Rebuilding My 1st 4-Stroke Engine...HELP ME !!! PLEASE

[660r2a400ex]

Hey I am a young teen and i have no experience with a four stroke engine. My 400ex started smoking super bad and later was blowing oil out the tale pipe. Why is this ? I figured I had blown the rings. It still started good and ran strong although I had noticed power loss. Well i bought a hi-compression piston and a hot cam, took my whole bike apart got the engine out, took off the head first, took the cam sprocket thing off and the chain, pulled the cam out, and took the cylinder off. took my stock piston off and now here i am, i am gonna put everything back to gether and i remember how to do it, but...how to i get my timing right and what steps should i take on rebuilding my 400ex. just throw the piston and cam in and run it or clean everything redo my valves and timing or what?

[Martin Blair]

Ok first off take that piston and your cylender to get honed to match. They need to remove the ring lip left buy the stock piston from the sleeve. Call a local bike shop they can help you find a place to bore it, if there no ones close to you I recomend GT thunder, TC racing, or FST if your on the east coast. And LRD or Sparks on the west side. Call them they can help with honing and mathcing piston/sleeve. This is very important if you dont do this you will be taking it apart all over again.

To fix the cam/timing problem get a manual, you can pick them up for about 25 bucks. Thats the best way, if you cant fingure it out find a bike shop, or your dealer if they are good. If theres no one near it would be better to either find someone near who knows, or send it off, its expensive but will save you in the long run. Just buy the manual.

You should have posted here prior to your starting, your leak problem could also be caused buy valve sea, did it go away when it got warmed up?

Most important make sure your get the sleeve and piston matched, if not you will be sorry. And buy a manual to figure out timing. Also make sure your studs in your head are tight there is a article in FAQ about this, also get a gasket kit, you cannot reuse them.

edit: the crf chain is only $26 from service honda not much at all.

[2003400exmnymds]

The timing is super easy, you need to take the 2 caps on the left crankcase cover, a 17mm socket and turn the motor the direction it spins without looking im gonna say CCW. Get the piston at TDC (Top Dead Center) you will know when you look through the little hole in thje left crankcase. make sure you have someone hold the chain for you and keep upward pressure ensuring the chain doesnt fall off of the bottom sprocket. Put the top sprocket into the chain ensuring the side says "This side out" and the two lines on the sprocket are horizontal with the cylinder head, not the ground, when you see through the window that you are on the -T and the top sprocket is horizontal you know you are TDC. Now important when you install the cam ensure the LOBES are DOWN. Dont forget to unscrew the tensioner it might pop by itself.

Here is a little tip, go to an auto parts store (Auto Zone) they sale lock tight, get the red kind and put it on the top sprocket bolts. When you install the bolts, install the top one and spin the motor backwards enough to get the other bolt in. Then spin the motor back to LOBES DOWN and you are TDC again. INstall the head cover and remove the valve caps ensure the valves are what they are suppose to be. Factory valves are .004 intake and .005 for the exhaust depending on the cam, I have a Hot Cam stage 2 and my intake is .005 and .006. You will need feeler gauges to get the valves done right.
Good Luck I hope I have been some help.