Cylinder pics....bad news?

Personally I wouldn't over think it...Considering that your cylinder still had good crosshatching showing before you even started, you should be fine...I would just replace the rings and call it a day...Just start putting some money aside for your next top end, at which time you should go all out and have the cylinder plated, new piston/rings, and get into the bottom end bearings, and possibly crankshaft, etc...

Should I hone a new OEM cylinder? Or is the factor job sufficient?

The cylinders are ready to use as delivered.

This is a bad cylinder. You can see the plating is gone....Oh btw gray, this cylinder only has slightly over the .002" wear. The .002" spec you quote is for the out-of-round limit (which makes no sense since the service limit for the bore size is 3.7402-3.7406, a difference of .0004")

The main concern is the clearance between the piston and the cylinder, .0016to .0026"

CIMG1114.jpg

Your cylinder you have looks like its fine. Check it if you must but I wouldn't hesitate using it for a while longer if the bike is not raced competatively (money or sponsorships involved).

....Oh btw gray, this cylinder only has slightly over the .002" wear. The .002" spec you quote is for the out-of-round limit (which makes no sense since the service limit for the bore size is 3.7402-3.7406, a difference of .0004")
Check again. The bore size is given as a normal range for a new or refinished cylinder, not a wear limit. The only wear limit given is the out of round. :cheers:

But it does point out how little wear is truly tolerable in these. The question is, when you are looking at a cylinder that is still plated, how thin is the plating, and how long until it looks like that one?

The bore size is given as a normal range for a new or refinished cylinder, not a wear limit.

But it is still considered a defacto service limit: and the reason is the cylinder is considered a 'non-servicable' part. If the wear falls much outside this range the cylinder will not have correct piston to cylinder clearance. As I'm sure you are aware, back in the old days, when a new piston was purchased the diameter had to be measured before the machinist finished the cylinder and the variation from one batch of pistons to another from any given manufacturer was quite large. Now, because everything uses plated cylinders instead of spun-cast iron liners the tolerances have been tightened up considerably by the piston manufacturers. Gone are the days where you "make the cylinder fit the piston". There are some manufacturers that offer A, B, C, sizing for pistons but this is more to accomidate matching A, B, C, sizes on cylinders than making up for wear in the cylinder. The same thing goes for cam lifters on the YZF, WRF (most people dont realize that the valve tappets are available in different sizes to match tolerance ranges on the cylinder head). The important thing to remember is the condition of the plating and, again the most important thing to shoot for is the correct piston/cylinder clearance. Too much and you wont get a good ring seal, not enough and you risk siezing.

I guess my point is that the cylinder pictured at the beginning of the post still looks pretty good and the owner has done a good job of maintaining his machine. I lived and worked in a world where customers would balk at spending $350 for a cylinder when the original was good for one more season. But of course there is the occational bone-head that tries to stick an Auto Zone air filter (no joke!) on their machine and can't figure out why it smokes so much and uses oil (that's the pic I posted. I have two more cylinders like it).

Typically plating like this is .001"-.002". A good indication of wear on the cylinder is bore is the ammount of remaining cross hatching. If there is not enough of a ridge at the top of the cylinder to detect with your finger nail I'd let the cylinder go for 1 more piston.

I'm aware of all that, but you're still off the mark on the bore size specification. It's given as the new manufactured range, and is not a wear limit of any kind. Note that the piston to bore clearance ranges from .0016" to .0026", with a limit of .004"

You can have any opinion you like regarding the OP's cylinder, but the idea that you can call it safe based on remnant visible cross hatching at mid bore when the ring shadow at the top of the bore is an obvious area of deeper wear is not really something you're going to be able to sell me. If they don't clear with a quick pass of a ball hone, they're cause for concern.

I'm aware of all that, but you're still off the mark on the bore size specification. It's given as the new manufactured range, and is not a wear limit of any kind. Note that the piston to bore clearance ranges from .0016" to .0026", with a limit of .004"

That limit of .004 for piston/cylinder clearance gives you a max of .0014cylinder wear assuming the cylinder and piston were at the high limit when new. In my experience, a cylinder with .0014" of wear has no or very little remaining hone marks and appears much worse than the one at the begining of the post. Maybe after working as an aerospace machinist doing close tolerance work (some stuff with a tolerance of .00006" (that's sixty millionthes of an inch) doesn't qualify me for anything but I have a pretty good eye for gauging wear depths based on the Ra finish.

Again the most important item to measure is the piston/bore clearance. fitting a new piston and getting a .004 clearance is unacceptable and would indicate the cylinder is worn beyond service regardless regardless of the bore size (assuming the piston is at the high limit on diameter). Measuring the cylinder alone accomplishes nothing, it is really meaningless tp do so without subtracting the piston diameter. That's why Yamaha doesn't give a wear limit for the cylinder.

To tell someone the cylinder is bad because because it is worn .002" without knowing what the piston/cylinder clearance is not sound advice. A plated cylinder with .0014" of wear looks REALLY bad (not as bad as the one with the plating worn off). There will be little evidence of hone marks in the top 33% of the cylinder with this much wear.

Well, then, what's your opinion of the completely missing cross hatch in the ring shadows?

You're kind of all over the map on this, aren't you? You've said that if a cylinder has .0014" wear, it won't show a cross hatch, and that indicates it should be refinished, and then you say that it's incorrect to state that a cylinder with .002" wear should be refinished without considering the piston clearance when .002" is the stated limit.

Sorry, but I'm having a hard time tracking this one.

Anyone know if my performance issues can be caused by a faulty flywheel? I've had to take it off a few times and each time required me to tap/ hit the flyweel with a hammer for it to pop off while under pressure from the puller. When tightening the bolt that jams into the crank on the puller after so much torque it just doesn't feel right. So to prevent from messing up the crank by cranking down too much on the puller I tap the flywheel and it pops off eventually.

You should not tap on the flywheel in that situation. It's far less risky, and much more effective to strike the end of the pressure screw sharply once or twice.

What performance issues?

Anyone know if my performance issues can be caused by a faulty flywheel? I've had to take it off a few times and each time required me to tap/ hit the flyweel with a hammer for it to pop off while under pressure from the puller. When tightening the bolt that jams into the crank on the puller after so much torque it just doesn't feel right. So to prevent from messing up the crank by cranking down too much on the puller I tap the flywheel and it pops off eventually.

Catch us up on what you did with the cylinder...Your last post just said you were going to call a local shop...What was the outcome? Did you at least use new rings? What are the symptoms of "performance issues"?

I'd rather put a little extra torque/pressure on the very end of the crank with the puller than hit the flywheel with a hammer anyday...But yeah, if it's really stuck on there maybe the woodruff key wasn't lined up in the groove correctly or something???

Well unfortunately all the shops around here are bad and don't do any kind of cylinder work at all. No measuring, honing nothing. So I just put it back together with the same piston/ rings that I had just put in less than 20 hours ago. I put in new SS valves and gaskets. I never had and still don't have low compression so the rings are seated I would believe.

The problem is somewhat like an air leak, yet I can find no air leaks and have checked anything and everything replacing intake boot, rebuilt carb, replaced gaskets, etc.

The bike runs slightly better now than it did before I tore it down, but still not where it should be. The power is uncontrolable and comes on way to fast and tops out at like 1/2 throttle. THIS IS NOT NORMAL as some have tried to tell me it is. This bike used to have a smooth powerband with somewhat mellow bottom and a midrange hit and would pull for a while at WOT. Now it has an instant hit at 1/4 throttle and revs out at 1/2 throttle.

Oh yeah forgot to mention jetting. I have tried lean, rich, super rich to no avail and nothing cures the problem. I rebuilt the carb as I mentioned and put it to stock yz settings as my engine is tuned yz. Didn't help.

The power is uncontrolable and comes on way to fast and tops out at like 1/2 throttle. THIS IS NOT NORMAL as some have tried to tell me it is. This bike used to have a smooth powerband with somewhat mellow bottom and a midrange hit and would pull for a while at WOT. Now it has an instant hit at 1/4 throttle and revs out at 1/2 throttle.
You changed your exhaust cam, didn't you?

Yes I did I put a hotcam auto decomp in. It didn't run like this when I first rebuilt it and put the cam in. Also I have read from you and others that changing the exhaust cam does not mess with the power hardly at all. Many people have put this same cam in and there is no way they would ride the bike as it is now.

The bike runs lean from what I feel, how white the spark plug is and how hot it runs. I just don't see how it can suck air after replacing all seals/ gaskets that have to do with air travel/ compression.

...I have read from you and others that changing the exhaust cam does not mess with the power hardly at all.
If you go from a WR to a YZ cam it does. That's the only real difference in the two engines.

But I'm having a lot of trouble understanding your description of the way it runs, what with the "revs out at half throttle" thing and all.

I had YZ timing for the last 5+ years, stock cams are the same on the WR/YZ 426.

In other words 1/2 throttle and up is useless and does absolutely nothing when you twist that far. It's like 1/2 throttle revs at the rev limiter now. I haven't actually felt the rev limiter (I would guess it has one?), but the feeling of it and sound of it is what I'm going by. The bike is hard to start and I have to twist the throttle slightly to get it to fire. Once fired it idles fine. 1/8th to 1/4 throttle is decent but after that it just explodes with power and the power tops out at 1/2 throttle. It does not gain any more power after that, or even have rev changes. The throttle cable is new and adjusted correctly. No cracks in the slide, new seal on the slide. Slide is installed correctly, carb is fully rebuilt.

'01 WR426 intake cam: 5BF-12170-10-00

'01 WR426 exhaust cam: 5BF-12180-01-00

'01 YZ426 intake cam: 5BE-12170-10-00

'01 YZ426 exhaust cam: 5BE-12180-01-00

The cam lobes are the same, but the lobe centering (timing) is different on all four cams. But be that as it may.

Try looking at the top of the needle jet (main discharge nozzle); the brass part where the needle goes. See if it's visibly worn out of round.

I did already check out the needle jet and could not find anything wrong, it was not ovaled out.

So are you saying that if you time a WR with YZ timing there is still a difference from that to a YZ? I guess that could be but there are tons of threads on here and I've never seen anyone say that.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now