Pipe dreams

Fitting new exhaust systems to my motorcycles is nothing new to me. I even mix it up a little like what I ended up with on my RC46 but this one was always going to be a bit trickier.

My VFR750 RC25 GH had the standard four into two exhaust which was now mostly made of oxides of metals long since departed and exhaust repair tape.
 I very briefly toyed with the idea of making this into a four into two into one system but thankfully a stainless Motad system for a FJ/K came up on ebay. Looking online told me that nobody was saying this could be done, neither were they saying it couldn't and knowing the engine hadn't changed, I went a head with the idea of fitting it.

The can that the system came with however was too heavy, restrictive, low and on the wrong side. Something would need to be made to sort that out.

Off with her head[ers]

The first job was to get the old system off. This involved lots of heat and penetrating oils. Hammers and swearing also got into the mix but save for two broken studs I ended up with things not looking too terrible.

The cans themselves were in terrible condition. The link pipe between them had rotted through completely and had been rebuilt with exhaust tape, clamps and putty. None of this mattered as the pipe just rotted around it anyway!
The exhaust hanger bolts came out with no fuss and the clamps were cut off the collector boxes but there was no way to separate the pipes without simply cutting them. No great loss there though as there wasn't much material left anyway.

The front down pipes came off with one stud snapping at the manifold and another that had clearly been bodged from a previous removal gone badly wrong as part of the barrel was missing!

The back end is very tricky to get to.

Removal of the rear subframe and shock is a must to get anywhere near the rear pipes. The steel shield that sits between the shock and pipes had become a little more light weight than Honda might have planned for over the years but to its credit it did come out with no fuss at all.
Access still wasn't the best and removal of the swing arm makes the job of getting these pipes out a lot easier. I was taking that off anyway so I didn't mind to much however I'd imagine most would be a touch underwhelmed for a simple exhaust system change.

With basically everything removed from the back of the bike; we can now finally get a good look at the rear headers.

Wasn't it nice of Honda to put long nuts on the studs to make them easier to remove on the rear?
Being well protected, these pipes and studs were in far better condition than the fronts despite the shield having clearly worn out a while ago.

On with the System

The motad system I intended to fit was in sound condition but it had clearly been fitted to someone machine for a while and in doing so had collected a fair amount of grot.
An absolute age was spent with emery cloth, scotch-brite and autosol till the whole system was back to some semblance of shiny.
I didn't bother with the end can aside from a quick shine up and sold the thing on. I had other ideas for the end can!
 The system fits the bike with no real bother so long as you don't want to run front exhaust gaskets or a centre stand. I used copper silicone gasket for the front headers (rears use gaskets just fine) and had to remove the centre stand anyway.

Link pipe

The VFR750 RC24 6x ran a 4 into 2 into 1 left hand exiting pipe that I wanted to replicate.
As this would be my first exhaust fabrication, I clearly wasn't starting with an easy one and to make it more difficult; I couldn't afford to buy a stack of different radius bends so decided to buy a couple of meters of pipe and pie cut the lot.
I'm no fabricator or even welder for that matter so I was massively playing it by ear and learning on the job. The purchase of an Evolution Rage miter disc cutter mad the job a hell of a lot easier, making fairly consistent pie cuts quickly.
I started with two straight pipes with four cuts in one end witch I splaid open to allow them to slip on the two header collector boxes (just about). The longer of the two pipes was placed on the right side to give the spacing I wanted before the first pie cuts were welded on starting flat into the shallowest angle indent on the saw.
For each subsequent pie cut pipe section I would flip the pipe through 180 degrees (as best I could by eye balling it penned lines will be used in the future!) before making the next cut to get that triange appearance, continuing the curve through each section. I could control the length of the curve by changing the length of each section  rather than change the angle which would be much harder to weld.
Each piece was carefully flattened off, lined up on the bike, marked for alignment, taken off the bike to be tacked on, rechecked before welding on fully.










Doing things this way allowed me to clean the pipe from the inside after each stage.
I wasn't back purging my welds so was getting a lot of sugaring inside the pipe which would put a dent in performance.
The down side of doing things this way was that I would need a lot of imagination to get this thing made right and offered no going back if I got it wrong.
Another problem I had to deal with was keeping the sections pressed together whilst tacking or the cooling metal would cause the sections to open up after the first tack was made.

Welding as I went was about to get far too tricky to carry on with once I got to the vertical section of the link pipe.

I had an idea to make the pipe into a loop then cut into it to add a larger pipe which would feed the end can. This would save me fabrication a collection box out of materials I didn't exactly have laying about.
I cut the various sections out and adjusted them till they lined up properly before tacking it all together.
I only had to make one cut and adjust with a final thin "keystone" fitting in nicely at the top which the disc cutter managed without mangling it to my surprise.
As you can see on the left; I part welded some sections on the inside radius as I knew they would be near impossible to do when assembled. I would appreciate this later!

Once I was satisfied, the pipe was taken back to the shed to be welded up.
Welding stainless is tricky compared to BMS as it blows through much quicker. As such it is very important to get your mating faces as close together as possible.
For the most part I worked each area in sections, doing the area I could get to on each weld line before moving the pipe and starting over again.
Some areas where the pipe fit was poor or I had blown through benefited from a low amperage "lay-wire" technique to close the gap before I made a second pass to pretty things up.
The gouch of the bend was the tricky bit which, with a lot of stick out and careful torch angle was finally buttoned up and pretty tidily too. All testament to my R-tech digital tig 170 .

A suitabe lenght of 51mm OD stainless steel was then cut, shaped and profiled by hand to marry up to the  large bend I had made. Once I was happy with a position that would give a good gas flow balance and angle; I marked its location and set it aside.
Next up I took a new 50mm hole saw to the pipe which threw its teeth all over the shed whilst gently tickling the stainless steel it was meant to cut.
The best I had was a 25mm hole saw of substantially better quality. With that hole cut I used a die grinder to expand the hole so the edges just met the edge of the 51mm tube I wanted to weld on.
Whilst I was here I could also take the die grinder to any sugaring inside the pipe to smooth it out for better gas flow.
Once I was happy this was tacked, checked then finally welded in place forever.

This was the linkpipe basically complete but I did have a little problem with fit.
Due to the way I had splaid the end of the pipe, it didn't want to stay on. Using a hydraulic pipe expander was the right answer but I don't have one of those so I used a mechanical one that only really makes the pipe round at best.
This made matters better but even with clamps it would blow off too easily so I decided to weld on some stainless spring tabs.



Matching tabs were welded onto the collector boxes so a spring could be attached on either pipe on the outside.
This would be enough to assist in holding the pipe on yet would be easy enough to remove in the field should I need to get the link pipe off.

End can 

The end can itself is a Kerker can that I picked up in the states for $40 off of an ATV. This is the exact same style of can that the VFR750 6X ran back in 1986 and an absolute bugger to find in the UK.
I was super chuffed to find one so cheap and was lucky enough that one of my racing team mates was heading state side and was willing to bring it back with him.

The can was pretty grotty and took a lot of polishing but it came up well in the end and more excitingly I noticed I could remove, flip and re-rivet the name plate on so it would also be a true left hand can. Perfect!
After an inaugural run I decided the system might be too loud and could require a decibel killer.Before I did that though I thought I should explore a repack first though.
Once I had convinced the can apart with the aid of a large socket and some extension bars (oh and a big hammer)  I found the fibreglass was patchy, old and full of mud and straw!
The old packing was binned and the core was thoroughly cleaned and repainted whilst I waited for some new packing material to arrive from m&p direct.
Their 54x34cm packing was a perfect fit for this silencer which repacked and slipped back together without too much argument.
A thin smear of copper silicone on the end cap was applied to ensure a leak free tip (nobody needs that) and everything was bolted back together with a little thread lock to prevent the short screws from dropping out on me.

 Hanger

I decided not to use a strap on the can as this would spoil the look. The silencer was pretty light and securely fitted on the link pipe anyway.

Instead I used part of an unused pie cut which I shaped into a wide half moon. I drilled an 8mm slot into the widest part of this shape and welded it onto the back of the link pipe to act as a hidden mounting point. I then made a very sturdy aluminium hanger that this would bolt to the link pipe for support and to hold the link pipe off of the swing arm which it seemed to want to lean against.

The result? Well I am very proud. I think it came out okay and I can almost weld now.