The Service Department

THE SERVICE DEPARTMENT

JOHN DUNN

SMALL PROBLEM

My small problem turned into a bill of over $100, and I want to try to do my best to prevent it from happening again, so I come to you for help, and suggestions/answers. I have a ’67 Honda CL160, and the left exhaust valve broke-completely off. It went right through the top of the piston, down into the crank. As a result, the head could not have new valves seated, it was too chewed up-so, one new head, four new valves, two bored cylinders, two new pistons, rings, clips, and gaskets. Is this usual, and if so, can there be steps taken to prevent it? The shop said it wasn’t commonplace, but offered no solution. I always kept the oil changed and the bike tuned. I use Speed Sport, which is recommended. Can this happen again very easily, either on this bike, or on a Triumph 650, which I had ideas on for my next bike?

Paul A. Severson Franktown, Colo.

I do not consider “dropping a valve” a small problem, Paul. In the majority of cases the resulting engine damage is severe. Providing the engine is operated within the manufacturer’s recommended speed range, and considering the great advances that have been made in valve materials, manufacturing techniques and inspection procedures, actual valve breakages are a rarity today. However, if the engine is overreved, loss of valve control will occur, causing the valve to deviate from its intended position, normally determined by the timing characteristics of the cam profile. If the piston does contact the valve, the latter will be bent and be hit an additional 40 times per sec. by the piston when operating at a crank speed of 10,000 rpm. It is no wonder that excessive damage occurs.

Valve breakages do not always occur when an engine is overreved. Incorrect tappet clearances (valve lash) can cause a harmonic malfunction of the valve train, which results in valve to piston interference. Continuous high speed operation not only causes wear, it also accelerates metal fatigue. All the components in an engine are subject to eventual fatigue failure. With normal use, this usually will not occur within the expected life of the vehicle. However, as the speed and load increase, the life of each component is shortened at an alarming rate. Some racing engines are so overstressed that certain critical components, such as connecting rods, pistons and valves, must be replaced after a very short period of use. In other words, they are nearing the end of their fatigue life. Sometimes early breakages take place as a result of faulty material or heat treatment procedures. In these cases, failure usually will occur very early in the life of the engine. Inspection by

means of magnafluxing, dye checking or x-ray invariably will show up these manufacturing defects. There is always a small chance that you may experience a similar trouble again for one or more of the previously mentioned reasons. However, reoccurence should be considered very unlikely either with your present machine or the 650-cc Triumph.

OIL AND SMOKE

I own a 1954 650-cc Triumph which has given me very good service over the past three years. The machine is used solely for pleasure touring and has never been driven hard. It has suddenly started to use large quantities of oil and smokes heavily on acceleration. Before this trouble started the engine was fairly oil tight and used approximately one quart every 500 miles. The rear tire now gets soaked with oil; in fact I cannot use the machine now until I get this trouble fixed. Could you please give me some indication of what is causing the trouble?

H.A. Lowe Racine, Wis.

Your trouble is almost certainly the result of a faulty scavenge pump. The Triumph is equipped with a “dry sump” lubrication system which employs a remote oil tank. The oil pump, which is contained in the timing case, has two functions. One side of the pump is the pressure pump, the other is the scavenge pump. The pressure side receives oil from the oil tank under a gravity head (the tank is higher than the engine), and pumps oil under pressure to the engine bearings and all other parts that require lubrication. When the oil has done its job, it falls to the bottom of the crankcase. As soon as the oil starts to accumulate in the crankcase it is sucked up by the scavenge pump and returned to the oil tank. If the scavenge pump fails to work, the crankcase then will fill with oil, and oil will then be blown out of the crankcase breather. It is normal for the scavenge pump capacity to be twice that of the pressure pump, to make sure that the crankcase is fully scavenged at all times.

(Continued on page 18)\

Continued from page 16

On the Triumph, the oil pump is of the plunger variety and is driven by an eccentric off the end of the inlet camshaft. Remove the timing case cover. Remove the oil pump and completely dismantle same. Note position and order of assembly of all parts. The pump has two plungers; the larger diameter one is the scavenge, the smaller is the pressure, or feed, pump. At the base of each plunger chamber there is a ball-and-spring non-return valve. Check the condition of the balls, springs and seats. If the seats are badly dented they can be recut with a drill sharpened to a 45-degree angle. If the balls and/or springs are suspect, replace them. Completely clean all parts with gasoline, then reassemble the pump with clean engine oil. The pumping effect of the pump can be checked by inserting the plungers and working them up and down. The trouble you have been experiencing I am sure is the result of a stuck non-return valve on the scavenge side. Another possibility is that the scavenge pipe that goes from the pump to the bottom of the crankcase may be defective or leaking at the joint.

THE SPOILER

I own a 1968, 350-cc Honda with 1700 miles on the odometer. This machine is a joy to ride except for one problem that has persisted since it was new. Although the idle has been correctly adjusted by myself and the dealer’s mechanic on several occasions, the engine speed often will start to increase from the normal idle speed up to about 2500 rpm when the engine is hot. What is the cause of this annoying problem that spoils what I consider to be an otherwise perfect machine?

Jim Law East Lansing, Mich.

This is a common fault with the 350-cc Honda. The solution, which is apparently approved by the factory, is to open up the valve lash from 0.002 in. and 0.003 in. to 0.005 in. for both intake and exhaust valves. This should be carried out very carefully. A clearance in excess of 0.005 in. will cause a clicking from the valve train. If this should occur, readjust until the clicking just disappears. If you are in any doubt as to the correct method for checking and adjusting valve lash, have it carried out by your dealer as there is a correct sequence of operations.

EXCEPT ONE THING

I am owner of a 1966 Norton 750 which I am very pleased with, except for one thing. There is a very bad vibration on the front end at road speeds in excess of 70 mph. This has occurred since I fitted a new tire two months ago. There is a very uneven wear pattern on the front tire. Could this problem be due to a faulty tire? I have also had to tighten loose spokes in the front wheel on three occasions. Please advise what action I should take as the machine is now restricted to 70 mph because of this annoying problem.

Jack Russel Van Nuys, Calif.

Your machine in its present condition is not only annoying to ride, it is dangerous. It is surprising that you have not mentioned a serious navigational problem, particularly at high speed. The trouble is almost certainly due to a bad out of balance condition, or that the wheel rim or tire is not running true. It is also possible that one or all these adverse conditions are accentuated by worn or incorrectly adjusted wheel bearings.

First, make sure that the wheel bearings are in order. Check that the wheel rim is running true, both radially and laterally. Check that the spokes are evenly tightened by rotating the wheel, and hold a wrench so that it lightly touches the spokes. The musical note emitted is caused by the tension of the spokes, and the note should be the same from each spoke. If the wheel is not true within a maximum runout of 0.031 in., or if there are numerous loose spokes, have the wheel serviced by an experienced wheel builder. This is a difficult job to do successfully unless you have sufficient experience.

Check that the tire is squarely fitted to the rim. There is a raised guide rim on the side of the tire which should be an even distance from the rim all the way around if the tire is fitted correctly. Most tires made today have a white dot on the sidewall to indicate the light side of the tire. When the tire is fitted, the dot should be located adjacent to the inner tube valve. This helps to counterbalance the weight of the valve. Now rotate the wheel and note where the rim stops. The heaviest place will always come to rest at the bottom. To counteract the heavy place, it will be necessary to attach a suitable weight to the opposite side of the wheel until the latter can be spun without coming to rest in any one position. A wheel that is correctly balanced will make approximately twice the number of revolutions that a badly balanced one will make from the same spin. The normal method of applying a weight is to wrap lead wire around a spoke. A badly balanced rear wheel is not as easily noticed as the front one, but also should be carefully balanced to minimize tire wear. Any out-of-balance condition will absorb power that could be more usefully employed to help propel the machine. Only 1 oz. of out of balance at the rim can exert a force in excess of 200 lb. when the wheel revolves at high speed.

(Continued on page 22)

Continued from page 18

A TALL ORDER

I have a 1968 Honda CB77.1 have installed a Harmon and Collins 1933 7194 grind cam. The engine is bored to 337 cc, and has a super valve job to assure proper seating. I am using Type C racing springs shimmed to 0.060 in. on the intake and stock springs shimmed to 0.060 in. on the exhaust. The intake ports are opened a little to remove the hump and roughness. I plan to use NGK D12 H spark plugs with the stock carburetors. I also have a set of megs of unknown origin which really seem to help performance. They have what appear to be stock mounting brackets and apparently were designed for the machine. They measure 26 in., opening to a maximum diameter of 3.75 in., with a small lip closing them down to 3.375 in. at the noisy end.

Now comes the fun part. Using the equipment I have mentioned, plus possibly some velocity stacks, what would be the best carburetor setting for top end and/or drag racing. Also, what would be the best sprocket gearing for dragging and for top end. I guess that’s a tall order, but CYCLE WORLD is a tall magazine.

Flip Reinersman Cape Canaveral, Fla.

The megaphones you have acquired appear to be factory race conversion units manufactured for 250 and 305 CB models. The lip at the large end usually is referred to as a reverse cone.

Altering the intake port shape is risky, unless one has the use of a flow bench. A slight enlargement and polish is good practice, but the shape should not be changed. Removing the hump will almost certainly improve air flow, but may cause a drastic reduction in thermal efficiency because of poor directional flow into the cylinder. A good port shape is a compromise between sufficient air flow, good directional flow into the cylinder, and good turbulence characteristics.

You have made no mention of compression ratio. Many people are under the impression that the higher the ratio, the higher the output will be, with the limiting factor being determined by detonation. In practice this concept is far from true. Again there is a compromise, this time between the ratio and a reasonably compact chamber shape. How ever, the majority of engines will accept a ratio of 10:1. You mention using NGK D12 H spark plugs. These, I can assure you, will be far too cold. They are very rarely employed on full race machines, except on a very fast track where full throttle is maintained for long periods. I would suggest you employ a D 10 to start.

(Continued on page 26)

Continued from page 22

Final jetting can only be arrived at by making full throttle plug checks and observing the condition of the spark plug. This is another reason why the correct heat range of spark plug should be used. A cool running plug would give a rich indication and a hot plug would appear lean.

For good all-around performance, the standard gearing should give good results with the increased engine output. The Honda CB77 is considered to be slightly overgeared in standard trim. If the machine is to be used for racing, optimum gearing will be determined by the nature and length of the track.

2000 COUNTRY MILES

The engine performance problems outlined below apply to a 1967 Norton Atlas (strictly stock) with 2000 country miles and 200 city miles on the odometer. The engine is fitted with A mal Monobloc type 389/88 and 389/87 carburetors.

There are two engine performance problems: one at three-quarters to full throttle and the other at idle to one-quarter throttle. Because the carburetors are adjusted in five phases, beginning with three-quarters to full throttle, I will relate the high speed problem first.

Power loss occurred when the throttle setting exceeded three-quarters. After checking the obvious trouble sources (fuel and air restriction and ignition failure), I discovered that a reduction in main jet size solved the problem. The standard No. 350 jets have been replaced by No. 320 jets-the largest size that can be used without power loss. However, the Norton shop manual states that the main jet size “should not be altered save for some very good reason. ” Do I have a “very good reason?”

Main jet size appears to have no effect on the low speed problem. During the first several minutes of operation, when the engine is at ambient temperature, performance is excellent at all throttle settings. However, when the engine is hot, jerky running is experienced in any gear at steady speed below one-quarter throttle. Running is smooth from one-quarter to full throttle.

With the machine on the stand and the gearbox in neutral the following problem can be demonstrated: 1. Open throttle until engine turns 3000 rpm. 2. Close throttle. 3. The engine requires over 5 sec. to slow to idle speed; it will then drop below idle speed and stall. 4. By temporarily using the throttle to prevent stalling, idling without throttle assistance can eventually be achieved. However, a minute or two of idling is followed by a stall. 5. When proper idle speed is obtained, quickly opening up to one-half throttle produces spitting in the air intake, indicating a weak mixture, until the engine is off idle speed.

The high speed problem has been solved by a jet change. The following futile steps have been taken to solve the low speed problem: 1. New needles, seats, and floats have been installed. 2. All fuel ducts, hoses, filters have been cleaned. 3. Tappet clearances have been set. 4. Compression has been checked (hot and cold). 5. Throttle valves and associated cable assemblies have been checked for smooth operation. (There is no sticking.) 6. Numerous combinations of throttle and pilot air adjusting screw settings and jet needle settings have been tried. 7. Magneto timing and output was not checked and is assumed adequate because middle and high speed performance is satisfactory; cold idling is smooth. 8. Spark plugs have been replaced and cables to plugs have been tested for electrical leaks and excessive resistance. 9. Air valves are fully open.

(Continued on page 30)

Continued from page 26

A problem I have not investigated is that fuel drips past the pilot air adjusting screws if the machine is left standing with the fuel petcock open.

In short, every effort has been made to ensure that fuel, air, and spark reach the cylinders as required. When the engine is cold it’s great-when it’s hot I’d like to junk it.

J.D. Ellis Richland, Wash.

The reduction you have made in main jet size would appear to be justified, considering the apparent rich mixture at throttle openings from three-quarters open to full throttle. However, I would suggest that you make some full throttle plug readings to verify the mixture situation with the smaller main jet. A mixture that is too lean will cause overheating and subsequent engine damage. The statement in the Norton shop manual with respect to main jet changes means exactly what it says. There are a lot of owners who fiddle with main jet sizes unnecessarily, apparently under the misapprehension that they are doing a bit of super tuning. They very often cause damage

Based on 90 percent of your comments I would consider that the engine is running extremely lean on idle. Reluctance for the engine speed to drop rapidly when the throttles are snapped shut would almost certainly be a result of an air leak in the induction system. The location of a leak can be found quickly by squirting a small quantity of oil on the most likely places with the engine running. Do not rule out the possibility of a porous casting. I also would recommend that you thoroughly check the idle circuit on both carburetors. Remove the idle jet and make sure it is absolutely clean. Also, thoroughly clean all the passages on the idle circuit. The system on the Monobloc carburetor is extremely sensitive to the presence of small particles of dirt and gummy deposits. If you find evidence of hard or gummy deposits, change to a different brand of gasoline. Check that the pilot air adjusting screw is not bent or that the pointed end is not damaged. It is possible, if this screw is over-tightened, to break off the tip of the point, leaving it stuck in the passage.

The spitting back in the intake, experienced when the throttle is snapped open, could be caused by the throttle valve cutaway being too large. It may be well worth trying a one size smaller throttle cutaway. Although the cutaway size is theoretically only effective from one-eighth to one-quarter throttle opening, a change does in some cases influence the idle to one-eighth phase.

Finally, it is bad practice to leave the machine parked either on the center or side stand with the fuel cock open. There is always a good chance of leakage and flooding.

IT MISSES

I recently purchased a Kawasaki 350 A 7 Avenger, and ever since I got it, it misses at 6000 rpm. I thought after the break-in period the miss would go away, but it didn’t. I took it to my dealer for the 500-mile checkup, and he said it was a weak condenser, but didn’t have the parts, so for the 1000-mile checkup he replaced both the condenser and points. It still missed. He monkied around with the carburetor and float and made it run worse than ever.

I have had it back to the dealer twice since, and he could not help me. It leaks gas on the left carburetor at idling at times. It runs fairly well when the engine is warm, and when it reaches operating temperature it runs as I described. When hot, if I shut the gas off, it runs fairly well. Spark plugs don’t foul. I just took a compression test and it checks out O.K.

I now have 1700 miles on it, and it keeps running worse with each mile.

Ernest Zimmerman Oneida, N. Y.

From the contents of your letter, it would appear that your 350 Kawasaki is running rich. First, have the float chamber fuel level rechecked. Check that the air cleaner is in good condition and is not restricted in any way. If the trouble persists, try dropping the carburetor needle two notches. If this only partially does the trick, try going down to a No. 10 in main jet size. When checking the fuel level in the float chamber, make sure that the floats are in good order and that the fuel needle valve is seating properly. ■