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Jamie, that's great you're making a comparison between silicon o-rings from the big bag supplier and Fredette's o-rings. Good idea and many of us are greatly interested in your results.

Chopperpilot wrote: 12:25 pm Mar 27 2025 I just got a customer satisfaction query from them, perhaps a bit of tit for tat is in order? I can tell them there's a community interested in purchasing these seals and perhaps they could make them available. Should work unless they bought up all the NOS and are just hoarding them for their kits?

Chopperpilot, I'd tell them if they'd take the time to earnestly consider our forum's question and provide a serious answer about the correct seal will go a long way to keep forum members fans of MT's services. I'd continue by saying, even if the answer is, "We don't change it," we'd remain fans. I'd also include something like, "To date, MT has not seriously addressed the recent interest communicated by paying customers about what seal MT installs on the righthand power valve rod."

Update: I installed one of the silicone O rings from the 50ct bag. 8mm od, 5mm id, 1.5mm cs
The assembled engine passed a 5 minute 5psi leak test and the KIPS is opening and closing as it should (as observed from the LH side blipping the throttle with the slotted cover removed).

Still waiting on Fredette's O rings so i can compare, but early evidence suggests that the above size O ring might be on to a useable off the shelf fix. Turns out it's also easily found made from Buna, so that might be even better if the silicone proves to be too soft.

Hope to get some riding in and have another update later this week

THANK YOU!!

jamiethegiraffe wrote: 08:03 pm Mar 30 2025 Update: I installed one of the silicone O rings from the 50ct bag. 8mm od, 5mm id, 1.5mm cs
The assembled engine passed a 5 minute 5psi leak test...

...Still waiting on Fredette's O rings ...

jaimegiraffe, it's terrific that you thought to test a Byna rubber o-ring in this way. Very curios what you'll report with the silicon "Fredette" O-ring

Just to be clear, I’m using a silicone o ring now. I have not yet purchased a buna o ring of the same size

Got it! Even better.

jaimegiraffe, please identify source for the silicone o-rings you purchased. Thank you in advance.

billie_morini wrote: 01:31 pm Mar 31 2025 jaimegiraffe, please identify source for the silicone o-rings you purchased. Thank you in advance.

I bought them on ebay. It looks like they're available from amazon as well. "uxcell" is the manufacturer. I'm putting a link below as well as a screenshot for posterity.

https://www.ebay.com/itm/126950118107

I received the Fredette O rings today. They are not completely identical to the one's i bought on ebay- the color is slightly different and the material feels maybe ever so slightly firmer. There's no measurable or discernible difference in the sizing.

ebay O rings on top- FRP O rings on the bottom:
Here's the ebay O ring installed. It would be nice if one could find a 8x5mm O ring with a larger cross section, but my searches haven't turned anything up besides 1.5mm CS

i got to take the bike out for a couple of hours this afternoon. The weather was really nice and the motor felt in top form. Powervalve is definitely functioning properly and gone is the popping on decel and hanging idle i had last week when running the worn out OEM 'packing' seal. This O ring seems like a winner if it holds up, and if it doesn't, I'll try the same size made in buna.
I have a bag of 49 of these things so if any of my fellow KDXers want a couple to try, i'd be happy to send them to ya for the price of postage.
Just send me an email: jamiethegiraffe@gmail.com
Still interested to see if Kawibunga goes forward with his machined groove + X ring solution, and still wish Millenium would tell us where they're getting those OEM lookin' seals!

jamiethegiraffe wrote: 08:34 pm Mar 31 2025 Still interested to see if Kawibunga goes forward with his machined groove + X ring solution, and still wish Millenium would tell us where they're getting those OEM lookin' seals!

My plan is to still give it a try! But great we got another solution going that works

Will update as things progress as there's along........

jaimegiraffe,
thank you for the positive report and notes, inclusive of the photo of a green motorbike in the forest leaves.

You expressed interest in a slightly wider o-ring. I wonder how much the o-ring widens from squishing when the rod is installed.

I located a silicone o-ring that has a 1.78mm cross section, but inner diameter that is slightly less than 5mm. If interested, then:
1. Go here: https://www.oringsandmore.com/1-78mm-cross-section-2/
2. Scroll down to SKU 447178MMS to see 4.47mm ID x 8.03mm OD x 1.78mm C/S

Do you think this o-ring offers potential promise? If so, then I'd buy some and trade some of yours for some of mine!

jamiethegiraffe wrote: 08:34 pm Mar 31 2025
Here's the eBay O-ring installed.

I got to take the bike out for a couple of hours this afternoon. The weather was really nice and the motor felt in top form.

***...and gone is the popping on decel and hanging idle i had last week when running the worn out OEM 'packing' seal.***

This last part really hit home with a eureka moment for me...
I've been fighting a pipe bang type popping on closed throttle deceleration for a few years, adjusting Lectron metering rod settings and Keihin jetting up and down with excellent performance but an inability to get rid of the popping / pipe bang on deceleration...

I'm waaaaayyyy overdue on a top end inspection and cleaning (like 375+ hours on the current top end in 4 years...), so perhaps I'll swap this packing seal out and clean my KIPS & inspect the plating, piston, & rings sooner than later...

The amount of hours on my engine go to prove that 40:1 running a good synthetic/castor blend pre-mix is vastly superior to KTM's unprotective 60:1 recommendations and how little oil their late model bikes use - causing everything to wear out rapidly including launching pistons through their cylinder heads inna total destruction episode...as well as 2 or 3 yr old Austrian bikes needing bottom end rebuilds....

THANKS FOR THAT COMMENT!

billie_morini wrote: 11:51 am Apr 01 2025
You expressed interest in a slightly wider o-ring. I wonder how much the o-ring widens from squishing when the rod is installed.

I located a silicone o-ring that has a 1.78mm cross section, but inner diameter that is slightly less than 5mm. If interested, then:
1. Go here: https://www.oringsandmore.com/1-78mm-cross-section-2/
2. Scroll down to SKU 447178MMS to see 4.47mm ID x 8.03mm OD x 1.78mm C/S

Aren't those the dimensions of the -008 size o-ring?

billie_morini wrote: 11:51 am Apr 01 2025 Do you think this o-ring offers potential promise? If so, then I'd buy some and trade some of yours for some of mine!

Billie, I think it does offer some promise, though as chuck just pointed out, that’s the same dimension as the 008 X ring he posted on page 2 of this thread. I guess if I had the option to choose between the two, I would probably try the McMaster 008 X ring.
But wait a sec, isn’t that exactly what kawibunga is already working on??
Does that mean that the 008 X ring has been deemed “too big” when fit to the KIPS rod without any machining?

Chuck78 wrote: 11:54 am Apr 01 2025 I'm waaaaayyyy overdue on a top end inspection and cleaning (like 375+ hours on the current top end in 4 years...), so perhaps I'll swap this packing seal out and clean my KIPS & inspect the plating, piston, & rings sooner than later...

Holy crap! 375 hours on a piston is pretty wild. The packing seal definitely might have something to do with your popping on decel, but the only way to know for sure is to leak test the motor and verify that it’s not sucking air from anywhere else. When sprayed with soapy water, you’ll see bubbles form near the KIPS actuator shaft/rubber boot if it’s the packing seal letting air by.

Chuck78, looking forward to hearing if the Fredette o-ring solves the negative engine behavior you've been chasing.

jaimegiraffe, yes, the additional o-ring I hyperlinked for you has the same dimensions as the McMaster 008 x-ring that both Chuck & Kawi identified. Also yes, this is the x-ring that Kawi is working to determine the required groove depth for.

Kawi also told us that x-rings have less thickness and greater width than o-rings. Therefore, Kawi said, an x-ring groove is not as deep as an o-ring groove AND an x-ring groove is wider than an o-ring groove. Through the course of this forum thread, you've provided 2 photos that help many of us see this.

Most recently, I was trying to find a wider o-ring because you expressed interest in this. While I found an o-ring slightly wider than Fredette's 1.6 mm wide o-ring. I wasn't thrown for a loop even though the inner diameter is smaller than Fredette's 5 mm ID o-ring.

Given an o-ring has only 1 contact surface compared to an x-ring's 2 contact surfaces, i thought this additional o-ring my work. You have much more practical experience with this seal and the KDX engines. This is partly why I offered to get some of these o-rings for you to experiment with. Also, I partly offered because you offered to share your non-Freddette o-rings with all of us. I will ask you for some, but would like to reciprocate your generosity. I'll email my mailing address to you soon.

Just to be clear, an 008 Xring and an 008 Oring, are designed to fit and seal in the exact same groove profile with the same squeeze. The difference is the Xring with it's kinda square profile, will not "roll" during dynamic applications and provides more point's of contact. The oringal packing, all though it's top profile is Xring like, is not an Xring, as it's flat on the ID. It's cross section is wider than it is thicker as well. Standard Orings & Xrings all have a profile that is the same width as height............ hence us not being able to find a perfect fit for the existing groove. Because the oringal packing is a 2mm wide x 1.25mm high cross section.........

I'm still going to machine my shaft, but I have a some suspension parts I damaged that are going out at the same time for machining and I have to complete those drawings, hence its not quite being done yet. Maybe this weekend!

Thanks, Kawi. You sure know a lot of interesting stuff and your willingness to share is greatly appreciated.

Thanks for clearing that up fellas. Our H series KDX progeny will surely sing your usernames for years to come

Billie, I’d be more than happy to send you some silicone Orings- no strings attached! Though I certainly appreciate your desire to reciprocate. Same goes for Chuck, Kawi, or anyone else here looking for a quick fix- a round of O rings for the whole bar!

Sounds like the 008 sized O ring will be a tight fit, but If you do order some, I would be curious to perform a “squish” / drag test with one installed in the cylinder. It would just have to wait until the next time I pull my engine for a top end (or finally go pick up the spare basket case 220 motor waiting at my dad’s house!) otherwise, I’ll be out riding