The Service Department
THE SERVICE DEPARTMENT
JOHN DUNN
STROKER KITS
I have been inquiring about big bore and stroker kits to increase the power of my Honda 55. I would like to know if the claims to increase power are valid or not. (For example, they claim that both a big bore and stroker kit will increase my 55 to 85cc.) I would like to know the risks involved if I have my engine converted and to know of any other bike you have tested or seen that has been converted.
Ken Gerrard Kerrobert, Sask. Canada
There are several big-bore and stroker kits on the market for the 55cc Honda, so it would be difficult to individually comment on each. Generally speaking, the stroker kits have not proven very success ful, mainly from a mechanical reliability point of view. A stepped crank pin is used to obtain the longer stroke and it is not possible to assemble the conventional big end bearing without splitting the bearing cage. This appears to be the main cause of failure. If you do have the stroker kit fitted, have the work carried out by the kit manufacturer with the understanding that if premature failure should occur, they will reimburse all the costs involved.
The big-bore method of increasing engine displacement has proven far more successful, providing it is not overdone. The removal of too much material from the cylinder would be unwise because of mechanical and thermal loadings involved.
ONLY 65 MPH?
I have a Honda S90 it'hich hits top speed of only 65 mph. I would like to increase top speed to 85 mph. 1 would be grateful if you could tell me if this can be done, and also the approximate cost of the work required. 1 use my bike for street use, so can I use a racing fairing on it, or would it be impractical? - -
E. B. Rigsby Tunnel Hill, Ga.
You have a 3-mph free bonus to start with, as Honda only claims 62 mph for the S90. To obtain a genuine 85 mph from your machine and still be able to use it on the street, would be practically impossible.
A racing camshaft and high-performance valve springs would provide an increase in top-end performance, and when combined with a racing fairing and an improved riding position to reduce the frontal area of the machine and rider, would result in a higher top speed. Because of the increase in power output and reduced drag, it would also be possible to pull a slightly higher over-all gear ratio.
Any attempt to improve maximum speed performance will quite naturally impair low-speed performance and snap acceleration, making the machine very difficult and sometimes irritating to ride under normal traffic conditions.
A camshaft and valve springs suitable for the S90 can be obtained for your machine from Webco Inc., 218 Main St., Venice, Calif., as detailed below.
No. 1166. One set of S&W type E valve springs, complete with top and bottom spring retainers. Retail price per set — $9.95.
No. 1605. Harman & Collins, regrind exchange camshaft. Retail price — $27.50.
By careful attention to detail, selection of the right gear ratio and riding position, it should be possible to approach a maximum speed of 75 mph with your machine and still be able to use it on the street. When altering the riding position, make sure that you are comfortable and can easily use all the controls without resorting to feats of contortion.
DREAM VS. HAWK
I have heard that the Honda Dream Touring is superior to the Super Hawk because the Dream is more reliable and easier to keep in tune with its single carburetor and single set of ignition points. Since I am thinking about buying either a Super Hawk or Dream, and plan to use it only on weekends and ride about 60 to 70 mph, 1 would like to know which would be the better buy for me.
(Continued on page 22)
continued
Billy De Long Summit, Miss.
I cannot agree that the Dream 305 touring machine is superior to the 305 Super Hawk, because they are two entirely different machines to ride. The Super Hawk is a true sportsman’s machine, and when in proper adjustment and tune, is a hard machine to fault. However, correct ignition timing and carburetor adjustments are critical, and improper adjustment or lack of maintenance does have a very detrimental effect on the performance of this machine. The handling and braking, when in proper adjustment, are very good.
The 305 Dream is completely different. Setting the ignition timing is relatively simple. Carburetor adjustment presents no problems, as you do not have to bother about balancing dual carburetors. Highspeed handling is adversely affected by the very soft suspension. This machine was never intended to be “rushed” down a twisty road. It can be ridden all day at speeds between 60 and 70 mph without distress. At near maximum speed it is subject to high frequency vibrations. The pressed steel frame is mainly responsible for this. The handlebars are rubber-mounted in an effort to minimize the effect. When the machine is on the over-run, there is a loud groaning from the transmission. accompanied by frame vibration. The transmission medium is virtually the same on the Dream and Super Hawk and this transmission noise and vibration can only be attributed to the pressed steel frame. Strangely enough, the original 250cc CA 71 Dream, which had a pressed steel frame, did not suffer from this problem.
Before you make any decision between these two models, I strongly suggest that you have a good demonstration run on both, and, if possible, try the Super Hawk with a lower over-all gear ratio.
SURE CURE
1 read the letter inquiring about fixing an oil leak where the generator is mounted to the timing case cover on a Triumph.
1 purchased a new T-120 in ’59 and after a year of riding, started to have the same problem. A new gasket only cured it for a little while.
It’s rather simple to cure, however. Figure out how much over size you can drill the existing hole. Purchase a stud bolt this size. Coarse thread is best. Now remove the generator from the machine and drill out the hole in the timing case cover. Next dismantle the generator and drill out the hole in the end plate. This will have to be slightly undersize, as you have to tap this hole (check a chart). When you have it tapped, screw the stud bolt in far enough to put a flat nut on the inside of the generator to lock the stud bolt in. Reassemble the generator and mount as before, putting the stud bolt through the timing case cover. Now you can put a selflocking nut on the stud, preferably one of the fiber washer type to do away with a washer. Now, you can draw it up good and tight. 1 don’t know if this is an accredited method, but it surely solved my teak.
Ralph A. Korson
North port, Mich.
Thanks for relating your experiences and cure for the Triumph generator flange oil leak, Ralph. For readers who want to go this route, one should make sure that there is no way that the lock nut inside the generator can come undone. Also, I would suggest that a flat washer be used behind the fiber inserted lock nut to prevent damage to the timing case cover.
We thank you again, Ralph, and wish that more of our readers would pass on their methods used to cure persistent problems.
RING EATER
I have a Honda CL-72, modified for TT racing. It is equipped with an H&C Track Grind Cam, Webco valve springs and rocker arms, milled 0.045 to raise the compression ratio. It turns about 11,000 or 12,000 rpm.
(Continued on page 24)
continued
1 have a problem. It breaks rings. This problem has about driven me crazy trying to find the solution. 1 have tried reboring and installing new pistons and rings on the theory that my pistons were worn and that it had too much ring gap. To alleviate the chance of overheating, I have left the piston skirts uncut and cut four oil grooves in the skirts to ensure proper oiling.
These preventive steps were all in vain. One race and “crack,” they are broken.
Gary Dougherty
Long Beach, Calif.
Vou do not state whether all the piston rings are breaking or that only the top rings are failing. The action of a piston ring is quite complex, particularly at the very high engine speed mentioned. Any minute irregularity in the cylinder wall would cause instant failure. After boring, it is essential that the bore is carefully honed to assist rapid ring “break-in.” Insufficient clearance of the ring in the ring land, combined with generally higher piston temperatures brought about by the increased compression ratio, may cause sticking and, therefore, lead to premature failure. The trouble could also be caused by detonation. Your problem can only be solved by attention to detail and careful analysis of all the components after failure.
I do not know whether you are aware, but milling the cylinder head or barrel to increase the compression ratio will also retard the camshaft timing.
TOO HIGH
In your 1966 Road Test Annual you have a write-up on the 450cc Honda. 1 am home ported in Yokosuka, Japan and 1 can get this machine for $690 complete. But before I get the bike I would like to have some help from you on a new chain drive ratio. The ratio 1 would like to have is a 5.98-1 over-all. To do this, 1 will have to switch to one of these ratios. First is a 16 to 32 and second is a 15 to 30, both of which will be two to one. This and the 2.984 to one primary will give me this ratio, With this ratio, 65 mph should come at about 5,300 rpm, which is close to the mid range of the machine. Will this engine take this new ratio without cutting the performance of the machine down too much? 1 plan on using the bike for touring, so acceleration is not important at this time.
As close as 1 can figure, this new ratio will give me the following gear ratios over-all: first, 15.95:1; second, 9.25:1;
third, 6.85:1; and fourth, 5.98:1. With standard tires and at 9,700 rpm 1 figure the bike will do around 45 in first, 76 in second, 103 in third, and 118.5 in fourth.
In short, what 1 am looking for is a ratio that will let the engine turn the least rpm at normal road speed and without overloading it.
1 have been to the Honda dealers in Tokyo, but they can’t seem to help me with this problem. 1 would like also to know where I can get a shop manual on this machine.
William P. Fry USS Oklahoma City
I have checked the figures and calculations stated in your letter and agree with the results. It is assumed that the 2.984:1 primary ratio to which you refer, is actually the top gear ratio at the gearbox output shaft and was obtained by multiplying the primary ratio of 3.304 by the internal gearbox ratio of 0.903.
I would think that the 5.98:1 over-all ratio mentioned by you would be too high and impair the over-all performance of the machine. In fact, it may be impossible to obtain maximum rpm under anything but ideal conditions with this high gear ratio.
An over-all ratio of 6.35:1 would give better all-around results and can be obtained by employing a 2.125:1 final drive ratio. This can be achieved by using a 16tooth final drive and a 34-tooth rear wheel sprocket. A top speed of approximately 110 mph should be available at 9,700 rpm.
(Continued on page 26)
continued
Try American Honda, 100 West Alondra Blvd., Gardena, California, for the workshop manual.
NEVER TOO OLD
One of my machines is a 1962 Allstate “Compact.” When it gets above 30 mph, it skips out of third gear. Does this come from age, or can it be fixed?
Andrew Ruff San Antonio, Texas
There is no reason why your machine cannot be repaired, even if the trouble that you are experiencing is caused by age and normal wear and tear.
It is difficult to point out any one item that may be causing the gearbox to jump out of third gear. It could be due to one or several adverse conditions. Excessive end float of the gearbox shaft, on which the gear slides, caused by a worn bearing or one that is loose in its housing, would allow insufficient depth of engagement of the gear engaging dogs. Insufficient depth of engagement could also be caused by a bent or worn selector fork. General wear of the internal shift mechanism may also be the problem. This condition may be causing insufficient travel of the selector actuating mechanism and it is therefore not obtaining full engagement. It could also be that the selector locking medium is weak, allowing the selector to move out of engagement.
The shift mechanism can be checked by removing the engine side cover. If there is an internal fault within the gearbox, it will be necessary to remove the engine from the frame, remove the cylinder barrel and head, dismantle the primary drive, and then part the crankcase halves.
SCRAPEGOAT
1 would appreciate it if you could tell me how to decarbonize a two-stroke motorcycle without using the careful “scrapescrape” technique that seems to prevail.
1 have decarbonized my two-stroke motorcycle in the past, using a small screwdriver — carefully — then finishing off with fine emery paper. However, I'm afraid 1 might slip someday — a big gouge or scratch on the cylinder head, on the piston crown, or even in the exhaust port!
Is there a different technique for decarbonization that is less dangerous (to the soft aluminum alloy parts) and somewhat less tedious? (Maybe some chemical can help carbon removal, or overnight soaking in some strong detergent solution.)
Your answer would help me decide whether or not to continue with twostrokes or change to four-strokes when 1 buy my next motorcycle (1 do an awful lot of slow-speed town driving which “carbons-up” a two-stroke quite rapidly).
Keep up the good work. Your magazine certainly is head and shoulders above (Beep-Beep) Magazine!
Kirk D. Ainslie Tamaqua, Pa.
An alternative method of decarbonizing can be employed by using chemical solutions. A strong solution of caustic soda provides a good cleaning medium for ferrous (materials that rust, like iron and steel) components. This solution will remove dirt, oil sludge, carbon and paint from a component after a few hours of being immersed. After the part has been cleaned in the solution, it is important that it is thoroughly hosed off with water. Have some form of lubricant handy, because the part will rust rather rapidly after the cleaning treatment.
Now, a word of warning; do not clean non-ferrous (material that does not rust, like aluminum and magnesium) components in a caustic solution. Caustic soda has a highly corrosive effect on non-ferrous materials and will cause severe damage to any part that is immersed in it.
A good solution for cleaning the parts manufactured from non-ferrous materials is carburetor cleaner. Again, immerse the component in a container full of the solution for a few hours, and after removal, thoroughly clean with water. It is good practice to occasionally agitate the part in the solution. If the part is not thoroughly clean after being hosed off with water, replace it in the solution for another hour or so.
After this type of cleaning or decarbonizing, the piston crown or combustion chamber can still be polished with a mild abrasive paper.
EASY AS PI
Could you tell me how to figure displacement on a two-cycle engine?
C. B. Scott Williamsburg, Va.
The method employed for working out the displacement (capacity) of a two-cycle engine is no different than that used for a four-cycle engine. The displacement is actually the swept volume of the piston, or in a multi-cylinder engine, the total volume of all the cylinders.
The following calculation can be employed for all engines having cylinders of equal size.
Trr2 x S x NC, equals engine displacement.
Where,
7T = 3.14
r = half the diameter of cylinder bore
S = stroke
NC = number of cylinders.
Note: Either inches or millimeters can be used in these calculations, providing they are not mixed (if inches are used for the stroke dimension they must also be used for the bore dimension).
Example of a twin-cylinder engine having a 60mm bore and a 54mm stroke:
3.14 x 302 x 54 x 2
= 3.14 x 900 x 54 x 2
= 2826 x 54 x 2
= 152604 x 2
= 305208 cubic millimeters or 305.208cc.
If inches had been used for the bore and stroke dimensions, the answer would have been in cubic inches.
If you or any other readers do not fully understand this calculation, please let me know, and I will try and explain further in a future issue. ■
