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I'm working on a top end rebuild for my '01 KDX200.

I measured the ring end gap by placing my new Wiseco rings into to the top of the cylinder and pushing them down a little ways with the new piston.

I came up with measurements of between 0.40 - 0.45mm. The manual says the Specification is 0.15 - 0.35mm and the Service Limit is 0.65mm.

Does it look like my end gap is OK or is it going to be a problem?

Did the manual specify a certain distance down inside the cylinder to measure it?

If so and you are at the correct distance, then you are less than the service limit. Is that what you are asking??

Jason wrote:Did the manual specify a certain distance down inside the cylinder to measure it?

If so and you are at the correct distance, then you are less than the service limit. Is that what you are asking??

Thanks Jason. I'll double check what the manual says.
So if it's 'less' than the service limit that is OK, but if is 'over' the service limit that would be a problem?

That's correct.

The ring is softer than the cylinder wall. It will wear over time on the outside due to the rubbing. It will allow the ring to expand, causing the gap to increase.

Jason wrote:The ring is softer than the cylinder wall. It will wear over time on the outside due to the rubbing. It will allow the ring to expand, causing the gap to increase.

So I went ahead and measured the end gap using my old rings, and the results are about the same.

I'm not sure what to do now.

Could I have gotten a bad set of Wiseco rings?

Should I just send the cylinder off to Millenium for a replate?

Should I put it back together with the big ring gap and just ride it?

I'm kind of stuck on what I should do. Do you guys have any suggestions?

What did the manual say?

Jason wrote:What did the manual say?

The manual didn't specify how far down to place the ring before the measurement.

I put it about 1 inch down in the bore and did the measurement.

The manual says: Specification 0.15 - 0.35mm; Service Limit 0.65mm.

One of the new rings measures between 0.35 and 0.40mm and the other new ring is measuring between 0.40 and .045mm.

I'm probably over thinking this, I've never done a top end rebuild before and I don't want to mess it up.

If the cross hatching is wore enough you would need to replate. A worn bore will cause the ring gap to increase. I just got my top end finished with a new Wiseco piston and rings and I had Millennium replate the cylinder. My ring end gap was .15

That could indeed be the difference.

javjacob wrote:If the cross hatching is wore enough you would need to replate. A worn bore will cause the ring gap to increase. I just got my top end finished with a new Wiseco piston and rings and I had Millennium replate the cylinder. My ring end gap was .15

Thank you Java. I thought that gap seemed awfully big. I'll work on getting it ready to send to Millennium.

Jason wrote:That could indeed be the difference.

Thank you Jason. I think I''ll just get it replated.

I just went through this last month with a Wiseco on my XR400 build. The end gap was substantial on my freshly honed cylinder using the Wiseco piston & rings. Unfortunately Honda didn't list the service limit on end gap but I was almost triple the specified end gap per my service manual. I decided to run it since a 4S has multiple rings staggered to cover the gap. So far so good, no smoke on start up & plenty of power. I would call Wiseco& Millennium before sending off the cylinder to verify if the gap is OK or not.

fishwater wrote:I just went through this last month with a Wiseco on my XR400 build. The end gap was substantial on my freshly honed cylinder using the Wiseco piston & rings. Unfortunately Honda didn't list the service limit on end gap but I was almost triple the specified end gap per my service manual. I decided to run it since a 4S has multiple rings staggered to cover the gap. So far so good, no smoke on start up & plenty of power. I would call Wiseco& Millennium before sending off the cylinder to verify if the gap is OK or not.

Thank you Fishwater for this. I called Wiseco and the tech seemed to think that the gap I was getting was just fine.

I also called Millennium and the tech suggested getting the bore diameter measured. Since I don't have measuring tools I might swing it by a machine shop and have them give me a measurement.