2001 Factory Honda RC250M

I waited a while to go online with this project but now I have collected all the major parts to start building, I would like to share the process of building a 1992-2001 Factory Honda CR250 engine with you guys. It will be very detailed since I have learned a lot about the factory engines last few months.

Prior to this project I have restored a 1980 Honda CR125R Elsinore to showroom state. I worked more than a year on this bike and I liked this bike very much but when I had the opportunity to sell it, it kind of cleared the road for a new project, and so the bike was sold and shipped to a MX museum in Sweden.



Aspired by the BBR Honda CR60R factory replica. I bought a 1984 Honda CR60R to do the same trick, but after a few months I decided I would do a frame up showroom state restoration on this one too, keeping it original. This project is halfway and you can follow it on my website.



The idea of building a Factory Honda CR250 engine originated when I finished my CR60R engine. I always start on the engine when restoring and when I finished the CR60R engine I welded a simple engine stand to display it on my workbench until the chassis is finished. I liked the look of a restored engine on my workbench and when I came across a HRC sandcast magnesium right side engine case for the 92-01 CR250 engine I bought it. Just like Newmann, building a bike around one works part .



When I received the right side engine case I also found out it came with the original HRC powervalve governor, lucky me. The governor is hard to find and the original governor won't fit in the casing.



I located a '94 HRC Power-Up kit manual and armed with a lot of HRC part numbers my search for factory parts began. Almost every part comes from a different source and I have met some amazing and inspiring people along the way. Most parts are specifically for the 1996 engine, others fit all years so I am not trying to replicate an engine of a certain year or rider. From here on I will just update with the parts that I have tracked down and bought, I already have a NOS right side crankcase and a NOS left side crankcase is coming my way so assemble shouldn't take that long.

Here is a used waterpump cover and NOS powervalve cover which I blasted with glassbeads, I'm thinking of anodizing them a grey color but don't know how dark yet.



This cylinderhead is one of the characteristic 1996 parts, as it has the sparkplug in an angle. It is a new HRC part, the dome is polished from the factory. You can recognize a HRC cylinderhead by the milling around the sparkplug thread.





One of the internals is the HRC gearbox, consisting of the mainshaft and various gears, OEM gears where used to complete the gearbox.



To assembly the engine I need gaskets, and since the quality of OEM Honda gaskets is second to none, there was no doubt I was going to use original gaskets.

Not all of the gaskets are “works” HRC gaskets, in fact, a lot of them are just stock gaskets like you’ll find in any 92-01 Honda CR250 engine. HRC gaskets are fitted for the iginition cover, clutchcover, head, cylinder and reed valve. The ignition cover and clutch cover use paper gaskets instead of rubber gaskets like the stock engine does. I assume that is because the magnesium covers are so fragile that grooves for o-ring gaskets would only be a higher risk. The cylinder base gasket is steel like the head gasket and were offered in different thicknesses.



The cylinder I will be using comes off Stefan Everts' 1997 RWJ Honda. It has a few marks in it and will need replating. There is some tuning going on on the intake side, where two extra boost ports where made. It's not done very neatly, I assume this was a testing cylinder, maybe I will finish it myself before it gets replated.





The HRC piston I have is for the 92-93 HRC kit, but it's basically the same as the 94-96 piston. A third variation is the 97-01 piston which has windows on both side above the pistonpin. This would be the piston of choice since I have a 97 cylinder but until I find that piston this one will do the job.



The HRC piston features a single pistonring in stead of two, and is also less thicker than a stock pistonring.



The pistonpin is lighter and stronger than the OEM pistonpin and as far as I can see there was more effort put in the total finish of the pistonpin compared to stock.



To complete the cylinder I had to find the HRC powervalve parts that belong in it. Stock valves will do the job but as the perfectionist I am HRC valves had to be found. I found a used set of 1998 valves to fit my 1997 cylinder, they do have to be cleaned before installment. When using HRC valves, some of the surrounding parts should be replaced with HRC parts too, like the screw to adjust the roller. The OEM powervalve system only uses one bearing, on the right side, and a bush on the left side. When using the HRC valves, the bush on the left side should be replaced by a bearing, which I found too.



The reed valve and intake manifold are from Stefan Everts too and appear to be stock items having some area’s machined for a better flow. The reed petals are carbon HRC items.



Most of the parts where offered by Honda and you could order them (for certain prices) at your local Honda shop, but there are some parts that where not available to public like this steel shiftlever. Provided to factory riders in various lengths, bends and widths to suit their needs. It was not easy to find but I was very lucky that a collector had one spare and was prepared to sell it to me. It's from a late 80's RC500 but fits shaft on the CR250 engine.



The 1996 ignition I found is in excellent shape and features the heavier flywheel, which was an option aside from the original HRC flywheel. The mass increased flywheel gives the motor more torque and better acceleration when racing heavy sand tracks.



The HRC ignition should only be used with the matching HRC CDI box so I was lucky to find this one too, the Denso partnumber is 071000-0830 NHA.



The HRC CDI box features a socket where you can plug in a coupler. Two different couplers where available and I have them both NOS. The grey coupler which was included with the CDI and provided standard power and the blue coupler which was an option to down-tune the power for muddy or slippery conditions, making the engine less aggressive.



I may end up putting this engine in a bike some day but for now I am building the engine only. Stay tuned for updates, there are a few more parts on their way!

Corné - The Netherlands