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Old 05-25-2004, 03:41 AM
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Jeep Wrangler exhaust manifold needs preheating prior to fitment

My friend Martin had a Jeep Wrangler towed into his workshop several weeks ago. Stupid (Jeep owner) says the motor's lost oil pressure, is knocking and wants Martin (mechanic) to find out what's going on. Martin opens bonnet. No engine under bonnet! What the? Martin tells stupid that he needs the engine to find the problem. Engine arrives, sump's rattled off, spun bigend on number one. Martin looks at lube sticker, mmmmmm, engine had'nt been serviced in 50,000km's. Oil has solidified like lard on the rockers and head bolts
Enough of the gag. It's a pretty straight forward repair, and with Martin being the very competent mechanic that he is it should be running like a Swiss watch once done all the necessary repairs. The bores and slugs look fine. The motor will be stripped, sent out to be tanked, crank reground, etc
Here's your que. Martin's found out that the exhaust manifold must be preheated cherry red with an oxy acetelyne torch and then have all the bolts torqued to the head. If this is not carried out then there's a very real chance the manifold would crack. Do any of you know anything about this procedure?

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Old 05-25-2004, 06:07 AM
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Just have the manifold resurfaced flat on a surface grinder (machine shop). Saves a lot of problems!
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Old 05-25-2004, 08:08 AM
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Gee, BOB, I'd gladly forgo any profit on the resurfacing job just to watch some idiot try to do that with the manifold!



tom
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Old 05-25-2004, 08:15 AM
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???

Tom, i would also like a ticket to this show. It might be worth the price of admission......

Keith
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Old 05-25-2004, 08:44 AM
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Re: ???

Quote:
Originally posted by k-star
Tom, i would also like a ticket to this show. It might be worth the price of admission......

Keith
"Specially if they leave the FI unit on when they do it! Bring your hot dogs!



tom
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Old 05-25-2004, 11:27 AM
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That would certainly be an interesting installation!
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Old 05-25-2004, 03:43 PM
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Hey guys, everytime I heat the manifold cherry orange it gets too hot to handle. Then I just stand there and watch it cool again. Could I just paint it cherry orange to install it? Lemme know quick, the crowd outside the shop grows larger and larger....
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Old 05-26-2004, 01:33 AM
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Here's the progress report fellas. The motor's been repaired successfully and installed into the Wrangler. We decided to heat the manifold in the recommended manner till it got cherry red. All was going really well till the EFI fuel line ruptured and spewed flaming petrol (gasoline?) all over the place. We thought we got it contained until a nearby open drum containing thinners went up into one big fireball. Man the explosion caused in inferno. We lost the Wrangler along with an XB Falcon Mad Max replica, an original Lamborghini Miura, half the workshop, Martin's eyebrows and Rusty the 3 legged dog. Martin has no insurance and has no option but to file for bankruptcy.
Now that I've distracted you guys from your GI Joe dolls and have your attention I've give you the real low down. He he!
An associate of Martin said that he once had to weld a cracked exhaust manifold on a Wrangler. The manifold was professionally welded and was machined straight. The manifold cracked once again once the heat had soaked in. This guy rang up our motoring body and was told that these manifolds must be preheated prior to torquing up the bolts to help prevent cracking. He did just that the second time round and that manifold is still free from cracks.
I did'nt know all the details when I asked you guys that question and was a little taken back, but amused somewhat with your humor. Next time I won't bother.
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Old 05-26-2004, 05:45 AM
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oop's

Sorry man, I thought the way you had written it was a joke ???? I really did not realize you were serious..... At any rate, never in the 25 years that i have been wrenching have i needed to heat a manifold cherry red to install it. So i can't be much help. One thing i do know is that welding cast iron sucessfully has only been mastered by a hand full of people and even they will tell you it's hit and miss....... So if your buddy had a manifold welded by a professional and installed it and it cracked,,, It probably would have cracked even if it was pre-heated when installed.... What i can't seam to get straight in my mind is how do you install a manifold that to hot to touch. Even if you put gloves on then you can't handle the bolts to do the install. If you have one guy holding and another putting the bolts in,it might work... But i would not want to be the guy putting the bolts in,if you slip and touch the manifold you got burned knuckles...... Someone else jump in i just don't get it?????

Keith
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Old 05-26-2004, 08:09 AM
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Actually kstar the comments you made were the thoughts that went through my mind when I was told of this. He's just gonna fit the thing cold and fire it up. Our main intention was to fit the manifold with the bolts loose, heating it up and then torquing it down. I suggested today that maybe we could start it up with the bolts loose to get the manifold hot and tighten the bolts. I know it's a insignificant subject, but a replacement manifold would cost more than headers and with you guys being American I thought you may know something specific to this model. I don't work there but I call in on him almost everyday to have a chat, help out and just to keep up with my old trade stuff. I do work for him the occasional day though. While we're on the Wrangler subject, I was wondering about the origins of the straight six engines fitted to these models. They look very similar to the Australian designed hemi 6cyl engines of the early 70's which were fitted to the legendary Chrysler Charger E38 and then the E49. The prototype engines on these high performance models were further developed and enhanced by Weber in Italy. The end result was the 265ci Hemi6pack with triple Webers in true GT style. and would kick the 1/4 mile to death in 14.2 secs. Pretty good stuff considering the 350 sbc powered Monaro of the time would'nt crack 15.5's with weights being similar. In fact, the E49 could accelerate to 100mph, stop, accelerate again to 100mph before the 360 v8 Chrysler By Chrysler would reach 100mph.
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Old 05-26-2004, 03:36 PM
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Heating the exhaust manifold to cherry red? C'mon.

If this was so important then why can't you just start the truck and torque the bolts once the manifold gets hot? I will be looking through my Mitchell manuals tonight to look for this.

BTW my next door neighbour has a 258 ci I6 in his Jeep and I did the exhaust manifold gaskets last year for him, I never preheated anything and it is still running fine. If you are having cracking problems its from the weld not from some special install procedure.

Hope the three legged dog had insurance.
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Old 05-26-2004, 06:31 PM
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Jeep actually had problems with their some of their 4.0 I6 exhaust manifolds cracking but not from installation error. We replaced them with newer style manifolds with a short length of flexpipe in them to prevent future cracking. I have never heard of pre-heating an exhaust manifold cherry red prior to installing it.


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Old 05-27-2004, 02:44 AM
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dmorris1200 thanks. Least someone knows something on this topic. The manifold we have is not cracked and we intend to keep it that way.
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Old 05-28-2004, 10:32 PM
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Jeep Wrangler exhaust manifolds are very well known for cracking
due to off roading,body lifts,and just raising hell in general.But Jeep has redesigned there 4.0L manifolds in the last few years.
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Old 05-29-2004, 01:08 AM
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Thanks JeepTech. Much appreciated.

Last edited by club327; 05-29-2004 at 01:26 AM.
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