DT125R ARCHIVE

oh **** myn 58.00 , arr shis is just some straight up davied copper field ****.

set the pv in the closed position half at a time and just make sure theres 1mm clearance no less

iv had to alter all the pv systems on my motocross bikes when fitting big bore kits or just os bores, u should always have no less than 1mm clearance

easiest way to do it is leave the power valve in in its closed position

sit the barrel on a bench and with a red marker pen down the bore draw round the radius of the exhaust port and colour it in what u can see u mite need to take the tip out of the pen to get at a right angle if u get me, theres only about 12 mm of valve that covers the port if that

then remove the valve halfs and you will have a semmi circle of red pen on the valves, grind away all the red marker so you have 1mm of cealrnce

no problem glad to help have fun

Same thing happend to me. i had 57mm bore. No fixing with the pv. Went good. was driving with a brp9 plug. But then i had this great idea about switching back to the stock one brp8. Was up a hill. accelerated to 60 mhp, When i released the throttle i heard a slight click. dint really mind it any further, After the hill there was a long straight line, then a downhill. i drove carefully over the hill at about 40-50 mph. then when i started going downhill i heard that the bike would stop when i pulled the cluch, It would go idle. So i stopped when i got down the hill.

Looked a bit at the bike trying to figure out what was wrong. Tried starting it whit the electric starter, No weird sounds or anything, just wouldnt start. Tried running it into starting, It worked. But it was coffing a bit when it got up on the rpm. so i just drove at 40-50 mph all the way home. tried giving in some throttle on the last bit untill i got home. and it would just cough and sound all ****ed up.

Got home and took of the cyllinder and piston to see what was wrong. The same thing happend to me, and i found a piece of my piston ring inside my exhaust xD.

But thats why i love my dt. Even though i cut it sometimes, 3 times to be honest, only once did it stop completely for me. Was one time, i had done 250 km 500km is what is reccomended for driving it in. I accelerated up to 80 mph. Then the rear wheel locked itself, Had a passanger on too. was scary as hell, i pulled in the cluch and when i realised it it was all fine, just a bit of noise from the piston rings. Drove home the 60 km home. Had to change the piston and rings because i didnt have any new rings for the same piston that was on it.

Still, Gotta love the dts, they can really handle quiet a beating !.

Wen i got into DTR engines, was green as grass, first engine rebuild blew up, pizzed right off i was. That build was spot on too. 80mph off the clock. at 600 mile running in it went pop.

The engine was bedding in real well. mineral oil all the way for perfect ring seal... It was getting faster and faster each day, the rings were sealing perfect, compression was very good. efficency was getting greater and the heat produced the exspansion in the piston, head. and barrel. Till the point of when it all met. Thats was 56.5mm rebore.

Riding it normal, would`nt of noticed i rekon, i was racing a clio back home a 80mph for about 15 miles on windy roads. Very hot engine, till i backed off the throttle and coasted in top gear for a length of time, then metal parts flew out the exhaust. The PV was red hot, along with piston/rings the pv rotated back and hit the rings. That day my bike was a demon, so dam fast. pickup from 50 to 80 really quickly.

Hate to think at 57mm how long it would take to hit the rings.


It was`nt till i stipped it and found out. Not best pleased. only if i knew before, i would of done the PV. its not sort of common knowledge.

Second rebuild was sorted, then the Magneto side bearing permaturely wore, and thats another story. Soddin engines..lol

if you are looking for a new barrel check this on ebay 300646740120 £10

3mb.

PatMan wrote:

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Thankyou satelliteone mate for dotting it out, I SALUTE YOU

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 aup mate this is what i was onabout other day....

http://dt125r.activeboard.com/t47212329/power-valve-modification-for-over-sized-bores/

Powervalve is now dremmaled down, and fits great with no piston hitting it also top gasket grinded down in centre so no lip hanging over thankyou so much for your help!!!!!

-- Edited by PatMan on Monday 16th of January 2012 12:41:02 PM

Im scratching my head, when i stripped my bike the power valve turned away from the piston, put it all together and now it wants to turn into the piston! So i have had to pin it open for now as i have a +2 tzr piston in and i dont want it hitting. I cant work out what i have done different putting it back together and the cables look like they only fit one way. Anyone got any ideas?

Thanks bud i will give it a go..

Finally got back to the power valve problem yesterday, and im still left baffled! lol
Thanks for the reply Nev, i had done as above, but it turns clockwise instead of anti. I have tried to switch the connector block as suggested by Norfe, but it only goes one way. I have tried crossing the cables over but even with the cable adjusters at max/min the hole don't line up and the valve just moves from a quarter closed one way, to quarter closed the other.
So...now my power valve turns into the piston, i have had to grind down the power valve down like the guide above.
I'm still baffled because if the power valve turns away from piston, surely there would be no need to grind it down, anyway here are some pics..

Seem that disconnecting the servo wasn't enough to keep my PV pinned open, luckily there doesn't appear to be any damage to the piston..


How it IS turning (before grind down)


How it should turn??


Open..


If you guys have had to grind your PVs down, does that mean that your PVs turn turn towards the piston as well? I'm sure it turned away when i checked when stripping the bike down, but i did smoke a lot that day, ha
But then, there were no marks on the PV back then either..

Yeah i have completely stripped and rebuilt the bike, i left the cables in the cable housing the whole time and i didn't mess with the adjusters as the PV was set up perfect when i stripped it.

Here is a pic of how it is now, wires uncrossed..


Tried crossed, no good..


Best before shot i got..

satelliteone wrote:

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Riding it normal, would`nt of noticed i rekon, i was racing a clio back home a 80mph for about 15 miles on windy roads. Very hot engine, till i backed off the throttle and coasted in top gear for a length of time, then metal parts flew out the exhaust. The PV was red hot, along with piston/rings the pv rotated back and hit the rings. That day my bike was a demon, so dam fast. pickup from 50 to 80 really quickly.

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You should NEVER EVER shut the throttle off when blasting the bike. You have to remember that the oil pump runs off the throttle. If you rev the engine hard for a length of time and then shut off the throttle that you starve the engine of oil! After a lenghty blast you increase the heat. Oil burns faster. Also the fuel helps keep the engine cool so give your bike blips: downhill, after long blasts and just generally is good for the engine!