Hawk Talk

[Ariel Red Hunter]

Originally Posted by pete

PMSL.......

seal = tar /bitamin.... or what ever you fella's over there call it...

But I think you buggers are just taking the piss....

"taking the piss = having a joke"


..




...

tar/bitumin = asphalt/blacktop

[Ariel Red Hunter]

Originally Posted by pete

PMSL.......

seal = tar /bitamin.... or what ever you fella's over there call it...

But I think you buggers are just taking the piss....

"taking the piss = having a joke"


..




...

Pete, surely you don't think we are cracking your 'nads. Americans aren't that clever, some of my Pommie friends used to tell me.

[Ariel Red Hunter]

For those who ride mostly on-road, and looking for more top end, let's look at some options. A Mikuni VM26, or perhaps a VM28 with the starting enrichment circuit, not the butterfly choke. A quality exhaust system, including the copper o-ring gasket between the head and the head pipe. An one inch to inch and a half intake spacer, to move carburetor furthur from the head. Make this out of plastic to also act as a heat sink. Make sure the inside of this tube is smooth, and exactly the same internal size as the ports on the carburetor and the head. Go to the most open air-cleaner that you can find. Remove the air box completey, or extensively modify it in order to make a "still air" box out of it. Run a 17 tooth front sprocket and go smaller on the rear sprocket. Run the narrowest road tires that will fit the rims. Change the front brake line to one of the stainless steel ones of high quality. Tune carburetor pilot jet, and throttle cut-away for all the low end you can get. This saves the clutch. You know what to do about the main jet.

[Ariel Red Hunter]

While I'm sure that ARH lectures on engine design are pretty boring, I'm going to risk boring you'all just a little longer. I've heard those comments on the superiority of overhead cam engines, especially of Japanese ancestry. But all is not as good as it could be. In fact, there are a surprising number of cam tensioner failures with around ten thousand miles on the bike. Now it may be due to either not enough oil changes, or terrible oil being used. But whatever the reason, cam chains are stretching enough in comparativly low mileage situations to indicate something is wrong. Now, in Classic motorcycle engines, singles especially, only one factory, spread over two brands, successfully used chain driven overhead cams. AJS who came out with the first one, while they were still an independent company in the mid 1920's, and Matchless. During the depression, AJS went down the tubes, only to be bought out by Matchless. Their engineering department at AJS worked the bugs out of their chain drive system. Now we come to the 1960's, when a far eastern tidal wave (Honda) washed almost every other manufacturer away with the tide. With a line of chain driven over head camshaft engines. But with a difference. The chain ran at crankshaft speed, all of the reduction taken at the sprocket in the head, and they buried the drive way inside of the engine on the twins, and as far inside as they could get it on the singles. The AJS and Matchless engines used a gear reduction so that the chain ran at half crankshaft speed, and was mounted outside, on the timing side of the engine. Easy to replace, and much less whip, because it ran so much slower. Because the whip was so much less, AJS used a Weller type chain tensioner. The Japanese, and clones used a pushrod type tensioner, probably because there was too much chain whip for a Weller type tensioner. And these automatic pushrod tensioners are breaking, dropping little metal bits into the works. Think about that before you decide that a pushrod engine with gear driven cam is so hopelessly out dated as to be safely ignored.

[Ariel Red Hunter]

Un fortunatley, cam chains suffer from more than just whip. It's called fling. Fling is even harder on a chain than whip is. With whip, at least some oil gets in to lubricate the links. With fling, not so. When a chain is running between two sprockets, there is a chain speed (in feet per minute) where the chain is tight all the way around, and no oil gets to the loaded side. This overheats the roller axle ~ disaster comes, sooner or later. Running a chain at high crankshaft speeds can cause fling. By reducing chain speed with a reduction gear, the chain never turns fast enough for fling to happen. It has by now surely occured to you guys why modern OHC engines don't use reduction gears for cam chains. It costs more. The only way you can get close to the cost of a pushrod engine with a gear driven cam, is to eliminate the gear reduction of the timing chain. Even relatively low rpm OHC engines have chain problems. This surprised me, but 650 Suzuki Savage are even having this problem.

[Ariel Red Hunter]

Those of you who have been following this thread may have noticed that I haven't said a word about ignition or AC vs. DC alternators. That is because when you get very far past a magneto, or a generator and points/condenser ignition system, well, I'm over my head. But when it comes to thermodynamics, hydraulics, and mundane things like why you want the crankcase to run at a partial vacuum, and even wheel and tire sizes, then I know something. I even understand motorcycle frame geometry. I can even tell you why something ought to be there when it isn't there. I was even a production engineer at International Harvester for a while. If I worked for Bashan, the first two things I would change are the location and/or type of rear wheel master cylinder, and the swing arm bushings. I hope the reasons for this are obvious. Next would be the rear chain quality issue. Note that two of these problems are vendor problems. When you are producing as many motor cycles per month as Bashan is making, you can swing a pretty big stick. Bashan should be telling those two vendors that if you can not find a way to improve the life of these two parts, Bashan will have to look elsewhere for swing arm bushings and drive chains. And at the same or lower price. If you think this can't be done, you are wrong - Ford Motor Company does it all the time. To illustrate that point, when Ford bought Jaguar, one of the first things they did was to see where the warranty claims were. Electrical problems. Since Jaguar started in the 1930's, they had been using Joseph Lucas electrical parts. Now to the younger set, in the old days, Joe Lucas was known as "The Prince of Darkness". Need I say more? So Ford told Lucas if they couldn't get the quality up to current standards, they were going to switch to Bosch, or Motorcraft, or Autolite, or even Delco-Remy. Lucas got the quality up.

[Ariel Red Hunter]

I ran across an old interview with Joe Craig today, and I thought I would share a few snippets of it with you. Joe Craig was the guru of the Norton racing department from 1930 until they quit making Manx Nortons. He brought the single cylinder motorcycle to as close to perfection as anyone ever has. I'm going to put him in quotes. When a quote ends, and another one starts, then a new quote. "High performance is achieved chiefly by admitting the greatest weight of charge (at high piston speeds) and burning it efficiently. The highest possible weight of charge is obtained through having a long induction period and by making maximum use of the kinetic energy of the exhaust gasses from the previous stroke. The pressure difference across the exhaust valve encourages the new charge to flow readily into the cylinder. Engine torque is of prime importance, and although an increase in bhp may be possible between, say, 6000 and 7000 rpm (he is talking about the 30M engine, which had a stroke of 100 mm, very close to 4 inches)the torque at this speed may be decreasing. Briefly, we aim for the highest torque at the highest possible engine speed while ensuring that the torque at lower r.p.m. does not suffer unduly in consequence." Now think that statement through. If you have looked at very many torque curve of gasoline engines, you will notice that torque makes a gradual climb to peak, and thereafter falls off rapidly. HP is generally assumed to be torque, in foot-pounds, times rpm, and then this total divided by 5250. Everyone (even me) has one of those pocket calculators that make charting this stuff easy. So take the Hawk's torque figure at 5500, and elevate it to 6500 run it through the calculator and see what happens. And here endeth the lesson for today.

[Ariel Red Hunter]

Those of you who have struggled through reading my posts, may have noted that I talk about eastern riding and western riding as if they are two different worlds, well, they pretty well are. Except for the Pacific North-west, which has similarities to the east. Eastern woods terrain may well be better traversed with trials type tires,because of traction over wet rocks, stream beds and coming out of a stream bed with tree roots to get over, and logs to get over in the woods. Out west, where I grew up, cow trailin' and desert riding was what we did. And fire roads. Knobbies work well for that type of riding. So to forks. You will find it easier to ride in the east with lightly damped front forks. One of the primary techniques for getting over logs is to approach it slowly, put your weight on the handle bars to compress the forks, then pull back on the bars and give it a shot of throttle so the bike rears up to get the front wheel on the top of the log, then feather the throttle, and using momentum to get the rear over. Too much throttle and the rear wheel will spin and leave you "high centered". You will eventually learn to lean forward again a little bit in order to get all of the rear suspension extension possible. It's sort of a motorcycle ballet. You will have to practice this. It will take more than 10 minutes to learn this skill. Lightly damped forks work well for this. Lightly damped realistically means thinner fork oil. For pavement riding, heavier fork oil is indicated, also for western riding.

[Ariel Red Hunter]

The "Wizard of Bracebridge Street", that was Joe Craig. Joe was a great engine man, but not really a chassis man. From the end of the TT races on, he was scheming and working to win the next one. Joe was interested in two things - useable engine power, and reliability. Bracebridge Street, in Birmingham, was the home of Norton Motors for about fifty years. So, to go on with Joe's interview - - "When the best compromise of inlet and exhaust port shape has been established in cojunction with the length of valve opening period, diameter of the valve head, and the (mechanical) displacement of the valves dictated by the shape of the cams and the required "overlap," work begins on improving the combustion of the charge. The aim is to provide the optimum amount of "swirl" -- agitation of the mixture-- and so improve the evenness of the burning. Swirl is influenced by port shape, diameter and angle, valve diameters, and the configurations (shape) under the valve head. Governed in this way by compromise, the best set of conditions is established. The combustion-chamber shape then receives attention so that the fuel is burned as efficiently as possible. It is of the utmost importance that the surface-are to volume ratio is as low as possible, for it is this ratio which decides the proportion of heat that will be retained in the charge and the amount that will be dissipated through the head, barrel, and valves. Heat retained is capable of doing useful work, but heat dissipated is responsible for many of the troubles with the internal combustion engine". Now, ladies and gentlemen, I think that is enough to chew on, and digest for one day.

[pistolclass]

ouch you hurt my cerebrum.

[Ariel Red Hunter]

Originally Posted by pistolclass

ouch you hurt my cerebrum.

Sorry, such was not my intent. I put this up here as a guide for those who are searching for more power than a simple carburetor and exhaust change can supply. Food for thought, in other words.

[Ariel Red Hunter]

For me anyway, the best way to get something out of technical topics like this is to read them over, at least three times, over three days. Then the salient points sort of percolate through your brain, to be re-called on demand. So let's read on. "No advantage is to be gained by allowing a Manx engine to turn over at speeds in excess of 6200 rpm for the 500cc, and 7200 for the 350cc. Engines will usually withstand a sudden increase of, say, 500 rpm momentarily, as for instance a gear is missed, or a chain breaks; but when an engine is over revved the big end (rod) bearing, gudgeon pin (wrist pin) and piston bosses are subjected to excessive overloading. It is difficult to take any steps to prevent this occurring, apart from impressing upon the rider how harmful and expensive the practice of over revving can be." - - "While there is at present there is a tendency towards "squarer" (shorter stroke) engines, we feel that our 71X88mm (350) and 79.62X100mm (500) power units have been - and are - quite successful in the hands of the general racing public. Although we agree that the squarer (shorter stroke) engine may have the ability to rev more for similar piston speed and inertia loading, one should not overlook that higher engine speed is of no merit unless accompanied by a substantial gain in power." - - "The material for the inlet (valve) guide is phosphor bronze and for the exhaust, chromium bronze. The high thermal conductivity of chromium bronze enables full use to be made of sodium cooled type exhaust valves. In other words, the hot stem of the exhaust valve is able to lose its heat rapidly through such a guide, thereby lowering the temperature of the exhaust-valve head." - - "In an exhaust system for a racing engine, the gases must be dis-charged so that the piston works against the minimum possible gas pressure. The kinetic energy of the (exhaust) gas must be utilized in such a manner as to produce the maximum negative pressure in the cylinder towards and at the end of the exhaust stroke. Use can then be made of a large valve overlap to get the inlet gas moving in readiness for the next filling stroke. It has been established that the combination of exhaust pipe length and diameter is important in achieving the best possible results, and that no one combination is equally efficient over the whole speed range of the engine. Usually a long pipe of small diameter is good for power at low rpm, while a shorter pipe of larger diameter is better for power at high rpm. It is necessary to compromise with a pipe diameter and length wich gives the best results at the most used part of the engine-speed range. The length is often less than the regulation requirements for (road) racing, and in the early days the megaphone was introduced to bring the length of the exhaust pipe to that required by the regulations. In later years, however, the exhaust pipe has been subjected to intensive investigation, and the angle of the taper of megaphone have been found to be important in achieving the greatest possible extractor effect, and the consequent benificial influence on top-end performance."

[Ariel Red Hunter]

For those of you who have been reading this column, thread or whatever it is, let us discuss what we may have gleaned from 'ole Joe's rantings. What he has to say about surface-to-volume ratios is beyond our control with the Hawk's engine. The port size is pretty well fixed, and from what I've seen of it in various pictures posted on C/R, the shape is pretty good. So is the finish. The problems start on either side of the head. The standard carburetor is very difficult to find jets for, as I learned to my sorrow in the 1960's when I was wrenching a 125 Honda twin road racer. I had read, in Phil Irving's book "Tuning for Speed", why moving the carburetor away from the head's inlet port helped cylinder filling, and increased torque. I tried it and it made a big difference. We made, on a lathe, a three inch inlet manifold as an experiment, out of a piece of magnesium alloy that was laying around the shop. We even turned cooling fins on it. The cooler the mixture, the more it weighs - hence better cylinder filling = more torque = more power. It worked fine. I weighed about 225 in those days, and it would accelerate in fifth gear up hill carrying me. Pretty impressive, it actually surprised me. If you are riding mostly on the road, you probably need all the torque and horsepower you can get, so the exhaust system is the next problem. I have seen photographs of the inside of the Hawk (and brothers under the skin) head pipe. You don't want any restrictions in the exhaust that don't serve a purpose, like muffling. In the pictures I've seen, sloppy welding, and a furry gasket between the head and head pipe is bad news. Never mind having a tiny catalytic converter stuffed in there. The head pipe is really stifling horsepower. Next comes the muffler. I don't know how restrictive it is, all I know about it is I would change it too, partly because I want an exhaust just loud enough that I can hear it with a helmet on. I would even consider making a Brooklands Silencer for it. I think the pipe diameters are spot on for this engine, and the uses we have for it. So, you need a new head pipe and one of those Honda copper o-ring gaskets for it. A Brooklands Silencer will add about 1 horsepower over an open pipe, for your information.

[BlackBike]

I tell you red, you need to get one of these cheapie bikes to tinker with and get you a young test pilot for trials.

[Ariel Red Hunter]

Originally Posted by BlackBike

I tell you red, you need to get one of these cheapie bikes to tinker with and get you a young test pilot for trials.

Good idea! Also good to know that everyone reading my deathless prose knows what a Brooklands Silencer is, so I don't have to try to describe it.