DT125R FORUM

PS Same issue, bottom of gasket is dry and the top has oily wet channels…

Have you lowered the coolant level in the expansion tank to the centre marking.

Also try measuring the head stud length that is protruding. Then again between the barrel top and washer with the dome nuts screwed down.

I’ve got the same problem with gaskets blowing. In my case it’s getting sucked into the chamber causing white - grey smoke.
Trouble is i don’t trust the local mom&pop engineer firms. The last job was a re honing shit show.
PJME skim heads?

dont buy from ebay. buy from pjme.
the bearings shouldnt of failed. were you running it in or caning it? did you make sure only to use the outer edge of the bearing to drift it in? if you pressed against the centre race it could of distorted, even dented the balls giving it a very knoychy feel...

I’d clean the carb. Also post info about the colour of the spark plug…

Can anyone please chuck me some links for replacement front wheel bolt clamps?
I seem to remember a titanium one?…

Cheers
Richy

Less is more then cheers guys. It’s the reason I used hylomar red before, it’s easy to apply thin and evenly…
I’ll get out the black mechanic gloves and dab on some RTV…

I’ve never used silicone RTV to seal the cases before. What is the best way to apply it? Should I use a bead (if so what size) or dab it on lightly and evenly by hand (with gloves)
I proper worry about the excess beading out into the crank case and gearbox. I’ve taken one apart that was awful…

Any advice is appreciated

Yeah, a closed void would be subject to repeated heating and cooling stress. It’s also really handy for helping get the cases split
I remember that I crapped myself when I first found it. I covered it with sealant

@Michaelashbrook

Doesn’t matter which side they go, as long as they run through.
Is that what you were asking?…

fitted the new base gasket, the old one was soggy and leaking under the exhaust manifold into the barrel. Still pushing out white smoke! i went back on some of my threads from 18 months ago when i built the bottom end and found out that i'd used hermatite red instead of silicone RTV to seal the crank casings. I think it's failedwhere the coolant flows from the barrel to the block.
I'm gonna have to split the casings and use proper RTV...
At least i kno2w why it was running hot. Also learned not to use mismatched casings. Mr Yamaha obviously used different castings for various iterations...

tzr pipe?

No body know when 4BL,s were about?

@mbmO8

Head’s still leaking bud. It’s probably best to replace the base/barrel gasket as well.
Myself, I remove the studs from the barrel an lap the top in with a square of plate glass and some 240-ish wet and dry sand paper. Then do the same with the cylinder head. Just to remove the crap.
Doing up the head nuts really needs a little 1/4 in drive torque wrench to get it right. I do it in three stages…

I know that it’s no consolation but I’ve just had to put a newly rebored barrel and head on and had to go through all the fuxin hassle of it myself 🫤 …

It’s starting with JYA4BL

I don’t know if it’s a Dtr or a DtrE

Ta!…

@mbmO8
Sorry for late reply.

It’s since you did the top end build I’m thinking about, not before.
It can take a while for sludge to build up.

Is it loosing coolant from the radiator? Check the level …

Have you checked the thermostat?
Is the coolant in the radiator staying at the same level, or are you constantly topping it up?
The only reason for the expansion tank to be full and overflowing is if the head gasket has blown and is pressuring the coolant system, which results in loss of coolant through the expansion tank.

P.S. yes the expansion tank is connected to that part of the frame by a small rubber tube. it lives up behind the side panel above the rear wheel. there's a min & max level about halfway up the tank. Check it out to see if it's full to the top...

Any decent fan kits to mount to the radiator? Adjustable thermo activated switch, shrouded to pull air through from the rear of the radiator?…

I’ve got some work to do first, there was oil scum in the radiator and I guess all the way through the thermostat, pump and system. (I’m wondering if the stat is all gummed up) The pump rotor and seals were replaced when I rebuilt the bottom end…

It’s not the head gasket blowing though, it’s not pushing coolant into the expansion tank or noticeably lowering the level in the radiator.
I had problems with a slight step in the casings at the rear of the barrel which I thought I had fixed. There’s a ‘wet line’ between the barrel and inlet manifold that seems to support my theory.

I’m waiting on a new genuine base gasket, thermostat and some Loctite VHT copper RTV sealant, as well as the thermostat and gasket…

@Calum

It’s a shame that they’re shite, because I think the radiator is the main problem. If it was the thermostat I’d of thought that it would overheat from the start, but it keeps cool enough for a while depending on how hot it is and how slow I’m going (less air flow over the radiator). The radiator is well hot to the touch!

I’m waiting on a new stat and gasket from PJME and I’m going to flush the radiator that’s on the bike with a hose in the meantime. The fins on the back are better than my other radiator, which is originally pristine in every way apart from the rear fins being the worst I’ve personally seen

@Corswolds89DTR

It won’t be a 1989 diagram you need. Look through the other years models till you find one that looks familiar…

Cheers guys!...

I've got a half decent rad i bought a while back. alot better than the used stuff you normally see on fleabay. i'm gonna flush that and leak test it, as well as checking for decent flowrate. Ill order a new thermostat and do them both together...

Has anyone looked at the replacement rads on fleabay? there's a chinese one for £90 and a chek one for £114. i'm leaning towards the chinese one just because the quality of the TIG weld looks to a much better standard.