Clutch

[TEGRITY RMX]

When you get the needle let us all know how it works out in a “JD jetting kit” thread. ? Be interesting to know how the hash marks relate to the taper on them. ?

 

I still don’t understand how putting a bunch of axial groves in the chamber are supposed to make anything better with those RK heads.

I thought about trying to duplicate one, but cringe at the thought of pulling out the die grinder and going to town on one of my tight swish band heads.

The purpose of a squish band is to create a tight tolerance to promote swirl, shield the gasses at chamber edge, and get as much possible of the A/F mixture into a smaller, hemispherical combustion chamber, to quickly ignite it all before anything can reach self ignition temps…

Machining in a bunch of high and low spots, just seems wrong to me. Lol 

Rode with a fellow a couple days last month riding a new YZ250X. Pretty easily left him in the dust, and I was very rusty, not even riding all that well…?

Edited November 10, 2021 by TEGRITY RMX

[ricky racer]

The flutes in the RK head are very shallow. Couple thousands. There are some good articles out there on that thought process. The head made a crazy difference in my 300. I had a identical bike of my brothers in my shop while I was making changes to mine so I got to test every step of the way against a stock bike bought at same time from same dealer. The change with the head included raising the port timing .5mm and setting squish to .040" if I remember right was amazing! I forget what the compression was. Also lots of time spent tuning the power valve which resulted in the softest spring with less preload so the exhaust valve starts opening pretty early now. Anyway it is a monster and I raced 500cc bikes in MX for a while when I was younger so I'm no stranger to big bore power and my 300 is giving up nothing. Anyone that rides it cant believe how much power it makes and how crazy smooth the power is. HUGE window of power ? Smooth but not lazy. It will lengthen your arms hahahahaha

[TEGRITY RMX]

Never seen one in person. Photos probably make the RK machining appear deeper than than it actually is, and every one I’ve seen throughout all the 2 stroke forums look damn near identical to me. Narrow squish with a wide shallow chamber. Upper end focused power. 
 

I need to do more head testing myself. Not so sure I agree with Mixxer on the wide squish band heads for the power I’m after. or at least with my setup… Lost some top end with the last two heads I’ve tried on my 98, but I’m also not needing so much turbulence/squish velocity to make up for the lack of ignition timing with the stock RMX CDI. 
 

I do miss my old CR500 sometimes, but it was pretty impractical for most the single track stuff I ride..?

[ricky racer]

15 hours ago, TEGRITY RMX said:

Never seen one in person. Photos probably make the RK machining appear deeper than than it actually is, and every one I’ve seen throughout all the 2 stroke forums look damn near identical to me. Narrow squish with a wide shallow chamber. Upper end focused power. 
 

I need to do more head testing myself. Not so sure I agree with Mixxer on the wide squish band heads for the power I’m after. or at least with my setup… Lost some top end with the last two heads I’ve tried on my 98, but I’m also not needing so much turbulence/squish velocity to make up for the lack of ignition timing with the stock RMX CDI. 
 

I do miss my old CR500 sometimes, but it was pretty impractical for most the single track stuff I ride..?

When I did the head and raised the cyl. .5mm it made more power from bottom to top. His design definitely works. He's great to talk to and has much knowledge.  Before I learned about you I was going to ask him to do the RMX head. 

[TEGRITY RMX]

Funny how one topic here turns into another. 
 

I had to use my “Moderator” privileges (lol) here to move a bunch of Power valve info from the ‘Rear Fender’ topic, into its own new topic last week. Hope no one took offense, but who’s gonna look for PV info in the Body and fender Sub-forum…

No worries here, unless a billet hub gets discovered, there’s not much to add to this topic….

But yeah, I bet he’s added a bunch of compression (OE plays it real safe there) to boost your low end power, then the combination of head shape, opening the PV sooner, and raising the cylinder is helping out your Husky’s top end power. 
 

I’m skeptical that the axial machine groves have anything to do with the power  characteristics, or are even beneficial. Any air/fuel mix trapped in the squish band doesn’t contribute to power. The stock RMX heads are a prime example. The domed piston and square edged squish “ring’ traps a bunch of A/F mixture at the combustion chamber edge. RMX is so de-tuned in ignition timing, that it luckily doesn’t get a chance to ignite, but tuned lean enough, it could…

Getting that trapped 2cc of A/F mixture into the chamber, by itself, adds 10-15% more power, then the swirling action of the mixture getting shoved into the chamber (using Mixxer’s anology) is like lighting a fuse in a blender. Instead of one fuse getting lit from one end, there are multiple short fuses all getting lit, and quickly burning to their ends before radiant heat has a chance to self ignite remaining mixture…

 

There are sooo many different aspects to tuning a 2 stroke, it’s ridiculous.? Endless ways to create the type of power you’re after…

I never expected using the Power Jet to alter low end A/F mix would have such a drastic effect and extend my power band so low, but it does make sense now.

Richer mix and adding ignition timing slows the sonic wave in the pipe down, so now it’s arriving at a lower RPM than before, and set just high enough, there’s no low end rich burble.

Always wondered why the OE manufacturers didn’t consider this. Suzuki thought about it on the late model RM’s, but dropped the ball and set the Power Jet opening RPM so low, (2000 RPM), that’s it’s not even noticeable… They also set the closing RPM on the 250’s (10,300) so high, that’s not even noticeable either….

Yamaha even seemed to mess up the Power jet opening/closing on their 250’s, and it doesn’t work all that great with their N3XX series needles.

To work well, the Yammi PJ needs to be opening at 1/3 throttle, instead of 1/2. Seen lots of complaints in the YZ forum about being lean at 1/3-1/2 throttle, and that was my experience with e N3CJ needle too….

When I had Zeeltronic build the new PDCIS-MX11T I wanted both, RPM, and TPS control over the Power Jet. He went overboard with the number of points, but, gotta say, it worked out extremely well…?

 

I’ll be welding/cutting up a new batch of heads this winter. Got myself a new electric rotary welding table to play with. Gonna make the welding process soooo much easier. ?
 

Are you happy with the head you have, or would you like to try something different?

I could definitely cut you something more like the RK heads, just without the radial groves.

I’d need a CNC mill combined with my rotary table to do something like his….

A narrower squish, and even raising the cylinder with double base gaskets, should add more punch to the top end power with the Gnarly pipe…???

That was the thing I didn’t like about the Gnarly. No top end….☹️ Ran it for two weekends, than sold it for a huge loss…. Last time I’ll ever do a 99¢ eBay auction!!! lol 
 

Direct head swap, test both back to back, just cover shipping…?

Edited November 12, 2021 by TEGRITY RMX

[ricky racer]

Happy so far! I want to finish tuning it but yes I would test something different. Let me know and I’ll cover shipping ? 

[ricky racer]

Got the new Pro-x basket installed today. The Pro-x pressure plate is designed for the extra plate?

[TEGRITY RMX]

8 steels, 9 frictions?

I don’t recall having enough room on my MDR basket, or on the hub, to install extra  plates. IIRC that last friction was right on the outer edge…

Edited December 4, 2021 by TEGRITY RMX

[ricky racer]

If you don’t use the extra plates you can’t use the pro-x pressure plate as it bottoms out. Thought I took pictures of it but I didn’t. I will tomorrow. 

[ricky racer]

Maybe they updated the parts?‍♂️ 

[TEGRITY RMX]

Interesting. 
 

I have a Pro-X basket and pressure plate, but don’t recall them being any different than the stock baskets dimensions. I didn’t look all that close at the pressure plates 
 

My stuff would be older. Purchased around 2017. 
 

I do remember some differences in the RMX hubs and pressure plates across the years was how the pressure plate keyed into the hub. Early models IIRC keyed into the inside of hub, later, keyed into the same outer splines as the steel clutch plates.  
 

Maybe you somehow got 92-93 parts? Those years used the 9 frictions 8 steels. 
 

As long as the pressure plate is not hitting the clutch cover while dis-engaged, should be golden. ?

Speer1993 had a interference problem on his ‘93 IIRC. Wrong inner/outer covers for his clutch. 

Edited December 5, 2021 by TEGRITY RMX

[ricky racer]

I will take the pressure plate back off tomorrow to show pictures as that will be easier then trying to explain it lol. The only difference in all the parts is the pressure plate. Basket ear height is the same between my stock one and pro-x. Hub is same height. My stock basket and hub would take the extra plate but the pressure plate is different. You will see in pictures. 

[ricky racer]

The pro-x pressure plate will bottom out before touching the plates if only trying to use 7S&8F 

Edited December 5, 2021 by ricky racer

[TEGRITY RMX]

What clutch kit did you use?

That might be the difference if the overall stack is thinner. 

[TEGRITY RMX]

I’ll have to take a closer look at the Pro-X pressure plates I have. 

I didn’t take any photos of my 96’s clutch besides this one, but I do remember the outer friction was very close to the edge of the basket. No way I could have gotten another steel and friction on there. 
 

[ricky racer]

The frictions and steels measure to the large side of spec in manual. As I said if you don’t use 8&9 it’s not even close to clamping with the pro-x pressure plate. Here are the pictures so you can see the difference. First picture is stock pressure plate on top sitting where it would with only 7S&8F all other’s dimensions are the same. Spring pockets and alignment teeth all the same. Actuator is also the same depth. Only the clamping area is designed different as seen in picture. Bottom of first picture is the basket assembled with new pressure plate and 8S&9F?

[ricky racer]

Oh little side note. This engine also took the early main bearings. One being smaller 89-94. 95 & on were the same size both sides. This bike was sold as a 1995 to a long time friend of mine and I’m the second owner. Must have been a 94?‍♂️ It is a J112. Suzuki did some goofy stuff with the RMX. 

[ricky racer]

[TEGRITY RMX]

Interesting discovery. 

Can you verify the part number on your PP?

Package? or receipt?

If it is a 18.3394, then Pro-X must have changed the pressure plate at some point after 2017 when I bought mine?
 

Kinda looks to me like you have a 18.3392, which was used in the 9F-8S 92-93 RM250 and 91-93 RMX. Or, perhaps, you got a mis-packaged one?

Here’s my 18.3394

Identical to the OE plate I pulled from my 1996…

Now you have me curious… Gonna have to pull the clutch cover off my 96 to see if there’s room on the hub and basket for another steel and friction. Pretty sure there wasn’t…

 

Anyone else here bought a 18.3394 PP recently?

Edited December 6, 2021 by TEGRITY RMX

[ricky racer]

I got the 18.3392 sent to me. I didn’t even look at the part number as I could see immediately that it was for more clutch plates and I had plenty of room? now had I discovered that it wouldn’t have worked I would have started looking at part numbers but I had the extra plates so I just stuck them in. Even the original basket and hub had plenty of room for the extra plates as long as you use the correct pressure plate for it. The new hub also didn’t have the holes in it?‍♂️