Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

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Tech Corner

Triumph clutch troubles

Q: I have a question for you regarding troubleshooting the clutch on my 1973 Triumph Trident 750. I have recently replaced the clutch plate. When riding the bike I cannot shift into neutral, and when stationary with the clutch pulled in the engine is still engaged. I have adjusted the clutch lever and the main clutch nut under the circular clutch plate cover. Should the clutch nut be loose enough to turn by hand? How much should the clutch arm move up and down inside the clutch case? — Nick/via email

A: Adjusting the clutch on a Trident is one of those things that can take all day: Finding the sweet spot for three things at once can be difficult. You want the clutch to fully disengage when you pull in the lever, fully engage when you release the lever, and not load the bearing buried deep in the clutch basket when engaged. The original manual calls for the clutch nut to spin freely with 0.005in clearance, but the collective wisdom of Trident owners is that this is too much clearance. Setting it to the factory clearance usually results in difficulty finding neutral and creeping in gear with the clutch pulled in. The generally accepted method is to adjust until you have almost no clearance, then lock it with the locknut. If you can still turn the big nut by hand when the clutch is relaxed, you have it properly adjusted. Start by adjusting the cable so that the arm on the actuating mechanism inside the transmission outer cover is between 3 and 4 o’clock when the clutch lever is released. Make sure the arm isn’t touching the case stop. Tighten the pull rod through the big adjusting nut until it is just tight. Keeping the adjusting nut steady, loosen the pullrod about 30 degrees. Lock it down using the locknut without moving either the adjusting nut or the pullrod. It helps to have three hands for that part of the procedure. Try to rotate the big adjusting nut with your fingers. If you can then the clutch is adjusted properly. Any minor adjustments should now be possible from the adjustment screw at the clutch lever. MC


Tech Corner 

Honda oil pressure

Q: I have just finished rebuilding a 1970 Honda CB750K. It is my first attempt at rebuilding this type of engine. I have rebuilt other types with good success.

I now have about 480 miles on the engine and it is running great. It sounds good and doesn’t leak a drop. My problem is the oil pressure. Lately I find that after running the engine for about 30 minutes the oil pressure light comes on at an idle. I suspected the oil pressure switch. So I pulled it and have installed a pressure gauge. When cold the pressure starts at about 65lb. After running for about 15 minutes it drops to 60lb and remains there no matter how long I run it. — Daniel Pensyl/League City, Texas

A: According to the shop manual, the oil pressure bypass valve is set to 56.9psi at 4,000rpm for an engine temp of 176 degrees Fahrenheit. It looks like your engine has the correct oil pressure. An old rule of thumb was 10lb of pressure for every 1,000rpm, which makes your setup exactly right at about 6,000rpm. If your oil pressure light continues to light, it could be the switch that’s faulty. They’re still available for about $35. If you look for it on a parts schematic, it’s part no. 37240-P13-013 on the starter motor schematic. MC


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

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