Cycle News - Archive Issues - 1960's

By Roy Baumprdner Every once in a while someone comes along and they say, "what's the advantages or disadvantages of the coil valve spring over the hairpin valve spring?" Actually the disadvantages aren't as great as they used to be, nor are the advantages, but it all started out years ago when racing wasn't what it is now and they didn't have the metals that we have now to make springs out of. At that time the hairpin valve spring proved to be the best spring rather than the coil. This was also due to the fact that the hairpin valve spring could be designed to stick out into the air flow and be air cooled. We stil1 have this today in the design of the Norton Manx. This was back in the days when a 500 single turning 7,000 rpm was considered something really fantastic and with the metals we had then, the hairpin valve spring just held up better. The coil spring completely enclosed simply couldn't take the temperatures. It tended to get weak, and fatigue, under too much heat, especially on the exhaust side of the engine. And if you made them much harder, or bigger. in diameter, they tended to get brittle and break. But today with the metals that we have, the coil spring has deinitely come to the fore. It'll take far more rpm than the hairpin spring ever could, and you get better valve control with the coil spring, too. But we'll go into that later. Sometimes yO;;; find ..·.,;,'ii sPring t1iat's'wound progressively, that IS, the coils at the bottom are closer wound than the coils at the top. This is called progressive winding for a reason. That is,~when the cam lifb the valve off it's seat, the spring takes up the load slowly and progressively. There's no sharp snap to it. This greatly cuts down on the chance of the spring breaking, especially at high rpm and with the very wild cam designs we have. Also with the coil spring, we can put another smaller spring inside it and we have the two-coil spring set up as we know it today, with the inner and outer spring. By going to lighter or stronger pressures on either one of these springs, we can arrive at all kinds of spring rates, and by fitting the inner' spring to where it's just a tight push fit we can dampen out all kinds of surge at high rpm. This surge is a bouncing or fluctuating at high rpm, sometimes called cycling, or flutter and it can break springs in a hurry. But when we put the two springs together tightly like this, it acts like a friction damper and it reduces the problem. Of course, rather than put up with all of this trouble, you might just go to a two-cycle engine and get rid of all of them. Or cry on the shoulder of your local dealer. By N. W1l11ams BRUSH PRAIRIE, WASlI.;"'Jwie 29, 1969 - WI tho the smallest turn out of riders in over two years It was st1111l good hard riding bunch. 46 riders turned out after a week ofrainhadc1osedallotbertracls. Lucky Spokes runs rain or shine but riders do not like to ride mud races in the summer. The dlI,y cleared off and the track was dry and fast. I'll bet there were a lot of riders that wished they had come out. All after noon was sunny and It could have been a big race. (Results on page 20) WORLD CHAMP MOlOX IN U.s. IN 10? Plans are being laid to promote one U.S. Meet of the 1970 World Motocross Championship Series In July next year • Probable location: Southern Callfornia. This will bring all the top riders of the world, and may decide the winner of the championship series. Estimated cost of appearance money and transportation: $18,000. Inter-Am promoter Edison Dye Is backing It. FORDYCE HONORED More than 4,000 military and clvillan personnel attended the opening exhibition at the "101 Critical Days" safety campaign at Norton Air Force Base In San Bernardino, Callf. Lt. Col. Forest II. Riddell, Chle' of s.letJ, 63rd 1I1111MJ Airlift Wine, Norton Air Force B.... presents special aw..d to Skip Far· c1Jee for hi s pailclpatlon In -.aual Air Force Safety plOlfam. For his participation in the exhibltitlD, Skip Fordyce, Fordyce Motorcycle CeDtel' in Riverside, received a special award Monday, June 30, from Lt. Col. Forest M. Riddell, Chief of Safety, 63rd Military Airlift Wing. Fordyce also received a letter of commendation from Brig. Gen Louts G. Griffin which said, in part, "The productivity of your outstanding presentation and riding demonstration can be measured by the fact that the 63rd M111tary Airlift Wing did not experience a single accident during the long Memorial Day weekend." Prior to this event, six out of every eight reportable accidents on the base this year involved motorcycles. The lUirpin h. been the . 0 _ for moton ........ spring cooling is a pro....m. Also. it is relatively _ to change. A good example of this is the Honda racing machinery, that is their 4, 6, and 5 cylinder machines. If they needed anything like desmodromics, they'd just plain put them in. But they stick with the coil spring. So about the only reason for using the hairpin spring today is the space available. The hairpin spring is about half the size in height although it's twice the size in width of the coil spring in the space available. Also if the hairpin spring is air cooled, that is, if it sticks right out in the air flow, it's very simple to change a broken one. You can change one on a Manx probably anywhere from 2 minutes to 15 minutes with a large pair of pliers that are especialJy made just for gripping this spring. Try this with a coil spring sometime. And most of this time is spent hunting for the pliers. Ducati still sticks with the hairpin spring even though they've completely enclosed it, but someday they'll probably change from these ideas, too. Now, the coil spring usually relies on oil flowing all over it when it's enclosed in the engine and this gets rid of the heat. This is the way Ducati does it with their hairpin spring also. There are other advantages to the coil spring, too, like once you're set up to produce them, they can be made much cheaper, that is all things being equal. The coil spring provides mora accurate and controlled val.. return. The progressive spring usually goes with a progressive lift cam. This is particularly true on racing engines where the lift and the duration of the cam are extremely radical. We. usually have big valves for racing machinery so that the motor can breathe as much as possible, and we've got to get that valve open quickly, keep it open as long as possible, and then get it closed quickly to get it out of the way of the piston. With the valve speeds involved and the temperatures involved you can't just slam that valve back on its seat. If you do this long enough, eventually you 'U take the head right off the valve and this is good bye. So we use a cam that's known as progressive lift. It starts o'!t lifting very slowly, and then more rpaidly and puts the load on the valve slowly and steadilY, but yet overall quite quickly. And, of course, our progressive valve spring also takes up the load and the shock carefully. AD in all, we get rid of all the shock, or I should say most of it. And once it's time to close the valve, we can lower it very quickly almost to the seat and then very slowly ease it onto the seat. Of course all of this happens in the twinkJing of an eye at 10,000 rpm. .. TWIS MUST BE ~ ~ST SO-CAL RUN", NGK Spark Plugs (U.S·.A.) Inc., 4010 Sawtelle Blvd., Lo. Angel••, California 9OO&ll

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