DT125R ARCHIVE

bkray · DTR Senior Member

RE: Coolant issues.

Dingle001 · DTR Senior Member

I've got both 3BN and 3MB heads here and the only difference I can see is a different shape combustion chamber. Got to be worth a go.

bkray · DTR Senior Member

ok, im assuming its blowing because ive had my head skimmed quite a lot of times and its over compression? i cant really put it down to anything else. Thanks, ill let everyone know how it gets on soon enough.

And yet another question, would my base gasket be anything atall to do with it?

-- Edited by bkray on Sunday 2nd of October 2011 09:03:54 AM

Brewski92 · DTR Member

My bike used to do this, I had broken my water pump gasket and resealed it with waterproof gasket paste but there was a tiny gap that was sucking in air and pressurising the system and forcing all the coolant out through the bottle at the back of the bike

El_Faggo · Forum idiot

Hey guys, new to forum but an old DTR tinkerer, Right, look at the water in the top of the rad when it settles, if it has scum on the top that looks like oil its the gasket, tricks for changing gaskets on the DTR125 and all 2 strokes, this was shown to me by my brother who is an engineer, when I was 17, 11 years later still using it.

1.Clean the Head and the barrel where it contacts with the gasket with alcohol, let it evaporate.
2. give the head and the top of the barrel a fine coat of two stroke oil and i mean fine, spread a drop with your finger so that it shines and that's it, do the same with the gasket.
3. put on the gasket and head then tighten as per rating.
4. get a ratchet and give all the bolts quarter to half of a turn more.
5. Take bike for a 5 minute spin, come back and tighten bolts again about the same, don't do it too much though.

Over Skimmed Head; There is a simple solution, Bottom gasket, put another one in, I did this to a friends bike because it looked like some fool skimmed his head with a chainsaw, after getting it skimmed smooth he wasn't left with much head, to check your gap between the head and the piston get a piece of solder wire, bend it to 90º, stick it inside and give the motor a full cycle, how squashed the solder comes out is the clearance that you have, refer to Haynes for the correct clearance, you can even do this on a bike with a non skimmed head, you will lower compression and make the bike more reliable, you might have to play with the mix though and check that you are not running hot or cold by checking your spark plug.

If none of the above helps then you need to start looking for other solutions, One thing you can do is pump smoke through the system, long story and hard to do but if you have the kit then you can find leaks, you need a compressor, smoke bombs, and a glass jar, drill the lid and put 2 connectors in it to connect tube to, drop smoke bomb in jar, one pipe goes to radiator and is fastened on tight, best to use a bung with the pipe through the middle, other pipe to compressor with a valve, put the lid on the jar and give it some air, not a lot though, bit by bit, smoke will exit through leaks, if you cant get smoke bombs look how to make them on Youtube, doesn't need much smoke so don't over do it, rinse the system out thoroughly with water afterwards to get rid of any residue left by smoke.

Never trust a torque wrench, go to the level and over tighten.

Hope this helps.

satelliteone · DTR Senior Member

in the manual Warpage limit is 0.03mm , that is not alot. same with the barrel. check the manual if ya dont believe me. and yes, the barrel can be warped too., get a steel ruler across it, and see if you can see light between the barrel and the edge of the ruler across the steel liner to the outer alloy edge. more than 0.03mm?

another thing you said the amount of skims the head has head?. this is the doughnut shaped head (squish)?. (3bn) skimmed to much the compression on the edges goes thu the roof. U need the 3MB head ideal for the higher compression.

The 3bn head was more designed for lower compression, eg, dtr125R , limit really 1mm skim max. about 40thou then ya get bucket of worms via head gaskets blowing. Its just not even enough in the squish area.

hope the info helps.

satelliteone · DTR Senior Member

have a look at the hollow squish, if ya skim too much on the 3bn, the outer edges trap compression. leading to problems.

3mb

3bn

El_Faggo · Forum idiot

If you have warpage that is close to the tolerances then get a sheet of glass, check with ruler that it is flat, place sheet of sanding paper on the glass (start 180 grit and move up to 220 or higher depending on seriousness) and sand in circles without any pressure just with the weight of the cylinder, keep looking to make sure wear is even (will see where it has sanded) and checking warpage with ruler, solution for high compression is as I have written above, adding a second lower gasket, other solution is to get a Dremel and reshape and polish the head, but don't play with it too much as the shape is really important to how the engine works and remember the closer the head gets after skimming the closer the plug gets changing the point of ignition of the fuel, you will also with a higher compression suffer from pre detonation, the pressure alone will detonate the fuel and will cause a melted piston.

Raising the barrel with a second lower gasket will also adjust the inlet and exhaust timings, fuel will enter the motor sooner and exhaust will exit sooner, detonation will still happen at the correct time.

To be honest I don't know why you lot are so bothered about head skimming etc, in the 5 years that my friend and I rode our dt's we never once skimmed a head or a barrel, yeah a large chunk my mates piston did exit the lower of his crankcase in the end but that was his fault, whilst he went for a few more HP in tuning i went for more reliability, he lost the battle and an expensive one it was for him.
Just tighten the head more and even if you have to do it tighter than Haynes says it doesn't matter, heck half the time we didn't even use a torque wrench. Oh and if you want to know why I talk in past its because I haven't seen my bike since moving away from it 7 years ago .

Dingle001 · DTR Senior Member

For some reason, DTs seem to be sensitive to head gasket failures. The 2 main causes seem to be a warped head or a pattern gasket. I dont think excessive skimming will create enough pressure to blow a head gasket and I am convinced in this particular case there is another problem, such as a cracked/porous head or barrel as skimming the head a number of times would mean there is a fundamental problem elsewhere in the build.

I'm just in the middle of a rebuild myself and re-fitting the studs back into the barrel. One thing to check is the length of the studs protruding through once the head is fitted. Make sure the length is shorter than the depth of the domed nut as this may stop the head being torqued down properly. Good luck!!

El_Faggo · Forum idiot

Good point there, this can be checked with Tipp-ex, paint the ends of the bolts with it and when it has dried put the nuts on, see how far it gets, if it is touching the head of the bolt then it will mark the Tipp-ex, try getting hold of some longer nuts (lol) or just use standard ones with some copper grease on the threads.

bkray · DTR Senior Member

well, ill replace all my gaskets. and try again i guess...

El_Faggo · Forum idiot

Try just tightening the nuts first it might work for you, I have had a gasket blow before and I re tightened the nuts, It lasted for about 6 months and a trip from North Wales to York without any problems roughly 4000 miles in total and it was caned ALL the time, most of the time I have seen blown gaskets on friends bikes, they had tightened the head with a cheap torque wrench, my brother gave me one from his work for me that they were going to throw away (RAF for you) for nothing more than the fact that it had expired its service life (lol whut), this was a seriously expensive torque wrench and I used to check the torque on blown heads when people asked me to change them for them, most of the time they were under torqued due to them having been done with a cheap torque wrench.

satelliteone · DTR Senior Member

before you strip your bike, try this stuff.. meant to awesome stuff,

http://www.kalimex.co.uk/our-products/k-seal

tiz on egay for tenner. you might be surprised!

bkray · DTR Senior Member

ok, so, im gonna re-tighten it then, if not, ill replace all the gaskets (water pump etc) and then still if nothing, ill put my other head on.

Dingle001 · DTR Senior Member

So, how's it going, anything to report??

bkray · DTR Senior Member

Not just yet. Im gonna get a picture up of this other cylinder head i have, hasnt been skimmed yet (you'll be able to tell) just want to make sure its in good nick for using :/ looks battered.

bkray · DTR Senior Member

Dingle001 · DTR Senior Member

Dont worry about it being battered! Get it skimmed or use a piece of glass and a sheet of 400 grit wet and dry if its already pretty good.

DT-R_bradders · Guru

hey bk wen u do replace ur head for that one^ do u wanna sell me ur old one if its 3mb tht is??

bkray · DTR Senior Member

Bradders, the one im going to put on is a 3mb, just took a 3bn off mine at the minute. haha, sorry Bradders. so your search continues. :(

Wilksiee · DTR Respected Member

Fixed mine... took head off, wet and dryed all of the **** offf & polished slightly...wacked it back on with a new ****ty gasket and now it has fixed the problem :D! Br''aaaaap!

before

After

El_Faggo · Forum idiot

Excelent, glad to hear you got it all sorted, for an even better finish on heads than just wet and dry you can polish it on the glass only with some rubbing compound on there, that's what I do with all the barrels , heads etc to get them even smoother.

bkray · DTR Senior Member

Im still having issues. haha, FINALLY got my head back from pjme after what seems like forever and got all my gaskets through, replacing my head, base, waterpump and the thermostat gaskets. :D hopefully that will sort it.

El_Faggo · Forum idiot

Good luck mate.