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Guest Message by DevFuse

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Head-to-exhaust bolts

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10 replies to this topic

#1 sidekickin


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Posted 15 December 2006 - 10:10 PM

Noticed about a week ago that I was developing an exhaust leak around the engine area. Didn't think much of it until today when it got extremely loud. Souded like the pipe was disconnected from the engine or something. I peek under the car and there was a noticeable gap where the Y-pipe bolts to the head on the passenger side. I figured the bolts just came loose, so I went to tighten them. They would not even start to tighten. I could just turn the wrench freely and neither bolt would tighten. I'm guessing the threads in the head are stripped. Has this happened to anyone? I am just wondering how this even happened. Out of all the years of owning this car I have never touched those bolts; so it wasn't like I overtightened them at some point to cause this. The exhaust leak developed rapidly over the past week and have never had a problem before this. How could the threads in the head strip out by themselves? I am baffled. Is this common? And how do I go about fixing this? Is it expensive? Thanks.

#2 Gravityman



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Posted 15 December 2006 - 10:52 PM

Just Relax first,

Before you jump to any conclusions take a more detailed look to find out what is actually wrong. Pull out the studs first. The exhaust is held in by studs not bolts (Basically a threaded rod with a nut that you tighten on after threaded into the head). Check and see if they stripped, if so order some new ones from subaru or an oem manufactuer. Check the holes the studs came out of and see if they are stripped. If the holes are stripped you will probably want to drill and retap the hole the next larger size and then buy a new stud and bolt to fit.

Remember that these studs rust easily due to the heat and failure is not uncommon. Good luck!

If you have a picture that you can post, please do. Thanks

#3 ecky


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Posted 15 December 2006 - 11:13 PM

I believe they eventualy fall out, because the heads are aluminum and the studs are steel, and they expand at different temps. over time they fall out. I took mine to an exhaust shop and payed to have new studs locktighted in. Wasn't much, would prolly go that way.

#4 Phizinza


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Posted 15 December 2006 - 11:28 PM

I have had this problem with 3 of my 4 studs on my EA81. I messed around with cheap options. But I think the best bet is to get it helicoiled properly. I know have a helicoil kit, but if you don't want to pay the price for one, I suggest getting someone (mechanic) how has one to do it. You shouldn't need to remove the engine if you put it over a pit or on a lift.
One thing I must say (this is why it went so horribly wrong for me) do not drill any deeper then the holes are already.. It's like 4mm before you get to oil passagers, then you are stuffed, like I was.

But yeah, first pull the manifold (Y pipe) away and check the studs, you never know what might be wrong till you look at it better.

#5 sidekickin


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Posted 15 December 2006 - 11:28 PM

Sorry about that....they are in fact threaded studs with nuts. I should have chosen my words more wisely. I will try to remove the studs tomorrow to see what is going on. I'm hoping this will be an inexpensive, easy fix.

#6 mikeshoup



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Posted 16 December 2006 - 12:08 AM

If the threads are stripped in the heads, do as I'm about to do. Tap the threads to the next largest standard sized, 7/16-14 (or -20 if you like finer threads). Then use stainless steel bolts with lock washers. That's what I intend to do on my XT.

#7 NoahDL88


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Posted 16 December 2006 - 01:16 AM

I had the 7/16th on my wagon before the motor swap too, it was easier than geting a helicoil in there, and it was much more permanent.

Get yourself a tap and die set ( just the size you need, the whole set is mucho dinero), and drill out the hole to clean out the threads and then tap the hole to the size stud that you have. use some loctite on the stud as it goes into the head and you should minimize your problems down the road.

#8 RonVee


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Posted 17 December 2006 - 01:34 AM

I tryed all the different 'patches'. None lasted very long. If the threads are stripped the 7/16 tap fix does the job.

Do the 7/16-14 plug tap, then 7/16-14 bottoming tap and install the 7/16 studs. Try to get the stainless studs/nuts/washers like mikeshoup said.

This worked for me.


Happy Holidays to the Board!

#9 sidekickin


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Posted 17 December 2006 - 02:44 AM

OK, I fixed my problem. I got two 3/8"-16 bolts 2" in length. They threaded right in with no problem. Didn't have to tap or drill the hole or anything. They tightened really good too. Not sure if it is going to be a permanent fix or not...only time will tell. But it works great right now....no exhaust leak at all.

#10 Gloyale


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Posted 17 December 2006 - 03:05 AM

I've done that fix before and it only held so long because 3/8 is not much larger than the original holes and you basically just catch whatever is left of the original threads. It definatley works though. The better option and still very cheap is to tap the hole out to 7/16 properly and then use new studs or bolts to your preference. Studs are the more pro way but if you don't plan on tearin the exhaust back off often then bolt's work. But every time you remove/reinstall the threads get weaker in those soft alloy heads.

#11 4x4_Welder


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Posted 17 December 2006 - 02:41 PM

The real problem is that the aluminum is verysoft, and cannot hold the exhaust up with that short of threads. The PO of my Hatch had gone all the way out to 1/2" bolts, and those were stripped, so I rotated the flanges to the other pair of holes, drilled and helicoiled those, and have had no problems. I'll probably do this as a preventative measure on the new engine, just to prevent any issues.
One thing to look out for is any damage to the exhaust system, or a plugged catalytic converter. Either can cause excessive backpressure on the systm, and speed any damage at that end.

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