Sheene

Oliver's Mount did a Barry Sheene tribute in June. Tee's are still available if you are a fan:

Oliver's Mount Barry Sheene Festival 2016 Motorcycle T Shirt | eBay

Its another one.

I have built 3 thus far. One way back, another in 2013 and now this.

The basis of this TR is a period race bike that was crashed years ago. It then spent 30 years with two owners who did nothing with it, I think it was so bashed up that they thought it was best broken for spares. It came to me around Christmas 2013 via a swap for some early CB750k (1969) stuff I had collected for another CR project, I had matching cases and frame also a lot of the difficult stuff, no where near a complete bike but a good basis for a 69, all the parts were good needing little work. The TR on the other hand was a mess; the chassis was bent, the tank had a 3" inch deep crease across the top. engine was weather seized, carb slides seized solid, two of three exhausts ripped off. No seat, no fairing, no front wheel, broken yokes which the seller suggested I weld , no forks, one calliper. It was a real mess.

When I saw it, I put half of the CB750 stuff back in my van and the deal was done.

Result below as photographed October 16. It has a works lightweight crank, one of two both went to Sheene. Suzuki TR dry clutch and TR gearbox. Since the photo I have removed the cans and replaced with stingers, have fitted a correct rear master cylinder, correct front disc (mag carriers), 3x VM36 Mikunis, and made a gear lever of the correct type. Also fitted a period fuel filler cap and a few other things to make more period. The forks are RG500 Mk1, wheels are XR14 Morris Magnesium, yokes are also XR14. Loads of titanium too, spindles, fasteners etc.

The bike didn't take long to build but it took nearly took 2 1/2 years to find parts at good prices. The wheels for example were advertised as Kawasaki and part of a Suzuki GT550 project, I bought it for £500, put the wheels with the TR put some ropey GT380 wheels with the 550 project and sold it for £800! This method gathered most of the pats for the build, wheeling and dealing for stuff, some bits I had though like the crank. The fairing came from a autojumble, new but slight damaged for £45, but the screen cost £50 and is RG500 Mk9.

Teazer said:

Stunning work as always.

Just out of idle curiosity where did they remove metal to lighten the crank and how much lighter was it? On a reed motor, a smaller crank ie more crankcase volume is usually a good thing. Back in the day Suzuki used to love high primary compression ratios which push revs up and narrow the power band. Modern snowmobiles often use pork chop cranks which would have been an absolute no-no back in the day. It's always interesting to see how things change over time and to get a view into what was done back in the day.

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1st thing this engine does not have reeds or power valves. Both reed and power valve help control pressure varying the pressure inside the engine effecting fuel transfer. I have seen pork chop type cranks for these engine and I have no idea why its done, perhaps its all about balancing the crank and reducing vibration, if its meant for performance and raising the revs then increasing volumes does not help and even a standard GT crank if pegged and race prepped has a very short life past 9000rpm. Its a waist of time and money.

The Tr crank is lightened in a similar way to a Yamaha TZ with matching holes bored into each flywheel. On the standard TR and Yamaha TZ these holes are left open but depending upon the engine these can be fitted with nylon slugs or even filled with polypropylene poured, set and trimmed. On the TR above there are 6 lightening holes per flywheel, standard TR has 4 just like the TZ. The crank isn't significantly lighter.

The reason for the lightened crank - by 1975 the TZ was becoming dominant and having ridden both the TZ and TR I can say the TZ has the jump out of the corners, it picks up quicker. In an attempt to compete Suzuki did a few things - The TR got a better lighter frame XR11 type, engine with lighter crank and light magnesium covers. Disc centres, yokes, wheels etc were also magnesium. Alas it didn't really work as Yamaha just reacted with a better TZ. Strangely The TR is quicker when its really flying over 9000 in top, they are real torque monsters and the reason why the did well on the big fast circuits. Sheene didn't like the light crank as it made the bike more difficult to ride.

"so, are pork chop cranks less efficient at charging the cylinder?" = Yes.

Your comments are all correct BUT its not that simple.

So much depends on the engine and what its being used for. A race engine is not a chain saw.

Increasing volume in the cases by pork chopping a crank in a traditional stroker will improve low rpm power but it slows down the charge through the transfer ports, does allow better scavenge (gases still get trapped) but results in a weaker charge for the firing stroke ultimately you loose power. The easiest way to increase volume in a reed engine is to add spacers behind the reeds and a dam sight cheaper than removing lumps from the crank. Minimising volume in say the TR (no reeds) will result in a greater primary compression and a bigger charge through the transfers but will make the engine more sensitive to pipes and "more" exhaust gases can get trapped. Its a balancing act between port timing (and piston skirt length), pipe volume, case volume plus other engine settings like transfer port volume.

Getting the balance right on a road bike is one thing, ride a GT500 and try revving it past 8k but a race bike like a TZ750 will rev until it explodes.

I guess if you guys want to build bikes with a broad spread of horse power and flat torque curve stick with 4 strokes.