Kirk Willis

Ogre Ultra 510: The Thumper That Honda Should Have Built

Cycle World's Senior Editor goes off the deep end. This is what he brings back.

Ogre Ultra 510 wheelie action
Ogre Ultra 510Kirk Willis

“Why would anyone want to screw up a perfectly good ’88 CR500R like that?” said a bewildered Ron Lawson. “You took the world’s best Open-class motocross bike and replaced its light, powerful, two-stroke engine with a Husqvarna 510 four-stroke engine that’s heavier and slower. I just don’t understand.” I pondered his question for a few minutes, wondering how to explain my motives to a guy like Lawson, a motocross rider who has spent his entire, if comparatively short, life on two-strokes. I finally decided it was impossible and just mumbled something about him probably being right. The truth is that explaining my latest project bike to most members of the younger generation would take as much energy as the project itself. But someone of my generation, someone who grew up hearing and feeling the unmistakable boom of big four-stroke off-road Singles, can fully understand. There’s something magically appealing about a 500cc four-stroke Single, even though that appeal is hard to rationalize.

Anyway, this project was driven at first by curiosity as much as anything else. Could it be done? Could the lightest 500cc four-stroke Single engine currently in production find a happy home in the best Open-class chassis in existence? Such a creation should weigh only about 240 pounds, and could easily be the perfect off-road racer/playbike. And I also liked the idea of benefitting from the other things that Honda continues to do so well: magnificent disc brakes, perfectly placed and easy-to-operate controls, and steering that has the precision of a surgical laser beam.

There was one final—and very compelling—justification for this project: After a recent binge of tool-buying, I had a new metal lathe, a vertical mill, a MIG welder and a metal bandsaw, all just waiting to be broken in...

Finding a liquid-cooled Husky 510 engine was hard enough; Cagiva doesn't sell engines, only complete bikes. Luckily. I stumbled onto a 510 that had been in a gasoline fire during a Baja 1000 race. And, by a stroke of good fortune, the owner was willing to trade it for a CR500 engine. So, I bought Cycle World's 1988 CR500R test bike, made the swap, and started what would eventually consume two months of my time and involve about 500 hours of labor.

Ogre Ultra 50 rear wheel details
A new rear-brake caliper mount was fabricated from a block of aluminum. Brake strength and feel is unchanged. Using a 1989 CR500R rear wheel rather than an '88 reduced weight by one full pound.Kirk Willis

"Once the engine was mated to the frame, the real work began."

After measuring the CR frame and the 510 engine, I was sure the swap was possible; but I also concluded that it would require a lot of modification, some of which might destroy the frame or, worse yet, the hard-to-find engine. The rear of the crankcases (the portion that is also part of the swingarm pivot) would need to be narrowed by 1.5 inches, and I’d have to fabricate new bushings. But luckily, that narrowing process ended up being simply a matter of carefully trimming away the extra width; the Husky cases had adequate internal casting webs to allow the thinning, and there was room for the addition of new gussets to ensure strength.

After that, the engine slipped into the CR frame with relative ease once the shock was removed. And the 510’s front engine mounts rested inside the CR’s double downtubes, meaning that I could bolt the front mounts directly to the frame without using loose plates. The lower engine mount went through the frame tubes, reinforced with machined sleeves for the bolts, and a couple of small steel plates were welded to the tubes for strength. It was easier than I had anticipated.

Ogre Ultra 510 dirt track action
Ogre Ultra 510Kirk Willis

Engine height was another matter, however. The tall 510 motor didn't touch the frame's backbone crosstube, but it came so close that pulling the cylinder and the head would have required the removal of the engine. Honda and Yamaha four-strokes also require engine removal for top-end repairs, but a stock Husqvarna Thumper can have its head and barrel pulled with the engine in the frame. Not only that, the Honda frame would not accommodate the high carburetor placement of the Husky engine. So, I removed the frame crossbrace, built a new, shorter one and added considerable gusseting. The carb then had adequate room, and top-end repairs can be performed without yanking the engine.

The next problem was behind the carburetor, where the frame arch was too low to permit airboot installation. The offending gusset was removed and a thin steel plate fabricated to raise the arch as high as possible. A second layer of steel, plus another wrapped over the top rear section of the backbone, helped strengthen the altered frame. That modification allowed me to use the stock airbox and connect it to the 38mm Mikuni TMX smoothbore carb via a homemade airboot.

"I was out of control at this point and found it difficult to stop making trick stuff."

Husqvarna doesn’t use a headstay on its bikes, but I wanted one to help reduce engine vibration. So, I machined a new rocker-cover cap, one with a mounting lug for a stay, from a block of T-6 aluminum, then welded a couple of nuts to the frame. An aluminum head-stay from a YZ250 Yamaha finished the job.

Once the engine was mated to the frame, the real work began. The CR500's radiators are the same size as the 510's, but they had to be spaced farther out on each side of the frame to make room for the four-stroke's dual headpipes. I used a combination of Honda CR and Husky 510 water hoses to connect the radiators to the engine.

Trying to fit a fuel tank over the tall engine proved the next stumbling block. IMS and Acerbis were nice enough to supply me with a variety of tanks to try. I eventually decided on adapting a tank designed for a 1988 CR250R, an IMS 3.8-gallon unit that has lowered sides to carry the fuel low on the frame. Making it work only required, oh, about 15 or l6 hours of my time reshaping it with a heatgun so it would fit over the engine. But it was well worth the effort. The finished tank holds 3.5 gallons, most of it below the frame’s backbone.

I didn't know it at the time, but the fabrication work was just beginning. The drive sprocket on the 510 is on the right side of the engine, the CR's on the left. Consequently, the Honda's rear wheel had to be turned around, and a new brake-caliper carrier machined from T-6 aluminum. It took several tries to get it right. A braided steel brake hose was fabricated and routed on top of the swingarm, held in place by rubber-covered, stainless-steel Adel clamps. A modified chain guide from a 250 Cagiva was installed, and a T-6 guide cover fabricated after several failed attempts to retain the stock part.

Ogre Ultra 50 handlebar and clamp
Ogre Ultra 50Kirk Willis

I then built the pipe—a two-into-one with an equal-length headpipe, based on a design I had used on ’87 and ’88 Husky 510s—and fabricated an aluminum megaphone with a Cobra internal silencer and spark arrestor. The pipe mounts to the frame with stock CR mounting brackets. Using an oval shape for the front part of the megaphone let me keep the pipe tucked in close to the frame, and the stock side numberplate and heat shields fit perfectly.

At least choosing the suspension parts was easy for me. An aluminum Works Performance Ultracross shock with a finned remote reservoir is very light, and I think it’s the very best off-road shock available; ditto for the White Power “upside-down” fork. This externally adjustable, cartridge-style fork is three to five pounds lighter than most others, and it works perfectly for me once it’s dialed in. White Bros. did the valving in the fork, and making it fit involved only pressing the CR’s steering stem out of the stock triple-clamps and into the machined-aluminum White Power clamps.

I mounted an Answer Aluminite Honda-bend handlebar and an Accu-Trax bar clamp to the stock, rubber-mounted CR handlebar pedestals. For throttle and clutch operation, I modified stock Honda CR cables, built a new engine clutch arm of aluminum, and pressed a small sealed bearing into the end where the cable clevis fits. The combination of the bearing and the CR cable makes pulling the clutch child's play. The handguards, front numberplate, fenders and front-fender brace all are from Acerbis.

Ogre Ultra 50 engine details
The 510 four-stroke engine fits nicely into the CR500R frame.Kirk Willis

Now the bike was starting to take shape; but I was out of control at this point and found it difficult to stop making trick stuff. I lathed a chunk of aluminum into an ignition cover, and fashioned a piece of T-6 plate into a lightweight skidplate. Then I made the mistake of polishing one of the aluminum parts. Before I knew it, I had polished every piece of aluminum on the bike, from the swingarm to the brake lever. It was a laborious job that I knew was silly, but I did it anyway. A D.I.D. O-ring chain, new tires and tubes, and ACP wheel-balance fluid completed the project.

Except for a name. I think a one-of-a-kind bike like this deserves a name. And since the Cycle World staff insists on calling me "The Ogre" (must have something to do with my great warmth and sensitivity), I christened the bike the Ogre Ultra 510. By the time I took it out for its maiden voyage, though, I was praying that it wouldn't act like an Ogre, that it would work as good as it looked.

Much to my relief, it did.

The only thing better than a four-stroke Single off-road bike is a light four-stroke Single off-road bike. And this one came in at the exact weight I figured it would—240 pounds even, without gas. The Ogre 510 is the same width as a stock CR500R, and once it starts moving, it feels even lighter than its 240 pounds. There is only a hint of the usual four-stroke top-heaviness, thanks to the lightness of the 510's top-end components and the low-slung fuel tank. The bike turns and corners just like, well, a Honda CR50OR—and that's saying quite a lot. The front end is much lighter than that of a Husky 510, so the wheel is easy to loft over bumps at fairly high speeds. Engine response is greatly increased due to the 38mm smoothbore carb and an Answer Roost Boost. So far, the jetting isn't quite dialed in; once I get that ironed out, the motor should be even more crisp and responsive.

"The Ogre 510 is, by far, the most ambitious project I've ever undertaken."

Ogre Ultra 50 frame crosstube details
The frame crosstube was removed and replaced.Kirk Willis

But I shouldn’t have to do much more with the super-plush rear suspension. The rear tire follows the nastiest bumps perfectly, and landings from killer jumps go almost unnoticed. The fork had a great deal of oil-seal friction for the first 150 miles or so, then the ride smoothed considerably. After the seals got broken-in, I replaced the fork fluid with Spectro’s new 125/150 cartridge oil set at a level of 150mm; fork action then got even smoother. And the fork’s external compression and rebound dampers offer such a broad range of adjustments that I found no need for internal revalving.

That’s fine with me, because I already have an enormous amount of time and work invested in the Ogre 510. It is, by far, the most ambitious project I’ve ever undertaken. But to me, it’s been worth every moment of work and every drop of sweat. It’s a truly unique machine.

And perhaps most satisfying of all for me was Lawson's reaction after riding this "ruined CR500" for the first time. He pulled off his helmet, looked at me with an ear-to-ear grin and said. "It's great. Will you build me one?"

No, Lawson, don't be stupid. But maybe, just maybe, you now understand.