The Service Department
THE SERVICE DEPARTMENT
JOHN DUNN
REBALANCING
I have a 750cc Norton Atlas and have done considerable work on the engine. I am now running M-C pistons, 12:1 com-pression, and they are considerably heavier than stock, thus requiring an engine bal-ance job.
Three different establishments have had a go at this task and I’m still being shaken to pieces on each run. Perhaps this vibra-tion doesn’t affect performance, but it’s very unpleasant to operate the bike and difficult to keep bolts tight.
I’m a machinist and do 90 percent of my work myself; however, I’ve yet to have someone explain the following details:
1. Can an effective balance be obtained by a bench job using knife-edged parallels and attaching the proper weights to the throws and using the “rocking”
system to find the heavy and light spots on the flywheel?
2. What balance factor should be used for English vertical twins?
3. Does the oil in the sludge trap have a weight worthy of consideration? In other words, should the passageway be filled with oil when balancing or not?
Also, I would appreciate any information you could pass along on changing from gas to fuel on Amal carbs or any other details necessary.
I enjoy your articles in CYCLE WORLD and think it’s a very informative magazine.
J. H. Terrell Silvis, Illinois
Being a machinist, you should not have any trouble in rebalancing the crankshaft of your 750 Atlas to suit the heavier pistons. Yes, you can use the parallel knife edge principle if care is taken to remove the same amount of material from each bob weight. If this is not done evenly, the crank will not be in dynamic balance even if the knife edge method has shown good static balance.
I would have the crank dynamically balanced to a factor of 62 percent by using screwed in balance plugs. If 62 percent does not do the trick, it will be easy for you to put lighter or heavier plugs in to alter the factor. It may be necessary to go as high as 72 percent to suit your purpose. It will be necessary to remove the connecting rods to have the crank dynamically balanced. The big end of the rods and bearing shells should be balanced in a horizontal plane. This is rotational weight and should be counterbalanced in full. Weigh the small end also in a horizontal plane. Weigh the piston complete with pin, rings and circlips. Add the weights of the piston and small end. This is the reciprocating weight. Now, compute the desired percentage (62 percent) and then add the computed weight (reciprocating) to the weight of the big end. (Rotational.) This is the total weight to be counterbalanced. The usual method employed when dynamic balancing is to make a split collar of the same weight and clamp it to the crank main journal.
You must include the weight of the oil in the sludge trap when balancing.
When converting to alcohol fuels it will be necessary to increase the flow capacity of the complete fuel system, including fuel tank tap, fuel lines, fittings and unions. The through-bore size of the supply system should not be less than 0.250 inch at any point. If a Monobloc (Amal) carburetor is employed, ensure that all internal drill ways are of adequate cross-sectional area. In this respect the Amal GP carburetor is a much better proposition when an alcohol fuel is being used.
A complete range of alternative jets are available, and the internal drillways are large enough to handle the high rate of fuel flow. Special needle jets and needles are available for use with alcohol. Alcohol fuels are not very sensitive to jet size, and a very rich mixture can be employed without a reduction in power output.
With methanol or a chemically similar fuel, it will be necessary to increase the main, jet by 150 percent. This can be calcu lated in the following way:
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Required main jet = percent increase + original jet size 100
REPLACING GENERATOR BRUSHES
My problem is a Yamaha YA6 125cc wit/i 10,300 miles on it that uses up a set of generator brushes in about 2,500 miles. What can be done to help this?
N. D. Emerson Tulsa, Okia.
Excessive generator brush wear can be caused by incorrect brush spring tension, brushes manufactured from the wrong grade of carbon, or by the commutator being worn or not running true. When replacing brushes, make certain that they are a genuine Yamaha replacement part. It is also good practice to replace the brush springs to ensure proper tension. They are a relatively inexpensive part. With a dial indicator check that the com mutator is running true. If the commutator is worn or burnt, it will be necessary to have it machined by a reputable auto motive electrical repair establishment. Af ter replacing the armature, again make sure that the commutator is running true.
CHAIN LUBRICATION
Could you please inform me on the prop er care for final drive chains? Most man uals only mention that chains have to be lubricated; however, they do not mention the kind of lubricant to use. Some man uals do mention the particular kind of lubricants, but they are not available on the local market.
The most common lubricants available on the local market are as follow:
Engine Oil SAE 30, 40, 50 Engine Oil SAE W10-30W Engine Oil SAE W20-40W Gear Oil SAE 90, 140
Chassis Lubricant (Grease) No. 1, 2, 3. Please inform me which would be prop er or a good substitute from the above mentioned lubricants.
Car/os 0. Forticli Ma/a ybalay Bukidnon Phi/ippines
The rear chain is probably the most abused and uncared for component on a motorcycle. The blame in the first instance lies with the manufacturer in the majority of cases. There have been a few machines manufactured in the past having a totally enclosed oil-bath chain. Chain life on these machines was extremely good. A few manufacturers today do provide a metered supply (from the primary chain case) of oil to the rear chain. However, none of these systems are totally adequate, and it is usually necessary to keep the chain wet by using an oil can every 500 miles. Any grade of engine oil can be used as a lubricant, SAE 30 to 50.
Currently, some manufacturers fully enclose the. rear chain to keep out abrasive dirt and dust, but do not provide a means of positive lubrication. Due to heat generated by the chain and poor ventilation, condensation takes place, causing the chain to dry out and rust. Frequent (every 200 miles) lubrication is required with an oil can to keep the chain in reasonable condition. I have heard of instances where the chain case has been half filled with a medium chassis grease, resulting in fairly good chain lubrication.
The chains that suffer most are the unenclosed ones. They should be kept wet with an oil can, but will require frequent cleaning. The best way to do this is to remove the chain, remove excess dirt with a wire brush, then soak it in a tin of gasoline or cleaning solvent. Agitate the chain to free any tight links. When clean, with all the links free, hang the chain up to dry or blow it off with an air line. The best way to re-lubricate the chain (this should be done every 2,000 miles) is to soak it in a tin containing melted tallow (or medium chassis grease) and powdered graphite. Agitate the chain thoroughly to obtain good penetration of the lubricant into the rollers. Hang the chain up above the tin to allow surplus lubricant to drain off. When in use, keep the chain lubricated with engine oil from an oil can. Be careful when heating the tin of lubricant; it is highly inflammable when melted.
OIL BURNING AFTER REBUILD
After 4,000 miles my CB 450 started to burn oil in the right cylinder. This occurred when the engine was hot and after times of high manifold vacuum. A check of compression with chokes and throttles both open showed that the engine had 145 lb/ in. at cranking speed (electrical starter) on both cylinders. After boring to the first oversize, pistons were fitted to .002, rings checked for end gap, new valves, and ground and lapped seats.
The mechanic who ground the valves seats said the guides were satisfactory and showed no signs of seizure. I myself checked the new valves in the guides and they showed no excessive clearance. 1 fitted the engine with all new gaskets and O-rings and washed all abrasives from the cylinders.
After assembling, the machine still burns oil in the right cylinder, which is evident both in the plug and the exhaust. The machine has 150 lb/in. compression on both cylinders. The only thing that would seem to help would be new valve guides for the right cylinder and a check of the mating surfaces.
Please advise me on a solution, as I hate to dismantle the machine again without results.
Gerald Devereux Kelly Lake, Minn.
It would appear from the contents of your letter that oil is being pulled into the right-hand intake port. The Honda 450 is provided with two valve guide oil seals. One is of the inverted cup type; it is fitted over the valve stem and stops oil running down the stem of the valve into the intake port. I would assume that these were replaced when the valve job was carried out. There is another seal in the form of an O-ring that stops oil leaking down the outside of the valve guide into the port. (Due to the high expansion rate of the aluminum cylinder head, this can allow a leak path between the head and the valve guide.) It will be necessary to remove the valve guides to replace the O-rings. The removal of the valve guides will almost certainly alter the position of the valve in relation to its seat. It will therefore be necessary to rework the seats to ensure that they are concentric with the valve.
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Also, pressure check the intake ports for porosity. It is possible that a porous area is allowing leakage from the oil contained in the cambox. When fitting the new valve guide O-rings, look for porosity or a faulty casting at the point where they seat in the cylinder head.
VICTOR HANDLING
I am one of what, I feel sure, must be a vast army of readers who follow your column with interest. Not only is your technical information exact, but your general advice always seems sound. It is a little of the latter I would appreciate.
I recently purchased a BSA Victor, influenced a great deal, I might add, by the test info in your magazine, and while it is a going machine, I am not happy with the front forks’ performance. I know that Ceriani forks are available at a price, and wonder if you think the conversion would improve handling sufficiently to be worth the investment. They also make a rear shock and, while less publicized, I wonder if it is worth it also.
As a word of explanation, I might point out that a dirt rider in the Rocky Mountain area has rather rough going. The term “Rocky Mountains” may apply to the big chunks sticking up 14,000 feet, but closer examination also reveals that most open land areas are extremely generous with their supply of six-inch chunks.
Incidentally, 1 didn’t quite understand about that special, longer swing-arm that your magazine recently tested on the Victor. Is it supposed to improve dirt performance? I can see where it might help hold the front wheel on the ground, but 1 was under the impression that a short wheelbase is desirable for ease of handling. Is it a question of how fast you will be traveling in the dirt?
D. A. Lauterback Denver, Colo.
The action of the BSA front fork is very greatly influenced by the quantity of oil there is in the system. It is therefore most important that each leg is equally filled with the correct quantity and grade of oil. Before refilling, make sure that the old oil has been completely drained. To achieve this, unscrew and remove both of the fork top nuts, Also remove the drain screws from the bottom of each fork leg. Do not remove the damper rods from the top nuts. Allow the forks to drain for a short while; then, while holding the front brake on gently, work the forks up and down until all the oil has been expelled. Replace the drain screws and refill each leg with 190cc (0.40 US pints).
At temperatures below 60 F use Shell XI00 — 20W or equivalent; between 60 and 85 F use XI00 — 30, and for temperatures above 85 F use XI00 — 50. If the front fork action is too soft, this can be altered by employing a spring with a higher rate. BSA manufactures a sidecar spring for the big twins which is color coded Blue/White. It has a rate of 40 pounds per inch. The standard spring for the Victor has a rate of 34 pounds per inch and is coded Green/Pink.
If you cannot get the desired effect from the BSA forks, it would be logical to go to the expense of the Ceriani forks. They have a very good reputation and are used by 80 percent of European motocross riders.
A pair of Girling spring shocks (which are now fitted to your machine) will take considerable beating. However, it may be necessary to experiment with spring rates to fully suit your weight and the type of use to which you intend to put the machine.
A short wheelbase will give very good control and maneuverability at low speed. Lengthening the swinging-arm does improve handling at high speeds over rough ground, particularly if the center of gravity of the machine is high. This is usually the case with most motocross machines, to provide adequate ground clearance. Lengthening the rear fork will quite often make the machine easier to power slide. When traversing a series of ruts or ripples at high speed, a short wheelbase machine is more likely to “see-saw” (a bouncing action, alternately landing on the front wheel, then the rear).
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LEAN-RUNNING SUPER HAWK
7 am experiencing difficulties which I suspect are not unique, but very annoying just the same. 7 own a Super Hawk and recently had an overbore kit (338cc) installed. The carbs were rejetted from 150 main jets to 160. Sparkplug indications showed extremely lean conditions to exist, so by the end of the 500 mile break-in period 1 was up to 190 jets with no change in plug readings or operating conditions.
7 should also mention that we progressed from NGK D-8 plugs to D-10Hs while rejetting and increased the oil (Valvoline) to 40 weight.
With lean indications, 190 jets and needle valves in the highest positions, 1 did my best to see how fast my “new” engine would go. 1 found the engine to always falter around 5,500 rpm in fourth gear and more often than not in third. The engine felt as if it was flooding but immediate plug checks showed no soot or carbon whatsoever.
Remembering that CYCLE WORLD installed a similar kit in its Hawk I referred to the October and December ’63 issues and found that you did “a bit of fiddling with jets and sparkplugs,” but that you found yourselves “right back with the stock jets.”
1 too went back to my original jets (150) and plugs (D-10H) and found I had some kind of tiger in my tank or something, as performance was outstanding. Unfortunately 1 had an equally outstanding lean indication from my plugs. Fearful of severely damaging my “new” engine,” 1 retained 160 jets and fully raised needle settings, as this has lately only limited fourth gear rpm.
1 have put 5,000 miles on the bike, so 1 consider this to be a safe — though far from satisfactory-condition operation. To add to my current state of confusion, 1 have just discovered the beginnings of radial splitting of my right muffler. I again went to my dealer for help and replacement, to which he recommended installation of a megaphone type “muffler” rather than replacement by a stock item. Now, again using CYCLE WORLD, April ’67 issue, I find a statement that “no exhaust system” performs better than an “unaltered Honda muffler . . . usually two full horsepower are lost by fitting . . . megaphones.”
Gary C. Van Brunt
San Bruno, Calif.
The lean indications being experienced are not uncommon, even on standard unmodified Super Hawks. In most cases it is caused by a low float chamber level. There is a prescribed method, set forth by Honda, for checking and resetting the fuel and float chamber levels. A detailed procedure is illustrated in all of the Honda workshop manuals.
Another point that is worth checking is the fuel tank vent hole. This is situated in the fuel tank filler cap. Quite often the tank cap sealing washer becomes squashed, and either partially or completely blocks off the vent hole. A completely blocked vent will usually result in the engine completely dying after a few miles of running. A simple way to check this is to try operating the machine with the tank cap removed. Also check to be sure that the fuel filter screen is not clogged.
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Until you have the lean symptons solved, I would continue to use the D-10H spark plugs. It would also be well worthwhile to recheck the ignition timing, making sure that you have the correct advance and that both contacts are properly balanced. The ignition automatic advance and retard mechanism is contained in a riveted-together assembly (weighted assembly between the camshafts). It is not uncommon for the rivets to work loose, causing erratic ignition advance. Late (retarded) ignition timing would cause overheating and poor performance.
I have heard of numerous cases of Honda mufflers cracking radially, at the weld, just behind the muffler support bracket. There is a lot of unsupported muffler sticking out beyond the support bracket. Vibration or continued road shocks would cause the muffler to fail at the point described.
In spite of this, the stock muffler is very efficient from a performance point of view and I would suggest that you stay with it, as it would be folly to make any changes until you have solved the present problem.
SOMETHING NEW?
I follow the development of motorcycles with great interest — especially the rapid growth (both in size and popularity) of two-strokes. Although my knowledge of engines (especially two-stroke tuning) is very limited, an idea has occurred to me.
In a two-stroke twin, the crankcase chambers are divided by a sealed partition to maintain proper crankcase pressures. Would it be possible to have two such seals with a chamber between them?
What 1 had in mind was a single carburetor feeding the chamber in which two rotary valves fed mixture to the cylinders alternately. It seems to me that a good velocity could he maintained in the intake tract, and, depending on the cut of the valves, a higher-than-atmospheric pressure could he maintained in the chamber at the time one or the other of the valves was opening.
With larger engine sizes and rotary valves, engine width becomes a drawback, and sufficient cooling becomes more of a problem. If this method of induction were possible, it would help cure both these problems. The spacing of the cylinders and crankcase halves would allow for more finning between the cylinders. Is this system workable?
I realize that experts in the field must have thought of this approach and discarded it, because of prohibitive or insurmountable problems in construction or tuning or something. But I thought I’d write anyway, even to he told why it won’t work.
Ross Aiken Los Angeles, Calif.
A two-stroke twin built on the design outlined by you would work. In fact, the British Anzani twin, built in the 1950s employed a very similar principle. A central chamber fed by one carburetor, with induction to each crankcase controlled by a rotary valve. Instead of a disc valve as indicated by you, a sleeve valve that formed part of a hollow crankshaft was used.
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The Maico 350cc and 400cc Typhoon twins also employed a central chamber; in this case, induction was controlled by the piston skirt in the conventional manner.
Both of these engines had very good mid-range torque and acceleration; however, top-end performance was below par when compared with conventional engines of similar size. The fall-off in performance at the top end would almost certainly be due to poor volumetric efficiency (breathing ability) at high engine speeds. For optimum top-end performance it is essential that the intake tract is as direct as possible, requiring a separate carburetor for each cylinder. I cannot agree that the chamber would be capable of providing pressures exceeding that of atmospheric. The condition in the chamber would be no different to that which exists in any intake manifold supplying a multiple of cylinders with one carburetor.
FRAGILE LOWER END
I own a ’66 Lightning (A65) that has a very expensive problem. It eats crankshafts. To date the engine has been rebuilt three times, and each time all new parts were put in — including all ignition parts and oil pump, etc. The thing is ready to go again (rod is knocking), and as 1 am not a multi-millionaire, I am quite distressed. What’s my problem?
Neale Watson Ruxton, Md.
The BSA 650cc Lightning is equipped with a high-performance engine that is prone to excessive vibration and knock when operating under a variety of adverse conditions. It is very sensitive with respect to ignition timing. An advanced timing will produce engine noises very similar to bigend bearing knock when operating under load at low engine speeds. Twin carburetor engines are provided with a manifold balanced pipe between the carburetors, and if there is an air leak on this pipe, the engine will knock excessively when idling. Loose engine bolts are often the cause of very bad vibration and engine noise.
The fact that your engine has previously been rebuilt on three separate occasions, due to the repeated failure of the main and rod bearings, clearly indicates that there is a serious malfunction of the lubricating system. This should have been rectified at the time of the first rebuild.
Lack of oil circulation or inadequate pressure would be the most logical reason. Any restriction in the system will reduce flow capacity and pressure. Check that all filters are clean and correctly installed. There is a wire mesh filter situated in the oil tank which is located behind the hexagon filter adaptor in the bottom outside face of the oil tank. Another mesh filter is located behind the removable plate situated in the base of the crankcase. Also check that the oil tank feed and return lines are connected to their correct unions. When they are fitted correctly, the pipes will cross over each other. The feed pipe (outside pipe union on the oil tank) should be fitted to the inside pipe union at the engine. If these pipes are not installed correctly (connected to the wrong unions), no oil will be sucked from the oil tank. Maximum oil pressure and oil pressure buildup is controlled by the pressure relief valve which is situated on the right-hand side of the crankcase just below the timing cover. If the valve (ball valve held on its seat by a helical spring) is not seating properly, or has been reassembled incorrectly, oil pressure buildup will be inadequate, resulting in extremely low oil pressure at low engine speeds.
After the first major failure, was the complete lubrication system thoroughly cleaned to ensure that all the metallic particles had been removed? Failure to do this would result in early destruction of the rebuilt engine. (The complete system naturally includes the oil tank and oil lines.)
Replacing the crankshaft with new components must have proved very costly. It is possible to have the BSA crankshaft journals reground to accept undersize main and rod bearings. Main bearings are available in 0.010 and 0.020-inch undersize, where rod bearings can be obtained 0.010, 0.020 and 0.030-inch undersize.
To my knowledge, the trouble you have experienced is not a common fault with BSA twins; however, if any other readers have experienced a similar problem, I would be pleased to pass on the information.
