as I haven't installed the engine yet, but it held full torque spec, plus a bit more.
In theory, as long as the helicoil or insert is the same depth of thread, it will be as strong, if not stronger than the original aluminum threads. You will have more threaded surface area being acted upon in the aluminum after the insert.
I got the timesert insert and my exhaust manifold installed. The timesert was not hard to install, and the stud hole just barely had enough depth for the timesert to fully open up (the insertion tool has to pass through the insert 1/4").
The only issue I had is that I can't get the stud torqued to 22ftlbs. The stud gets close but keeps turning, and it wound up a little deeper than other studs so I stopped and left it as is. I am not sure if it's beginning to mess up the outer threads of the timesert insert. I was able to torque the nut on the stud down correctly once the manifold was installed though. If anyone thinks that stud will be a problem let me know and I'll keep messing with it.
I was worried about not being able to torque the stud enough, so I took it out and sure enough the end of the timesert insert’s threads were messed up. The flat part of the stud had gone right through those threads which was why the stud wasn’t getting tighter.
I ran a tap through the hole and reinstalled the stud with some lock tite. The stud now sits a few millimeters lower than the others but isn’t in the bottom of the hole. Instead of trying to torque to 22ftlb I just tightened it by hand with a regular ratchet until it was snug.
Will this be enough? The 3 other studs are torqued down without a problem. Im not sure what else I can do.
Edit: I measured the studs current torque at 20ftlbs... ALMOST the spec (22-26)
Not sure loctite will do much, other than before first start-up, permitted upper temp range is somewhere around 200C from what I remember.
The grip section of the stud should be the stop when it contacts the timesert, so not sure how that is working, unless the timesert counterbore is deeper and torquing it is winding it in? I'd be wary running a tap through too, idea is the fastener forms it's own threads, at the lower levels at least....might be tempted to remove and reinstall a new one. Only time I've worried about torque on the studs in that area are turbo to manifold, where you could crack stuff if you go nuts.
12-16-17, 05:17 PM
