The Big One Exhaust system fitting

  • Hi,
    New to the forum, I'm just referbing my 1992 dt125r and I have to replace the exhaust system. I've bought the above system and beginning to wish I hadn't. Has anyone fitted one of these and if so how did you seal the manifold and centre joints.

  • The big one pipe often gets slated by many users. So find that the dt will just refuse to rev as hard. Unlike the dep systems. What you gain in the mid range is said to be good, but the loss in over rev is disappointing. Never heard anything about lack of fitment though.

    I just sold my dep system and have got a hand made underslung. Well I've had it for two years and never had the chance to fit it.

  • The manifold should be sealed by an exhaust gasket that sits inside the exhaust port. They can be had for a few pennies off ebay.

    The center join you can buy rubber seals that sits over the top of the join. I went through so many of these its unreal.

  • Hi Calum, thanks for the info.
    I'm not too worried about the mid connection, I can use silicon rubber pipe for that. It's the manifold end I'm more concerned about. A chrome plated manifold came with the exhaust which obviously screws onto the exhaust outlet, no problem sealing that with a standard gasket. But the exhaust simply slides over that and is held with a couple of springs. Not a good seal at all.


  • To be honest, that's how 90% of performance bikes do it, YZ 125, Aprilia RS125 etc etc. I'm going to look into why this is the case as another member has literally just asked this question and for the life of me I don't know why?

    It must have something to do with the way the pressure wave is created and reflected back...but this one literally has me stumped.

    Check this space I will find out

  • A quick scour just says ease of maintenance and the fact that two strokes incur serious amounts of vibration which can undo nuts but the springs.

    By the sounds of things, loosing exhaust pressure through there isn't much of an issue.

  • Hi Calum,
    Might be ok for a bike going round a track a few times. But for a bike that's used everyday could be detrimental. I've read that it is crucial that the system is sealed as it greatly affects Carburaton, not to mention all the burnt oil etc. That will spread all over the engine. I think I will be returning the pipe and paying over the odds for a genuine pipe. Not risking damaging a perfectly good engine for a cheap bit of tat. I was told it was a direct replacement which it clearly is not.

  • It won't damage the engine in any way shape or form. The pipe will still cause an influx of fresh mixture. As for leaking unburnt oil, I know my Aprilia, road going bike, used to drip a little oil, but nothing excessive, and that thi nag was savage.

    By no means will it damage the engine.

  • Sorry Calum, but if you do a search on Google for leaky 2 stroke exhausts, you will find that a leaky exhaust will seriously damage a 2 stroke engine.
    I'm not going to risk it. Yamaha exhausts are welded for a reason.


  • Nah mate, absolutely not. Not sure where you read that. But that's utter rubbish.

    The two stroke expansion chamber causes lost charge to be forced into the combustion chamber. So yes, no pipe will result in the engine running lean, it'll also cause a loss in performance and the engine won't rev as freely, causing less fuel/air to combust therefore cancelling out the fact the engine would now run lean.

    Yes, the engine would run lean from NO expansion chamber.

    But a leaky one, nah, no effect on damaging the engine at all. All motox bikes run this setup. Lots of road bikes run it too.

    It will not destroy the engine mate I guarantee it!

    Not sure where you read that.

  • Yamaha also run spring loaded exhaust pipes on their factory mx bikes. So idea where you read that from.

    Fair enough getting rid of the pipe because it's not what you want, but don't let people tell you it'll damage the engine, because it won't. My exhausts have always been blowing, years, and years!