by Sonny Van Hook
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This is a follow-up to the How To Build A Stock Moto Guide that I wrote several years ago. That guide gave an in-depth view of building up a fast and legal Stock Moto engine from used parts. This guide has been broken up into "Top End" and "Bottom End" sections. If you are doing a top end rebuild, simply follow the "Top End Assembly" and "Top End Disassembly" pages. If you are doing a complete rebuild, then follow all of the pages. Let's get started! Because the Stock Honda package has become so popular, most kart shops stock all of the parts needed to fully rebuild the engine. Most of the parts for this rebuild are available from the tutorial's main sponsor, Fastech Racing. |
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| Is it really possible to build a race-winning engine in your garage? Absolutely! The engine that I put together in the How To Build A Stock Moto Guide has been a very solid and fast engine that I've done well with. Last year was my first full season in the extremely competitive IKF Region 11 Super Stock CR125 class. The picture to the right says it all. Additionally, the class champion for the last 2 years has a special motor builder, too: himself! If you are careful and pay attention to detail, it is possible to build a very fast and competitive Stock Moto engine. |
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To perform this rebuild, you will need a couple of special tools. From left to right, we have: Motion Pro torque
wrench adapter, a torque wrench, flywheel puller, universal flywheel/sprocket holder, and a case separator.
Only the first two are required for a top-end rebuild. The last one is only required if you are working on
an engine that does not have a "slip fit" crank and you wish to preserve that crank. The case separator
is not used in this write-up since I am starting with a slip-fit crank.
The remainder of the specialty tools can be purchased from Fastech Racing in the tools section of their site. You can also find them on eBay, but it will likely be cheaper to buy everything at the same time and pay for shipping only one time. Lastly, you will need a basic set of hand tools, a large toaster oven (for bottom end rebuild), a clean working area, and patience. |
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| Although I will provide most needed measurements and torque settings, you should have a Honda CR125 factory service manual. Because the CR125 "kit" engine is a hybrid of several years, several manuals are needed to cover all aspects of the engine. However, the most relevant manual is the 1997 manual since it contains technical information about the clutch and transmission. If you need information about the ignition system (the 1999 ignition system is the required one), you will need to purchase the 1999 manual as well. These generally sell for $30-$50 on eBay. |
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Although not strictly needed, I recommend buying the complete CR125 gasket kit if this is your
first full rebuild of the engine. It is pricey, but contains all of the gaskets that you will
need (and there are a lot of them). It also contains other useful parts like a new drain plug
washer, the rubber coupling between the pipe/silencer, etc. I will be using this kit for my rebuild.
If you are only doing a top end rebuild, don't buy the gasket kit. Just get a "top end kit" (more on that later). |
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