421cc Two-Stroke “YamaGamma” Hybrid

Smoke Show: Vic Shield’s Dual-Livery 421cc YPVS Smoker…  

The Yamaha RD350 YPVS — also known as the RZ350 or RD350LC II — remains one of the last and most legendary two-stroke street bikes ever produced. The 347cc power-valve twin put out 52 brake horsepower, which might not sound like a lot on the modern superbike scale, but this giant-killer weighed just 371 pounds wet…and was highly tunable. Cycle World gave the RZ350 a “perfect 10” on the fun scale:

“Yes, the RZ350 is less powerful than the bikes three times as big, but it is no less thrilling to ride, since it accelerates, corners and stops better than any bike its size.” –Cycle World, 1984

Unfortunately, this oil-burning rocket wasn’t long for the world. Emissions regulations had strangled the market for two-stroke street bikes, and the RZ / YPVS would mark the end of a heady era of two-stroke street bike evolution. However, a growing contingent of shed-builders and tuners, particularly in the UK, began developing “hybrid” specials, filling the gap where OEM R&D ended. Often, these builds involved modified Yamaha two-stroke engines surrounded by more modern chassis, brake, and suspension components. In many cases, builders went to other brands to secure these parts. 

Enter the “YamaGamma” you see here, built by our old buddy Vic Shield of Vic’s Custom and Classic Motorcycles. If you’ve been around BikeBound long, you’ll have seen some of Vic’s past creations — many of them two-strokes. Notables include The Mutant, Vic’s RZ421-Powered MZ Skorpion, and his Yamaha “RD375LC” street tracker. 

Hooligan’s Dream: Yamaha “RD375LC” Street Tracker

The YamaGamma consists of a 1988 Suzuki Gamma frame, late-model braced RG swingarm and USD forks, and a tuned 421cc big-bore Yamaha YPVS engine. Vic, who’d wanted to own one of these specials since the 1990s, picked up a road-registered track bike in poor condition and set out to build the Yamaha-Suzuki hybrid special he’d always wanted.

As befits the dual-brand creation, the YamaGamma has a two-sided paint job that honors a pair of racing legends from the two-stroke “Unrideables” era.

“The right-hand side remains the Kevin Schwantz Pepsi replica colours but modified to my taste with metallic decals, and the left side is a homage to King Kenny in yellow and black speed blocks. The 421 is the engine size and I thought an appropriate number.”

Below, Vic gives us the full story on this absolutely wicked two-stroke hybrid YamaGamma hybrid special.

In the Builder’s Words…

This is my YamaGamma. I’ve had the dream of owning one since the 90s and never had the opportunity. After building the flat tracker and The Mutant I did a few other builds but two-strokes are what I live for.

This mainly track bike came to me in a bad way. It was road registered; however, looked like it had been through the wars.
The engine was knackered and the suspension was quite crude in design. The wiring was a bird’s nest, and under the skin it wasn’t that well put together. However, the bike looked properly nice and had loads of good parts on it. A decision was made to strip it and start again.

Basically this is a 1988 Suzuki Gamma frame with a late RG swingarm and forks. The engine was a tuned 390cc Yamaha power-valve lump. The engine was a struggle to remove and the suspension brackets very heavy steel items that bolted into place. The bodywork was quite good and the exhausts were racing pipes. This was going to be a one-off hybrid special.

Firstly the frame was stripped and aluminium suspension brackets fabricated and welded in place and the frame braced. The frame was then cut and a removable cradle bolted in place to aid engine removal.

The engine was sent off to my mate and engine tuner for a rebuild. Another Athena 421cc stroke kit — this time not as tuned as the Mutant’s engine, yet still producing around 90 ponies at the rear wheel.

A set of 38mm carbs, new race ignition which doesn’t rely on a battery, and a heavily modified radiator were all there waiting to go onto the rolling chassis once the engine was sat in position.

I kept the exhausts because they fitted the look of the machine.

The colour scheme has been floating in my head for years and this was the next job to get underway. The fairings were repaired and the seat unit modified to take a two-stroke oil bottle (as this is a pre-mix oil in tank bike) and a tool kit, which is essential for any old or tuned stroker.

I fabricated a twin fake pipe / door to cover the seat opening and this is held in with push-button bonnet clips.

As the engine is a lot wider than the original 250 twin that Suzuki made, I had to fabricate new fairing brackets and a spacer to bring the side panels out a few inches on each side. I cut away a section on the right lower panel to show the lock-up clutch, and on the left side a slot was taken out to allow the side stand that I had to fabricate access to come down.

 

Stainless steel screen stays were made to support the upper fairing and a bracket to hold the excellent Acewell clock. This is a no nonsense unit that does the basics: RPM, speed, and engine temp. It can do more but I like simple.

Now the fairing was in place I was happy to take it away for painting and graphics. A graphic designer called Terry who has worked with me in the past helped me sort out the graphics, and as you can see it does do the job. As it is a hybrid of Yamaha engine and Suzuki chassis I wanted to make this clear in the final build.

The right-hand side remains the Kevin Schwantz Pepsi replica colours but modified to my taste with metallic decals, and the left side is a homage to King Kenny in yellow and black speed blocks. The 421 is the engine size and I thought an appropriate number.

The wheels were all white and it didn’t look right against the yellow, so I painstakingly masked half up and sprayed the Yamaha side in satin gold.

The whole project cost more than a new MV to build, but you won’t see another one in a car park near you.

Follow the Builder

Web: vicscustomautos.co.uk

More from Vic’s Custom and Classic Motorcycles

---