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Tech Corner
Technical Q and A for classic motorcycle maintenance and repair.


Yamaha RT1 Fork Tubes

Motorcycle Classics tech expert Keith Fellenstein
If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an email with “Keith’s Garage” as the subject.

Q: Hello, Mr. Fellenstein! My name is Tom, and I am a motorbike addict. (There — that’s out of the way!) I have acquired — for really short money — an early ’70s Yamaha RT1 and it’s almost all there, too! I literally got it out of an old barn and it needs a wee bit of polish and suchlike. Most of the parts are still available, although pistons are a bit thin on the ground. My question concerns the fork tubes. They are, of course, pitted. I’ve looked around on the ’net and in the mags and so forth, but I can’t seem to find anyone who replates these things in the U.S. I can get replicas or a set from Frank’s, but these are $400-plus with shipping. I find lots of places doing such work in England or Australia, but shipping is prohibitive. Do you know of a company who rehabs fork tubes in the U.S.? I can’t be the only guy in America with this problem! Many thanks for any information that you can provide.

Tom/via email

A: Given the cost of replating, not to mention the possibility that those old forks may have been bent in use back in the day, my advice would be to go with new. I do know of one replating service that you could get an estimate from the folks at Quality Chrome Plating. They advertise in this magazine and offer nationwide service.

1966 Suzuki T20 Rectifier Location

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Q: I am currently restoring a 1966 Suzuki T20. However, some of the parts were disassembled when I picked it up. One area in particular is battery/rectifier mounting. Where is the rectifier mounted? Also, there is a clip attached to the battery box that is made of copper or brass. What is that? Any help would be great. Thank you.
— Wayne Aretz/via email

A: I had no idea where that rectifier was located, so I had a look at the schematic on cmsnl.com to see if they could help. It’s not the clearest scan, but it looks like it bolts to a lug on the left side of the top left frame tube right in front of the cross bar toward the rear. As for that clip, a couple of things on that same schematic are possible answers, either the battery holder plate, or more likely, the brake switch holder bracket.

1968 Cimatti C100 Magneto Mystery

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Q: Hi, Keith. I enjoy reading your column. My question is simple, I think. I am doing repairs on a 1968 Cimatti C100 (Costuruzioni Morini Franco), Engine No. N001341. It uses an ASL226S Dansi magneto. How many degrees (or millimeters) before top dead center should the engine fire?
— Graham Quisenberry/via email

A: That’s a tough one. I’m not at all familiar with that brand. If you have easy access to the flywheel over the magneto, look closely at the perimeter of the flywheel. Oftentimes there are two marks on the flywheel, one for TDC and one before TDC for when the points should open. Those should line up with another scribed or cast mark or notch on the case itself. I’ll keep looking for a definite answer. Thanks for a tough question. Update: I have since received a phone call from Graham’s mechanic, who had better luck than I digging up information on the timing. The specifications call for the points to open between 1.8 and 2.0mm before top dead center. He also said there were no marks anywhere on the flywheel or case for reference points.

1981 Suzuki GS1000G Oil Pressure Gauge Correction

 Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

A: From the how-wrong-can-I-be department, here’s a correction to last issue’s column. Reader Leon Hogan writes in with this Suzuki advice. — Keith

“Hello, Keith, I am writing about a question you received for the March/ April issue from Dwight Plucker about adding gauges to his 1981 Suzuki GS1000G. I am the owner of a 1980 Suzuki GS1000G, and the last gauge you want to put on these bikes is an oil pressure gauge. This version of the GS engine uses a roller bearing crank and the oil system works on flow not pressure. I had made the mistake of installing an oil pressure gauge on mine and proceeded to figuratively have a stroke when I discovered it had virtually no oil pressure at idle when warm. Removal of the valve cover and running the engine showed plenty of oil was reaching the top end. Further research showed the switch for the oil light was for indicating no flow, not low pressure. However, a compact digital voltmeter is very important to have on these old Suzukis.”

Suzuki TC185 Timing

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Q: Greetings. I acquired a non-running Suzuki TC185. I tested it for compression and it showed more than 100psi. Next I replaced the points, condenser and the coil. Before it had no spark, but all the electrics worked great. Now I have strong spark, but the bike still won’t fire. I believe the timing must be off since the screws were all loose on the plate. Can I set the timing without the engine running, or at least get close so I can get it started and play with it? I would appreciate your advice.
— Steve Vancamp/via email

A: All I can find is info on a TS185 single. It says to use a buzz box or light on the black wire to the coil. Turn the ignition on and rotate the flywheel counterclockwise until the tester indicates the points are open. At that point look at the dimple on the case at about the 11 o’clock mark and see if it coincides with a line on the flywheel. If it doesn’t, you have to remove the flywheel to move the magneto plate, loosely reinstall the flywheel and test again. Repeat until correct.

1967 BSA Spitfire Flat Battery

 Motorcycle Classics tech expert Keith Fellenstein
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Q: I have a 1967 BSA Spitfire. I’m continually having problems with the battery, as using the headlight seems to be flattening the battery. What upgrades do you advise?
James Wootton/via email

A: Since daylight headlights were not required when your bike was built, the charging system was set up to keep the battery well charged with the headlight off, and slightly discharging with it on, on the assumption that most of the running would be in daylight hours and so the battery would be maintained. First of course is to make sure your battery is in good condition, and if it isn’t, replace it with a good battery. I prefer AGM batteries for my classics for their superior energy density and long life. An added bonus is you never have to worry about acid leaks damaging paint or chrome. There were two different alternators used, a two-wire and a three-wire. If you have the three-wire alternator, make sure the green/black and green/yellow wires are joined together to the green/yellow wire in the wire loom. That provides the maximum power output from the alternator. As usual, there are a number of ways to avoid flattening the battery and/or getting more power out of the alternator. You could switch the headlight and taillight bulbs from incandescent bulbs to LEDs, being careful to source LEDs that are made for positive ground. That’s probably the fastest and least expensive method, but may not completely fix the problem. Slightly more expensive would be replacing the two-part rectifier and zener diode regulator with a one-piece combination rectifier/regulator, which may provide a more efficient conversion of AC to DC, but again may not completely fix the problem. The most expensive method would definitely fix the problem, and would consist of replacing the rotor with a new and presumably more magnetic rotor, the single phase stator with a three-phase stator, and the regulator/rectifier with a three-phase version. That would certainly provide enough output to keep the battery charged and the lights on.







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