Tuesday, January 26, 2016

Exhaust Fabrication on the GSX750 Cafe - Part 1.

It's simple.
All I need to do is make a basic two-into-one link pipe to join the downpipes/headers to the reverse-cone mega's. The headers are made of mild steel (possible GS1000) and, in my wisdom, I decided to make the link pipe out of stainless. 

Because it'll look awesome!

The first thing that struck me was how hard it is to fit all that into the space I had left. Ideally, the collector would have collected a little closer to the front of the bike, but I'll work with what I bought on eBay (for the right money). 

The pipes arrived painted in some sort of grey, but rubbing it back slightly with 400 grit wet & dry had them looking great. Not bare metal, but more rough and ready, hmm... well I like  them.

The outlet was 3" in diameter, ok for a single can/silencer, but way over the top for twin pipes. So first job was to shorten the outlet and put in a reducer to bring it down to 2.5". A quick visit to Bernie at Hinterland Car Care and he put a nice taper on a piece of 2.5" pipe to fit straight onto my pipes. Top man!

I painted the stubs at the top in heat resistant black to match the cylinder head, and gave the rest of the pipes another rub down to get the required colour.

 The merge collector wasn't the prettiest job I've ever seen with big lumps of weld everywhere. I gave it a bit of a clean up with small grinding wheels to take the worst off.

 Now she'll breathe. 

So the idea is to have a slip-on, spring-loaded joint to hold the link pipe to the headers, and normal clamp arrangement where they meet the silencers. Of course, anything could happen yet. 

Making a merge collector, two-into-one, blah blah.
First effort this. Looked at a vid on YouTube which made it look very easy indeed. They had a bandsaw, chop-saw, sanders and I thought this will be a piece of piss with a hacksaw, angle grinder and file. But stainless steel is bastard hard! 
I have an adjustable pipe cutter which goes through mild steel like butter, on stainless you almost break your hand trying to grip it tight enough! It springs shut while you hacksaw it too, not as easy as I first thought but hey, I'm halfway through so I'll battle on.

Take a 180° 1.5" diameter stainless bend and cut at the correct angle. In my case, I guessed this bit. You get halfway through the tube like this and it tightens on the blade until it jams solid.

Once you have a couple of slash cuts, you can join them together as per. The  closer and neater you can get these parts, the better for a nice looking weld. I, however, am still practising this technique.

Meh! It's weld Jim, but not as we know it.

Then we cut the top off to leave a nice oval. A good time to fuse the inside of the join too.

I'm quite pleased with the way it looks (but I'm easily pleased), and it's very unrestrictive. Look out Mr Akrapovic.

Next comes the 2.5" collector.

The pipes cut down and there isn't much room under the bike. In fact it will have to be a lot shorter. Apologies for the poor quality pic (I think the camera came out in sympathy over the welding).

I now needed a collar to slip over the 2.5" diameter pipe from the headers. I was going to take it back to the exhaust shop and have a piece expanded, but then I just decided to make it from a piece of 3" diameter pipe. 

I cut a short 1" section off the pipe, cut through it and wrapped it around the 2.5" outlet from the headers. (Keeping up?)

I then cut the excess off and welded it up. With a bit of filing, grinding and sanding, it was sliding onto the pipe no worries. Finally, a few tacks and I welded my new sleeve onto the collector. 

Ended up with this. Needs a bit more manipulation to slide easily onto the headers but we're getting somewhere. The weld is so much better when you're joining two pieces of the same material. 

 Next job will be the bends up to the mega's. Keep tuned, I'll be back.