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Downpipe exhaust leak problems

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Old 01-17-03, 11:56 PM
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Downpipe exhaust leak problems

So I notice the other day that I have a small exhaust leak coming from where the downpipe attaches to the turbo manifold. I have the HKS downpipe. It hadn't been really cold since I installed it, and the first day it was, I noticed the leak. The car has that pissed off lawnmower sound. It goes away though, after it has warmed up a bit. I tried tightening the nuts down, and none of them budged. I didn't want to pull to hard, because I have heard horror stories about studs breaking, and needing to remove the turbo manifold. Any ideas on how to fix this without breaking a stud.
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Old 01-18-03, 12:34 AM
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so when u installed it the first time u had no leak? well its possible that when its cold, and the manifold heats up it expands creating a better seal.

As far as the leak, maybe your gasket blew? Its rare as far as I know, but maybe it did? Did u remember to put the gasket back on? because its possible that u managed to create a tight enough seal when the metal is warm enough and expands, but when its cold, it leaks some.

Id reach down and feel where its coming from as well, who knows, maybe its from your o2 sensor area? I dunno Im just throwing up ideas.
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Old 01-18-03, 01:34 AM
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Angry I have that same leak!

I called HKS and was told I must have purchased a black market version cause theirs have no flaws. Yeah whatever, anyhow my 2nd car is down so I can't remove and return.

I went to the automotive store and got some manifold repair goop. I used a screwdriver and filled in the gap and it's held good since.
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Old 01-18-03, 07:13 PM
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I definitely put the gasket on when I installed it. Perhaps there wasn't a very tight seal the first time, but it warmed up quickly enough to close the seal. Thats what I was thinking, just kinda hoping someone else would say the same.

GoRacer,
I don't think I purchased a black market version because I got it from the rx7store, i think they only have the real deal. I considered the "exhaust leak repair kit" type approach, but i wanted something more permanent.
Does anyone know how much the studs can take before they snap? Would a 2 foot breaker bar and full body weight be too much?
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Old 01-18-03, 07:20 PM
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I would remove the downpipe and have it checked to make sure the flange that bolts to the turbos is flat. If it is slightly warped, you will need to have it machined flat. This shouldn't cost too much. Replace the gasket.
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Old 01-18-03, 09:24 PM
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Are you absolutely sure it's an exhaust leak?

Reason for asking is that a LIM (lower intake manifold) gasket that is blown will give you the impression that there's an exhaust leak too.

David
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Old 01-18-03, 10:24 PM
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You can use a mechanic's stethoscope (or just a flexible tube held to your ear) to help pinpoint the source of the sound. Maybe you can eliminate the DP or the LIM that way.

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Old 01-19-03, 06:44 PM
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[email protected],
Wouldn't a blown LIM gasket give poor performance/compression? My gut feeling is that it's the downpipe, as I've never touched the gasket on the LIM, and I can't see it blowing when it's never been removed.

Adam C,
I'm trying to avoid removing the downpipe, but if worse comes to worse, I may have to. Do you have any ideas on where to get it machined? I've never done that sort of thing before.
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Old 01-19-03, 07:54 PM
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For a little reference. If you think a bolt is not tight enough, go to the trouble of removing it, cleaning the threads, appling a thread sealant and torquing it to spec.
For exhaust manifold, rust on bolts or threads could cause it to reach spec torque before it is fully tighten down.

As for the LIM, remeber there are some exhaust gas passages in it. One of those could be loose or have a blown gasket without affecting the intake ports.
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Old 01-19-03, 08:33 PM
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flunkysama,
thanks for the tip, i thought about removing the studs completely and tryin again, but some of them were such a b*tch to get in, i don't wanna. I guess i'm looking for an easy way out, when i should be doing it the right way.
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Old 01-19-03, 09:40 PM
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Originally posted by 911GT2
[email protected],
Wouldn't a blown LIM gasket give poor performance/compression? My gut feeling is that it's the downpipe, as I've never touched the gasket on the LIM, and I can't see it blowing when it's never been removed.
911GT2,

The fact that it is an original LIM gasket on a 93 only rises my suspicions... they used to be paper. There have been revisions to that part which now has it made of metal.

Mine (93) was never touched either and it was blown. As far as performance loss... it's the "exhaust leak" sound that got me on the problem, not performance loss.

David
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Old 01-19-03, 10:21 PM
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Originally posted by 911GT2
Adam C,
I'm trying to avoid removing the downpipe, but if worse comes to worse, I may have to. Do you have any ideas on where to get it machined? I've never done that sort of thing before.
Any good machine shop should be able to do it for you. I'm in CA, so I don't know anyone in your area.
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Old 01-20-03, 12:52 AM
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Dude... I hate to see you screws things up so here's a suggestion. Consider talking a road trip to KD Rotary Performance in Natzerath, PA.... Have Dave solve your problem.... Sure is cheaper an more fun in the long run... Best of all, you won't un necessarily disable your 7.
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Old 01-20-03, 11:51 PM
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I'm actually going to KDR in february, but i was hoping to get it fixed myself, it's just a pipe, right? shouldn't be too tough. (famous last words). If i can't, i'll have dave do it then, but it sounds like a friggen lawnmower right now, and i would like it fixed. If all else fails, i will though.
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Old 01-21-03, 10:32 AM
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Nobody wants to spend $40 or so for a new gasket when they do this job. Everybody thinks that metal gaskets can be re-used. Wrong. Completely wrong.

They ALL are designed to deform and seal only once after torquing them down - that's it. Even a couple of thousandths of an inch difference is enough to cause your leak. Especially when you are mating a new surface to the indentations formed from a previous surface.

Here's the professional way to chase down your problem:

Take a quality machinists straight edge (yes, you will need to buy one) and verify that the surface of the mounting flange is completely flat. Hold it up to bright backlight. You should see no light between the straight edge and the flange. It would be really unusual to see this flange warped. Check it on at least 8 different axis.
Check the turbo surface as well - a little difficult when on the car but it can be done with a bright flashlight, mirror and small straight edge. You'll need a helper to do this.

Before you go to a machine shop or spend big bucks at a repair shop, buy a new gasket from Malloy Mazda. Make sure ALL the mounting surfaces are clean and wire brush the bolts/studs. Put some high temp (emphasis on HIGH TEMP ONLY) anti-sieze on the bolts/studs before torquing them down. The anit-sieze will also act as a lubricant so that all the bolts torque evenly, and clamp the dp flange FLAT. If you ever need to take them out they will back out like buttah. You can use a drop of motor oil each instead but it is not the preferred way when working with exhaust components. Criss cross the pattern and do 20 lbs. first, then re-set to 28 to 38 lbs. It does not take a breaker bar to set this torque value.

If you don't have a torque wrench expect to pay about $100 for a quality unit. The cheapies are worthless.
Top of the line Craftsman or Snap-On are hard to beat.

Even with a new straight edge, gasket and torque wrench you are way ahead of the repair shop price.

Badabing, no exhaust leak.
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Old 01-21-03, 11:24 AM
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i'd say try not using the stock studs/nuts, you're crazy for reusing them if that's what you did

goto pepboys and get some exhaust bolts with the hex head
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Old 01-21-03, 12:02 PM
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Originally posted by 93BlackFD
i'd say try not using the stock studs/nuts, you're crazy for reusing them if that's what you did

goto pepboys and get some exhaust bolts with the hex head
I gotta agree/disagree:

It's always a good idea to use new fasteners, especially ones that have been heat cycled. They tend to get brittle over time... I missed that VERY important point, thanks.

If the the hex/socket head bolts don't have the same bearing surface (they are usually much smaller) as the OEM flange nuts then you are effectively focusing more force on a smaller area than with the flange nuts. This could potentially cause a crack in the flange or bowing of the flange surface and..... an exhaust leak. You could easily remedy this with a stainless steel (preferred) or Grade 8 (not mild steel) flat washer or bushing under the hex/socket head, as long as it fit in the machined recess on the dp without binding. The other problem is hex/socket heads cannot be torqued unless you buy an adapter for your torque wrench. "Hand" torquing is acceptable for small, relatively unimportant fasteners, but not in this case.

I aways try to duplicate what the manufacturer did, so I would go with NEW OEM studs and NEW OEM flange nuts. (that's what I did on mine) They are stupid expensive, but I hate re-doing stuff caused by going cheap when for a few bucks more you can get the right stuff.

Whoda thunk installing a dp properly could be so involved?

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Old 01-21-03, 01:03 PM
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Would a 2 foot breaker bar and full body weight be too much?
YES!
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Old 01-21-03, 02:28 PM
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Originally posted by RonKMiller
Before you go to a machine shop or spend big bucks at a repair shop, buy a new gasket from Malloy Mazda. Make sure ALL the mounting surfaces are clean and wire brush the bolts/studs.

After you remove the downpipe, inspect it carefully. If you have ANY doubt about it being flat, take it to a machine shop. You don't want to do this job again.
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Old 01-22-03, 12:14 AM
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Thanks for all the info, it's greatly appreciated. RonKMiller, your way definitely sounds the most thorough, if long and involved. I'll probably end up doing that. And what the hell, i'll need a torque wrench for many other jobs anyway, might as well buy it now.
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