Exhaust Pipe Rebuild
Contributed by Mark Read
Editor's note: Just 'click' on any image for a larger version. Mark did an amazing job, and my thanks to him for sharing.
Just starting a project which might interest you. As I'm sure you’re more than aware,JK pipes are getting increasingly rare and unlike the later models do not even have the option of a Delkevic version. Well , I am pretty much stuffed at the moment with my J model as a good rh upper pipe is the last piece in the puzzle to finishing her and have decided to completely disassemble one out of my stock of battered dented old ones then try and rebuild it to as near to perfect as i can get it. The whole pipe will be coming apart, even the sound deadening removed and replaced. As far as i know this hasn’t been done before or at least documented as a “how to” so I thought I would take high-res shots of the whole process from beginning to end with a blow by blow account for future restorers when all other options have dried up. This could also apply to later pipes or even to the unfinished Delkevics they sell, to add the sound deadening before chroming.
Ok, it’s game on then and full steam ahead with this one. I’ll try and cover as many avenues as possible regarding alternate ways of achieving the same result. My main concern is the well known problem of the pipes rotting internally after a rechrome if left standing for a period of time before putting back into commission.I have a few ways around this but need to consult the platers first. This is going to be a short term project as I need to finish it before my main work starts taking off again in the next few months.
I’d been struggling for months trying to suss out how to remove the end cone from the jk pipes when it came to me that you didn’t have to. As the cone is slotted in, and then brazed into the pipe i think it would be nigh on impossible to remove. Instead, when de-seaming the pipe I just continued on and chopped the cone in two. De seaming was a long and arduous job. My weapon of choice was a Dremel using the 0.75 cutting discs and a very steady hand.
A labour of love (they say). To be honest it wasn’t that bad with the thin disc (about three hours). Once you go about a millimetre down , the disc almost kinda finds the sweet spot where the pipe originally got fused together and almost follows it. I cut a thin groove down the length of the seam to be happy, then ran over it again this time about 3 to 4 mm deep and that was enough for the pipe to almost start separating itself. It made me jump a few times, it must be under some kind of tension. I got through a pack of 5 discs on the job. The main reason for using such a fine disc was that I wanted to retain as much of the original seam profile as possible.
Once the top and bottom seams/cones were sliced I attacked the weld which was holding the silencer to the header pipe. As the damage to J/K pipes is invariably to the outer part of the pipe, I deemed that was the part that needed removing so grinded away at that half of the weld and left the inner half of the silencer attached to the header. Also that would eliminate any header/silencer welding alignment issues later on.
I simply started to remove the weld and gently lifting from the cone end after a few mins the whole side seperated.Baffle plates I'm sure you know are attached only to the inner part.
The next few hours was spent scraping 40 years worth of gunge out of both sides. I chose this method as burning out I’m sure would have caused metal distortion as those outer silencers are pretty thin.
The next step was to remove the metal cages containing the sound deadening (asbestos/whatever it is). These again are tacked in so a few mins with a Dremel and they were out. A thin flat blade slid in under the deadening and with a bit of coaxing they came out in one piece.
I took the two sections of pipe + cages to the chromers for them to clean all the 2T residue from the silencers and burnt on stuff in the headers using hot caustic soda (nasty stuff). Once clean and with the old plating removed I’ll have those parts back and then it’s on with dent removal.
OK , bits are back now nice and clean , dents removed. The pictures don’t really do it justice.
Next step is to choose whether to replace the baffling with new or re use the old material. Then re tack the cages back into position. I’m just guessing at it being asbestos, and so I was thinking of just ditching it and replacing with new two stroke baffle packing instead. it’s cheap enough to buy in the sheet. In the end I decided just to renew the sound deadening. Two stroke baffling on a 500x320 sheet was cheap enough and is pretty much the same thickness as the original deadening. Simply cut and trim to fit.
Pipe back together now – 4.5 hours. Not as easy as it looks. Going to try and find some time during the week to dress the welds and tidy a few other areas up. A couple of things to check or be aware of when welding it all back together: once you have it stuck back together, check that the black cone and seal actually still fit right (before, for example, getting it chromed !), and secondly take extra care when you weld by the section where the rear rubber seal fits in as you will come across a small amount of braze that was used originally to hold the end cone in.
The jury is still out on how to proceed next. I could either chrome the pipe as it is, but that will leave the sound deadening saturated with chemicals which I feel is the main cause why pipes fail over here so fast if left for a period of time before being put back into commission. Was thinking of flushing and checking the PH until I can get it to neutral. Saturated a piece of deadening earlier to determine the drying time using various methods. I feel that drying the deadening is a crucial part in this project. Other option is to bung the pipe and chrome. Problem there being the expansion of air if there is no release could cause the bungs to pop out or even distort / buckle the pipe. Not to mention getting an object full of air to stay below the surface. Option three is fill the pipe with water then bung and chrome.
After discussing which method to use with the chromers, they deemed it ok, to just give the pipe a quick bath of a very very mild acid solution. Presumably this was to etch the surface. The pipe was given a severe washing in fresh water afterwards. When I got the pipe back and managed to PH test the cage with the aid of a piece of litmus paper attached to a bent piece of welding wire, there was still a slight acid reading coming off the wet baffling. Bicarb of soda was used to neutralise this.
Pipes came out far better than I could have imagined , although chrome is a pain to photograph. I’ll be PH testing the inside later today and if ok, then coat the inside with a rust preventative. They appear to have got the “where to and where not to” polishing right , just hope the photos show the inside of the pipe and inside of the header with the satin finish.
One additional editor's note:
Something I have noticed is that because the interior baffle plates are only spot welded to the inner pipe skin, if a removeable baffle gets jammed or stuck then these plates are easily damaged. In the photo below you can clearly see how the inner baffle plate marked with the arrow is bent and this will require some additional repair. These plates also (believe it or not) rust out, so plan to also have to fabricate/repair inner baffle plates if you try this yourself.