Yamaha dtr 125 head gasket problem !!!

[Dtr12503]

Hey this has been bugging me for some time .........so my head gasket keeps going on my dtr, I buy a genuine gasket and a few weeks later it goes again, the coolant overflows into my expansion tank until that fills up and goes through overflow (due to pressure in rad)

Didn’t bother me to much I would just make sure rad is topped up and don’t run dry, and of course a new gasket every month or so.

Decided to get head skimmed and barrel bored from 56m standard to 57m as there was a Nasty scratch down the barrel,

Now it’s all back together I rid the bike to work and noticed same problem, coolant overflowing, I’m assuming gasket gone again but this time it only took a day to go.

Why does the gasket keep going in the first place ?
Do I need a bigger gasket for the 1mm oversize bore ?


Thanks

[Riejufixing]

Have you tried previous answers?

Lots of information if you try this search with yoiur favourite search engine:

"yamaha dtr125 head gasket site:bikechatforums.com"

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A few tips.

With a latex glove on, smear a very thin layer of Threebond on both sides of the genuine basket and make sure you fit it the correct way up.

If the head has been skimmed, I can't see the barrel warping, so are you torquing the head nuts in order and to the right setting?

I normally made the central circle a bit larger in the hard gaskets of my race bike, but this was 2.5mm overbore. Please the gasket over the barrel. Is there a lip that needs removing? I think at 1mm, you should be OK, but worth checking. Squish will be tight, so it could be the piston banging into the lip of the gasket.

I take it the cooling system is all in order and the thermostat isn't stuck shut? Those £7 infrared thermometer guns from Ebay are awesome at checking which parts of a cooling system are at what temperature.
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[stinkwheel]

Do the head nuts need re-torquing after fitting on one of those?

I know on my enfield that I run the bike up to temperature after having the head off then re-torque and get another maybe 1/4 turn. Then I do them again at 5, 50 and 500 miles. I usually get about half a turn at 5 and 50 then maybe 1/4 turn at 500.

Anywhere else you could be getting pressure blowpast into the water jacket? They'd have noticed a cracked liner on the rebore.

Could it just be a straight overheat? Are the hoses getting hard with revs (I'd expect this with a significant head gasket leak)?
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[jeffyjeff]

maybe that nasty scratch was masking a crack and the shop didn't look for it or see it.

[salem1987]

If dome nuts are fitted to the head without washers it will cause the leak as the nut goes tight too soon.

This was the problem i found on one that had the same symptoms.

[Dtr12503]

Thanks for reply’s , I can’t torque bolts down because of where it’s positioned, one of them can’t even get a socket on, have to use spanner, but I do try and cris cross evenly tightening them up with washers

Hoses are solid

as for the thermostat could be a good idea to get the infrared gun to check temp



I can remember if the inner circle of gasket was overlapping bore as I didn’t think of the oversize 1mm could effect it, plus how would I obtain one to fit my bike with a bigger inner.

[stinkwheel]

[Easy-X]

Oh yeah, that's a usual problem with water cooled barrels: 3 out of the 4 nuts are accessible and the last is tucked away in a recess

Get a standard torque wrench and this for the last one:

https://www.ebay.co.uk/itm/Crow-Foot-Crowsfeet-Wrench-Spanner-Set-3-8-Drive-10mm-22mm-on-Storage-Rail/362827867078

https://i.ebayimg.com/images/g/BBYAAOxyJs5RakRS/s-l500.jpg
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[bladerunner]

deffo worth trying a different rad as well.Not like these bikes usually get coolant changed or are even run just with water for some time which causes the rads to block. I now have an RS125 rad on the RD125LC and thats over cooled now...easy fix with some tape at least
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