2006 YZ250 Top End Project....

While this is how I do it; others may have different view and opinions which I encourage them to post.  Also, different models have different designs so some steps may differ on a Honda etc.  Always use a shop manual.  So much for the disclaimers.

Doing a top end doesn't take any super skills or a host of special tools, but there are three things I consider mandantory and one I highly recommend.
1. A shop manual.  It will have all the torque values, disassembly/assembly steps and all information you may need.
2.  A torque wrench (or two).  No matter how well you think you can; you cannot properly torque critical bolts and nuts by feel.  You may think you can; but you can't.  To prevent damaging things or having things fall off, get and use a good torque wrench.  I have several dial type, 1/2 and 3/8 drive that cover about any range you may run into.
3.  Motion Pro makes a great Torque wrench adaptor ( Image )that allows you to get in and torque the cylinder base bolts.  Its also good when you use a 3/8 extension to loosen the bolts.
4.  Not mandantory but nice is a good spring puller for removing and connecting exhaust springs without killing your knuckles or sending them shooting off into space ( Image ).

Unless your dealer stocks a lot (like the old days but thats another subject) I recommend getting the things you will know you need.  All the gaskets etc.  Again; if the dealer is savy they can look it up and order it; but most bikes now you can look up your own part numbers on line and take them to the dealer (or at least compare their list with yours).

Once you have the parts and are ready; the next step is bike preperation.  Your doctor spends a lot of time getting himself and you all cleaned up before surgurey; since you will be doing surgery on your bike, spend some time getting it cleaned up.  I also keep a box of latex medical gloves.  They keep your hands clean but still allow normal feel.

After a normal wash job your bike will look clean like this (Image ).  But; once the wings, tank, etc are off you will see alot of dirt and dust under the frame etc Image ).  Wash it again to get rid of all this.  You don't want any of it falling down in your lower end or in your cylinder to mess up your new top end early.

Next I installed my Dr D (http://www.dubachracing.com/) hour meter.  No more guessing on hours on the engine.  You can use double sided tape or drill and tap two holes for screw mounting.  I used industrial velcro to mount it so its removeable, and then used bathroom caulk around it to keep dirt/water out; yet its still easy to remove if needed (Image.  You then just run the lead wire back to the spark plug lead and wrap it 5 times around the lead image.  

Trim any excess lead.  I used electrical tape to keep the winds tight and neat.  It picks up impulses from the spark lead which tells it the engine is running and it counts time in 1/10 of an hour.

Next I chose to repack the silencer (a messy job) and get that out of the way.  After taking the two bolts out that hold the silencer together, I gave it a couple taps with a rubber tipped hammer to seperate them Image.  I cleaned the inner core and outer shell and installed an OEM Yamaha packing core.  They are expensive, but come pre-shaped and last a lot longer than the simple repacking kits in my opinion.  I had tried a couple of the re-pack cartidges; but they seems to last for a short time. I got over a year on the original Yamaha core. A bit of high temp silcone to seal the unit and its ready to be put back on the bike Image.

While not mandantory; I took the sub-frame off to make it easier to move the carb out of the way.  My first surprise of the project came when I saw dirt on the slide of the carb Image.  I change the air filter generally after each ride (Twin-Air and No-Toil).  This summer with the
drought the dust was horrible (if any recall my post on air filter cleaning and pictures of the filters after an afternoon of riding).  Apparently some got through.  At this point I knew I was going to change the piston regardless just to be safe.  I took the carb off and
gave it a good cleaning then put it back together.  Other than on the slide it was clean inside and there was no signs of excessive wear.  All clean again Image

Next I removed the expansion chamber.  There was some carbon buildup at the first pipe bend (not uncommon) so I used a wire brush to remove it.  I tried to get a picture but my camera could not get a clear shot.  I also put new o-rings in the pipe end where it slips over the cylinder as mine are now 2 years old.

Next I drained the anti-freeze in a pan (if you use a clean pan you can re-use the anti-freeze; but since mine is 2 years old I will use new to refill).  I also run a bit of clear water down it to flush it.  Once thats done I put the drain bolt back it.

After removing the head stay bolts and head stay, loosen the head acorn nuts a bit at a time until they are are loose and remove them.  On the Yamaha, there are copper washers under them.  I choose to use new ones so the old ones I pitch.  Lift off the head and have a look.

Image As you can see, other than some carbon the head looks great (Later I will show how I clean it up).

Image Image Image I was pleased at the pattern on the piston.  Some carbon after two years but definitly not too much!  Shows that my jetting is good.  Not too rich and not to lean.

To remove the cylinder; we need to disconnect the power valve arm.  Take the cover off that covers the arm on the right side.  Its important to use the locking pin that came with the bikes spare parts to lock the arm while you remove the bolt.  If you don't use it and try to remove the bolt you will likely damage the power valve.  Insert the locking pin through the hole in the arm into the hole in the cylinder.  Now you can loosen the bolt safely.  Once the bolt is out you can slide off the arm and it will lay flat on the case out of the way.  

Take the pin back out so you don't lose it, you will need it again during assembly.

Next loosen the four cylinder mounting nuts, again each a bit at a time until they are loose, then you can take them the rest of the way off.  This is where the Motion-Pro tool is great.  I have an extension I snap into it which makes loosening them easy.

A lot of times, the cylinder will be stubborn and not want to lift up.  There are steel locating dowels on two of the studs and these can corrode and make it difficult. Don't use a flat blade screw driver or the like and try to pry it up as you can easily damage the flat mating surfaces.  Instead; take a rubber mallet and gently tap the sides of the cylinder up ward alternating until it lifts.

To my surprise; I was able to wiggle it loose by hand; it wasn't stuck at all.  As you lift the cylinder with one hand reach down and support the piston with the other until the cylinder slides off.  Considering I saw dirt on the carb; I wasn't sure what I would see.  I was happy that the cylinder bore looked great with lots of cross hatching still there Image.  The piston looked great and had NO blow-by! Image Image Other than normal wear marks for the amount of time its been run; the piston and cylinder looked good!  (This is a plug for the fact I run 32:1 ratio with Yamalube 2R).

I place one rag around the rod under the piston (so it doesn't flop around) and drape another around it like a Christmas tree skirt.This keeps anything from falling down into the crankcase while you are working.

Using a small screwdriver; carefulley pop out one of the C-clips from the piston.  Slide out the wrist pin and remove the old piston.  

I generally replace the wrist pin bearing, so I slid it out of the connecting rod and after lubing up the new bearing with 2-stroke oil, slid it into the connecting rod.

I had previously washed the new piston in hot water with Dawn dish washing soap (to make sure there were no left over debris from the manufacturing process).  I inserted one of the new C-clips (never use old ones, they are more prone to break which can cause a lot of damage in your motor) into the piston so I only have to out one in when installing the piston on bike.  Make sure the open end of the C-clip doesn't line up with the groove in the piston or it will be very difficult to remove it next time.

I then coat each new ring with some 2-stroke oil and install on the piston (the small writing on the ring ends goes up).  In each ring groove on the piston, there is a locating pin to prevent the rings from spinning while its running.  Make sure the gap in the ring is at those posts or you won't be able to get the rings to compress to install cylinder.

Place the new piston over the rod and slide the new wrist pin through the side you haven't installed the C-clip, through the wrist pin bearing, up against the C-clip you did install.  

If you don't have a rag around the rod to keep things from falling into the case, put one there now.  All thats left is to install the last C-clip.  Its not un-common for these to pop out when you are trying to install, so the rag is important.  Its hard to put in words the easiest way to install them, everyone needs to figure out what works well with them.  I generally lay a clean rag over the newly installed piston to protect it while I clean up the head and cylinder Image .

Now back to the cylinder.  Next I took the reed valve out and front cover off the powervalve.  The reeds looked great, no chips or cracks so I chose not to replace them.  I just cleaned the assembly and put it aside.  The powervalve is dirty Image, but not as dirty as I expected and it moved freely. Unless something is broken or its really carboned up, you normally do not need to completely disassemble the power valve.

Here is how I clean things up and get ready to re-assemble, starting with the head.  I spray some EZ-Off oven cleaner on the bottom of the head and wait 10-15 minutes.  Oven cleaner will start to pit bare aluminum after about 30 minutes, so don't let it sit for more than 20 minutes.  After 10 minutes I use a scotch-brite pad to easily clean off the carbon; then I wash the head immediately in hot soapy water (Dawn dishwashing soap) to remove any dirt or oven cleaner.  Here is the result Image.  Not bad.

Now; for the power valve I use a good professional grade of carb cleaner and hose off the powervalve and cylinder walls.  My valves cleaned up nicely and still worked smoothly after this Image.  

Next I sprayed some oven cleaner down the cylinder bore and again let it set 10 minutes or so.  Using a scotch-brite pad, I cleaned the cylinder bore by following the existing cross-hatch pattern to remove any build-up or deposits.  Immediately after this I use hot (HOT) soapy water (Dawn again) to thoughally wash the cyilnder to remove any oven cleaner and loosened crud.  If your power valves are carboned up you can spray some oven cleaner on them as well, but again don't let it sit more than about 10-15 minutes and wash thouroghly in hot soapy water.

I used my compressor with the air-gun nozzle and dry the cylinder (using hot water helps it evaporate faster).  Once dry I take a clean rag and wipe the bore down with 2-stroke oil and lube the pivot points of the power valve as well.

We are now ready to start installing everything back together.  On the Yamaha YZ-250, its nearly impossible to get the power valve cover on/off with cylinder installed, so using a new gasket install the cover on now.

Place a new base gasket on the cases (on the Yamaha gaskets, there is a side with sealer and writing, this goes down towards the cases).  There are two methods people use when installing the cylinder.  Some use the dry method, others use some oil on the cylinder.  The
dry method is supposed to cause the rings to seat faster (brief metal to metal contact during first start).  This goes against my engineering background, so I use "some" oil.  I basically make sure the cylinder and rings have a light coating of oil (I wipe as much off as I can; it doesn't take much).

The next step can be fun, holding the cylinder with one hand, line it up with the piston and compress the rings with the other hand.  The cylinder should slide down with little fuss Image.  

If it doesn't want to go it may be one of the rings isn't lined up with its pin.  Don't try and force it as you can damage the ring or piston.  Once the cylinder slides down, slowly move the kick-start lever to make sure the piston moves freely up and down in the bore.  Once you are sure everything is moving well, place the four nuts back on the studs and snug them down with your hand.  Once snugged by hand get your trusty torque wrench and Motion Pro adaptor out and slowly tighten each nut a bit at a time in a criss-cross pattern until each has been torqued to its proper value.  Again, move the kick
start lever to make sure everything is free moving .

At this point I like to hook up the power valve arm again.  Place the arm back over the end of the valve and place the locking pin through it into the case as before.  Now you can put the bolt back in and tighten it.  Make sure to remove the pin and put it away for future use.

Next we need to put the head back on.  Take the new head o-rings (again, don't re-use the old ones) and give them a light (LIGHT) coating of lithium grease (I put some on a finger tip and while holding the o-ring just slide it around).  This allows the o-rings to be able to slide and move a bit as the head is torqued down so they don't snag or twist.

Place the orings in place and carefulley slide the head into place.  Place a new copper washer on each stud and by hand screw on the acorn nuts.  Once snugged by hand, use your torque wrench in a criss cross pattern to snug each down a bit at a time untill all are at the proper torque.

Place the reed assembly (using a new gasket) into the cylinder and tighten the bolts again using a criss cross pattern to prevent warping and get a good seal.

Install the head stay back to the frame/head. Install the radiator hose back into the head. To install the power valve cover; I place a bit of Yamabond 4 on the gasket (its a good sealer, not RTV) and screw the bolts back on.  Place the carb back into the mount on the reed block (don't forget the throttle positioning sensor hook-ups if you disconnected them).  Install the sub-frame.  Install the expansion chamber and silencer.

Take a few minutes and give everything a once over to make sure you haven't forgotten something.  Next refill the radiator with anti-freeze.  (After the first run in, check the level again and re-fill as needed.)

Install the tank and seat.  Thats where I am now.  It was 65 degress when I started on Wednesday.  

Today, Friday its 26 and flurries.  I hope to start it Saturday and run it for two 15 minute heat cycles.  I'll post back on that event.  If all goes well I will then put the radiator wing shrouds on and call it a success.  
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Dave H 2006 YZ250
(2008 YZ 125 son)

wow, i read the majority of it. im favoriting this in the event that i end up with a yz250.  
2005 YZ250F
2006 RM250
Tragedy and hardship are the forge that produce men of steel

Your the man DJ. Great Top end and great Pics. I like the way you take great care to cover and wrap things as you go to prevent contamenation and dirt getting into parts.
You also take your time and make things easy on your self by taking the sub frame apart. I like the oven cleaner use. But i always thought it would pit the aluminum because it's so hard to get off.
But it seems the dawn does a good job.
I also use dawn on parts lol. And i can't get over the Condition of your piston and rings! After 2 years!
And your so right that when we say 32:1 and proper jetting is key to a long lasting 2 stroke, You just showed it. Cool.
As for the power valve i use break cleaner.
BAD? Also i like that you used oil to set the piston. I disagree with a dry fit to seat the seals. As well as a arp out a freash top end to do it. I like a gradual break in. And great call on the new packing. Way over looked. And with the new top end it's going to be sweet.
Looks like your bike is burning great. Would have liked a pic of your plug as well to show what a good burn looks like for others. Cool post DJ. Great info and step bye step. Will read again and maybe have a question or 2. Thanks for taking the time.  
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DIABETES SUX!

Nice, I will put this on the shelf incase I ever get that YZ250.  
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I love this dirt stuff.

I'll try and take a picture of the plug, its a nice tan color when riding at the track.  My camera doesn't seem to like close-ups; they tend to blurr easily.

The oven cleaner is safe as long as you don't let it sit more than 20 minutes and use hot soapy water to rinse it off.

Brake cleaner and carb cleaner are similar; so I think either does the job.  I read once where carb cleaner does clean varnish etc better than brake cleaner.

I was really surprised at the piston and cylinder condition (especially after seeing some dirt on the carb slide; that scared me...)

Really, as long as you have a manual and take your time; a top end can be done by the average weekend warrior easily.  
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Dave H 2006 YZ250
(2008 YZ 125 son)

And thats a by the book top end and more.
With great tips as well.
He just showed what attention to detail can do! And know this...The dealer will not come close to what he did as far as a full piston,power valve clean ect...let alone pipe and head clean. If it looks good they leave it and replace what is needed. And in some cases what Don't need to be replaced! This thread can save the averege 2 stroke owner about 150 dollers!
Hey Dave, Can you post what you paid for all said and done?
Also was wondering if you check the ignition timing before you put the head back to insure TDC and roter alignment?
Also i use hi temp blue goo when instaling the the head gasket. What do you use?
And i'v been using Bel Ray grease on my fly and valve. Your opinion?
Thanks. YZ WOODS  
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DIABETES SUX!

If your using a digital camara it should have a macro setting which is a picture of a flower most of the time. On this setting you can get as close as you want and it will be in focus.  
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I love this dirt stuff.

Nice instructions. I have been trying to decide if I could tackle a top end replacement. How much different is a KDX 220? I bought the bike in early spring, so this is my first season riding it. It's a 1997. I don't have a lot of history on this bike. What should I expect to find? I do have a manual but not alot of two stroke maintenace experience.  
chris

I don't have a 2-stroke and probably won't in the near future (I do like them though) but thanks for taking the time to snap pics and do the write-up, great demonstration.  

i'm about to do my topend on my 2003 yz 250.... this is perfect... thanks for taking the time DL cause its going to help a whole lot of people  
03 YZ250 94 WR250z

kytrailrider:
Nice instructions. I have been trying to decide if I could tackle a top end replacement. How much different is a KDX 220? I bought the bike in early spring, so this is my first season riding it. It's a 1997. I don't have a lot of history on this bike. What should I expect to find? I do have a manual but not alot of two stroke maintenace experience.

Should be pretty much a similar process on the KDX; I am not familiar with the Kawasaki power valve though; so I can't help there.  
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Dave H 2006 YZ250
(2008 YZ 125 son)

Basic costs:
Qty Description Price Each
1 O-RING GASKET Blk Head $3.14
1 O-RING GASKET Red Head $3.50
1 GASKET (PV COVER) $2.96
1 GASKET, CYLINDER-BASE $15.60
1 Piston Kit $88.00
1 wrist pin bearing $10.96
1 YZ250 SILENCER PACKING $88.00
$212.16

Plus 2 cans of carb cleaner and some Oven Cleaner.  Take out the silencer and its about $125.00.  The Dr D Hour meter was $36.00.  
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Dave H 2006 YZ250
(2008 YZ 125 son)

I have .3 hours (thanks to Dr D meter) and very cold hands; but it ran great.  Never gave it above 1/2 throttle buts it definitely spunky.

After it cools down (and I warm up) I plan to take it for another breakin run where I will let it rev up a bit more.  
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Dave H 2006 YZ250
(2008 YZ 125 son)

great post DL, we all can learn something from it. thanks  

Autismspeaks.org
Gilbert AZ
06yz144,05yz85,02yz85

Hamblin just to let you know that you are a legend for putting this up... i've saved it on my hardrive for future reference... thanks again!  
03 YZ250 94 WR250z