by the way I'm on a really tight budget and we only use the bike for crusing around town as a daily ride (we don't ride it hard for racing, nor high rpm going uphills hard etc).  if you guys think we could get by with just replacing the piston be okay for a year, please let me know.

thanks

i would not recommend using the cylinder until it had been replated.

sinful, on 17 January 2012 - 08:41 PM, said:

If you push/pull on the rod and if it has any deflection (side to side motion) then the lower rod bearing is toast. The bottom of the rod will slide back and forward on the crank pin, that is normal, but there shouldn't be any deflection from the piston side of the rod.

You would have to pull the crank out of the bike, separate it and pull off the bearing to see if there is anything wrong with it. Its easy to get the crank out, but its a 2 piece crank that needs to be separated very carefully and re-assembled then balanced by a professional. So even if you DID get it apart and put in a new bearing, you'd still need to get it back together. Its an easy process if you have the right tools, its more difficult if you do it at home in your garage. This is why on 2 strokes, you usually buy a crank/rod combo when replacing the crank.

I wouldn't run the motor without knowing what is going on with the bottom end... but then again, I'm use to building motors properly. To me, building motors half-assed just to have something that runs for a short period of time before going catastrophic again, isn't worth it for the money saved. But again, thats just me...

sinful, on 17 January 2012 - 08:41 PM, said:

The transmission and clutch chambers are separated by a wall from the crank.

Its pretty kool how 2 strokes work. As the piston rises up, it generates a vacuum and that opens up the reed valves, and sucks fuel/air mixture through the carb/reeds and into the bottom of the crank case. As the piston goes back down again, it generates compression which forces the air/fuel mixture out of the crank chamber and back towards the reed valves, which at this point are closed. With nowhere else to go, it gets pushed up the sides of the cylinder and into the combustion chamber. As the piston moves back up, it closes off those ports and the left over air/fuel are compressed in the combustion chamber and then exploded. As the piston goes back down again, the gasses escape through the exhaust port and into the resonance chamber. The reason for the big chamber is, it creates a resonance frequency which basically pressurizes the exhaust port so the next stream of incoming fuel/air mixture doesn't just escape through the exhaust on its way into the combustion chamber.

But yea, without the vacuum generated in the crank case, there would be nothing to suck in the air/fuel mixture. Obviously there are other ways to build a motor, but this method allows lubrication to be done through the air/fuel mixture and that is the simplest form without going with an oil sump, which is what 4 strokes have.

Hope that makes sense!

it is very possible the crank/bigend pin and its accompanion ( washer and the bigend crank bearing) in a total mess...
should check the bigend man..
been deal with some stuff like this, where my mechanic put non oem washer to the bigend crank pin...
bike is still well lubricated with motul800...
since the washer stop the 2t oil lubricating the big end.. all there turn in to shrimp crackers..
if this happen, no other way but to replace the con-rod.. since it lost the smooth surface where the bigend bearing rolls..

i guess even worst in your case no 2toil at all...


(we are all wouldnt let go, someone incapable to approach and do somthin to the beloved bike.. but sometimes 'friends' see it in different way)

i know for sure there is no push/pull play at the rod but now... i know what you mean. so theres a good chance things over heated down there.  thanks for the explanation..

so you guys dont recommend using this cylinder again?  damn why am i even asking these stupid questions.  i have built at least 5 racing engines in the past and should know better !!

tye1138, on 17 January 2012 - 12:52 PM, said:

I should probably just do this TO BEGIN with.


thanks for the info guys !

by the way..............any tips on how to take the crank out? do I need to take the entire motor out of the he chasis? I have a large work bench.  I'm pretty good with tools and such (I have air tools too).  anything I should look for or be careful with?

Glad your taking the crank out, the bearings need to be replaced.

Edited by madday, 19 January 2012 - 05:25 PM.

sorry i meant 5 different automotive engines.  not bike engines.  i should know better what a bad cylinder wall is. overall i just wanted to know what to do as far as repairs and who to deal with for parts and labor.


thanks guys.

i'll be taking apart the rest of the engine and post pics of the crank/bearings.

sinful, on 19 January 2012 - 04:27 PM, said:

I too have built car motors and full-on 4 stroke race motors, working on 2 strokes is so easy, its a joke.

Piece of cake, though you will need a flywheel puller tool, they are cheap on ebay. Yes you will need to pull the motor out of the cases and strip it entirely.

Pop the right side cover and basically unscrew everything. The main gear nut is on backwards, which throws a lot of people off, so just remember that. I usually use an impact gun to get that one off, but its a wise idea to stick a penny between the mating gears of the clutch and the main gear, so you can get the nut off cleanly, same goes for the clutch main gear, which is put on normally. I've done a lot of them and there are some tricks to make sure things don't go boing. You might find a video on youtube that could help.. most of the 2 stroke motors are similar enough that you won't be lost watching a KTM 300 or 125 video, they're pretty similar in design.

Edited by tye1138, 20 January 2012 - 10:02 AM.

Before you take the motor out and before you remove the rear wheel or any of the secondary drive, take the side covers off the motor and use an air impact to bust the fasteners loose on (in this order):

flywheel
crank shaft primary drive gear
clutch hub center nut

Having the bike sitting on the tires and in gear will hold everything for you. This is why you must do the clutch center hub LAST. Once you remove the clutch plates to expose this nut, there will be nothing keeping the motor from turning over.

If you skimp and just do a top end, IF the rod bearings have been compromised, you could toss the rod which at the very LEAST usually ruins both cases, and at worse can damage most of the motor (including your fresh top end).

okay I'm finally back in the game of taking this motor apart.  I will post pictures of the rod/crank bearings etc.

stay put

I hate to break it to you but if you want that 380 to have a future your going to have to drop some coin. Your cylinder is toast and must be re-plated. The crank if still serviceable will not be for very long. Sadly, the 380 crank is the MOST EXPENSIVE KTM crank ever made. I am sure this is due to it's rare nature. You best bet in the world is to box up the whole engine and send it to Andrew for a complete tear down and inspection of what is good and bad: http://www.cookseycrank.com/  Like others has stated your main bearings are more that likely wasted, your crank rod bearings are very suspect. Unless you are a very knowledgeable engine builder send it to Andrew.

If this was my bike I would do a complete re-build. New crank main bearings, and crank re-build, a re-plated cylinder with a new piston matched to the cylinder re-plate.

Now I get it your on a budget, aren't we all;) Your going to have to ask yourself is this worth it? You can go buy yourself a 250, 300, or even a 380 engine used for far less and slap it right into your existing chassis. Heck I bought a 98 380 a few years back for $500 and the engine was in great shape. If your into the 380 then it might be worth it. If this is just your back yard flavor of the day, part the bike out and call it a day.

Any way you slice it your buddies ass is in a sling and he owes you BIG time, I would be mega pissed if I was you.

Joe..........

guys I'm going to try something different here..............you will all hate me for this I'm sure lol.

I need a quick answer though............

How do I clean the oil or dirt that's in the crankshaft assembly without taking anything apart? is there a drain plug for this?

Some people will disagree with this but here goes. Ive ran cylinders that had much more damage with no probelms what so ever. Ran hard for 20  hours torndown and inspected and all was good. You could flush the bottom end out with premix or diesel fuel. No drain plug so best bet is to take the engine out of the frame so you can shake it and dump it out. Do it till it comes out clean. You will never get it perfectly clean but its better than not doing anything. If the crank turns smoothly after you maybe ok. There's always some oil that stays in the lower end and the first thing to seize is always the piston. So there's a chance that the damage to the crank and bearings is minimal. If the crank does not turn smoothly that will be your first clue as to how bad it is. Flushing it out may help.

You could get out of this for the price of a piston and the gaskets. It probably will not last ten years but it will be running.

your friend isnt gonna cover any of this?

its one thing if the thing snapped a rod, its completely different if he forgot to add premix to the fuel....

is there actually a friend? or just trying to save face?

Edited by mynewcr250, 14 April 2012 - 06:01 PM.

Okay I'm back after working on the bike for 8 hrs straight.  Decided to use the same parts, put my air die grinder and polishing kit to work instead of spending more time and money on this.  What made me take the risk was the rod and crank seemed to be in great shape.  No play, no overheating spots, bearings looked good, smooth when turning things over etc., with the exception of some small debri inside of the crankshaft assembly.  So I took the risk anyway, blew air inside of the crankshaft assembly to blow everything out, poured some 2 stroke oil inside and covered it up (to move on to the top end).


The top end.
So after carefully taking the piston rings off and cleaning them with soft sand paper, same with the piston grooves, I polished all the rough spots - gouges off the piston using the die grinder with a soft polishing wheel. This polishing wheel was awesome.. it was perfect for this job, will try to get the correct name for it, but it wasn't too rough nor too soft, good in size to take some rough spots off the piston (I'll find the name). although I have to admit the piston didn't came out that great after all but managed to remove most of the rough spots to where it felt smooth by hand.  And the rings came out good too, they moved freely inside the piston groove.

Now the cylinder head...I didn't want to touch it with the polishing stuff but did clean it just a little where the nickel had chipped off just enough to smooth out that one hole without going too much.  then with some really soft sand paper I cleaned the bore .  Also the reed mechanism seemed to be stuck and cleaned that with some w-40 until things got loose there.

Hell I didn't even bother to buy new gaskets or head o-rings.  Just cleaned everything up real good. tightened everything by the book.

With a compressor tester it gave me aprox 150-160 psi on the first few kicks.  Put everything back together and the bike is running again.


hopefully it will stay running for a few months lol


I was going to take some pictures of the process but figure you guys wouldn't be interested lol

Edited by sinful, 14 April 2012 - 07:13 PM.

before you guys yell at me............

I know I said things were going to get done the right way but did not.  I appologies hehe

I'm currently staying in Mexico, about 2000 miles south of the U.S. border.  Parts and nickel plating for this KTM are impossible to get down here.  I had planed to take a bus trip to San Diego with the KTM motor with me but it was going to cost me about a grand to make this possible.

tech857, on 14 April 2012 - 05:00 PM, said:

Yes I went this route.  I'm hoping things don't go south anytime soon (crosing my fingers).  or worse case scencerio begin to loose compression and run into power/ throttle issues.  ah