DT125R ARCHIVE

heres a "rough guide" on an engine strip

complete engine top & bottom end

cylinder head

1st remove the engine from the frame and get in a suitable ,clean workspace, then get a good selection of tools to hand & rags and some brake cleaner spray

THERMOSTAT

ON THE TOP OF THE head theres the thermostat housing secured with 3 m6 bolts

these will need to be removed to get access to the thermostat unit

once the cover is removed the thermostat is just sat in the water jacket and can just be lifted out for inspection

then

loosen the 5 m8 nuts on the head 12/13mm socket on the breaker bar work in a criss cross pattern

then remove the head from the studs

you may need to give it a light tap with a mallet to break the seal/seating of the head

then procede to wiggle the head off the studs as some times can get a little stiff then pull upwards untill its free of the studs

then you will see the cylinder bore and piston

depress the kick starter slowly untill the piston is at the bottom of the stroke/bore, and then you can have a really good preview of the condition of the bore

notice the arrow and F on the piston crown, this must always be pointing to the exh port

if fitted wrong the piston rings will catch on the ports and ruin a new top end

power valve removal (pinned version)

remove the end cap with the single securing bolt

then procede to tease it out with a blunt flat bladed driver, work around the edge dont just go mad as its easily damaged

then move to the other end and loosen the lock nut

then undoo  & remove the centre fastner

after the end cap is pulled off theres a bushing that fits over the actual power valve drum, just pull these out off the barrel and lay aside in order you remove them, this keeps things simple on assembly

notice the locator pin on the cover

this can be used to retain the pv in an open or closed position, if its installed with the bushing  notice the cut out in the bushing

move to the opposite side again and with an allen key remove the pv centre bolt

you will need to place a piece of wood up the exhaust port ,a small hammer'sd handle is just the thing for it, this locks the drum in place so the bolt can be un done

the pv drum is in 2 halfs and then can be pulled out from either side and layed aside for cleaning

cylinder removal

theres 4 m8 nuts securing the cylinder base these can now be removed ,same again as like the head remove the nuts in criss cross style again

the cylinder may need a couple of taps with the mallet again to break it from the cases

start to lift the cylinder away from the bottom end the gasket may need ripping off as it wil more than likely be stuck to both surfaces but its advisable to use new gaskets on rebuilding the engine any way

piston & rings

so now you have the cylinder off you have access to the piston and rings, take a good look around the piston and rings, looking for siezure marks or cracks,blackening down past the rings(blow by)

these are all common faults in a worn 2 stroke top end!

so to removing the piston off the conrod, if you look in the hole in either side of the piston side walls you will see a round steel clip (circlip) some have legs on others just sit completely in the grooves and can be tricky to remove, get some small long nose pliers and procede to grab the clip legs and twist while pulling out of the hole

if your carefull removing these and dont bend or crush they can be re used, but most people prefer to re-new and these are also included in all piston kits, these also can be a common cause of top end damage as people put bent clips back in then they just vibrate out and gouge the same size trench up the cylinder wall the same size of the gudion pin when it slides out of the piston on heat expansion cycle ! when re fitting the circlips make sure u hear a nice sharp snap noise thats a good sign and you will see the clip has sat in correctly

to remove the rings off the piston just find the ring end gap and lift one end out of the ring gap and slowly work it round the piston, then same agin for the bottom ring, these can be very brittle some times so take care

to remove the piston off the con rod you may need to warm up the piston slightly so it expands and the gudion pin can be pushed out

then pull the piston away and that will give you access to the small end bearing in the con rod

this can wear out so is a common thing replaced at service intervals, and is only around a fiver so its not worth not doing really

then you have full access to the (big end) this is the crank shaft, and turns linier motion in to a rotating motion powering the gear box/clutch

this is a part many people over look when doing rebuilds, because they think its mega expensive or to hard to do, but if your rebuilding a top end you need to make sure that the bottom end will be able to cope with the full power that the engine will then be producing once its renewed and back up to full compression, a new top end can be wrecked again if its over looked you end up with broken con rods, some times smashing the crank cases to bits, wich is soul destroying when uv just rebuilt the engine lol

so grab the con rod in your hand and try to feel any up or down play in ther big end, dont be to worried about side to side movement as this is normal on nearly all 2 stroke cranks !

spin the crank by pressing the con rod up and down get it going quite fast and listen to the noise, it should spin nice and easy with no rumbling noises, if its really noisey then the main berarings are shot, and need replacing, this consists of a complete bottom end strip,to which i will put another guide on when its done

another way to check the condition of the main bearings is to grasp the magnito in your hand and try and wabble it up and down & side to side, there should be no movement at all

heres another way to help remove the magnito centre nut, place a long extension bar through the small end in the con rod and place the bar behind the 2 rear cylinder studs and then with a decent size breaker bar procede to undoo the nut !like so

right thats that one done, i hope this is some use to some one ,i really dont think the haynes manual is much cop apart from spec lists and general info

refer to the manual spec lists to check all conponents for wear against the specified wear /service limits as they are all in the boox and gives explanations ast to which parts/places to measure for best results

im sure every one does things there own way so do what evers best for you at the time of doing it, take your time and take photos if need be to refer back to

the best way to learn is just to buy an old nakered engine and get ur hands on it strip and build it a few time, most 2 strokes are the same just differ in size and the odd parts, 

BOTTOM END TO FOLLOW SOON, IM STILL SORTING THRU THE PICS 

for the rebuilding its just the reverse with nice clean parts and new gaskets