The Service Department
THE SERVICE DEPARTMENT
GARY BRAY
PIPE DISCOLORATION
I’ve ended up riding a BMW R-27 which is just about right at my age, 56. However, even after a break-in of 1200 miles it runs hot — the pipe is a deep blue. It has the stock 120 needle jet and the altitude here borders on 2500 feet. We have tried the needle in the second and third holes, to no avail. Our local mechanics can’t seem to help much. Can you?
Le Roy Haring Rapid City, So. Dakota
It sounds as though the ignition timing might be slightly retarded. The timing should be checked and. if necessary, reset to factory specifications. The spark advance and retard mechanism should also be carefully inspected to be sure it advances completely.
The type of gasoline you use may also be causing some of the difficulty. If you are using a low grade regular, I recommend changing to ethyl. However, if the problem persists, and the performance of your R-27 does not seem as good as you think it should be, then have the cam timing checked.
Although this is a rare occurrence, especially with a BMW product, you may have gotten an exhaust pipe with a poor job of chroming. Your present exhaust pipe can be rechromed but be sure the work is done by a reputable chromer; otherwise the new chrome may bubble or flake off.
WHAT KIND?
1 own a 1949 Ariel Square Four JOOOcc. 1 would like to replace the original Solex carburetor with a more modern one. What would be the type to use?
Also, 1 cannot get the engine to idle without setting the idling arm very high. Is this in the carburetion or could the fault be elsewhere?
R. S. Powell Logan, West Virginia
The simplest and most effective carburetor change would be to use the old type one-inch Amal with removable float bowl. The later type Amal Monobloc will fit but is more difficult to jet properly. Installation of either of these carburetors will require a slight alteration to the rear right hand side gas tank mount. The S. U. carburetor, which was fitted to later model Square Fours, would give the best allaround performance but, unfortunately, your frame will not easily permit such an installation. Also, an adaptor must be used to mount the S. U. to your present manifold.
The difficulty experienced in getting your machine to idle may be due to the present carburetor being worn out, an air leak in the induction system, worn valve guides, poor compression due to worn rings or incorrectly set tappet clearances, badly pitted or burned valves, or improperly set ignition timing. Before attempting to change the present carburetor I would certainly recommend checking tappet clearance and ignition timing.
A word of caution. If you feel the cylinder head must be removed (this would be necessary if there is any doubt as to the condition of the valves and valve seat), be extremely careful upon reassembly, because these machines are notorious for blowing head gaskets.
MORE ABOUT HOLES
Regarding surface area, cooling, and drilling of cylinder heads and cylinders (June 1964 CW) you state that, “In my opinion, drilling holes in the cylinder and cylinder heads would certainly NOT help in cooling." You also state that, “Since the idea is to have a large area over which to dissipate heat, then it would follow that drilling holes just reduces that area."
To the contrary, cooling area can be either increased or decreased depending upon the size of the holes drilled. Holes, larger in diameter than the thickness of what is being drilled (for example, cylinder fins) will decrease cooling area, whereas; small diameter holes will increase area because they would eliminate area on the top and on the bottom surface of the fin just slightly, but would more than compensate for this by the added surface area created by the inside wall of the hole.
(Continued on page 12)
George M. Hadge Newton, Mass.
Yes, this is true. Surface area can be increased somewhat by drilling the proper size hole. To increase the surface area of a cylinder or cylinder head to any degree, the diameter of the hole should be less than twice the thickness of the material being drilled. In the event the fin is tapered, the size of the hole must vary proportionately.
To say whether or not this practice is beneficial, however, is debatable. Will engine performance or reliability be increased in proportion to the amount of work involved in drilling so many small holes? I think not. Of all the machines I have seen with holes drilled in the cylinder and cylinder head, none have even come close to following this rule. The holes may have been drilled to reduce weight, judging from their size, but this is another matter.
THE SPARK’S GONE
ƒ am having trouble with my ’63 Yamaha 250. The problem is that the right cylinder won’t fire. The only clue 1 have is that the spark disappears from the right plug when the throttle is opened. What is there in the electric system that could cause this? I’ve run the left cylinder from the right-side coil and had the condensers checked.
Ron Baird Butler, Penna.
Since the coils and condensers appear to function as they should, yet there is a failure in the ignition system, I suspect either poor insulation of the point assembly, a bad connection at the point assembly, or possibly a break in the primary wire to the ignition coil.
If after careful examination you are satisfied that these components are in satisfactory condition, I would then replace the point assembly. Occasionally a point assembly spring will lose its tension. If this has occurred, the spark will become erratic as the engine rpm is increased. You can make a rough test of this spring by comparing the amount of pressure required to open the points for the left cylinder, which is operating properly, with that of the right cylinder.
CROSS WIND
ƒ have a Honda Dream that runs good and handles well except for one thing. It behaves oddly in a cross wind, wobbling and so forth. It feels like it wants to lean away from the wind; at the same time the front wheel wants to turn into the wind — I can feel the torque on the handlebars. This is a most unstable state and only lasts for an instant when the machine is hit by a gust, but is very unnerving, especially when trying to hold a line in a fast corner.
(Continued on page 14)
This is my tenth machine and none of the others acted this way. It’s not the steering head bearings, which are in good shape and properly adjusted. Perhaps it’s caused by the odd-shaped fender and bulky forks. What do you think, and what can / do about it?
William M. Erickson West Covina, Calif.
Due to the small wheels and generally soft suspension, these machines are noticeably unstable, particularly under windy conditions. Stiffening of the suspension, which should help, can be accomplished by replacing the rear shock springs with CB-92 6116-3 springs. In the event this work is carried out, the rear shock covers must be left off.
To stiffen the front end. short lengths of spring should be added to the present setup (approximately two inches). Before attempting to stiffen the suspension, which is costly and certainly time consuming, try riding the machine under windy conditions with the front fender removed. A slight increase in tire pressure may also lessen the undesirable reaction.
MAGNA-WHAT?
One of your suggestions to cure the strange knock in Mr. Hastens 1956 BSA (Aug. 1964 CW) was to have his crank magnafluxed. This implies that the crank of an engine can get magnetized during its running life. How? What other effects on engine performance could be induced by a magnetized crankshaft?
James Barnett Northport, L.I., N.Y.
Magnafluxing is a process by which engine and transmission components can be checked for surface cracks or flaws that are undetectable to the naked eye. When I recommended that Mr. Hasten have his crankshaft magnafluxed, if no other cause was found for the noise that was coming from his engine, I felt there was the possibility of a cracked or partially broken crankshaft journal.
Magnaflux is limited in that it shows only surface flaws. In order to determine if an internal flaw is present, the piece should be x-rayed. •
