The Service Department
THE SERVICE DEPARTMENT
JODY NICHOLAS
BSA FORK CLANK
I have recently purchased a BSA Thunderbolt vintage 1970, and, while I am generally pleased with the machine, there are a few things about it that are quite annoying to me, although they are nothing serious.
First, and this is the most frustrating of all, the forks are too light for the bike. The forks on all the new BSA Twins are apparently the same. They will take the uphill part of a bump with ease, but coming down when the forks stretch themselves out again there is a resounding jolt that is felt all the way up through the tank. This jolting has already caused one broken oil seal and no doubt threatens to break many more. How would you remedy this? I have been thinking of heavier springs. Heavier oil helps a little, but doesn’t really do too much.
Next, what are the best points at which to shift? I have no tach, so I have been shifting according to sound and feel. The problem is the shift from second to third. It feels right at about 40 miles an hour, but at that point the shift produces a very noticeable clicking sound that doesn’t seem to affect the smoothness of the shift, but that is disconcerting, considering the fact that BSA gearboxes usually run strongly and quietly. Your opinions?
Lastly, off the line in first gear I experience a noticeable lag in performance from the initial movement to the point where first gear usually starts to move the bike. The engine usually bogs down until the bike is going about 15 mph. At that time it starts to exhibit some power. What do you think?
I would appreciate any time and information you can offer. I’m sure that whatever advice you can give me, I can rely upon. Your reputation dictates that you always know what you are talking about.
Robert N. Schwartz APO New York, N. Y.
No, the forks are not too light for your bike, but rather have springs with too heavy a spring rate for the weight of the bike and a normal rider.
The fork springs on the 1970 BSA Twins are some 7 to 10 lb. heavier in spring rate than last year’s models and this year’s Triumphs, which use the same springs.
Methods for reducing the spring rate include disassembling the front forks, removing the plastic spacer form between the sliding bushing and the fixed bushing, and cutting 3/8 in. off the top of it. Make certain that you remove this material from the top and not from the bottom. This will reduce the spring rate and lessen the tendency for the forks to “top out.” SAE 40 weight oil will also help and will improve the ride, if the ambient temperature is at least 60 degrees.
Another method is to replace the fork springs with those from the BSA B25 lightweight. They are the same poundage as last year’s big Twins. Be sure to use the 1 970 B25 part number when ordering.
Shifting difficulties such as the clicking sound you mentioned are very often produced because of an improperly adjusted clutch. The clutch springs must be adjusted so that the outside driving (steel) plate spins perfectly true when the clutch lever is depressed and the kickstarter is kicked through. This will help prevent the clutch’s tendency to drag, and will reduce the hard shifting.
The “bogging” tendency is the result of the Thunderbolt’s rather “tall” overall gearing. The easiest way to reduce this tendency to “bog down” is to fit a rear sprocket which is three or four teeth larger than the standard 47-tooth sprocket, but you will encounter higher revs at highway cruising speeds, with consequently higher engine wear.
The most accurate way to determine when to shift is to use a tachometer. You can mount one from a BSA Lightning with a new mounting bracket, and the necessary conversion parts are available from your BSA dealer.
SKULL-HEAD POCKETS
I have a 1966 Honda CL-77, which for the past four years has provided me with very good service. However, it has developed a problem, which I am certain will cause an end to this reign of good service.
The problem is that the engine has developed an oil leak around the right spark plug. I can wipe the area clean, but with a short ride the oil will reappear. It is not a rapid loss of oil, and I have confirmed this with the dipstick, but it does leave spots of oil on the spark plug lead cable and the right aircleaner cover. The cylinder threads appear to be all right. I have also checked with both of the local motorcycle shops, and they are unable to even guess what the problem might be. I thought I would try a compression check, but there are no gauges available. Removal of the right spark plug at any time will reveal a very black sooty plug. I have tried to adjust my air screws, but' this hasn’t helped. This has been happening for quite a while.
When I first purchased the machine in April of 1966 the mechanic made several indentations around the spark plugs with a punch; he said that this was done because this particular model has a tendency to develop a leak in this area, and apparently this has finally come to pass. I have kept up with all preventive maintenance on this machine since it was purchased, and it has never been rough-handled. I can get the machine up to 80 before I shut the throttle off without much trouble, except for the spark plug’s continually kicking up a bit.
I would appreciate it very much if you could give me any ideas or suggestions on what to do. The motorcycle has over 23,000 miles on it.
Roy Wentworth
Searcy, Ark.
Your problem is fairly common to Hondas of your machine’s vintage and is probably due to the fact that your piston rings are in need of replacement and are allowing excess oil into the combustion chamber.
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Your machine has an aluminum cylinder head with a cast-in steel “skull” for the combustion chamber. Due to heat and pressure, this skull often loses its perfect seating with the aluminum, and pockets form in which oil (that is forced past the head gasket by compression pressures) can collect. This is especially true when there is more oil than usual in the combustion chamber, as would be the case with worn rings.
Even though combustion chamber temperatures are very high, this oil does not seem to bum and evaporate because there is no air in these pockets, so it stays in a liquid state and eventually finds its way to the outside of the engine via the spark plug hole.
Sometimes this oil continues to leak from the area around the spark plug for several hundred miles after the rings have been replaced, but aside from dirtying the machine somewhat, it is no cause for concern.
PREPARING FOR STORAGE
I purchased a Honda CB450 K-3 last March, and no sooner had I put 500 miles on it, then I got drafted into the Army. Being so pleased with the bike, I had no desire to sell it. Now it appears that I’ll be going overseas soon, and I would appreciate any tips you could give me on storage of a motorcycle for long periods of time.
I’m wondering if gasoline should be left in the tank and oil in the crankcase, and should the battery be disconnected and drained, etc?
Joseph Maloney Fort Knox, Ky.
Preparing your machine for an extended period of storage is quite simple. First, drain all gasoline out of the tank, fuel lines and carburetors. Second, remove each spark plug, pour about a tablespoon of engine oil down the spark plug hole, and turn the engine over several times very slowly to spread the oil evenly over the cylinder walls. Replace the spark plugs. Third, remove the battery, carefully clean the terminals, and grease them lightly with Vaseline to prevent acid corrosion. Fourth, remove the air cleaners and cover the carburetor intakes with ordinarymasking tape. Also tape the ends of the mufflers.
If you suspect that corrosion of the chrome-plated parts might be a problem, grease them lightly with Vaseline, and, finally, park the machine on the center stand, and cut two pieces of 2 by 4 in. lumber long enough to fit under the ends of the front axle and raise the front tire off the ground. Cover your bike with some plastic and you’re set.
BIG-BORE TROPHY 250
I presently own a 1970 Triumph Trophy 250 and wish to obtain more power. I am considering replacing the stock cylinder and piston with the cylinder and piston from the BSA 44, thus giving the engine a 79-mm bore, a 70-mm stroke and a displacement of approximately 350cc. Is this possible? What modifications and changes would be necessary to do this? Also, is there a company which produces a hop-up kit for this bike?
I enjoyed your road test on the Triumph 250 Trophy. In the test you mentioned having to forego longer voyages at freeway speeds. How long do you consider a “long voyage?”
Doug Davis Danvers, Mass.
The swap you are contemplating is not impossible, but would be a costly and time consuming endeavor. You would have to purchase a BSA B44 cylinder, piston and cylinder head, plus a larger carburetor, just to name a few items.
Although most of the internal engine and transmission bearings are the same size on both bikes, the connecting rods differ in that the B44 rod is longer, has a roller bearing bottom end and has a larger small end bush than the B25. And, since the B44 cylinder is “taller” than the TR25W’s because of the longer stroke, a longer rod would have to be specially made, or you would wind up with a compression ratio of about 4:1!
Another problem is with the cylinder hold down studs which are 1/4 in. farther apart on the B44. The crankcase would also have to be machined out from 3 1/8 in. to 3 15/32 in. to accept the larger cylinder.
Balancing the engine for the heavier piston would require a significant amount of work, due to the difference in weight between the pistons. The conversion isn’t recommended, but a B44 engine unit will bolt right into your TR25W chassis.
Speed parts for your TR25W are available from Triumph through your local Triumph dealer, and some special parts are distributed by accessory manufacturers such as Webco, Inc.
In our recent road test of the TR25W we mentioned that we would forego longer trips at highway speeds, but neglected to specify why: most of us here on the staff prefer a larger machine for extended touring, such as a Bonneville or a Trident. Shortly after the road test was published, we received a telephone call from a fellow who had ridden his TR25W to California from New Jersey, and the only problem he had was a lost exhaust valve adjustment cover, which vibrated loose and fell off in Texas!
