Exhaust sealing

[tws7501968]

My new toy had the infamous cracked manifold.
So, having had it bronze welded eventually (some favours take ages) set about refitting it and it's new gasket.
And it sounded ten times worse than it did before.
Convinced it was the downpipe join, added a little fire putty and tried again. No change.
Stripped, cleaned and smothered in fire putty. No change.
Did same to manifold and low and behold... it didn't work.
Removed manifold, bought new nuts, and a couple of studs, including the lower left thermostat end one which incidentally can be retapped 19mm deep and a longer stud used instead of helicoiling, providing of course the original isn't too badly stripped.
Then i checked the mating flange for flatness and it is slightly banana shaped but only by about .8mm over its longest length.

Now, as it blows really badly for a minute or so, then purrs nicely until revved, when it barks, thoughts turned to heat expansion that maybe closing any gap.

Which brings my frustrations to two possible solutions. Either get the manifold skimmed if it is indeed too banana shaped, or find another method of sealing.

Google being my friend, it seems manifold gaskets are not the done thing in the states and more of a silicone sealant style application is popular.
Anyone have any experience of these sealants, types, longevity etc. I'm open to any comments, suggestions or recommendations as i'm rapidly becoming a master at manifold fitting and removal.

Simple enough job, yet my swearbox wont take many more goes at it.

Thanks

[Rifleman]

If it was me Baz, I would look at getting it skimmed AND fit the gaskets. I always fit new gaskets after a manifold removal and have never had any problems. Double check also, that the repairer hasn't missed a wee bit that is hard to see. There is no way that it will seal with a banana shaped surface though mate. Go for it.

[Sir-Doris]

I would stay away from using sealing products before the lambda sensor and catalytic converter. Lambdas are notorious for fouling when exhaust paste etc is used before. I would recommend a gasket at the manifold and the manifold/downpipe flange.

[tws7501968]

Following on from this idea, which i've given up on.... i got all new gaskets and tried again.
And guess what, same result.
So after a mild swear and curse session, i bought a manifold from a local engine reconditioner. Clean, crack free and straight.
Swapped it over and i still have the blow!!!!

Now i'm thinking it must be the upper flange of the cat/down pipe as i can't see it, and as i have another one to hand swapping them over shouldn't be much of a job.

But.... the confounded thing is undone and yet i cannot remove it from under the car. Is there some contorted position i need to be in, or do i have to remove part of the chassis to get this thing off? It just doesn't seem to want to come out, no matter which way i pull, push, slide or twist, it's stuck between the chassis and the underbody. Surely it can't be this hard to remove or have i missed something really mind bogglingly obvious?

Hayulp!

[tws7501968]

Rear and centre exhausts on the floor, downpipe still playing chinese puzzle and refuses to come out.
If it was a smaller plaything, thankfully i dont rely on it, it'd be in the skip by now.
Two lwb 2.2s job lot. Offers on a postcard.

[Sir-Doris]

If its the original Catalytic converter with downpipe then the car needs to be raised off the ground, preferably as high as you can get it on axle stands and that allows you to twist it enough to remove it. Ihad the same problem with the original one, aftermarket ones usually use a smaller CAT section and are easier to install. You could also remove the cross member with 4 bolts per side, but be careful as when I removed mine I snapped a couple of the spot welded nuts on the top side which are very difficult to re-weld back in.

[tws7501968]

Thanks Sir D. Think i'll be going for removing the cross member sometime over the weekend. Seems more dismantling than necessary, but if it means less wrestling then i'm all for it. Been a long time since i laid on my back scrabbling under cars of a cold dark night, or any other time, and i'd forgotten just how infuriating and time consuming it can be.

[Drift]

Hmmm not had a Frontera long then

Good luck

[Sir-Doris]

A long handled wire brushing and a liberal coating of wd40/freeze & unlock should make the bolts easier to remove. removing the crossmember is the easiest way to go but after I snapped a couple of bolts I went the wiggle wiggle twist route.

[Drift]

[Sir-Doris]

Dont you like the way I wiggle and twist?

[Drift]

kinda yer

[woodwizzard]

Hmmm, you two have formed that SPECIAL kind of bond, haven't you