Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

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Tech Corner 

Clutch issues

Q: I have a 1984 Honda Nighthawk 700 with a clutch problem. When I first started it after it had been sitting for three or four weeks, the clutch needed to be broken loose. Then it would work fine, but when stopped it wanted to creep. I rebuilt the master and slave cylinders. After this the pull felt better, but it did not fix the problem. With 30,000 miles on the clock I felt replacing the clutch would fix it, so I installed EBC plates and springs. I deburred the clutch basket and checked for smooth movement of the plates and steels, and all was fine. I still have to break it loose after the bike has been sitting for a long time, but now after riding for a while, if I stop to fill up, the clutch is locked up hard. It works fine if I do not turn it off. I spoke to EBC and they are sending me a new set of plates under warranty, but I would like your thoughts before I dive back into it. — Richard Porter/via email

A: Sticky clutch plates are a daily hazard on my old Triumph 500, usually cured by pulling in the clutch and kickstarting the bike. You might try that, but substitute electric start for the kickstart. How does it shift normally? Is it quiet or is there a clunk? I’m trying to figure out what would glue your plates together when the bike sits for a few minutes. I assume you’re using a good motorcycle-rated oil. Although failure to do so usually results in clutch chatter, did you soak the clutch plates in oil before you installed them? I’d love to hear from readers who have experienced this problem and how they fixed it. MC


Tech Corner 

The great oil question

Q: What type and brand of oil should I use in my 1992 Honda Nighthawk? It has 15,000 miles on it. Do I have to be concerned about using a certain kind of oil for a wet clutch? — Vaughn Giddens/Northeast Texas

A: Here’s a question with no answer that pleases everyone. Every brand of oil has its cheerleaders. The only thing I will say is that for a vintage bike with a wet clutch you should stay away from modern oils with friction modifiers. They will usually be identified as those oils with a very low winter (W) weight, i.e., 0w-40. The friction modifiers will make your clutch slip. Another topic for endless discussion is the amount of zinc dialkyldithiophosphate (ZDDP) added to the oil. This additive helps lubricate high pressure contact zones like flat tappets and camshafts. Unfortunately, phosphorus is poisonous to catalytic converters, so modern oil formulations contain less than oils formulated before catalytic converters came into widespread use. If you’re stuck using an oil with low ZDDP percentage you can always use an additive. Be careful though: Too much ZDDP is almost as bad as too little. MC


Tech Corner 

Oil-filled muffler

Q: While riding my 1971 Honda CL450 one day, a clattering noise came from the engine. When I returned home I left the bike idling in the driveway and soon discovered a pool of oil. One muffler was filled with oil and oil was dripping out through the bottom vent hole. What happened inside the engine that would cause this? - Wes Martin/via email

A: Unfortunately, any number of things could have gone wrong. Did the bike run any differently after you heard the clattering noise? Having one muffler fill with oil makes me wonder if an exhaust valve guide has come loose and is draining oil from the head directly into the exhaust. I’m afraid you’ll have to pull the top off the engine and do more research. MC


Tech Corner 

Sticking starter

Q: The starter won’t disengage on my Honda CB550. The instant you turn on the key, the starter motor starts to turn. What’s wrong? Is it my starter button? - Kurt Limesand/via email

A: It may be the switch in the handlebars, but there is also a strong possibility that you have a stuck starter solenoid. I’d start by disconnecting the thinner signal wires to the solenoid and turning the key on again. If the problem disappears, the starter button circuit is shorted out. If the problem persists, your starter solenoid is stuck and will need to be replaced. MC


Keith Fellenstein 

Back-end weave

Q: I have a 1976 BMW R90/6 that weaves to the left on acceleration and to the right on deceleration. This is definitely not a front end problem as the steering head has been checked and greased and is adjusted properly. I have installed new fork springs and a hydraulic dampener. The front end, in my opinion, cannot be the cause. When I ride I can see the frame snake underneath me as I’ve described. The frame is not damaged. I think it has to be the shocks or the swingarm bushings. From what I can gather, it is highly unlikely to be the swingarm bushings. How can I check the health of the shocks? They have been easy enough to dismantle, and they feel equally resistive when I test them by hand, but they appear to have resistance in only one direction. — Ralph Parsons/via email

A: You may be too quick to dismiss the swingarm bearings. They seldom give trouble on old BMWs, but if the locknut on either side is loose, the spindle that tensions the bearing can come loose, too. I would put the bike up on the centerstand so that the rear wheel is free to spin. Use a board under the stand if you must to get clearance. Then try pushing the swingarm left and right while watching the pivot point where the swingarm joins the frame. If you see any play there, the pivot bearings are misadjusted or worn. MC


Keith Fellenstein 

Suzuki misfire

Q: I have a problem with a 1979 Suzuki 1000E. It starts fine, but it sounds like it misses a little just off idle. The main problem is at 5,000rpm the engine misfires or cuts out. I cleaned the carburetors, installed new plugs, wires and coils. I am having trouble setting the engine timing using a timing light. I can’t retard the timing to the correct specs because the plate bottoms out on its screws, and you can tell it is worse when I back that down. The idle is about 1,200. Any help would be appreciated. — Ken Erdman/via email

A: This sounds depressingly similar to a problem I had with a customer’s Honda 750. It idled fine, but it wouldn’t rev under load, and the timing was hard to set. Sometimes these problems can be caused by something as simple as a bad connection in the ignition or kill switch that only shows up at certain RPMs due to vibration. It’s easy enough to bypass the ignition switch and run a wire directly from the battery to the coils. You’ll still be using the ignition switch to fire the starter, just augmenting the circuit with a direct link and bypassing the kill switch. If this improves matters, you’ll have to determine whether it’s the ignition switch or the kill switch. Another possibility is the points condensers. Look at the points as the engine runs. Is one set arcing more than the other? There should be barely discernible sparks between the points with the engine running. If one or both sets of points are arcing excessively, replace the condensers and see if that improves things. Bad condensers will definitely make it hard to time the engine with a timing light, as the timing will be erratic. Since you mention the points plate being at the end of its adjustment, it’s probably important that we establish that the auto advance unit (AAU) is in properly and working as it should. Before that, though, make sure you have the points gap set correctly. You can change the timing by having the gap set too wide or too narrow. Make sure you measure the gap when the points are opened their widest. The manual suggests 0.012in-0.016in, I usually set it to 0.015in as that’s the smallest wire on my wire feeler gauge. Check your timing again to see if you can now center the points plate. If not, the next step will be to remove the points plate and then the AAU. The points plate will come off if you remove the three screws holding it to the engine case. You’ll need two wrenches to remove the AAU: one to hold the crankshaft steady and the other to loosen the bolt holding the AAU in place. Once you have the AAU loosened, check that the locating notch and pin are in place in the AAU and the crankshaft, respectively. Those are there to make sure the AAU stays in time with the engine, and if the pin is missing or the notch is worn it could be why your timing plate is at the limit of its movement. Check the AAU to make sure it operates smoothly, lubricating it with a little light oil if necessary. If everything on the AAU checks out, reinstall it, making sure to engage the pin on the crank with the notch on the AAU. With any luck, you’ll find the solution before you have to do anything to the AAU. MC


Keith Fellenstein

Electrical problems

Q: My 1988 BMW R100RT has 43,000 miles and runs well most of the time. It loses power randomly and for various durations. So far I have changed the plugs, rebuilt the carburetors, cleaned the kill switch, cleaned the ignition switch, added contact paste to the heat sink next to the coils and synced the carburetors. Last time I had the bike running I kept hearing a random sparking noise when I was near the gas tank. I took the tank off and put the bike in a dark area to try to see where the spark was happening but I could not locate it. Based on what I have read, it appears that the coils might be the problem. I think it has the original coils on there now. Is there a simple test I could perform for the coils? Or if you feel that it is the coils please tell me where I could purchase them and which resistance spark plug wires I should buy. — Peter Economou/via email.

A: The random sparking noise may have been the coil wires grounding to the gas tank, so when you removed the tank you removed the spark path. If you replace the plug wires, use resistor core wire from an auto parts store with non-resistor plug caps. If you use wire core plug wires you’ll want resistor-type plug caps. Wire core wires and resistor caps are usually available at your local motorcycle shop. You may still end up replacing the coils but you may find your problem fixed by new wires. MC

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