Service
SERVICE
We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because of the volume of mail received, we cannot return any personal replies. Please limit your "Service" letters to technical subjects only, and keep them as brief as possible. Send them to: "Service,"CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.
TURBO TWO-STROKE?
It now seems the turbocharger epidemic has infected almost every manufacturer and engine configuration. They all have one thing in common: they’re all four-strokes. What about a turbo-charged two-stroke? Is it possible? What would the power band be like? What kind of compression ratio would it need?
What would be the ideal engine configuration for a turbo two-stroke and what would be its limitations and drawbacks?
AÍ Stern Dayton, Ohio
We’ll let you in on a secret if you promise not to tell the FIM or the AMA: You’ve seen all those high output twostroke race engines? Well, they’re all supercharged by their expansion chambers and aren't running normally aspirated at all. The pressure wave tuning in an expansion chamber forces the pressure in the cylinder above atmospheric before the piston closes the exhaust port, and that’s the secret of phenomenal tw<.. stroke power outputs. The best part all this is that there’s no lag in an expan sion chamber. When you turn the thre tie when the engine is in its power bam power comes on right then. None of th < waiting around for the compressor ,ig spool up to speed as with turbocharger.
If you were willing to give up inste >. throttle response, you could tur bocharir a two-stroke engine. You could g ut power and probably power band wid v ( but at the expense of added complexi :e and reduced responsiveness. The ide 1 turbo two-stroke would depart fro, crankcase scavenging and use an engir driven pump for low-speed scavenging This would allow a more rugged, bette lubricated bottom end and better piste , cooling, but would be another departn from current two-stroke simplicY y Without the use of direct cylinder fu injection, the emissions from a turrfi two-stroke would be no better than c n¿jS rent two-strokes, and that fact ale Y . . . . y . .-»ea a sures that this engine configuratio> un¡* only academic interest in the U.S. ¡iree
MORE LIGHTS FOR THE SAB'
I recently bought an 1982 Hond bre and would like to add two Cil ries 35 fog lights (rated 55 watts eac .. would like to know if the stock electrisystem will hold the extra load or il would have to change to a larger battery. The alternator puts out 300 watts a* 5000 rpm.
Phil Treadwell
Galveston, Texa <
As long as you use the fog lights c ? highway speeds where the engine is spin ning fast you should have no problems The Sabre electrical system is rated a 300 watts, and normal draw for light, and ignition is only on the order of 100-150 watts. By adding the additiona lights you’ll substantially raise thti break-even rpm where the battery is be ’ ing charged instead of drained, but thi ' won’t matter if the lights are used occa# sionally on the highway. n
As an aside, larger batteries aren’t a cure for electrical deficits unless you en ■ joy regular use of a battery charger, jf* the alternator can’t keep up with the electrical system demand any battery, no matter how large, will run down and have to be recharged. *
The additional 110 watts of your fog lamps shouldn’t be fed through the motorcycle’s wiring harness; it was neverH intended to carry that much load. Run wires directly from the battery to power the lights, being sure to include a fuse. If you want to switch the fog lights on with* ne high beam, you can do this by pitching the line from the battery with relay controlled by the high beam line, elays of this type are available in foreign auto parts stores where driving çhts are sold.
PS FOR JUMP STARTS
After seeing our advice on jump starts I jumper cables in an earlier service umn, a reader phoned in to give us s list of jump start tips:
!l) If you’re jumping from car to bike, n’t run the car’s engine as it will crank it far too much current.
2) Just in case there is a spark, hook > the cables to the car battery last. 'iat way you’ll risk flashing under the wd, not on your bike frame and 'dywork.
I Do use small wire in the jumper bles, as it serves as a voltage limiter.
4) Disconnect the cables immediately er the bike engine starts.
nont forget polarity, especially for British bikes with positive ground ics.
Take thought before making the start as to why the battery is dead. 2 genuine malfunction, as in a bare rounding or a broken battery, you lore damage with a jump start, er you fix the electrics instead of ing to ride home on the alternator.
HEAD SWAP?
Will the head from a Honda CB500T it on a CB360 engine? Would this conversion be reliable? Any help would be ppreciated.
Larry Spronk Orlando, Fla.
No, the cylinder head from the CB500T can’t be used on the CB360. In general, engine parts from one Honda model won’t interchange with parts from ther models. There are some exceptons to this, like the CB750F and B900F, the original XL250 and KL350, and the new 550 and 650 Nightwks, but you’d be far safer relying on ? parts book to determine what parts n be used in your machine. If you want improve engine performance, hop-up rts designed specifically for your bike are the best way to go.
MOTORCYCLE STAND
When working on the fork tubes of my motorcycle, I had the problem of supporting the bike with the front tire off the ground. I solved this with a piece of plywood and a 4-by-4. I cut the plywood large enough to make a stable base and hailed a piece of 4-by-4, long enough to support the engine with the front tire the ground, to it. All I need to do novt put the bike on its centerstand and tip backwards while a helper slides the star underneath the engine. This makes very sturdy support and allows me to . move any part of the front tire or steeri assembly.
David J. Brau Sheboygan, V
We've always used a milk crate wooden box for the same purpose, i there are motorcycles that have e hausts or frame tubes that don’t balan well on a box. Your stand would be useful alternative.
MARTEK DEMISE
In your April, 1983, issue you pi lished a letter from Dale Cunningha who asked about a breakerless igniti for his RD350B. In your reply you su gested the Martek 1000Y.
I don't think it’s wise for you to reco mend a unit by a manufacturer tha*" gone out of business. I purcha Martek 440 a year ago and the burned out in nine months. It had i year warranty so I returned it to N for replacement. It was sent marked “no longer at this address ter several hours on the phone I dif ered that Martek had gone out of b ness. I hope you pass this information to your readers as it may save them froi the same problems I had.
Gregory L. Havica\ Houston, Texas
Martek is indeed out of the ignitior business, and while rights to several / their products were bought by othe companies, the Martek ignitions are no currently available. No one else we knox of in the U.S. makes an electronic igni tion for the RD series. There are at leas two companies in Britain and Europ that make breakerless RD ignitions, bí we couldn’t find anyone importing thei to the U.S. If we receive any informatie regarding alternative ignition system for RDs (or other motorcycles), we’ll Y it in a later service column.
PESARO MOTOBI?
Could you give me the information as to where I might obtain piston rings for a Pesaro Motobi 50cc cycle made b> Benelli of Italy.
William B. Goodwin Marshall, 111.
Benelli parts are distributed in the U.S. by Cosmopolitan Motors, 301 Jacksonville Road, Hat boro, Pa. 19040.x phone (215) 672-9100. É
