A week or so ago CM wrote asking about operating temp differences left and right. Why does the rhs run hotter?

 

 

xsjohns, rip, engine temp recording … with cooler … left and right can run up to 30° or so difference

 

 

I’ve been out of town. Away from my computer. Exiled. Disconnected. But not deleted. Basically this is the answer I sent him.

Over the years I’ve heard many postulate. From aerodynamics to exhaust placement.

When you look at the engine design you see all the mechanical parts are focused to the right. As is oil flow.

Hot oil is sucked up through the pump. Slowed at the filter.

Mechanical action from the tacho, oil pump, primary and clutch all add frictional heat.

Aluminium is a good conductor. Heat gravitating upwards meets that from the combustion chamber and exhaust ports.

To the left we have the generator. In an air cell. Dry. Different thermal properties.

Allows the left to act more efficiently and effectively as a heat sink.

When Yamaha built the carbs they did so symmetrically. Jetting specs both the same. Each operating in different thermal environments. Built in imbalance. With appropriate feedback loops.

If you have adjustable needles it is possible to richen the right hand carb by raising the needle.

 

 

lowering the clip raises the needle … enrichening the mix

 

 

XSJohn, rip, ground needles with different tapers as a set. Left and Right. The canadian needles apparently are similar. Replace needle jets and jet needles together as a pair.

 

 

xsjohn, rip … on his needles … no grooves here, his production needles were grooved

 

John also built wings or foils to deflect airflow over the cylinders.

 

 

xsjohn’s wings … notice the deflector under the lower clamp

 

 

Others install oil coolers.

 

 

remote filter and cooler … so positioned the cooler will reduce air flow over the head

 

 

heidens side filter-cooler

 

 

Today there are many diagnostic techniques. Years ago I had an interesting conversation over too many beers with an Australian Naval NCO. Have never been fond of military types. Too rigid. Thinking actively suppressed. Later I was to learn the corporate world is, in theory, no different. In practise, a lot worse. Establishment meeting punk – the shock was mutual. He was a vibration analyst. Spent his time listening to machines sing. No different really to listening to your motor through a long solid screwdriver. He had a lot to say about the internal workings of Australia’s navy.

I would like to see a series of  Infra Red pictures of an XS650 motor running. Done in a resolution capable of  differentiating temp gradients within the 80-300° range. You would see some definite nodes on the right and fronts associated with temp assymmetry.

I come from the southern hemisphere. Live in the north. Apart from north and south there are other differences too. Here they drive on the wrong side. When you pull the bath plug, flush the toilet, water runs anticlockwise-the coriolis effect. I wonder what this does to other physical gradients .

When you talk with people who play with these engines, they will mostly tell you how solid they are. How destressed and strong they are built.

To a degree they’re correct.

This was the first 4 stroke motor built by Yamaha. So they were careful. Didn’t want expensive mistakes. The heritage was of course German. It was pretty solid to begin with. Add a little nervous over-engineering and you get the XS1. Built as a street engine. It didn’t have years of racing development behind it.

Many of the ideas were reworked into their second 4 stroke. The XT500. And look where the French took that. Bet Yamaha considered making Olivier an honoraray Japanese.

The fascination for Motocross and Enduro killed Yamahas’ interest in Flattracking while they were at the top. A real shame for Shell Thuet. Also for Bob Trigg.

The XS1 was immediately improved. Clutch. Forks. Crank. Brakes. Later, Percy Tait showed how to improve the frame geometry.

With some improvements the motor basically stayed the same for years.

XS1s make good restoration projects, although the heads breathe somewhat better. 447s make good café racer bases. And Specials lend themselves, with their layed forward rear geometry, to choppers and bobbers. Everyone’s happy.

Restorers will debate the interchangeability and logic of XS1 headlight bracketry or fork internals vs XS1B or XS1F and XS2. Corner carvers will relish the Standard frames improvements. Commuters the electric start. Easy riders the lower-slung specials. Sidecrossers and hillclimbers the simplicity and grunt.

They will all see strengths and weaknesses depending on the design problems they meet and the level of customising they do.

The further you go the closer to the limitations you come. The machines’. The machinists’. The mechanics’. The riders’. And your pockets’.

The problem is that, unlike global finance, the trickle down effect actually works in the real world of mechanics. Any changes you make here directly effect how that there works. Every action has an opposite and equal reaction.

In reality the reaction can be plural and the effects cummulativly overwhelming.

Means, you start playing with the motor, increasing the cubes, playing with the squish zone, allowing her to breathe, changing the timing and you begin experiencing the limitations.

Same with any system in balance.

Talk to the big cube and torque blokes and they tell you head design and the crank centre pin are the ultimate limiting factors. No matter what you do to the rest-it’s that pin that goes.  Some talk about converting the cases to take conventional bearings and running high pressure oiling. Or machining 1 piece auto style cranks and 2 piece conrods.

It’s not going to change the fact that they simply don’t like being shifted over 7500. The little end stretches. Any piston pin play and you have problems.

Fine. What gives next? Cylinder stud anchor points in the crankcase. Aluminium.

Liner thicknesses. Pistons.

Increase cubic capacity? RPM? You’re talking air. Has to come from somewhere. And go there too. Carburetion. Exhaust. Only as good as the head.

Also here the talk is porting. Cylinder centres and stud patterns. Machining existing DOHC heads to fit? Or making your own.

Got good flow? How to get it to the rear wheel? In a way you can control it?

 

8 valve head … wim mellendijk

 

 

And frame geometry.

None of this is new. Each pushes the envelope. Each tests the limits of it’s partners in crime. All is linked…ommmmmmm

Bud Aksland talked about..

‘…rephasing cranks, different firing orders, hundreds of valve, cam piston crown profiles, welded up ports,…the list was endless…the basic … was a stock set up with a weighted crank…the stock head casting was the limiting factor…is why the OU-72 was commissioned…purpose-designed casting with more favourable valve angles etc.’

‘…it is an engine with built-in performance limitations and if you are going to be successful in your attempt to extract more user-friendly power, it will have to be done with a systematic, integrated manner.’

Kenny Roberts talks about it too.

‘…Accepting the deal from Yamaha meant we had good roadracing bikes —real roadracers built by Yamaha.

But the dirttrack bikes weren’t so good. We had to make do with Yamaha’s XS650 twin, a steetbike, as the basis for a dirttrack racer…

…we struggled with the XS650 that first year. Still, I earned enough points that year to move from junior to expert.

In our struggles with the XS650, we too often resorted to using pistons from here and a cam from there and these valves trying to make the bike fast. We also managed to blow it up a lot!

…in ’72 Yamaha decided to get serious and added Shell Thuet to the team. Shell was an established motorcycle dealer in Los Angeles; he was very experienced, and he knew how to build a racebike. Like all good tuners, Shell knew how to make all the parts work together. He made sure to build reliability in before trying to build horsepower. Some things never change. This is still the best approach to building a competitive racebike’