Piping Hot !

I need a set of exhaust pipes for the current project (see this link) and NOS or excellent condition ones are not easy to find for the 1972/1973 model Suzuki GT750’s. Mark Read did a very nice write-up on how to rebuild the original pipes, which he graciously allowed me to post on my web site at this link. However, I am not as skilled as he is, so I wanted to look at other options. Delkevic makes reproduction pipes for the later 1975 through 1977 models which will also fit the 1974 model year. I have discussed with Skid Brown of the UK Kettle Club about whether Delkevic were likely to come out with a set of reproduction pipes for the early models and that answer appears to be a ‘no’ at the moment. I actually have a spare set of brand new, still in the box Delkevic pipes, so I thought I’d look at how to modify them to suit the 1972.

I knew that the rear pipe hanger location of the early frames was in the wrong place for the later pipe hangers, but had assumed that dimensionally the later and early style pipes would be close enough that I’d be able to  perhaps just swap the end caps, fake some cross coupler pipes (or not – I’m not actually a fan of them), and fabricate a new rear hanger mount. You know what they say about assumptions. 🙂

The first step was to hang a spare new style pipe and an old style pipe on the project and check a few measurements. As expected, the new style pipe hanger was about an inch back from the J style frame hanger position (there is a photo somewhere nearby showing this). Not I problem I thought – I could make a new hanger bracket of some sort and that would work. That is when it got interesting.

Photo by Ross Thompson

The old style pipes have an end can that a black metal cone fits onto. These end cans are  held in place in the end of the pipe shell with a single spot weld on the inside of the pipe, and then the rest of the can is silver soldered in place. The silver solder can be removed by heating the end of the exhaust pipe, and using compressed air to (very carefully !) blow out the molten solder. However there is a small snag.

The new style pipes are both longer, and also not the same outside diameter at the ends as the old style exhaust pipes ! In fact, the new style pipes are about 3mm larger in diameter at the end (98mm vs 95mm). What this means is that if the end can is mounted into the newer style pipe, when the black cone is fitted it looks terrible, and as the black cones are such a key design element of the 1972 and 1973 model machines, I was not prepared to do without them.

There are other issues as well. The indents for the centre and side stand barely line up, plus there is the question about what to do with the cross couplers. The new style pipes are a different radius, sitting tighter to the front of the engine and frame, so there isn’t room to clear the frame at the front of the engine if dummy cross couplers are added. I could live without the cross couplers, but the alignment of the indents for the centre and side stands is more of a problem.

The bottom line for me was that while not impossible, it all just seemed like a lot of work and cost for something that would still not be as per the original. So I’ve given up on the idea of converting a new set of pipes to look like old ones for the moment, and have decided to have an old bashed up set of pipes repaired by ace metal worker Ross over in Ailsa Craig here in Ontario. That way, they will fit, and also look correct. I do not plan to have functional cross couplers: these will be plugged off as getting them to seal so they don’t drip oil all over the place is just such a pain. The slight loss in torque is not something I’m concerned about.

As I needed some spare internal baffles and also end caps as parts for the pipes Ross is working on, I took some time to cut open a few old pipes that were beyond salvaging just to see what the internal differences were.

When you compare the new style pipe in the centre of the nearby photo with a sectioned J/K pipe above and below it, the differences are pronounced. The late model pipe has much bigger, better designed more rigid internal baffle plates, and actually has one more plate than the J/K style. And I was surprised to see that at least this specific pipe was spot welded on the outside as well as on the backside on the last (closest to engine) baffle. You can see the location of the spot welds in the photo (just click on any of the photos to see a larger image). Another difference is that while both pipes have sound deadening mesh overlaying glass fibre wadding installed, the J/K pipe has more.  You can also see why it is they are so hard to get clean for re-chroming as that wadding holds a lot of oil. That wadding also will hold acid, and as Mark points out in his article on my web site, that will ultimately lead to accelerated corrosion rates unless the acid is carefully neutralised after re-chroming. And I’m not 100% sure if all the late model pipes have the extra outboard spot welds. I did a close examination of a few other late model pipes and while on some they are evident, that isn’t true for all. This is possibly just due to variances in the quality control on the finish, or perhaps they are added for the later A and B models. I do know that I’m not going to continue to cut pipes open to see ! 🙂

At any rate – sometime in the next three or four months I will have a ‘just like new’ set of pipes for the project. All I have to do now is get everything else ready so that the pipes become the ‘final’ touch !