The Service Dept
THE SERVICE DEPT
JODY NICHOLAS
THE BETOR NAME is well respected in the field of suspension. Almost all Spanish machines come with Betor front forks and rear suspension units, and even the American Rokon has Betor suspension. But like everything else, rear suspension units wear out and/or blow seals and start leaking with age and hard use.
The nice thing about Betor rear suspension units is that they are rebuildable. Developing a leak or wearing them out doesn’t mean that you’ll have to fork out for a new pair. Both reseal and complete rebuild kits are available from most dealers or through AFS Distributors, Dept. CW-12, 229 East Third Street, Lewistown, PA 17044. The exact prices vary from model to model, but a kit is a lot less expensive than buying a shock absorber.
Items that you need to perform a Betor rear shock absorber rebuild are a 12-in. Crescent wrench, a 14mm open end wrench, a screwdriver and whatever wrenches you need to remove the shock absorbers from your motorcycle. Be sure to have a graduated cylinder on hand to measure the damping fluid you pour out so that the same amount can be replaced. An ordinary plastic baby bottle is graduated in both ounces and ccs and is impervious to oil.
Begin by cleaning the shock absorber unit thoroughly in kerosene or other cleaning agent. Then use a screwdriver to prise the shock spring retainer down so that you can get a wrench on the shaft nut (fig. 1). Stick a rod through the top mounting hole and loosen the nut.
Loosen the nut at the top of the damper rod (fig. 2) and remove. If no special wrench is available, use a Crescent wrench to loosen the nut on top of the shock absorber body (fig. 3). A little penetrating oil or WD-40 often comes in handy here to help free rusted or corroded threads.
Lift out the piston assembly, being careful not to spill any of the shock fluids (fig. 4). Then disassemble the damper assembly (fig. 5), being careful to note the exact location of the various, differently shaped, washers so that the new ones may be reassembled exactly the same. Make sure the washers are the same shape as the ones you removed. Otherwise, re-use the old washers to keep the same damping characteristics. Pour the shock fluid out into the graduated cylinder and note the quantity.
There are many shock fluids available on the market today, but the most readily obtainable is ordinary ATF (automatic transmission fluid), Dextron Type B.
Fig. 6 shows the Betor complete rebuild kit disassembled. If you run into difficulty, check this photo for future reference. It’s a good idea to obtain some Loc-Tite thread sealant before beginning this rebuild to preclude the shock absorber’s disassembly during actual use after the rebuild. Careful application of Loc-Tite is necessary to ensure best results.
Clean out the old shock absorber fluid and refill the body with ATF. Smear a little ATF on the rubber O-ring to ease reassembly and make sure the O-ring is seated properly in the shock body. Make sure the new spring washers are replaced on the shock absorber shaft the same way that they came off (fig. 7). Place the cup end of the spring toward the seal, retighten the top nut, reinstall the spring and you have a shock absorber practically as good as new, at a fraction of the cost!
SERVICE LETTERS
POWER WOBBLE?
Recently my friend was riding my 1972 750cc Triumph when he crashed due to a “power wobble” or “power shimmy. ” He apparently made no sudden movements but was traveling in a straight line on a well-paved interstate highway at 70 mph. I am aware there are certain conditions in the bike which will cause these “wobbles,” but due to some recent facts and hearsay, I suspect there may be more to the situation.
Let me start from the beginning. With 3100 miles on my bike this spring, I took it to my dealer to have everything checked before taking off on a short trip. This checkup included: tightening, oiling, greasing, new front fork oil, new pushrod tube gaskets (seals), replacement or repair of anything damaged or worn, etc. My rear tire is virtually new with only 2000 miles on it.
After this checkup and attaching a handlebar windshield, I spent 400 to 500 miles traveling the neighboring states, during which no trouble was noticed. Recently, not more than 20-30 minutes after completing another 200-mile jaunt, I allowed my friend to ride my bike and subsequently crash.
I weigh 200 lb. while my friend weighs 155 lb., and I carry 28 lb. in the rear tire and 26 lb. in the front. I was carrying 40 lb. in luggage on the last 200-mile jaunt and about 60 lb. of luggage on the 500-mile trip.
I also found the front end sensitive the last 50 miles on the last 200-mile excursion. Talking to others I found “power wobbles” to be a very special fear of numerous riders and, surprisingly, all the accounts I heard of occurred on Triumphs. My dealer even mentioned how wearing a certain jacket on his 750 Bonneville causes him to wobble. Changing the jacket immediately remedies the front end “shimmies. ”
The picture this paints is hard to believe, but maybe you have some insight into this problem. First, is this “wobble” characteristic of Triumphs? Although a worn rear tire, loose swinging arm, possibly even the clothes you wear may cause a high speed shimmy, might the/a windshield be responsible? Could my extra weight of some 80 lb. and the luggage be a factor?
If the windshield was/is a possible cause, would a well-designed fairing be safer? If so, what brand(s) would/could you suggest other than Vetter. Fm a poor man, you see. Do you know anyone presently riding a 750 Triumph? Have they experienced any front end shimmies? Do they use a fairing? How much do these people weigh? What additional factors lead to power wobbles Give me as much information and as many suggestions as possible since I hope to take a 4000-mile round trip out West soon.
Thomas Champion Waukestia, Wis.
The problem with a wobble on your 1972 Triumph 750 is a peculiar one, indeed; especially in view of the fact that you give your machine proper care and appear to have a good understanding of what is happening when you ride. If your Triumph was an early 1973 model, I would be inclined to suggest that perhaps the front tire was at fault. A few of the early 1973 models were delivered with front tires on which the tread was not perfectly true. The tire’s carcass was okay, but the tread was slightly “off,” causing a “shimmy” at some speeds.
There is some difference in your weight combined with the baggage you took on your trips and the weight of your friend. If you had the rear shock absorbers adjusted to a stiffer setting and didn’t re-set them when your friend rode the machine, that could be part of the problem.
The installation of a windshield will also make a difference in the handling qualities of a motorcycle, but if you noticed no difference your friend shouldn’t have had any trouble.
My suggestion to you is to replace your front tire, balance it properly, and be certain that both tire pressures are set according to the rider’s manual for the load the machine will be carrying. Also check that the rear shock absorbers are properly set for the intended load.
If the machine is properly set up, no undue problems with speed wobbles should be experienced, and “power wobbles,” whatever they are, shouldn’t occur.
REED VALVE IMPROVEMENTS
The 125/175 Yamaha engines for 1974 are now using the RD series reed valve that was described in a hop-up article in your June '73 issue. The June article went into detail on modifying the 175 CT Yamaha engine. Part of the modification consisted of using the big RD reed, with a DH spacer to make the whole thing fit. The article also suggested using the rubber carburetor adapter from the RD 350 Twin (Yamaha 345-13565-71).
Now with the 1974 Yamahas at hand, there is a better part to be used to adapt the carburetor to the RD reed valve. The 125 YZ for 1974 uses an offset adapter which gives the carburetor air hose more clearance around the downtube of the frame. This offset adapter (Yamaha 401-13565-00) should be used in place of the symmetrical RD-series carb adapter. The price is the same, and the offset carb adapter makes a much cleaner installation.
Dale Herbrandson Manhattan Beach, Calif.
