Quick Takes



Engines Only

Engines Only

1046 Dell Ave.
Campbell, CA. 95008










Big Bore by Engines Only


There’s so much to tell you here, I hardly know where to begin! First of all, this is not my first experience with a Big Bore kit for a single-cylinder Honda engine. In 1998 I installed a Powroll kit in my 1997 Honda 300 4x4. In that instance I ordered the kit, I did all the wrenching, and I had a local speed shop do the machine work (press out the old liner, machine the cylinder for the new oversize liner, and then bore the liner to match the new piston). I had never dismantled a Honda four-stroke engine before, but I got real good at it quickly, because over the next two months I had to pull the piston out four times trying to find out why it was smoking so badly! As it turned out, Powroll had sent the wrong piston rings, but it took several exchanges to realize that. Once the correct rings were installed, the engine took on a totally new character. I also installed their high-performance exhaust system, which produced a great deal of snappy performance, but at too great a cost in noise. In short, it was simply unbearable, so I went back to the stock exhaust. As it turned out, this was a good thing anyway, because with the Honda looking and sounding totally stock, its improved performance was usually attributed to my great riding skills! Who’s going to tell?


Quick Facts

Manufacturer: Engines Only, www.xr100.com

Big Bore Kit Price: $449.95 MSRP

Gasket Kit: $49.95

Installation: $400 (includes machining and a fresh valve job)

See text for more details about pricing and options

I also had a Honda 450 4x4 at the time, and with a friend’s help we discovered that the modified 300, upgraded from a low-compression 282cc to a high-compression 315cc, would run side by side with the 450 up to about 42 mph. Then the 450 would pull away, but who cared about doing 40+ on a 4x4? No, the big bore engine didn’t make as much power as the 450, but its lighter weight and lower gearing (for the smaller engine) made up the difference handily. In fact, the lighter weight of the 300 actually made it a more capable machine in extreme terrain. In short, I loved the results, and grew to like the modified 300 more than any quad I ever owned, to include a Kawasaki 400, the Honda 450, and a simply awful Suzuki 500. When I later came back to two-wheelers, all my quads were eventually sold... except for the Honda 300 which I still own and occasionally enjoy.

The stock 2004 Honda CRF230F is an extremely capable trail bike with surprising quickness in tight, technical terrain where mother nature says no one shall exceed 25 mph. Improvements can be made, however, and I was quick to open the air box to let the engine breathe better, slightly relieve the stock muffler to improve exhaust flow without making it noticeably louder, and of course re-jetting the carburetor accordingly, using the Honda Power-Up Jet Kit. Then I was quick to note the little engine’s incredible low-RPM torque. With the small carburetor, small diameter header pipe, and long-stroke engine, the CRF230F pulls better right off idle than some bikes twice its size! For me, this made it a great bike for playing around at observed trials, and a natural for the Trail Bike Class at trials events. The stock gearing, however, did not allow riding along at a walking pace (very necessary for trials) without significant clutch action, so I added four teeth to the rear sprocket to lower the gearing enough to allow a slower minimum riding speed. I lost some top speed, of course, but who needs 70 mph in the woods? It still does 64 MPH!


The Podium

  • Engines Only people are easy to talk with and pleasant to deal with
  • New engine runs perfectly on pump gas
  • Starts perfectly with stock starter and battery
  • More power from idle all the way to the rev limiter
  • Very satisfying power increase
  • Results are exactly what was hoped for

I was very happy with the bike at that point, and I enjoyed leaving many bigger and faster bikes in my dust when riding slow and technical trails. But then while riding the Honda 300 4x4 one day doing trail maintenance, I began to wonder if a big bore kit would do the same thing it had to the 300 4x4. With that seed planted, I began looking into several different possibilities. I finally settled on the big bore kit offered by Engines Only, and I had several conversations with the owner, Frank Nye. He not only listened to what I wanted, he offered advice on how to achieve it. I already had a CRF250X by that time, not to mention a couple of screaming KTM’s, so I wasn’t trying to make the 230 a screaming racer by any means. I merely wanted to enhance its already remarkable low speed torque characteristics, hoping to make the bike even better in trials-type terrain. I didn’t want to go around 30" logs and 15" rock steps, I wanted to go over them! I also wanted to keep the bike’s stock appearance and sound level, so I insisted on using the stock carb and exhaust. Frank understood what I wanted, and explained just what he could do for me to achieve it.

This time, though, I decided against doing the engine work myself. If I bought the big bore parts from Frank, but had a local machine shop do the work, who’s to blame if things go wrong? I decided to pull the engine and send it to Frank so he could do the whole thing. And that’s just what I did. It took me about two hours to pull the engine from the frame while tagging all the nuts and bolts so I’d know what went where, another hour to thoroughly clean the engine (always keep your machinist happy!), and damn near eight hours (I never would have believed it, but...) to build a satisfactory engine crate (the crate made it from Alabama to California and back, though, so I guess it was worth it).

The big bore kit sells for $449.95, and a gasket set cost $49.95. Complete installation, to include all machining and a fresh valve job, runs another $400. Then add shipping each way, which for me was twice $50, so the total bill was a dime short of a $1,000.00, nearly a third of what the whole bike had cost. This is not an inexpensive step, but the results can be soooo rewarding!

After checking with Frank to learn what parts he needed, I removed the carburetor, starter motor, and gear shift lever from the engine to save weight, and then shipped the engine to Frank. Two months later, an unhappy UPS man struggled to my door with my familiar 80 lb. crate.

The first thing I noticed when opening the crate was that Frank had stretched a large piece of tape over the engine’s clutch cover saying, “FILL WITH OIL!” Thanks for the reminder, Frank, but I’d sure like to know what prompted such a bold but thoughtful reminder. Had someone re-installed their engine and gone riding without adding oil? Oops!

Using my notes and tagged hardware, the clean engine went back into the frame easily. I’d kept the battery on my workbench, connected to my Yuasa battery charger, so once I added the necessary oil, I figured the engine was ready to start. But it didn’t. No matter how many times I pushed the button, nothing happened. What was wrong? I know the battery is good, because I can see it right over there on the work bench still connected to the...


Once the engine started, I let it warm up a few minutes, and then shut it off to cool again while I put all my tools away and swept the garage floor. Then I started it again and rode it around easily in my back yard for about 15 minutes, before shutting it off and letting it cool again. After one more 15 minute slow-riding session, I put the bike away and waited for Friday. You too get Friday’s off, right?

With eager anticipation but the self-control that comes with age (and I have a lot of both!), I hauled the now 247cc CRF230F to the local riding area, and set off on the trail alone. I don’t like riding by myself, but this was a special occasion. I didn’t want anyone to compete with, and I didn’t plan on riding at all aggressively. I rode easily for about 15 minutes, and then stopped to let the engine cool. Then I rode a little harder for maybe 20 minutes, and stopped again to let it cool. After that I rode non-stop for about 30 minutes, ending up back at the truck for a much needed drink of cold water.

The timing was bad for evaluating a new and more powerful CRF230F. I had just recently installed a fresh piston and a new Rekluse clutch in my KTM 200, and after breaking in the new piston and clutch, I’d been tearing up the trail on a 32 HP screamer that weighed little more than 225 lbs. Now on the 240+ lb. CRF230 with what, maybe 20 HP, it was, to say the least, somewhat less than exciting. Nevertheless, as I began riding more and more aggressively (self-control is so over-rated!), I began to notice that I was finding myself going wide in the turns more and more often. I was also using the brakes harder and more often than before. It finally began to penetrate my helmet filling that the bike was now accelerating to speeds I was unaccustomed to on this bike. To really test this theory, I’d have to ride WFO for a while, but since it was for scientific reasons... As I reported earlier, after installing the Trail Tech computer on my 230, I was shocked to discover that I was reaching speeds slightly over 40 mph in the few fast sections here. So that’s where I went next, ignoring safety concerns and basic common sense. I rode through as fast as I dared, and then stopped for a brief conference with the Trail Tech. Somewhere along the fast trail, I’d reached 47 mph! That’s at least 3 mph faster than ever before! And this time I knew beyond any doubt that my speed had been limited by the bike’s meager handling, but not by its power! My God, what have I done? (More on this later.)

Then I headed for my favorite trials riding area. Here the rocks and logs are too nasty for most riders, but the typical riding speed is still blazingly fast compared to ants on crutches and overweight snails. Riding fast here is like watching turtles stampede through peanut butter. The excitement comes from moving forward two feet and upward six feet, or climbing up on boulders, making a tight pivot turn, and then coming back down the same way. In first gear I actually felt very little difference over the stock engine. The why of that is simple - since there was seldom any need to use full throttle, there’s no advantage to having more of what you weren’t using anyway. But then I made a shocking discovery... second gear now pulls just as hard as first gear! I couldn’t ride as slowly in second gear, of course, because no engine likes to pull hard at 17-1/3 RPM! I proved that theory in numerous stalled engine incidents! But when under power, second gear would pull anything, even from a bare idle! Get all the way up to 10 mph, and third gear would play bulldozer too! Now this is fun! I can crawl along in first gear, snap the throttle open, and the front wheel instantly claws for the sky, making 15" rock steps and 3' sharp inclines seem like nothing! And there I played until the engine suddenly quit. It started again, but immediately died. I’m not going to tell you how much time I spent troubleshooting the problem before I finally turned the petcock to reserve.

Saturday morning found me hauling the bike out again, but this time to the old airport so I could make some timed runs on my flat and level, approximately 1/10 mile acceleration straightaway. Shortly before having the Big Bore kit installed, I’d made several timed runs here for a basis to compare the new engine. I unloaded the bike and was riding around in the grass when Pat finally arrived to handle the stopwatch for me. According to my notes, the bike had previously run a best time of 11.8 seconds, and a numerous-run average of 11.95 seconds.


The Pits

  • Two months turnaround time
  • Carburetor may ned re-jetting
  • Stock suspension may have trouble coping with the new power

The first three runs were unimpressive, with a best of 11.6, and an average of 11.7. But then I began shifting sooner to take advantage of the new torque instead of screaming the engine’s guts out. The very next run turned out to be the best of the day, at 11 seconds flat! But that run was supported by several others at 11.1, and pretty soon every run was 11.2 or better! That’s an amazing 0.8 seconds quicker than before, for just 530 feet! (For reference, my stock, 245 lb. with accessories, CRF250X takes about 9 seconds for the same distance!)

And now here’s the kicker: Although it runs great just as it is, the new CRF247F needs re-jetting, after which it is sure to run even better! I’d hoped to have the re-jetting done before writing this review, but some personal obligations got in the way, and now I’m facing some minor surgery which entails a four to six week recovery period (i.e., no riding!). Hopefully, though, Ken will allow me to add an update here after the jetting is sorted out.



Even though I didn’t want my 230 to become a loud, snarling attempt at a racing engine, some people do want that, and Engines Only is ready to serve, with the following offerings for the CRF150F and CRF230F. They also have products for several other bikes. Call or check their website for further details:
High or Low Outlaw Series Exhaust: $299.95
High Performance Intake Kit: $299.95
Stage 1 Torque Cam (stock springs): $179.95 exchange
Stage 2 All Purpose Cam (stock springs): $179.95 exchange
Stage 3 Racing Came (needs HP valve springs): $179.95 exchange
High Performance Valve Springs for Cam #3: $69.95
Head Mods for Cam #3: $199.95
Full head porting: $199.95
High Performance Clutch Kit: $89.95
High Performance Flywheel Mods: $125.00
Rev Limiter Eliminator: $49.95
Lightweight Chain Sets: $99.95
...and more! Call or see website for more details.


Review by: Gordon Banks, June 2005
Post comments and questions to Reviews Forum


Copyright 2004 CRF's Only. All Rights Reserved.