Hi Folks, I wonder if the knowledgeable people on this forum can shed some light on a dilemma I've currently got. I replaced the cats on the car and obviously the silencer has been off for this. To give a bit of background: Car developed a misfire, runs REALLY rich on tickover, failed MOT miserably on emissions. Cats proved to be disintegrated, bypass valve stuck open (not wired open, just seized). First thing that triggered the alarm bells was removing the n/s exhaust clamp (silencer/cat flange), the nut became jammed when unscrewing, to such an extent that it would neither re-tighten or further slacken off. The bolt subsequently sheared. Fast forward to re-assembly: Jammed exhaust bypass valve fixed, new HT leads, new cats in place (with new O2 sensors and thermocouples), everything loosely mounted to aid alignment. Offside cat to silencer interface lines up perfectly, both faces parallel, but the n/s cat interface doesn't line up, the faces are at an angle. No amount of rotating the cat will bring the faces parallel. Tracing the problem back, we have found that the manifold (original), where it branches to the bypass tube outlet and the primary cat outlet, is at a different height on both sides of the engine. The n/s is about 10-15cm higher than the o/s. So much so, the clamp for the bypass tube is almost touching the bracing bar which runs across the car. Does anyone have any explanation as to why the left and right manifolds could be so different? I'm sure if the end of the n/s manifold were lower, the cat would line up and the flange would go on without stressing the bolts. Sorry for the long winded post! I'm just not sure if we've missed something obvious, or the manifold is somehow distorted due to heat. Thanks in advance, Richard (Car is a RHD F355 Spider (5.2), Manual)
The seized nut and bolt, that happens a lot. Just replace them. The mis-alignment, that also happens a lot, you just need to loosen the rear flange, knock the flange around back and forth to align the faces, then put the clamp back. There was a recent thread when a know it all member posted that he can do this in 1 hour and accused people of making up facts to justify this to be a harder job than it is. Well, here is proof.
Aligning all of this can be a real bear. The flanges tap off the cats,not sure if you know this as they seem to corrode in place.... I replaced my complete system with all oem parts from the heads to the muffler tips.. Took ages to fiddle and get right before i was happy that it was perfect.. Like 3 hours of loosen this,lift that,adjust this etc... Wanted to make sure the rear bumper to tip was spot on.. There is some room for bumper adjustment also but not a lot..
Thanks for the responses, very much appreciated. I'd done quite a bit of research on the subject, so I already knew the flanges on the cats were meant to slide up and down the cat, to a certain degree. Also got the warnings on how fragile they are..... Didn't stop me breaking one though!! £100 later, with a nice new clamp in place, the o/s one now slides quite freely along the cat. Which coincidentally is the side that lines up nice. The o/s one is very tight and must be subject to the corrosion you mention. I've managed to get it a bit more free now, but it still doesn't slide like the new one. Scared of breaking this one also. Should have bit the bullet and purchased two new clamps. To complete this in one hour is either a miracle or a bit of b/s..! Believe me, I've spent many hours along with my dad trying to get this sorted. I've got replacement nut/bolt for the clamps, but soon as I was tightening you could feel the unnatural resistance, as the clamp tried to take up the misalignment emanating from the manifold. It gives me a better feeling knowing that its not just me who's experienced this! The unnerving thing for me was the difference in position between the left and right manifolds.
I wonder if one of your manifolds might be bent slightly... Are they from a known car that hasnt had a tap in the rear? If they fit the head correctly then its possible one may be bent..I dont recall such a difference side to side in height... Even with all the oem non damaged perfect parts it sure does take more than 1hour... I would expect 3-5 hrs from head to tips.. with bumper on to get it spot on. I replaced all the sealing rings aswell. They do crush a little but nothing like 10-15cm. I found in my case the bypass pipe was the tricky one to fit..
Andy, I think one of them must be bent. I have never posted the details of the car anywhere online. We paid to have it inspected by a very reputable independent prior to purchase (from a dealer) and it showed nothing in the closet. Having said that, a few things have subsequently come to light which I feel should have been spotted at the time. Thats another story. Think I'll try loosening everything off, from the manifold (bypass and cat flanges) back to the silencer flanges and try do some more "manipulating"! If anyone gets the chance to measure from the bracing tube down to one of the manifold flanges, that would be really useful as a datum to reference from.
Remove the clamps Loosen the cat converter nuts bolts at both ends Remove the M8 nuts and bolts holding the flange in place (the flange is the easily broken piece) Spray some WD40 or equivalent into the flange surface Fit the flange such that it fits at the top and there is a gap at the bottom Use a hammer and a punch to "punch" the flange so that it fits closer to the muffler Fit the clamps in place, tighten the clamp down and it will pull the flange the rest of the way. Them tighten the M8 nuts/bolts What you end up with is your flange will not seat perfectly square on the cat, that is ok, it will still seal. The 1 hour comment above refers to when the engine is out. That still leaves a lot of muscling around to get the out-of-geometry pieces to fit.
Yelcab, thanks for the detailed guide. I'll have a go at that. Will try and get some pictures up to illustrate the waffle in my initial post. BTW, Just spotted a typo in that post.... I meant 10-15mm not 10-15cm!!
Ok. Managed to grab a few pictures. The side on view of the manifold was taken prior to the others, not long after we got the car. Apologies if the photos are uploaded incorrectly. They show the general idea. You can see the shots where the gap (manifold flange to bracing tube) is big enough for 2 fingers, on the right hand manifold (o/s) and also the measurement from the x-member down to the bypass tube, big difference left to right. The shot from the rear, showing the silencer was taken to show the slight slope which occurs. This is with the right hand cat flange mated up flush. Soon as you nip up, or try to align the left hand one, the slope is much more noticeable from left to right. I should have posted these with the initial message, as its now just for a bit of clarity on the situation. Hopefully will get chance to run through the sequence kindly provided by Yelcab tomorrow. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Sometimes people have to pry that exhaust up in order to get the drive axle out during a CV joint replacement. The other side axle is quite a bit easier. That action may have bent your exhaust permanently.
