Yzf 426 rebuild. Take a look on those valves


I'm tearing down and rebuilding my 01' yzf426.

Today i"ve took of the cylinder head and cylinder. The connecting rod is like new. Please take a look on the photos in link below and tell me what do you think about condition of those components.

Many thanks for any help.


Wow, thats a yami for you, 7 years old and looks like new. Stil see cros hatching in the cylinder...

Why did u tear down this motor?

How do the valve seats look?

I'll take the photo of valve seats today. I tear it down because 5th gear sliped 3 times.

Valve seats look like new. But take a look a little later.

I wanted to inspect connecting rod and I'm happy that I don't have to change it. I'll mesure the cylinder and piston but I think that there is no need to change them. Do I need to change the rings?

The valves look alright now, but the coating on them is so thin that it's very difficult to tell when they will wear through it and sink. You can either reassemble the head as it is and get an unknown amount of additional service out of them, or replace them. If you don't you'll need to wonder how soon you'll have to pull the head again, and if you do, you'll wonder how much useful life you could have got from them if you hadn't. :banghead:

If you reuse the valves, DO NOT lap, grind, or refinish any part of the valve face or seat. Assemble them back into their original positions.

You should definitely replace the rings. The piston looks good as far as wear goes, but you may want to replace it in consideration of possible fatigue. At the top of the cylinder, you can see "shadows" where the rings reverse direction under pressure. Seeing this, you need to do two things:

> Check the clearance of the rings in the piston grooves to be sure the ring grooves are not worn.

> Check the amount of wear that has taken place in the shadowed area. To do this without having access to a dial bore guage, you can insert the piston without rings and use it to push a compression ring into the bore squarely. measure the end gap with the ring near the bottom, below the area normally swept by the rings, and again with the ring in the shadow. If you measure a difference, divide that by 3.1416 to get the bore wear.

The cylinder should also be honed before assembling it, but not with a fixed stone hone. You should use a "flex-stone" ("spring ball", "bottle brush") like the one pictured below and at this link:


Lube the hone with solvent, and turn it at about 500 rpm. To use it, insert it into the cylinder and as soon as you start the drill, begin running the hone up and down the bore so that one pass down the bore, up the bore, and back down again takes about 1 second. As you make the 4th pass back up the cylinder, pull the hone out of the bore before stopping the drill.

The cylinder will now have the glaze broken in a cross hatched pattern, and if the wear at the top is not significant, the shadows will be gone as well. This process removes virtually no material from the cylinder, but puts down a surface in which the rings will seat almost as soon as the engine starts.

Clean the cylinder thoroughly with solvent. Then follow up by wiping the bore with a clean, lint free cotton cloth and some ATF (auto trans fluid). You'll be surprised how much the ATF will lift out of what you though was a clean bore.


You can use soft scrib and a sponge and hot water to get the carbon off of the head and other parts and make them look new. Just dry completely and coat with a little oil when done.

Your engine is very dirty, should have made it sterile clean before tearing it apart. I can see grains of sand on the crank in the crank photo. Be extremely careful about keeping the engine clean inside, especially bearing surfaces such as the cam caps. Sand will tear these things up.

Those pictures has been taken right after removing cylinder so yes there was a little sand on the engine. But now it is sterile. Now I'm going to split the cases. Off course each part will be agian cleand right before instalation. I'm en engineer so I now that everything must be clean during this kind of job.

From experneice, it makes the job a lot easier if you make everything sterile before any disassembly. I know it's difficult sometime when you're anxious to get inside and see what's going on, but it pays off to be patient. :banghead: Good luck!

I can't remove swing arm bolt. :banghead: I'll try to heat it and punch.

The bolt is likely corroded into place. The are steel sleeves in the swing arm bearings, and two more where it passes into the crankcases. Give the whole assembly a good dowsing with the best penetrating oil/rust solvent you can find, and leave it sit for 12 hours or so, reapplying occasionally. The you can try heating the sleeves in the crankcase.

Since you have access to stuff like this, make a brass punch with a pilot on the end that fits into the hole in the bolt. Leave the nut in place at the top of the threads to protect them from damage for as long as possible.

Good Luck.

Gray could answer this better, but I notice the wrong color springs on the valves.

According to the head, they should be white springs. Yet, you have a mix of blue and yellow. I don't know for sure if the spring colors indicate tensile strength, or clearance....

Something obvious that I saw though.

At $8 US apiece, the springs are throw away items anyway, and should always be replaced during any rebuild.

It is a lot more expensive to buy new valve springs here in Poland but I'll do this off course.

I've made special turnbuckle for the swing arm bolt. Long pin (8mm in diamiter) with thread on both ends. On one end (thread end of axle bolt) I used 3 nuts on the pin, I put the pin through the hole in the bolt, and put hard plate on the other end. Then the hard nut. When I was turning the nut the plate stoped on the frame and made a tension on the bolt. Then I hit the pin on the bolt thread side and thighten the nut, hit, thighten.... And in this way I've moved the bolt 2cm (as the bolt seating in the frame let) then it was easy to remove the bolt completly.

Grayracer please tell me if my vlave springs are realy not those I should have in my head?

I'll change them but is MXGENE sentens true?

Good work with the bolt.:banghead:

On the spring color, I doubt the paint stripes are as significant as Gene is suggesting. After all, those were installed by the factory, no? Then, too, yours is a Euro model, which could have several small differences. I wouldn't worry over that point. However, changing them only for preventative maintenance would certainly be wise.

Here comes new photos of my cylinder head and small end. Please tell me what could have happend to my small end? One side of the surface is ok and one is scratched as well the pin.

Take a look:


Something got in there with the oil, it would seem. I actually put a kid's 250F back together with a rod like that, but I can't say it's a wise move. I touched it up with a brake cylinder hone and used a new pin. The bike still runs at this point, but....

Best thing to do would be rebuild the crank. It's getting expensive, isn't it?

I'll check it if the surface on the small end is worn under the orginal surfece or it is the pin material on it. But it is almost certain that I'll use new rod in this rebiuld.

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