Making the switch from Honda to ROK Shifter

The following is a continuing series ‘Begin Again’ by R.K. Siler. The series opened with the Going Back to My Karting Roots in early 2020, followed by Strains, Rains and Pandemics in April. The third column was offered in October 2020 with Support Your Local Kartshop and return in 2021 with Where Did Everybody Go?. The last installment came in August 2021 with The Track Jam. It has been nearly a year since we have heard from Mr. Siler, but now he is coming back with a two-part edition to the series.

It’s been a long time since I have last written, but all sorts of good things have happened in my karting program that I’m excited to share with you.  As the 2021 season wound down, it had become obvious to me that there were three areas in my karting program that needed to be addressed during the off-season in order to boost my performance in new season. In no particular order, these areas were the engine, chassis set up, and the driver (as the owner/team manager, I candidly wanted to fire my driver multiple times last year, but of course, since I am also the driver, that’s kinda hard…).  In Part I, I will cover what I have done with the engine and chassis, and in Part II, I’ll talk about what I’ve been doing to improve my on-track performance.

The first thing that I addressed was in the engine department. I had run all season with my trusty Honda CR 125, and while that engine is pretty much bulletproof, it is no secret that the Honda is no longer competitive against the more powerful Rok and KZ engines except if it is given a huge weight break. Since I personally weigh in at 185 pounds, there is no way that I could drop another 30 pounds of body weight to achieve the minimum weight of 375 pounds for kart and driver that the Hondas were given, as I was crossing the scales at 407 pounds with the Honda.  For comparison, at the two tracks I race at (North Texas Kartways and the Dallas Karting Complex), the Rok powered karts have a minimum weight of 405 pounds…so I was down on power AND spotting the competition 30-ish pounds, which is not exactly a recipe for success.

ROK Shifter engine package

Having decided to change engines, the question then became, which engine do I purchase?  For me, there were certainly intriguing factors to consider when looking at the Rok, IAME 175 or KZ engines.  The Rok is, for all intents and purposes, a de-tuned KZ with some beefier parts to improve the longevity of the engine, while the KZ is THE engine formula for shifter karting globally.  It makes a bit more power, twists up to higher rpms, etc., and it will set you back $1-2,000 more than a Rok.  I briefly considered the IAME 175 because the idea of a big displacement engine putting out big horsepower while turning fewer revs made a lot of sense to me, since that combination should equate to lower stress/better reliability on the engine compared to the high-revving KZ engines, but I quickly moved on from that engine as it seems to have fallen out of favor, for whatever reason.

At the end of the day, I decided to go with the Rok engine due to some guidance I had gotten from SKUSA Pro Tour champion Jordan Musser, who has driven all three of the engines that I was looking at.  While Jordan never told me what engine to purchase, he did a great job of breaking down the pros and cons of each power unit, and he very politely suggested that the Rok, given my experience and skill level with shifters, combined with the greater time between overhauls for the Rok (vs the KZ), probably would make for a happier experience for me. Since Jordan is about 3 zip codes past me in the speed department with a Rok, and only a few tenths quicker than that on his KZ, I decided to go with the Rok…I figured that if I could get close to Jordan’s times with the Rok, I was going to be competitive at the club level regardless.

With the decision to go with a Rok having been made, I then reached out to my buddy Mike Jones at the Dallas Karting Complex and told him to fix me up with a new engine.  About a week later, I found myself at Mike’s shop, working with him to install my new Rok engine.  I had stripped the Honda engine and its various components off my SodiKart prior to my arrival, so Mike and I immediately began to install the new engine.  Mike ensured that my engine came as a kit, so we had everything we needed to mount it to my kart, including the engine mount, water pump, hoses and all the accessories. After a few hours’ work, we were ready to put the kart on the stand and begin the break in process. Once that was complete, it was time to put it on the track.

Assembly done by DKC’s Mike Jones

There are two things that I need to make clear to anyone who is thinking of purchasing a Rok shifter: first, the Dell’Orto carb is delivered with an emulsion tube that is not to RokCup USA specification, so that needs to be swapped out with the one that is called for, which is the DQ268.  Second, due to the layout of your kart’s frame rails, you will likely need to install a SwedeTech shift lever extension to your shift linkage, which is made specifically for the Rok Shifter engine.  The extension allows you to place the shift rod in such a way as to miss the seat struts, and for the SodiKart chassis the shift lever extension is a must.

After a few weather delays, I managed to get out to North Texas Kartways (NTK) to give the new engine its first run.  The engine had sounded very crisp on the stand during break in, but when I drove the kart for the first time, the engine was terrible, it would not run cleanly, as it was bogging down and sluggish-it was clearly too rich.  Back into the pits and up on the stand, I pulled the spark plug and it was clearly running way, way too rich.  I checked the main jet and saw that I had a 160 installed at that time, and then I remembered that Mike had told me to lean the main jet down prior to trying to run it as the 160 main jet is for break in only. Duh!  I put a 140 jet in-I was just guessing what jet might work-and the engine cleaned up a lot but still was not 100% right.  So, the kart went back up on the stand, I put in a 135 main jet and then moved the needle clip to the top slot and now the engine was screaming that I had imagined it would!

Having now put a few hours on the Rok engine, I can tell you that the engine vibrates much less than the Honda, and the power delivery feels fairly linear.  The Honda has more bottom end torque, but once the Rok gets to around 10,000 rpm, things happen quickly as it really begins to pull and pull hard.  The engine also revs a bit higher than the Honda, so that takes some getting used to as well since you have to time your upshifts to keep the engine in its rev range.  One of the really interesting things for me is that with the new engine, I was almost instantly about 6 mph faster down the main straight at NTK, which means that my braking points have all changed for every corner and now all of the straightaways seem much shorter.  The bottom line is that I am really enjoying the engine and I am pleased with my purchase.

The other thing that the new engine did, with the increase in power, was it magnified the handling issues that I had been struggling with all during the 2021 season, especially with a green race track, such as after a rain storm.  So, after discussing it with Mike, it was back to the Dallas Karting Complex to go through the chassis set up to make sure we had a good solid baseline.  Mike had recently brought back chassis guru Sean Owens to handle all the tuning duties in the shop, so Sean took on the project of bringing my kart back to a neutral baseline that we could work off of.

Chassis adjustments done to the SodiKart by Sean Owens at DKC

Sean has years of experience and success tuning kart chassis, and he made some wholesale changes to my setup, including the installation of “zero” caster/camber pills, a standard steering shaft with the factory Ackermann steering geometry instead of a steering shaft designed for Bas Lammers (Bas could drive with it but I couldn’t!). He installed a standard rear axle, replacing the soft axle that was on the kart, and he replaced some worn out parts that he discovered.  Sean also gave me a set of medium length rear hubs to try out, but on the condition that I could only make this change after trying the kart with the new setup and the short hubs that I have always run with.

So, it was back out to NTK and sure enough, it had rained the day before and although the weather was beautiful, the track was green and super-slippery as all the rubber had been washed off the track by the rain.  With the neutral setup that Sean had put on the chassis, the kart was definitely more predictable and very much less “on edge”, but because of the green track, the kart was still sliding way too much, and I just could not put the power down.  It was time to find some grip.

I installed the medium rear hubs, set the rear track a little bit narrower at 54 ¾ inches, and then bumped up the air pressure a couple of pounds. With these changes, the kart immediately felt a lot better. By this time, several karters had been pounding around the track, laying down more and more rubber, so as the day went on, the track got faster and I could, for the first time, actually feel some side bite in the chassis, which was amazing.  Up until that day, I had always fought a loose chassis, but now the chassis was feeling much more planted and secure, so I was able to go faster by about seven tenths of a second.

In summary, the combination of changing over to the Rok engine and having the chassis brought back to pretty much the standard factory specification gave me a much more drivable, confidence-inspiring ride.  I am still not on the pace, but the gap to the fast guys has narrowed somewhat, and with that significant improvement in equipment came the realization that it was now time to work on the driver.  In Part II of this installment, I will share with you what I have done to improve myself as a driver, a process that is continuing as this is written!

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