Westfield Megabusa Build Diary

21 Feb 2008
Exhaust mounting and throttle bodies

We put the manifold back on the engine tonight ready for exhaust mounting. There are some studs provided with the kit, but the bike breaker kindly sent me the manifold bolts with my engine, so I thought I may as well use them instead as they are 800 miles old (like the rest of the engine). A couple were very tight and I had to cut down an Allen key to gain access, but it went in ok.

The exhaust is supposed to fit over the manifold with a sliding joint, but it will go no further than 35mm down the shaft. Even with loads of WD40, it still refuses to move any further down, and the tail pipe is hitting the rear arch so it MUST go on further. We take it off to examine...

There is an inner heat weld inside the silencer exactly 35mm down the shaft, so we take a Dremel to it and try to smooth it out. It makes a bit of a difference, but in the end brute force wins and the exhaust mounts up nicely.

It's about 1cm away from the body, so under a small amount of tension when pushed tight to the mounting point. This is probably a good thing though as it will prevent vibration.

The exhaust mounting is not documented, so I checked with Westfield first, and the steps are here.

You need to use a bracket very similar to what the reverse box lever fixes to. Mark and drill this in the correct location for the exhaust, but make sure you only drill through the body and not the aluminium panel. Now you need 2 M6 bolts about 25mm in length to secure the bracket to the body. If you remove the rear wheel you can actually fit your hand between the bodywork and the alluminium panel, where you can place a washer and a nut on each bolt to secure the bracket.

Now you mount the exhaust bobbin. I had been wondering what this thing was used for since day 1, and now I know! Secure this to the bracket from underneath. You can now re-fit the exhaust and the other end of the bobbin will poke through the exhaust bracket, so just bolt it down using a washer and a nut. It looks very nice indeed.

Before I went to bed I fitted the throttle bodies to the engine. They had been in a bag since I sent the fuel rail off to Westfield with the ECU loom (some 2 months ago) and I'm bored of waiting for it, so I fitted the throttle bodies without the complete rail.


Exhaust mounting bracket fitted. You can secure the bolts behind the panel by removing the rear wheel and squeezing your hand(and a spanner) in the gap between the body panel and the aluminium panel. Exhaust bobbin fitted to exhaust mounting bracket. Exhaust silencer secured nicely onto the bracket. Looks really nice.
Throttle bodies fitted to engine. Still needs a lot of work though.