300 EXC Top End Rebuild

Roy Menace did a excellent thread on his top end overhaul here somewhere. It maybe in the KTM section or in tech help, if you can’t find it let me know and I will track it down for you

TB

Menace’s 300 Top
end rebuild Tutorial

Just did mine a few weeks ago Roy.

In answer to your questions:
1) If your replacing the piston, replace the pin and little end roller bearing too. Note: You “typically” get the piston/gudgeon pin with a kit, you purchase the bearing separately. Double check this.
2) You don’t know the thickness until your putting it all back together. There are no markings on the gaskets to tell you what they are. Measure it/them if you trust the last mechanic who did it (which is fine). If your paranoid you grab a combination of gaskets from the dealer and measure the X dimension with feeler gauges. If you go ahead with the paranoid approach, you will want some valuable tips from us to make sure you make no mistake.
3) You can read about this on the ‘Net for hours. After much reading myself I decided on this approach: the liner on these bores are hard. F&&%&%g hard. You really have to metal on it with reckless abandon to damage it. I grabbed some wet and dry with some water and scratched the coating in nice 45-60 deg swipes. Down and up, all around. Avoiding the port edges where possible. No serious pressure either. Rinse and take a look in the light. I think I used 2×0 then 3×0 to finish. Many people use scotchbrite. The scratches in reality are so fine at best they break some of the varnish (good) but even then it may not even do that. Many people don’t do anything and just throw it back together.
4) I was planning on cleaning PV bits on my second piston change. Look up what o-rings and gaskets are needed if ant all. May as well check reeds for open/chipped petals. Clean carbie with carbie cleaner and compressed air. Seal up (for water) and wire (for safety) your throttle cable.
5) I wouldn’t worry about it. Hold the crank still and lift the conrod up and down to check for play. If you feel anything you would be lucky (or more to the point unlucky). Not side to side play, up and down only. Any excessive play would be from a fault or other unlikely problems. Report back for comment. Not enough hours in my opinion to worry about it.

Stick with Genuine or if your keen actual Vertex branded (same thing). Take note of the numbers on top of the existing piston. If your bore lining is seriously scuffed from the piston cold seizing or other “events” then you decide is a I or II is necessary. If it had a I and bore lining looks real nice, I would buy another “I”. If bore looks poor, go a II. If the piston you pulled out is a II, go another II. Simple. Whatever you put in there will not cause damage. The difference between I and II is SFA.

Menace’s write up is very detailed. Print it out.

Additional: Give the unused gaskets back to the dealer for a refund as long as you don’t dirty or get oil all over them. Also when using o-rings to seal the head on the barrel, apply vaseline or petro jelly to the o-rings so they stay in the grooves. The vaso works it’s way out when it’s hot, no probs. Also don’t be concerned about rusty cylinder bolts. Always happens. Just apply some WD40 lightly to them when you put it all back together if you like.

i believe that you do not hone the nicasil (spelling) bores.

once you have it apart, and see what condition the coating is in.

my 03 300 needed to be done after a seizure but needed the exhaust port welded they would have to have honed it, weather they honed it then coated it and honed it again i have no idea :unsure: . i didn’t get to see the barrel after it was coated, and i didn’t get to ask what they do when they re coat them.

its a piece of piss boys, just get into it :laugh: :laugh: :laugh:

reading back on my own thread, i noticed that it didnt really tell of anything too much but it is mighty encouraging :laugh: :laugh:
beer will do that :laugh: :laugh:

anyway, thats the key dudes. just have a crack.

take heaps of pictures, from all angles…

of everything you need to remove/replace/remember…..

before, during and after touching anything…

(just by doing this you will learn heaps, and may never have to look at the pics.)

cover everything new in 2 stroke oil as you rebuild it…

lube = love :laugh: :laugh:

honestly, its a piece of puss, even Rocket could do it :laugh: :laugh: :laugh:

good luck groovers

yeah, i had rag in it for all but the photos Jim.

i agree with evrything else too.

its all common sense really, if anything looks wrong,lipped,grooved,scratched etc, there is a problem.

otherwise its all good