TABLE OF CONTENTS Sep 2012 - 0 comments

More bad design bruises

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By: Jim Anderton, Technical Editor

Normally I don’t complain too loudly about OEM design practices; but as I write this, I’m bothered by a nasty little oxy-acetylene induced groove in my right hand. This is a result of one of the most badly designed common service areas in modern cars and light trucks today: the exhaust manifold. These things run hot, damn hot; and you would think that knowing this, OEM’s would make a small effort to make studs and bolts that can be removed without mashing knuckles, setting fire to the wiring harness or spending three hours on a simple exhaust fix. The picture of the exhaust manifold flange below is a case in point. I’m not going to tell you what brand of vehicle this was, because my point applies to all manufacturers. No amount of heat could loosen the badly rusted exhaust flange studs, which promptly broke off under my Vise Grips. This meant work with the right angle die grinder to produce the surface you see here. You can just make out the outline of the studs, which is good, because this was followed by four-step drilling of the stud then use of a bottoming tap to clean out the threads. Naturally, there was no room to work, and the design of the manifold made it tough to use a through bolt or stud with a nut on top. 2½ hours later, I had threads to work with, all to fix a misaligned and leaky downpipe flange. How do you tell a customer that the simple job took three hours? If you’re "on the book" you don’t, but that time has to be accounted for somewhere. And I was lucky … if this was an exhaust manifold change, I’d have to deal with equally rusted manifold bolts, with no way to extract the broken stubs out of the head inside the engine bay. If it happens, I’ll use the "gas axe" to cut off the bolt heads, just to make sure it leaves enough stud to grip. Ever notice that bolts and studs snap off flush with flanges and heads? Here’s my appeal to automotive engineers everywhere:

Stop using studs on exhaust flanges! There are clamp rings or you could use open "forked" flange bolt holes to retain regular bolts or "T" bolts. That way we could torch off the nut, withdraw the bolt and replace.

If you must use studs, leave enough room above the flange to run a tap or drill bit, and make the runners long enough to let us get at it without flaming half the engine compartment.

Design bolts and studs with a weak spot near the heads … so if they break we can remove the pipe or manifold and have something to grab when we apply heat

We know you use bolts with threadlocker already applied … how about anti-seize?

Do you have to put the oxygen sensor where I’ll either damage the wiring or can’t get tools around the flange? I damn near drilled a hole through the sensor on this job.

I know OEM’s count pennies when costing the assembly of a new car or light truck, but these solutions have been done before. My first car was an Austin Mini, and its downpipe was held to the manifold by a vee-groove clamp like the type used for big commercial water pipes … and that was a very cheap car, so it can be done. Hopefully, before my hands look like Frankenstein.


Jim's Cut Hand
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Caption: Jim's Cut Hand
Exhaust Manifold
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Caption: Exhaust Manifold

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