Motorcycle Repair: CB550K3 and oil temperature, lars leon, oversize pistons

Question
Hi. My friend and i have CB550K3 bikes we try to restore as best we can. We have rebored the first of the two engines and fitted oversize pistons (0,25), and overhauled the top. We measure full compression on all cylinders, and the valves are timed very carefully. Ignition is electronic. Carbs nice and clean at at specs. It purrs nicely in idle and runs great though maybe it hesitates a little bit at full throttle. We are worried about oil temperature, we were hoping to reduce some of the problem by renovating the engine, yet it seem to want to run real hot in stop and go traffic. The dial on the dipstick thermometer has a red mark at 248 Fahrenheit, and we both have seen our engines at that temperature. In normal highway driving condition they stabilize around 200. The oil manufacturers seem to hesitate sharing what temperature their oil stops lubricating. So we are a bit concerned, and wonder whether we should look for external oilcoolers, or if there are other measures we can take to bring down the temperature. Or can we simply live with it and just pull over when it is critical. Best regards Lars & Leon, Denmark

Answer
Lars, air cooled engines are going to heat up in traffic, when air flow is limited. Honda has designed the bikes under grueling conditions, so I wouldn't be too concerned about occasional temperature spikes.

There will be some additional friction in the engines after overhauls, while the pistons/rings are getting seated in the cylinder bores. As they seat in, the friction will be reduced and temperatures will fall somewhat.

With all of your work, there shouldn't be a hesitation at full throttle, so I have to wonder if the main jets or needle positions are in need of correction. Check also the spark plug caps and secondary wiring. It should pull cleanly all the way to redline without any hiccups or hesitation.

Once the engines have 600 miles or so on the new rings, you can switch to synthetic oils to ensure that you have adequate protection for your engine. Always be sure to use motorcycle oils in the engine, which meets Honda's recommendations. Automotive oils are not very compatible with the shearing action of the transmission gears.

With your short riding season in Denmark, I wouldn't think that an oil cooler would be necessary. If you do decide to add one on, be sure that it has a thermostat, so you don't over-cool the oil, causing sludge and other related issues.

Bill Silver