A few questions about rebuilding my 02 yz426

Im in the process of pulling the engine out of the frame and have a few questions

1) What tools will I need, I am going to replace the transmission (2nd gear is gone), piston, piston rings, cam chain and what ever else I can find in there that isn't in spec.

2) When I install the piston do I need to hone the cylinder first?

3) What are cheap ways to gain power?

4) Are there any good threads with pics or videos on how to do this?

5) What octane gas will I need to run with a 13.5-1 piston?

Thanks

Joel

Edited by jojo1224
Added a question

Once you split the cases, You will need a pair of snap ring pliers to remove the indiviual gears. You will also need that pair of snap ring pliers to remove the snap ring that holds the piston pin. It is also handy to have a case splitter.

I usually give the cylinder a quick hone with a glaze breaker.

You can run pump gas with the high compression piston.

You will get a little extra power with a high compression piston but not a crazy increase in power. You can send your head out to get some porting done that will run you around 300 bucks from a person that knows what he's doing. Porting is a great way to make power.

I would invest in a Hot Cams exhaust cam for your engine. That way you can get rid of the manual compression release. Plus you may see a little increase in power with that cam also. Dont forget to replace the cam chain also.

I went on a tool shoping spree today, now I got the head and cylinder off well the head looks good and same with the cylinder except for one spot it looks worn. I will upload pictures as soon as I can get them off the camera.

This is the bad part, its on the intake side.

TyQ8L.jpg

The Valves.

u96se.jpg

The exhaust side of the cylinder.

h6DhP.jpg

This is the bad part, its on the intake side.

TyQ8L.jpg

The Valves.

u96se.jpg

The exhaust side of the cylinder.

h6DhP.jpg

Is any of the scoring deep enough to catch your finger nail if you run it across the grooves? If it is you need to go get the cyl replated.

There appears to be transferred aluminum form the piston on the intake side, but it's hard to tell from a picture. If there is, replace it or replate it. If not, make 3 quick passes with a 4" bottle brush hone (280 grit, aluminum oxide or softer). If that eliminates the visible scratches and "shadows" from the top ring at the top of the bore, then the cylinder is usable IF the clearance to a new piston is correct and iy measures straight/round within tolerance.

The valves should be tested for leaks before disassembling by filling the ports with solvent. Seepage is tolerable, but more than that and a valve job is in order. Eveb if the valves pass a leak test, they should be inspected for wear. DO NOT mix them up if you intend to reuse them; make sure you know which port they came from. Here's a guide to what you're looking for:

Valve wear

Anything that looks more worn than the one at the upper left should be replaced. Replacing valves REQUIRES the seats to be refinished, and this is a job fro a professional machinist with specialized equipment. NEVER lap a titanium valve.

With a 426, you have the option of using the stainless steel valves from the 2000 model, which cost about a quarter of what the Ti valves do. Be sure you also buy the correct springs for the 2000 valves.

Is any of the scoring deep enough to catch your finger nail if you run it across the grooves? If it is you need to go get the cyl replated.

Nope

There appears to be transferred aluminum form the piston on the intake side, but it's hard to tell from a picture. If there is, replace it or replate it. If not, make 3 quick passes with a 4" bottle brush hone (280 grit, aluminum oxide or softer). If that eliminates the visible scratches and "shadows" from the top ring at the top of the bore, then the cylinder is usable IF the clearance to a new piston is correct and iy measures straight/round within tolerance.

The valves should be tested for leaks before disassembling by filling the ports with solvent. Seepage is tolerable, but more than that and a valve job is in order. Eveb if the valves pass a leak test, they should be inspected for wear. DO NOT mix them up if you intend to reuse them; make sure you know which port they came from. Here's a guide to what you're looking for:

Valve wear

Anything that looks more worn than the one at the upper left should be replaced. Replacing valves REQUIRES the seats to be refinished, and this is a job fro a professional machinist with specialized equipment. NEVER lap a titanium valve.

With a 426, you have the option of using the stainless steel valves from the 2000 model, which cost about a quarter of what the Ti valves do. Be sure you also buy the correct springs for the 2000 valves.

Ill take the cylinder to a local shop to get it honed, if it is still to bad ill get it bored and replated. What solvent should be used to test the valves?

  1. Shop solvent (Stoddard solvent)
  2. Mineral spirits
  3. Paint thinner

My one thing I recommend is several zip lock bags to keep all the parts in and together. I like to group the parts together by use and location. Best of Luck on the rebuild.

Bill

My one thing I recommend is several zip lock bags to keep all the parts in and together. I like to group the parts together by use and location. Best of Luck on the rebuild.

Bill

Way ahead of you, I bought a box of big ziplock bags and a sharpie.

Good deal, best of luck with your rebuild. Mine has held up very well with one piston replacement. I keep the valves checked, the gear box and fork oil changed by time on the SenDec timer and good chain and sprockets.

Bill:thumbsup:

Well I didn't have any solvents so i used some new oil from a bottle laying around (10w40) and the exhaust valve furthest away from the exhaust valve leaks alot but nothing from the other 4. I pulled oil filter cover and a bunch of oil filled with shavings came leaking out and it looked like a unicorn jizzed in the oil it was so sparkly. When I took out the bottom oil filter cover bolt it looked worn and had some threads stuck to it. Also the oil bolt on the head was stretched and had some threads stuck to it. This is going to cost me alot more then I expected it to. Well thats what I get for buying a 8 year old bike for $1400 CND that I knew had a blown 2nd gear and a lot of hours.

Edited by jojo1224

My mom picked up my cylinder from the local dealer and they honed it and said its fine but also said it will smoke and that I should get it bored and replated later on if I plan on keeping the bike. They quoted $305 CND to get it done, is there a cheaper place in Canada that I could ship it to and get it done?

If it's "fine", why would it smoke?

Not sure, I will upload a picture of the cylinder when my mom gets home in 2 hours.

I have not gotten around to take a picture of the cylinder but looking at it I notice marks going vertical that I didn't see before it was honed but my finger nails don't get caught on them. Im in the process of checking the ring gap, the top ring is at .28mm and in spec, 2nd ring is .55mm and out of spec by 5mm, and the 3rd ring is .98mm and way out of spec.

I have hit a snag, I can't get the clutch basket off and also can't get the sprocket off. But I have found out I need a new crank. Who sells one for cheaper then $500?

It is $475.74 from TT for the complete assembly, thats way to much. Is there a cheaper place?

EDIT: It is $465.11 from Cheap Cycle Parts for the same part. It seems after market ones haven't been made for this bike for a while.

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