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RMX Advanced Squish Band Design

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First off... It's an honor to be nominated (lol) to this group of gearhead's and wrench spinners!

I'm not worthy in that I'm not am RMX encyclopedia by any means... Decent general knowledge base, but I'm sure I'm the toddler of RMX specific knowledge in this group...

Love my 97' RMX250 (Buzzard) to death.... Last of the great Japanese Enduro 2 strokes before the Orange Tide from Austria swept over the world...  

First off... Time to pay homage to the true encyclopedia of all things RMX, performance guru, machinist first class...and founder of this forum...

Jeremy/ TegrityRMX...

my favorite mod to my RMX is one that would not have been possible without Jeremy's talent and drive for performance... A cylinder head modified to get both higher compression while gaining more detonation and pre-ignition control/ safety...

In order to correct for the I adequate squish band on the RMX the head needs to be welded and re machined... 

I had searched all over my local area of machine shops merely looking for someone to make 2 cuts on the stock head...

Cut squish deeper / then cut deck...

And literally every shop acted like I asked them to build the space shuttle from billet for me... Nobody could do it...

Then I stumbled across Jeremy's work... 

Welded, re shaped... Complete re design of the chamber to get much better squish and higher compression... I ended up with 210psi .. 10 kicks open throttle engine cold...

Couldn't be happier with the changes to my low end power and better throttle response and hit everywhere in band!

By far the trickest and most exclusive mod on my bike...

I don't have pics handy to post at the moment.. maybe Jeremy can help out on that...

 

Anyways , thanks for starting this club Jeremy...!  The RMX deserves a forum beyond "general clump of all Suzuki 2-strokes"...

You can only read titles like:

"anyone know if a 1982 rm125 crank will fit my kids 98 rm80 without any mods needed??"

just so many times...

 

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It’s an honor to have you here!!!

For those that don’t know, Mixxer has WAY more than just a “general knowledge base”. Ha ha. Correct me if I’m wrong Mixxer, but he was founder and owner/primary engine builder of Venom Performance, a hardcore tuning/dyno shop that built engines for many podium winning racers.🏁

Awesome first topic!

Yes, a modified head makes a world of difference on the RMX. This was one of my very first mods I did to my RMX right after I bought it. The combustion chamber shape is awful, to say the least. Lol

Stock on the left, and one that I welded about a decade ago. 
D79EFDB6-1D0A-4A06-9A2C-7A0FF9A89EAB.jpeg.ef534ef40551d2d0052c97da4ff22673.jpeg

This here is the first one I cut in 2000, before I had a buret and really knew what I was doing. Ha ha

9D5442DB-C05F-41A9-BEBA-B145714A19F3.jpeg.c364c0a86adea75c47614e890929b726.jpeg

2016 I discovered the ‘RMX head topic’ here on TT and after YEARS of lurking, finally joined. Started welding and machining heads again. 

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While I really didn’t intend on selling heads, I felt greedy about posting picts of these and keeping all to myself. Sold most all of this batch to guys that requested one. 
 

Met RMX250_rider on here, turned out he was local to me, and has become a good friend, and my new riding buddy. A few guys recently requested heads that work well with the FMF Gnarly pipe. So, since he ran one and has a mostly stock engine, I had him do some testing for me with a new batch I welded this year. 
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We’re both going to be experimenting more with the single layer MLS gasket heads this year (top two on left). One of his favorites is the welded 89 RM head (top center). Plug sits 3mm higher than the RMX heads, so easier to get a wide squish and good combustion chamber shape/volume. Unfortunately a hard to find, one year only head...

Another that I’ll be experimenting with myself this year is a non-welded 26cc SLS head. Only problem with ditching all the gasket layers is the plug gets moved closer to the piston. Doing that can have a tendency to heat the piston crown a bit more...

BC469B27-6CEA-4BC9-93C2-09BE3F10D021.jpeg.93946015f0943e5018b5594f4bd9eb11.jpeg
 

Then, I got myself a 89 RM head to test out this year. 

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Excited to try this one. 👍

But, Yeah. I was kinda hoping someone else would have started a club for the RMX, and I’m definitely no encyclopedia, (ha ha) but it’s about time!!!  

Gotta give credit for everyone that shared their RMX knowledge that I learned a bunch from. Unfortunately most seem to have got burned out by the Suzuki 2 stroke forum, and don’t come around anymore...

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Hi! It's been a while since I got on TT, and while searching my mailbox for threads I rode in the past about modified heads, I found out that TEGRITY RMX has sent me an invitation for this club.

I contacted TEGRITY RMX back in february for information about getting my head modified. I was pretty much set to wait for the test with RMX250_rider, and get my head machined accordingly.

To make a long story short, things didn't happened the way I intented... With mucho free time,  I reverse-engineered the stock combustion chamber as a covid lockdown project, using what I had on hand, play-doo and a digital caliper, and made a 3D CAD of it. I rode a bunch of information about combustion chamber design, and started evaluating different shapes in CAD. Then put that project on a shelf. 

Got a new job with a new-to-me CAD software, I decided to learn the software by modelizing the modified head. Last week, got an opportunity to use the cnc mill at work, and things started moving. I jumped on the squish bandwagon!

image.png.14ab3d15131ef86d64eea0341294ace2.png

 

I did a 2hr ride yesterday and there is a nice improvement in low-end torque and responsiveness, even if the compression ratio is't raised that much (I aimed for -1cc in CAD)

I didn't planned to open the engine, so I reused the stock-thickness Moose head gasket , using hi-temp gasket-maker as a temporary fix for damaged cardboard. I just ordered a cooper head gasket on ebay, and I hope to receive it before it start snowing!

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Nice work. 👍

I apologize if you were waiting for the test results from RMX250_rider. I was under the impression that modifying your head or getting one from me was more than you wanted to spend or do...

Back in February RMX250_rider was in the middle of moving, and ended up having to do a bunch of renovations to his new house, so that delayed him being able to test the different combustion chamber shapes/volumes. Things definitely didn’t happen as I intended this year too, and I think many of us are/were in that same boat....

During our ‘lock-down’ they even closed the ORV parks here, which was my opportunity to get out and test heads myself, and play with my new rear shock valving. ☹️
 

A couple of pointers I can give you for the Gnarly pipe is it doesn’t like the volume reduced much. 0.5cc reduction with a 1.2mm gasket worked out good and didn’t suffer too much pumping losses at high RPM. If you’re looking for overall power increases your best off keeping the volume stock, or around 180-200psi on a accurate compression gauge.
 

If you’re looking to gain high RPM power, increase the volume. I cut one that was a full 2cc larger with a nice tight 0.8mm narrow squish band. He said that one was a screamer, and was still making power above 8000RPM with the Gnarly pipe. 
 

To me, your head looks to be reduced more than 1cc. I’d narrow up the squish band a bit, and make sure it’s nice and tight, around 0.8-0.9mm. I’d also verify the volume, and or, check PSI with a good gauge.
 

For a copper gasket you’ll definitely want to clean up that gasket surface. Wouldn’t be a bad idea to slightly undercut the surface a bit around the coolant ports, so it has more clamping force applied to the gasket around the inner and outer parts of the circumference. (If that makes sense). 
 

Out of all the heads in my above post/pict of the 6 heads, the toroidal was the worst, (weird idle issue?) but he said it was still a improvement over stock.
 

His favorite is the raised plug 89 RM head, and one I’m excited to try. Since those heads are difficult to find, I may try making some this winter out of the RMX heads by welding/re-machining the spark plug seat higher...

 

Hard to go wrong with a functional squish band on these bikes, but the only way to get true linear power is by ditching the stock CDI and going programmable ignition. That made a world of difference on both my bikes. Stock CDI’s idle at 0* advance, goes all in 15-16* at 3000RPM, and drops off at too fast of a rate above.. Timing and MSV need to work together for best results. 
 

The Power Valve solenoid on my 98 is another excellent low end power booster. (Probably not necessary with a Gnarly pipe) I’ll be adding that to my 96 next top end rebuild. The primary springs on these are far to light to actually keep them closed at low RPM’s. The solenoid traps the blow/by that gets around the valves, and with the drain port plugged, keeps them in place pneumatically. 👍👍

Edited by TEGRITY RMX
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I use a pro-circuit exhaust. i'm looking for responsiveness and clean running at low throttle (most of the time, I ride with my two yougn sons, 6 and 9)

according to my cad, the stock head have a 22.4cc volume, and my design is 21.5cc. In theory, the squish is reduced by 0.45mm/0.018". 

I mesured 1.4mm / 0.056" with the stock 1.7mm gasket. So with the 1.1mm cooper head gasket, I should be right around 0.8mm. The thinner head gasket should reduce the combustion chamber by 2cc, so most of the gap reduction / compression rise will come from it

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Ok. Lol. It’s starting to come back to me now. Ha ha. Had to go back and look at our PM’s from Feb. This has been a chaotic year, to say the least!!!
 

I did have a head set off to the side for you. I just completely spaced getting in contact after RMX250_ rider was done testing. I actually had a second batch for him to play with, but we never got around to it...

This guy here;

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22.4cc., 0.8 squish with the optional 1.2 MLS gasket. 
 

I do my cc measuring with a buret. Unmolested stock heads with a BR8ES plug come in around 23cc~ plus or minus a couple tenths.

 

Notice on this head the steeper angle at the squish band to chamber, and the roof has been considerably raised? Those are done to regain volume once the squish band gets welded in. That’s why to my eye yours looks reduced more than 1cc. Looks can be deceiving though. Ha ha. 
 

The only two real drawbacks to going too high on compression on the RMX is, it can make getting it started cold a bitch, (the magneto on the RMX is small and weak), and a loss in over-rev. You don’t need to worry much about detonation, since the RMX timing curve is so far de-tuned...

An easy way to check squish, and that it’s centered, is to lay the head on the cylinder with no gasket. At TDC measure how far the piston lifts the head, and that it lifts evenly side to side, front to back. Lift, minus gasket thickness, equals your squish clearance. 👍 I recommend to everyone that gets a head to do this. Manufacturing tolerances are terrible on these...

As a side note, head lift trick doesn’t work with single ring Pro-X pistons, since they have a lower deck height...


But anyways, for clean running and responsiveness at low throttle positions the starting diameter of the carburetors needle is important. Prior to going Zeeltronic ignition with the electronic YZ carb, I swapped the DDJ with  a DDL needle (clip 4) in my 38 PWK...👍👍

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Amazing talent and knowledge, Mr Tegrity🤘

I don't remember which one of the Pro-X pistons I used with my RMX , but I remember you being surprised with how thin I went with the head gasket to achieve tight squish clearance....

I remember telling my son while we were bolting it together that I would be very happy to end up with at least 205psi , but would be a but apprehensive about safety and 93 octane if I had gotten much over 215psi....

And it came in at 210...! Perfect!

If i remember correctly , Pro-X has 2 series of part numbers that are both advertised as fitting the RMX... 

a 3310 series and a 3311 series....

I went with one of the "B" fractional oversize pistons last time and will go for a "C" size sometime over this winter...

I will have to look up which ones are RM specific Vs which ones are RMX specific....  I would rather use the taller deck height as that also would have the desired port timing effect (albeit small) for the powerband I prefer...

As far as making the RMX easier to start under all conditions... Especially with higher compression or advanced base timing... I can cast a vote for inertia...

Say hello to my lil friend 😎

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Thanks Mixxer. 👍

Right back at ya. 👍

Had it not been for your advice, I’d probably still be cutting “textbook” 1.0-1.2mm squish clearances... 
 

Yes, be sure to update which piston you used. I had no idea at the time that the Pro-X sat so much lower in the bore, and like you’re saying, that’s increasing your port timing, raising the RPM’s of your powerband. I was kinda surprised that you thought it hit too abruptly too, so that all makes sense now. The second stage of the PV does a damn good job of smoothing out the hit in the 5200-5700RPM range, but yours is probably fully open when you get on the pipe. That was another thing I really liked about the Zeeltronic/Power Jet carb combo. Nice smooth hit at a very low (throttle position adjustable) RPM... 👍👍

Curious what the Pro-X weighs in at with the pin too? The OEM single ring pistons I have are the heaviest ones in my stash.  

 

RMX250_rider and I were just BS’n about electric start options a few nights ago, and the thought did cross my mind when I started on the 3 phase stator, that I’ve yet to actually finish winding... No reason the stator couldn’t be a ‘Brushless’ motor... lol
 

Hybrid-electric start RMX. 🤘

https://www.shindengen.com/products/electro/motorcycle/ecu/
 

Im sure I’d need a higher pole count stator, beefed up backing plate, and a flywheel with more, stronger magnets, but how cool would that be...???

Zero additional moving parts too...😁

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My first motorcycle was a 1967 Kawasaki 175. The stator and electric start were integral.

It would start it in first, and get it rolling without the clutch.  Had a large 12v battery.

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