RogersvilleCycle.COM & ATV Hilbilly Bike

Since many of the Hillbilly Grand Prix bikes are not the latest year models, it occurred to us that most of them probably require maintenance, repairs, and upgrades. We decided to build a bike to compete in select races of the Hillbilly GP series 2005/2006. Maybe some of you can relate. We originally started with a 1998 Yamaha YZ125, but sold it two days prior to the first race at Thayer. We are now getting the 2002 Yamaha WR250F ready. It will be my first attempt at racing a modern day four stroke, and it is already clear that some adjustments on my end will be required. If I can get past the hurdle of starting it, things should improve at a more rapid pace.

Initial Race - Seymour
The bike that we chose was in average condition.	We started with a fork rebuild, as the left seal was leaking (see article Rebuilding Forks).

We ordered a Pivot Works fork seal kit, complete with bushings, seals, wipers, the heavy washer under the seal, and the copper washers that are used on the base valve to seal it. It was also clear on this bike that the front wheel bearings were loose and would have to be replaced. MSR has bearing/seal kits for this task.

Rebuilding the forks requires some special tools, fortunately, we have those and the job was fairly straight forward, with the exception of the issues outlined in the fork rebuilding article. Lots of moisture and dirt in both forks.

This is typical. This is why the pro’s go through theirs every week. Forks and shocks are the most precision parts of this motorcycle. A small piece of debris or inconsistent oil (diluted with contaminants) can make them work worse than an old set of non-cartridge forks. I twisted the bolt that holds the brake line protector off while trying to remove it. These appear to get dirt in the threads in the backside. We had placed a socket over the bolt, once it became obvious that it was stuck, and smacked it with a brass hammer in attempt to dislodge the hung threads, but it twisted anyway. We were able to drill it and rethread it and replaced it with a new one upon reassembly.

Wheel bearings are also straight forward. The seal opposite the odometer drive was first removed to allow inspection for a possible snap ring (there wasn’t one). Old wheel bearings were removed with a punch and the inside of the hub was thoroughly cleaned.

A bearing driver was used to install the sealed bearings that are provided in the kit. Using the proper bearing driver keeps the pressure on the outside bearing race, in order to keep from “flat spotting” the balls. Hitting the inner race causes flat spots to develop on the balls, which in turn, get larger every time the race rolls over them (just as a pothole in the road does), eventually causing the bearing to fail earlier than it should. The seal was then installed, taking care to insure that it is straight once in the wheel, then the inner lip of the seal should receive a light coating of grease. This allows it to turn on the spacer easier, reducing seal wear, and helping the seal to maintain a water tight seal on the spacer. The inner seal on the odometer drive was also greased for the same objective. On this bike, the spacer was made from aluminum and the aluminum was severely worn from seal contact with the old seal.

It will be replaced when the new one arrives. In the short term, we were able to install the seal a bit deeper in the wheel than the last one was, letting the seal lips actually contact the spacer beside the grooved areas made from the old seal and making a water tight seal. As far as I am concerned, keeping water and debris out IS the life of the wheel bearings. If the bearings can stay in a clean environment, they will last nearly forever.

The bike was checked over for missing/loose bolts. Only one tank bolt installed, the other was missing and the rear tank strap was unhooked. The throttle didn’t work smoothly, so the throttle pipe was disassembled and the handlebar and throttle tube were cleaned. The front brake lever was bent so it was replaced as well. I cannot stand to have to look for the controls. I want everything to be RIGHT THERE. I pulled the handlebars back for better fit for me. Then I loosened the master cylinder perch and the clutch perch so that they can be rotated around the handlebar by a smack of the hand. This helps keep levers, perches, and master cylinders from getting broken in a crash. I removed the valve cover and checked valve clearance.

I decided to install a Hot Cam with the auto decompressor made on it for (hopefully) easier starting. I installed the cam and adjusted valve shims, drained oil and cleaned the oil filter (Yamaha uses a wire mesh filter, it doesn’t require replacement unless damaged, only cleaning). Then I removed lower frame oil line and removed the sump screen and cleaned it. I installed the Silkolene petroleum based oil, per Hot Cam recommendations for camshaft break-in.

The final drive chain shows a bit of wear, probably be fine for this race. Other things to tend to and running out of time. Check spokes, brake pads, and chain adjustment. Adjust chain a bit tighter. Roll rear wheel to check that this adjustment is completed in the tightest spot for the chain. Worn chains develop “tight spots”. Adjustment must be made in the tightest spot, otherwise the chain will be too tight when landing from a jump/bump and can damage the countershaft bearing, break the cases, or most likely, break the chain (possibly breaking the cases). Needless to say, this is a compromise (can get a bit like Russian Roulette) and the best thing to do at this point is to replace the chain and sprockets. Let me see if I like the bike first. Replace rear tire with new Dunlop 739. Old tube is coming apart at base of valve stem, so it was replaced as well. Air filter is dirty, but air boot to carburetor is clean (no fine sand type debris, this is VERY good, and unusual for a used bike). During cleaning it is apparent that the air filter is beginning to show signs of falling apart. New one on order, will service this one (see Proper Air Filter Maintenance) and run this weekend. Connected the taillight wires that were not connected when seat was removed. Oh, and replaced the kick starter with a new one. The old one was worn slam out! Worn shorter than it should be and folded back a bit too far. It was Hard to kick it and keep my foot on it. Since it appears that this will likely be needed a lot, I replaced it.

I started bike and let it run for a couple of minutes and checked the oil again. Topped oil off. Started and checked lights, all work. Can’t be sure at this point why taillight wires were disconnected. Probably from an encounter with removing/installing the air filter. I should tie them to the side frame rail, but will wait until the filter is replaced. We will run Phillips 66 110 octane fuel from Bill’s Quick Stop in Rogersville, MO. Having seen the effects of 91 octane pump gas on cylinder plating and pistons, not worth the risk. We will run the better fuel and avoid those issues.

For me, everything starts with washing the bike. The bike is washed on the side stand, then laid on the right side to expose the bottom and other areas not seen when the bike is upright, and finally laid over onto the left side and washed again. Spin the wheels to wash the hubs and rims over the complete circumference. Stand the bike upright and finish washing and rinse. It can be amazing how many things you will observe while doing this. I was introduced to a saying years ago regarding race preparation, from a veteran of the auto racing world. He explained that “Opportunity is when luck meets preparation.” It is obvious that you cannot win the race, no matter how many people crash or break down, if your bike breaks down. Washing the bike after the race is the first step in preparation. It is recommended that you do this the next day after the race (if not on the way home from the race). That allows the most lead time to order parts that might not be in stock.

Install new air filter after oiling it, cleaning the airbox with shop towels and WD40, heavily grease the lip of the filter so that dirt cannot leak between it and the air box face. Re-routed the taillight wires this time to get them out of the way of the filter opening. Check spokes, tire pressures, adjust chain (one more time), pull down the dust wipers to see if dirt is sitting in the seal area (very clean, very good!). Need to work with the low end carburetor jetting a bit, but the jets didn’t arrive yet, so will wait until after this race. Bleed front and rear brake systems so that new, clear fluid is coming past the bleeder. Dirt bike brake systems can be easily overheated, then the brakes get vague for the rest of the day. I have discovered the Silkolene DOT 4 Pro Racing 2000 fluid. It is pricey, but is far more refined than standard DOT 4 fluids and has a much higher boiling point (383f vs 311f or 20% higher). On a weekly basis, I only bleed the systems until I see that the fluids are clear, then stop.

Building a Hillbilly Grand Prix Bike See the results ?