Exhaust Flap Update

Editor Bob Mack

Why are we interested in this subject? The sticking exhaust flap, particularly on twins seems to have been with us since they were first introduced on some of the range.

There’s some uncertainty about its actual purpose and whether it matters if it sticks wide open. Two things we do know for certain are that:-

  • If it’s on a more recent model a warning appears on the dashboard.
  • If it’s out of warranty there is a huge cost to replace the exhaust system.

Geoff Clough’s RT had a sticking valve so between us we decided to take a look to see if something simple could be done to unstick it.

It was relatively quite easy, to free it off and lube the moving parts. Geoff did a talk, with pictures, about it during a recent Zoom social. Our feeling was that it wasn’t a permanent solution and we didn’t fully understand why it sticks.

We decided  that it would be helpful to find a scrapped, seized valve, try and free the mechanism as we did with Geoff’s and then may pull it apart to better understand why it seized up and how to prevent it from happening again.

Steve Moxey spoke to Barnstormers and they kindly gave us a scrap valve.

After treatment with solvents, diesel, and lube it was really free and sprung back very easily except from the fully closed position where it would sick.

It seemed that we had gone as far as we could with applying potions but still didn’t understand why it stuck in the first place, or in one position and why some do and some don’t.

At this point I started to take it apart and made a discovery which may provide the answer to our questions. More of that to come soon.


Author: bobmack70

1 thought on “Exhaust Flap Update

  1. I was told after my last service (Bahnstormer) of my RT that the exhaust valve was only 37% open. They said that they were not allowed to repair it but could replace it for £1200 as it was attached to the catalytic converter and down pipes. The service guy said he was not supposed to tell me but people usually wire them open if this happens as it makes no difference to the performance. I took the the bike to Vtec motorcycles in Postcombe run by my old friend Dave Hawkes who has been a motorcycle mechanic for as long as I can remember. It took him about 20 minute to free it of using various potions and working it manually. He also told me that wiring it open would have an effect on low speed torque due to the lack of back pressure. He charged me £20. It’s been fine ever since . He also told me that many more bikes have exhaust valves these days due to European noise and emission requirements, but on all but the BMW you can replace the valve quite easily as it’s a separate unit . He regarded the BMW arrangement as a design fault.
    Frank Butler

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