1980 Austin Princess mild custom - 1951 Lanchester LD10

Took the Princess to the local trusted exhaust place and the one guy there that knows his old stuff had a look. The conversation was mostly "You're on your own with that one!", which was entirely fair. Basically, the problems we're having getting it to seal is normal for this kind of exhaust and if it's a poor quality exhaust to begin with, my experience of it blowing eventually is also normal. This is from someone that has fettled with BL exhausts since they were much newer than mine is and still fettles with exhausts now for a living. His advice was not to waste the cash on getting them to try and seal the exhaust as they'd be likely to have the same success/failure rate as us anyway and it'll probably blow again soon after forking out to have it fixed. I appreciate honesty like that, rather than being messed about, and it was reassuring to know that it is actually genuinely a problematic set up rather than us being inept.

We were given some tips on fitting, at least. So far, we've done mostly everything right but actually getting the manifold-to-downpipe join sitting as snug as possible before sealant and clamps is the most important bit. That might sound a bit daft, but given the design it's easy to think you've got it lined up perfectly when it's actually just a bit off, which in turn can cause the issues I've been having.

So, disconnect the blowing join, clean it up, make the flange as perfect as possible and wiggle everything about until it's lined up as close to perfect as possible without the clamps. Then use some paste, tighten the clamps and get the rest of the exhaust secure. It should then seal, or at the worst only blow a tiny little bit.

Ideally, replacing the cast manifold with a suitable custom one-piece banana bunch that goes into a good flexi joint and on into the rest of the system is the best solution. Unfortunately for me, a custom exhaust is out of my budget currently so we just have to do the best with what we've got and do the exhaust when I can afford it.

Sometimes it’s worth dismantling the next joint, and dropping the rear part out of the way, so you can concentrate on getting the downpipe/manifold flange exactly right without the other end being held rigid. Once you’ve got the front joint on square, tight and leak free you can force the rear part of the pipe into place to suit the next section.

We used a different approach with the reoccurring ones by chopping 150mm out of the downpipe just above the exhaust bend at the base of the bulkhead / floor pan and then sleeved it with a length of steel flex exhaust which was brazed on at each end - this would give the flexibility to the downpipe to obtain the correct fit and continue to offer flexibility throughout the use of the vehicle - no matter how good the engine mountings were you will always get some torque reaction / rotation with the BLMC transverse engine range has the clutch is released and the wheels / tyres transfer the grip to the road surface - I think on some models this flex joint in the exhaust was original equipment (certainly was on my late stepfathers Wolseley 6)

I had a similar issue with one of my many Minis back in the 90s. The downpipe to manifold would not seal no matter what was done to it. I swapped the manifold for an identical one from my mate's garage and the problem was solved. Sometimes there's just a tiny problem that you can't see. It doesn't help that it's such a god-awful design. If you have a spare manifold then try that. It can't be any worse. 

Hope you get it sorted. 

Good idea but it's not that simple the manifold & the downpipe have external flanges that mate with each other and are then retained by a clamp - some models had a sealing ring between the two flanges and then the clamp - hence its not your normal flat face's that you are sealing a gasket against

When cash is more free flowing, custom exhaust is what I'm doing. Today I have learned my exhaust is very much not fit for purpose.

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Exhaust then I suppose today. Drive over in the Princess as normal, nothing amiss beyond the exhaust noise and I find the throttle getting gradually stiffer until I'm approaching lights and suddenly the throttle jams completely. Fortunately I was next to a bus stop so could throw the car into neutral to stop it running away and turn it off to coast to a stop. Hazards on, bonnet up, have a look. Somehow, it was earthing through the throttle cable again even though all systems were normal. I had noticed a dip in the ammeter with the headlights on, much the same as yesterday, but it was stable so just assumed the battery was a little low from lack of use. I let everything cool down and the throttle returned to normal, I then carried on to the unit with the headlights off, which I don't like doing on a drizzly day, but it was less than a mile of the journey to go and nothing untoward happened.

Wasn't particularly thrilled about this so the first job was to investigate the earth issue and we thought we'd resolved it when we noticed the headlight earth point was a bit dirty. Made a brand new earth point which improved matters, but after a while the throttle cable started to warm up again if the headlights were on (and only the headlights), so I need to find out what's going on with that. At the moment the earth points check out fine and there's nothing obvious, all I can say for certain is that something on the headlight circuit isn't routing electricity as it should and further investigation is required.

Exhaust next then, since I didn't want to chase electricals until that was sorted. Air filter box, carburettor and heat shield off first for access. I never disconnect the cables going to the carburettor because the end of the cables always fray and I can never get them back in again, so I always make use of the flat bits of the engine bay to keep the carburettor out of the way and still connected. Unconventional, perhaps, but saves me the expense and hassle of fitting a new pair of cables every time the carburettor comes off... which has been a lot lately.
20180219-01 by Angyl Roper, on Flickr

Mike and I wanted to make the exhaust components that were leaking as clean as possible so we opted to remove the manifold rather than dropping the exhaust this time. This was also a consideration after folks on my various threads suggested the manifold casting can have flaws that cause issues with sealing, so we could deal with that too if it turned out to be the case. The exhaust downpipe flanges didn't look too bad, with the exception of some exhaust paste to remove of course, so that was something.
20180219-02 by Angyl Roper, on Flickr

20180219-03 by Angyl Roper, on Flickr

With everything cleaned up, which took forever, we aligned the manifold to the downpipes and immediately a problem became apparent. We moved things around a fair bit to double check and played with the clamps and dry fitting to be sure, but it looks like one of the downpipes is at the wrong angle and if you bent it to be at the correct angle, it wouldn't sit in the correct place to meet the manifold. This is probably the root cause of the exhaust blow and only a replacement exhaust is going to solve that. I was therefore okay to accept the exhaust will blow when reassembled, I cannot do anything about this at the moment.
20180219-04 by Angyl Roper, on Flickr

After fiddling about with the clamps and the jack and the exhaust, we got a better fit than the above photograph by sort of wiggling the manifold down onto the pipe with me bracing various pieces while Mike got the clamp tightened up with a little exhaust paste. Then the chore of refitting the manifold while it was attached to the exhaust, which is about as difficult as you can imagine since it goes on with bolts rather than sitting on studs and there's a gasket to fit at the same time, so you need about 6 hands attached to two arms. It was like playing Twister, just a whole lot less fun. With it all bolted up the extras were reattached so the car could be started and here's an idea of the access available to you if you don't remove everything first.
20180219-05 by Angyl Roper, on Flickr

20180219-06 by Angyl Roper, on Flickr

The end result, on starting the car up, was that the driver's side clamp has sealed perfectly. The passenger side one has a little bit of a blow, it's tolerable and should go through an MoT at least and will likely quieten down a bit once the car has been through a few hot/cold cycles. Partial success at least. Annoyingly the carburettor then decided it was just going to pour fuel out of the overflow while idling and didn't want to respond to any sort of attention and the headlights are still trying to earth through the throttle cable.

So the Princess has been left in the sin bin at the unit for a bit to think about what its done while I try and find the next bit of free time to go through the electrical issues with Mike. Carburettor is probably just a stuck inside component, low oil in the dashpot or simply because SU. I hate problems like these because they take ages to find and sometimes, even worse, mysteriously fix themselves.

My first port of call, once I figured out what it was doing, was to check the main earth strap and it's fully secure at all points and perfectly fine with no sign of damage, heat or sparks when you start the car, nothing is loose. It's a very odd fault and I'm expecting it to be something weird like I was getting when the original cigarette lighter had got loose and was shorting out causing weird lights issues.

It could be related to the duff bulbs in the dashboard so that's going to be the first port of call. It's odd that it would do this today, but not the last time I took the car out.

It doesn't really have an inside, it's one of those flat braided types. Apart from seeing if it's hot or frayed, I'm not really sure what you'd check on that sort. A second earth strap I can do, I have a couple of spare cable-type ones which might be better?

Why didn't we think of that? That's a brilliant idea for fault finding!