Yamaha dt125re rebuild

  • So last night after during the match I decided to take the bike for a ride out see how everything was , bike felt great really responsive but loud but exhaust needs sorting

    Come out for work this morning bike fired up felt great work is only 5mile away iv got just round the corner and my red light came on and the bike was steaming pretty bad I coasted it to work and iv lost all my coolant I’m aware this could be down to the head gasket but I’m hoping it may be something else.

    There was pressure in the radiator when I took the cap off and the expansion bottle cap has stayed on any one know what else to check before I order a head gasket ?


  • Her she is looking pretty 🤔

  • @bradt have you bled the system of air?

  • I did but maybe not long enough cannot see where the coolant is coming from it’s just dried all white over the barrel and head

  • @bradt coolant doesent dry I’ve had my fair share of leaks on hot engines and never seen it dry

  • @declan surely any liquid would dry and leave some kind of substance after touching a hot engine. Iv reckon iv found the culprit there a little house what connect to carbs what isn’t fully on and can see it coming from there but the amount iv lost surely hasn’t come from there I’m unsure tired and frustrated and still gotta rude home on it tonight after work!

  • @bradt Be alright, just take a bottle of water with you. Don't open that radiator cap until it's cooled mind you!

  • So iv got back and did a little test on the way,

    So when I’m cruising (not full throttle) the bike fine doesn’t smoke out the exhaust and no steam off the engine, so on a little open bit of road iv throttled the bike started slowing down and there u go smoke and steam

    So seams to me when the pv kicks in I’m loosing coolant any ideas ??

  • @bradt Head gasket failure, happened to me two weeks ago. The water pump is driven off the crank so the higher the engine speed the more water is pumped round the engine and thus the more pressure in the cooling system so the higher the engine speed the more coolant will be lost to the crankcase. Just order a new one as it isn't a problem that will fix itself but rather will leave you stranded when you most need to get home! - I used an Athena head gasket and so far no issues, I think it was around £15.00 off ebay. It's pretty straightforward job, you'll need to check that the head isn't warped before reassembly by putting it on a known flat surface i.e a glass table or a granite work top and if you can rock it side to side, then it is warped. If it's warped you'll need to have it skimmed before reassembly - you can do this yourself or have someone do it for you.

  • Wasn’t that long ago I head the skimmed and new gasket carnt see any visible leakage from bottom of the head top of barrel, I can see the odd drip coming from the hose where it connect to the head from the radiator.

    But will be replacing the head gasket anyways done it plenty of times so it’s an easy enough job

    But thanks for reply mate

  • @bradt You won't be able to see any visible leakage as it will be leaking internally - the coolant will be draining into the combustion chamber

  • I'd say head gasket. Can only use Athena or genuine head gasket on these engines. Other copies fail.

  • Iv only ever used Athena gasket for my rebuilds

    Iv emailed pjme for a quote on rebore re skim and new piston to fit just in case the worse

    Going to re do the gasket over weekend and see how things go

  • Hi does anyone know what size the studs should be for the exhaust ?

    Sitting on the bike , the right hand stud / bolt the threads are stripped does anyone know what size it should be because at the minute I’m only getting a m14 to fit but the other side is a m12

    Does anyone know how deep how wide it should be thanks ?

  • M8 on my bike lol. When you say M12 or M14 do you mean the spanner size?

  • Yeah M8 on mine too, my last cylinder had one M8 and the other drilled and tapped to M10, I'm guessing these alloy threads are easy to strip.

  • I’m taking it round to me mates tomorrow he’s gunna tap and thread it properly while I change the head gaskets

  • So today I got the head gasket sorted head not warped lucky enough got it all back together and back home for a wash and wax when the weather cooled down.


    Now wanting to change the white out to back so as the months go by I’ll be changing a lot more going for a stealthy look withs Yamaha blue.

    Will keep more pictures uploaded 👍🏻

  • Looking really smart mate!

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