XJEEP01

Hello everybody,

I am removing the exhaust manifold on my 2001 xj. I have all the bolts and nuts off but I can't get the manifold off. I think the front and rear studs may be threaded through the manifold? I thought it was supposed to just pull off but the end of this stud looks like it is made to be removed with a reverse torx head. Any info?

http://imgur.com/qBPsDTG,BsZQ5Bb

CCKen

Looks to be corroded in place. Use some pentrating oil on them and give the manifold a tap or two with a small ballpeen hammer. The manifold should free up.

EMAXX620

x2 on some penetrating oil. It's a stud for alignment, there should have just been a nut on it, but the stud itself doesn't need to come out.

5-90

That is a stud, it should pass through a smooth hole.

There are typically either two or three studs - there will be one at both ends, and there may be one at the top centre.

If it's "corroded in place" (likely,) I've found it useful to lay a brass drift against the flange near the stud and smack it once or twice with a mallet to break the crud.

The studs may be replaced with pieces cut from brass threaded rod. 3/8"-18 thread, match the length, and get new nuts (the OEM nuts are threaded 3/8"-24. There are sound reasons for doing this, but they don't apply in this case.)

Retain & reuse all of the "dished" washers, unless you're going to replace them with true Belleville washers (I have yet to determine exactly how many are needed, but I would probably use two, nested together.)

OEM screws removed should be replaced - I prefer using aluminum bronze or silicon bronze (threaded 3/8"-16, match length. I think they're 1.25" UHL.) But, if you can't get those easily, use SAE Grade 5 screws - they will actually retain more strength after repeated heat-cycling than SAE8 (I have verified this experimentally.) Carbon steel hardware, used in exhausts applications, should always be replaced when removed. It's cheap insurance.

There is only one grade of LocTite that will work in this application. I don't recall the number specifically, but I think it's either #272 or #277 (it's a medium-strength threadlocker - like #242 - formulated for high heat applications. Anything else will break down, or render the assembly non-serviceable.)

Otherwise, don't bother.

A thin, even layer of RTV Copper on both sides of the new combination gasket won't go amiss, and I find it useful to check torque on manifold screws annually (as part of an overall inspection.) You'll often find that the lower rear screws have loosened - I have explained why this happens elsewhere, if you're interested.

PocketsEmpty

^All that info makes me want to go and rip off my manifold now and redo it. Thanks! lol

XJEEP01

Thanks for all that great info 5-90. I'm going off of a crappy haynes manual as it is.

sgjii

I have a question on this. I read in another post and on a catalytic converter mfg website, when I was researching issues related to my P0432 code, that to never use an RTV or silicone product on exhaust manifolds/gaskets. It has to do with contamination of the O2 sensors and Catalyst by being coated by any silicone that is exposed to exhaust gas/heat and passes through the exhaust system. Is "RTV Copper" a special product for exhaust applications and is it labeled as Senor and/or Catalyst safe?

sgjii

I went looking for the info again and found similar but not the same website data.

"Also note that silicone from either antifreeze or RTV (silicone) sealant, can clog an oxygen sensor and make the mixture rich and in time will ruin the combustion chamber the sensor should be replaced. When using a silicone sealer, make sure it is oxygen sensor safe."

Here is an interesting tidbit about intentionally damaging an O2 sensor with RTV. "There is s huge secret that has not made it into the public domain yet but here it is: If you remove a rear oxygen sensor and pack it with red RTV silicone it will destroy the oxygen sensor in a way that will trick your car's computer into thinking the catalyst is okay because it can not sense the oxygen coming out of the sensor. But the sensor will still generate voltage enough to pass the cars oxygen sensor activity test. Never do this to a front oxygen sensor because it will mess up the fuel system. Well there it is one of the best kept secrets in the smog loving world. This works nearly 100% of the time. You will never find a mechanic that will do this for you so you best be prepared to remove that sensor yourself and put it back in."

I am not advocating the above sensor trick, just found it interesting and related to Silicone sensor damage.

Found this post on a Camaro website regarding RTV copper damaging O2 sensors: http://www.camaroz28.com/forums/lt1-...r-safe-425783/ It specifically references RTV Copper. The thread is a little long for copy/paste here but short answer is they felt the RTV killed O2 Sensors.

Lastly a quote from a Toyota forum, "I did speak to the Tech Support guy at NGK Canada and he also thought that having even 'sensor safe' silicon that close to the O2 sensor could be causing the problem. Just to wrap up this thread, the cause of death of the two brand new O2 sensors was definitely the use of Loctite Red High Temp Sensor Safe Sealant on the O2 sensor flange. The truck has been running fine for several weeks with the 3rd new sensor which was installed without using the sealant on the flange (see previous post for details). I guess even though this sealant is OK to use on header gaskets (as indicated on the label) the contamination caused by having it in close proximity to the O2 sensor will kill the sensor within a couple of weeks. So, although I will continue to use Loctite products, which typically do a great job, as advertised, I caution anyone against using any silicon based sealant, even if it's 'sensor safe', right next to the O2 sensor itself."

5-90

A good-quality RTV (like Permatex) will list itself as "sensor safe" - which means it's formulated to not outgas and clog the sensor pores.

Just don't get stupid with it - smear a thin layer on (if you do more than 1/16", you've done too much.)

I have been using copper-bearing high-temp RTV on exhaust gaskets for years with no negative results - from "classic engine" applications up through OBD-II.

Of course, I flatly refuse to use cheap crap - I use Permatex, or don't bother.

Most recently I've done this? A couple of months ago, on both exhaust manifolds for a 1998 Explorer V8-302. I'd replaced the HEGO sensor about 6 months before (EOL,) and no trouble reported since.

As far as on the sensor threads/flange proper? The only thing that should go on there is a nickel- or copper-based anti-seize compound. Don't bother with anything else, and don't forget to use it! (Unless you want to pay someone like me a couple bills to get it out, because it's now frozen in place...)

5-90

I have a Haynes manual - it's saved me having to cut a new leg for my workbench for the last several years (it's only actual utility to me.)

Get a Chilton's, until you can find/spring for an FSM.