The Service Department

THE SERVICE DEPARTMENT

JOHN DUNN

BIGGER HONDA

With how much difficulty would the Honda 90 engine fit in the Honda 55 frame? I would like to have a dependable trail bike with enough power for hills, yet light enough to handle.

Do you have the address of a supplier in my area that could sell me a Honda 90 engine? Would I have to change the transmission or adapter?

Would it be cheaper to soup up the 55 engine or replace it with a 90?

I would like to have a telescopic front fork. Is there one that would fit the Honda frame? Which is the least expensive? Do you think it would be worth the money?

Duane Byerley Sweet Home, Ore.

It is possible to install a Honda 90 engine in the Honda 55 frame. The ohv 90 engine oyt of a CT 200 trail bike will go right in without any difficulty. It is also possible to install an S90 ohc engine, which incidentally develops 2 bhp more than the ohv 90 engine. However, it is necessary to file the left-hand rear engine cover to obtain adequate clearance in the frame. The S90 also employs an external condenser (the ohv 90 has the condenser fitted to the contact breaker back plate), so it is necessary to obtain and install the correct condenser.

Whichever engine you choose, use the correct carburetor for that type of engine. A change in jet size should not be necessary.

The ohc S90 engine can be obtained with either an automatic or manual clutch, so choose the same system as your Honda 55 employs.

Late type trail 90 engines have provision for the Honda final drive ratio quick change. If this unit is not used, it will be necessary to plug off the hole (approximately 0.25-in. diameter), situated in the left rear side of the crankcase to make sure an oil leak does not occur.

Consider the cost of this conversion very carefully, as you may find that it may be nearly as economical to trade your machine for a trail 90 with an ohc engine.

CW has no direct knowledge of adaption of telescopic front forks to the Honda 55 frame. However, if any other reader has successfully carried out a modification of this type CW would be pleased to pass on the details and cost figures.

BIG BORE AND STROKER

1 am in the process of modifying m v. Honda S-90. I intend to use the Columbia Engineering 103-cc Big Bore and stroker kit, and a Harman & Collins track and street grind cam. It is claimed that total displacement is increased to 133 cc. 1 have been told that the Columbia stroker kit fails because of the nature of the stroker pin. It was said that the rod bearing cage must be cut when assembling the offset stroker pin of the kit. Failure of the bearing, cage, and thus the rod was attributed to this method of assembly. Is this true and has it been corrected? Is there another company which makes a better kit which is not made this way and does not have this weakness?

An amateur engineer tells me that if 1 enlarge the exhaust header pipe by removing the innerpipe (exhaust pipe) and use just the outer tube (discoloration prevention pipe) that I will lose power due to interference with exhaust gas flow from the cylinder. If this is so, what should 1 do, if anything, to modify this for better breathing? The head is to be ported, and I hate to waste efforts to increase breathing by restricting gas flow with the smaller pipe.

Finally, from whom may I obtain a carburetor to replace the stock one? Are there any modifications that could be made to this stock carburetor? When replacing, what size would you recommend? Would the stock Honda carburetor be sufficient, or should one from a larger Honda be used? Would there be any advantage to mounting the carburetor directly to the head, or does the engine perform better by using the long intake manifold?

Robert S. Guy

University, Miss.

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With regard to big bore and stroker kits, you have brought up a very controversial subject. I believe that the big bore kit is a fairly safe way to go, providing it isn't overdone. There must be sufficient mechanical strength left in cylinder wall.

All stroker kits, to my knowledge, employ a stepped crankpin (if any stroker kit manufacturer uses an alternative method, I would be pleased to hear from the firm, particularly if specific details are included). Because of the offset of the stepped crankpin and the maximum required internal diameter of the bearing cage, it is impossible to assemble the latter without cutting it in half. This is not accepted as good practice, even when the cage is specifically engineered for this purpose. I have heard of many cases where failure has occurred with the stepped pin stroker method. However, it is normal to hear more about bad results than good ones. I would like to hear in detail from the people that have employed stroker kits without problems. I would advocate one thing if you decide to go ahead with the stroker kit: Have all the necessary work carried out by the kit manufacturer.

To obtain proper results from the Harman & Collins camshaft, it is important that you obtain the correct valve springs and insure that they are installed at the specified set height.

When the head is dismantled, make sure that a first class valve job is carried out. Have the valve seats narrowed to obtain 0.030 in. on the intake and 0.040 in. on the exhaust.

A good general guide to adequate exhaust pipe (header pipe) internal diameter size is to treat the diameter of the exhaust valve head as a minimum, and 15 percent larger as a maximum. Blend the exhaust port outlet to suit the exhaust pipe internal diameter.

If only the big bore kit is employed, quite good results can be obtained by using the standard carburetor. It will of course be necessary to rejet to suit the larger displacement. Unless the compression ratio has been raised , it will be in order to use the standard NGK D-9H spark plug.

If the displacement is increased to 133 cc by using both big bore and stroker kits, it would be of advantage to use a 22-mm carburetor from a Honda 250-cc Dream. By reason of its integral float chamber, the Honda carburetor will only work in a horizontal, or near horizontal, position. This will mean that a new intake pipe will have to be made to suit the larger carburetor bore size. Mounting a downdraft carburetor directly on the intake port would result in an extremely short intake arrangement. However, if you can locate a downdraft instrument with the desired choke size, it may be worth a try. using a straight intake pipe. Try to obtain an intake length of between 8 and 10 in. The intake length should be measured from the intake valve head to the end of the carburetor bellmouth (air horn).

TWO-YEAR LAYOFF

To begin, I wish to commend you and the rest of the staff at CYCLE WORLD for your excellent coverage of the motorcycle scene; everything but a color fold-out "motorcycle pin-up." What-da-ya-say?

Second, is a request for advice regarding my 1965 YDS-3, which I've had to leave in unmaintained storage for over two years. Mileage was 3000, and it ran well, though there was a sharp "pinging" sound on revving the engine. I was told it needed rings. I plan to return home soon and my question is this: Upon preparing the machine for use, what kind of general maintenance/inspection plan should be followed for successful refurbishment after such a period of dormancy?

Robert W. Baker Vacaville, Calif.

Two years is a long time to leave a motorcycle standing, particularly if the machine had not been previously carefully prepared for storage.

I would suggest that you go through the machine thoroughly, paying particular attention to the following:

1) Tires — Inflate tire to recommended pressures. Spin the wheel and make sure that the tire is running true. If the tires have been flat, it is possible they may have become permanently distorted, or that the bead of the tire has wedged in the well of the rim, possibly trapping the inner tube. It also is possible that the inner tube valves may require replacement.

(2) Brakes — It is possible that some deterioration has taken place due to corrosion. Remove the brake backing plate assemblies, complete with shoes. If necessary, clean rust from the brake drum liner. Remove the shoes and springs from the back plate. Check that the brake cam spindles are free, and lubricate them if necessary. Lubricate brake shoe pivot and cam, then reassemble the shoes. Check wheel bearings for wear, and lubricate.

(3) Chain — Clean and lubricate chain with a graphite grease. With a wire brush, clean any rust from the chain sprockets.

(4) Control cables — Remove all the control cables, and lubricate them by immersing them in a light engine oil. Work inner cable back and forth to insure that the lubricant penetrates well into the outer casing. Lubricate all control lever pivots.

(5) Fuel tank — Drain and flush the fuel tank, making sure that any sediment is removed. Remove and clean fuel tap.

(6) Carburetor — Remove and completely dismantle the carburetor. Clean and blow out all the internal air and fuel drillways and passages. Check and clean jets, paying particular attention to the pilot jet. Make sure the throttle valve is free in the carburetor body. Reassemble with new gaskets and seals.

(7) Generator — Check the generator brushes for wear, and insure they are free in the brush holders. Check and clean the ignition points, and reset them to the recommended gap.

(8) Battery — Remove the battery, and take it to an auto electrical specialist to have it checked and recharged.

(9) Engine — Remove cylinder head and barrel. Have the cylinder bore lightly honed to remove any rust. Fit new piston rings, making sure that they have the correct end gap. Before installing the rings, clean any old carbon from the bottom of the ring grooves. If the piston shows any sign of corrosion, remove and clean. Decarbonize ports, head, and piston crown, and reassemble with new gaskets. It may be possible that the crankcase has filled with gas and oil, if there has been any leakage at the gas tap or oil pump. If so, drain the crankcase. Drain and refill the transmission and primary drive case. If the clutch will not disengage, dismantle, clean, and reassemble.

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KAWASAKI ROAR

/ have a small problem. I recently purchased a Kawasaki 250 Street Scrambler (A ISS) and I like it, except for one thing: When in first or second gear, at 5000-7000 rpm, the bike makes a real roaring noise (red line is 8-10 thousand). The police have said it is too loud, but the dealer says the baffles in it are standardt

My question: Would a "muffler" (like on the Honda 305) help? Would it hurt performance? What brand of bike muffler would fit on my bike? My second question: What would cause oil to leak near the exhaust pipes and skid plate? Oil sprays on underside of engine case up front.

Lee Tar sha Toledo, Ohio

The 250-cc Kawasaki previously tested by CW developed maximum power at 8000 rpm. There is little point in exceeding this speed. Most machines, when driven at near maximum engine speed in the lower gears, tend to be noisy.

Most two-stroke engines, when given full throttle from mid-range engine speeds, will make a roaring noise. The noise is not from exhaust, but is made by the intake arrangement. The Kawasaki in standard form has a very efficient (from a noise point of view) intake system. Is the intake on your machine properly silencd, or has it been tampered with? Even the removal of an air cleaner on a two-stroke can make a big difference in noise level.

If the exhaust system is standard, I would not advocate altering it by adding a muffler. Contact the manufacturer's agent if the noise level is considered objectionable. If this is a common problem, it is something the factory should know about. Altering the exhaust system in any way could drastically affect performance of your machine.

It is not uncommon for a two-stroke to spew oil out of the exhaust port, particularly if the engine is run on light load most of the time. It also is possible that the oil metering device requires adjustment. Oil leaking from the exhaust pipe joint at the exhaust port may indicate that there is a gas leak at this point, thereby causing the excessive exhaust noise.

INTAKE INVERSION

Last week I heard about an easy, powerincreasing modification for my 1965 Bultaco 175-cc Mercurio. I am told that by inverting the intake manifold so that the carburetor assembly is tilted about 30 degrees upward from its original horizontal position, the breathing is greatly improved. I have tried inverting the manifold as suggested, and — except for running on the rich side — the performance does seem a bit better, and I assume that lubrication is improved, with the "straight shot" into the main bearing. My questions: Is this modification harmless to my bike? Does it really constitute an improvement? Finally, whv is the engine running richer, and how can 1 lean it out?

Bryan A. Frame Madison, Wis.

If the 175-cc Mercurio runs better with the intake manifold inverted, why didn't the factory emoloy it that way? I cannot agree that the inverted manifold will flow more air. The air flow characteristics will be mainly influenced by the angle of the intake port in relation to the cylinder and the developed cross sectional area of the complete intake system.

By inverting the manifold, you have altered the angle of the carburetor. This will have resulted in a different float chamber fuel level. The incorrect fuel level is quite possibly the cause of the rich mixture.

I cannot see that inverting the manifold will have adverse effect on the engine, providing the float chamber fuel level is readjusted to suit the carburetor angle.

I would personally leave the intake arrangement as originally intended by the manufacturer.