Yeah it's usually a sign of water contamination.

Due to the localised pressurisation of the water pump, it's possible for coolant to leak into the gearbox, without the oil going into the coolant.

@declan no the whole aluminium bit snapped in half

@declan @Irongamer727 thanks mates, will look into that

@irongamer727 well, tap water has minerals in it which will be deposited inside the coolant jackets as time goes. This can affect the cooling. Also iron parts may catch rust as well. You may have to flush your cooling system more frequently compared to using distilled water.

@oldman Any help is amazing bro! will see how it is tomorrow and go over some of this stuff

My wr200cc/dt125r hybrid engine runs with lid cut off. I ran it also with the 125 engine. You just need to jet accordingly.

@ninja As a general rule of thumb, the greater the compression ratio the lower torque spread but the greater the peak power. I don't know the figures, but I'd look to go with a domed head.

All depends why reboring it, if the cylinder measures size you say then never been rebored. The cylinder on your year although called 56mm is actualy 55.95mm, if the cylinder is not damaged then just get it honed. If honing the cylinder then this piston is what you need.
https://www.ebay.co.uk/itm/Yamaha-DTR125-DT125-R-DTR-125-56-25mm-Bore-Namura-Piston-Kit/292513505226?hash=item441b29dfca:g:jyEAAOSwwbdWQwnA

Whatever size piston you buy whoever is reboring it will bore and hone to match what piston you supply. The best reboring is done by Karl at KPM as had them do a
few and also by PJME. Karl charges £30 for a bore and hone with return postage at £10-16 postage depending on courier and insurance required.
He will also fully port your cylinder for £100, just have to tell him what your after like more midrange etc or more mid and topend like a YZ.
http://www.kpmotosolutions.com/

The DT has now undergone a kickstart conversion! Feels so cool!

@sgt-robuck-5 doesn't work like that. Air pushes coolant up in the expansion tank filling it and then spits out on the road. Then returns to normal once cool. Just open the radiator cap and bleed it, problem solved.

@irongamer727 I’d say so yes

Aww cool, it's a belgarda engine.

Italian import, you get mega props for owning one. They have wicked Motori Minerelli Stamps where the original DTR engine doesn't. It's super cool engine.

Slow as balls though. It's just not comparable to the SP.

@calum That’s pretty cool might have ya have a check some day

@irongamer727 The stock Pilot Jet is (25) , My advice is to try (27.5) to support your mods.

Also dont forget about Needle height! Very important aswell

That will also do

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The clutch cover gasket doesn't need to be anything special.

@irongamer727 for what bud?

Right also, don't be so quick to slate Yamaha for using the bolts that they did.

I'm not going into here, you can easily Google that information, but trust me when I say there is a perfectly justifiable reason as to why they used the bolts that they did.

@gilera-sc you have the best of knowledge right here on this forum

Mine slipped with Castrol Magentec. I just use Castrol GTX Semi 5-30w