Hmm now what (A Rebore!)



  • Riding home from work I had a pedestrian do a lemming impression causing me to lock up my rear. Not the first time, but as this happened I heard a metal clattering sound followed instantly by reduced power and engine note change. Keeping the revs up to 4 or 5k at idle I managed to get home, but as expected once I allowed it to idle on its own, it died on me and wouldn't restart. Thinking oil pump, top end, possibly water pump, anyone had a similar experience that might point me where to look?

    Guess I'll be back in the car tomorrow 🙄



  • How odd.

    I suspect the emergency stop and the engine are unrelated.

    But as you mention it and think it's of relevance. The only thing that springs to mind is something has failed on the clutch. Since if you didn't pull the clutch in and went for an abrasive stop, the engine will still want to turn the wheel over, but you apply the brakes stop that happening, so the clutch should slip to compensate.

    But that sounds far fetch to me.

    Be a good place to start though, whip the clutch cover off and investigate.



  • Yeah, once I've a chance to look at it in daylight, I'll pop covers and check the plug and see what gives.



  • To rub it in my replacement swing arm chain guide turned up, so I stuck that on quickly and gave it a kick while it was out there. It didnt start but just from the feel of the kick I'd say its lacking in compression and dont feel smooth. It had a little backfire strangley too, hmm, Right now I'm thinking top end



  • @Pablo13 Worst case scenario, these bikes are a doddle to work on. So don't panic.



  • To be honest it may be top end, or even bottom end. because with a 'lock up' of the engine the engine gets ALOT of stress, just like a heat seazure. actually the same stress from heat seazures on the crank and bearings. and not @Calum , the clutch doesn't do sh*t under hard breaking or even heat seazure.
    i've seen a dt125r seizing at about 140km/h, and even with grippy tyres(Pilot Street) the clutch didnt budge, he reacted quick and pulled in the clutch, saving him from eating asphalt, if you think correctly an emergency stop without clutch is a seizure the other way around. this can still break your piston, bearings, conrods etc.



  • @DanRacing Yeah I think its a bit odd that applying the brakes would damage the engine. Sounds a bit far fetched to me.

    But it's easier and cheaper to whip the clutch cover off than it is to take the top end off.



  • @Calum alt text

    😢

    Still not stripped, but my best guess is a snapped ring right now. That is what you get for forgetting to pull the clutch in I guess.



  • @Pablo13 Not at all mate.

    The bike would have been tested heavily to slam the brakes on without engine failure.

    Something would have gone eventually.

    Either engine was due an overhaul, or it wasn't built within tolerance, or any number of reasons.

    You applying the brakes should not have killed the engine, that would be a shit design.



  • Little off topic, what compression in bars should a healthy dt125 have?



  • @Irongamer727 The manual indicates 6.8 😉



  • @Calum does he maybe mean he engine braked?



  • @declan Two strokes don't really engine brake though.



  • Oooo err, its a bit of a mess in there, hang on....



  • https://farm5.staticflickr.com/4829/32868499598_e399f7de9c_z.jpg

    alt text

    alt text

    Piston is shagged, looks like something has got in or been in there for a while bouncing about, plus det marks, there is even a low spot on the crown from det. The Head I'm most concerned with hopefully it will tidy up. The bore isnt too sad at all, a light rebore should do it, new piston and see what happens lets hope 🙂



  • @Pablo13 Yep that looks well fooked for-sure. I would also check the bottom end for any loose fragments floating about, just to be sure. Get one of these and give it a couple of swirls to pick up any debris floating around. 😉

    https://www.ebay.co.uk/itm/New-Flexible-Magnetic-Pick-Up-Long-Reach-Strong-Magnet-Grabber-Stick-w-Light-UK/113535422657?hash=item1a6f3d10c1ⓂmUSgt17pTEhDHzy-QODYJNQ:rk:33🇵🇫0



  • @NINJA I'll have a little fishing session with some magnets and see if I can find anything left behind.



  • @Pablo13 I would be surprised if the heavy braking incident caused all that damage, by the looks of it your engine was in decline and had suffered some internal damage most likely from detonation, over an extended period of time. The incident was just the tip of the iceberg and the straw the finally broke the camel's back. You were dead lucky the engine maintained power and you were still able to ride her home. Sadly the price we all have to pay from owning a used bike and not knowing the true history of our pride n' joy.



  • @NINJA Yeah I agree. She is a French import, although it was the runt of the litter so to speak, and had expected stuff to go wrong and I guess the mileage is about right for a top end. Just surprised that any plugs I pulled looked fine and it always started first or second kick right up until that incident.

    I've run it on super while I've had it, so I guess it must have had some crap French fuel a while back and just managed to hold it together pootling about French lanes until I got my hands on it 😀

    On the upside this may well go to explaining why it wasn't too happy revving over 9k, so if it solves that issue at the same time, I'll be happy. 0.5mm oversize piston, small end and gaskets have been ordered today and the bore and head are at the machinists. Hoping for a quick turnaround 😬



  • Hard to tell in the pic but looks like the gudgeon pin circlip is missing? Unless you took it out before pic.


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