Question-------------------------
Followup To
Question -
I have a Honda CB750 and am having a problem with oil burning/disappearing in traffic. I have run the bike for 500 miles on the highway and did not have to add any oil. However, if I go 1 mile in heavy traffic I have burned/lost over 1 qt of oil. I only lose oil in traffic and the problem has become so bad that last weekend I was in traffic for about 5 miles and burned through 3 quarts of oil. Any help would be appreciated.
Answer -
Ron, you didn't mention if this was a SOHC or DOHC or other version.
Losing a quart of oil in one mile would produce clouds of smoke if it was being used up internally. That kind of consumption, only at idle and low speeds is generally related to valve stem/guide clearances and stem seal failures. Even so that is a lot of oil going past the guides in a short period of time. No doubt a top end rebuild will help it a lot.
SOHC 750s only held 3 qts of oil, so I hope it wasn't that version, as it would be empty and start seizing a lot of parts inside.
Run a compression check and perhaps a leakdown test to see if there is compression loss in the motor and repair as necessary.
Remove the plugs and see if any/all are fouled with oil. That will point you to perhaps a ring failure or maybe a partial seizure on one or more cylinders.
SOHC 750s had a small oil line that went from the back of the oil tank to the back of the crankcase, which must be there or you will lose oil.
Check the breather tube coming from the top of the cylinder head for being kinked or pinched off. If the bike is from the 1975 later era, there was a closed crankcase system that rebreathed the oil fumes from the crankcase back into the air filter.
Be sure that the bike is completely tuned to factory specs as incorrect ignition timing, etc will drastically effect the engine's performance and fuel/oil consumption.
Bill Silver
Bill, thank you for your time. I have a DOHC and am still curious about one issue. Why does this problem only happen in traffic? I do not lose or burn oil when riding on the highway. Also, do you know the difference between oil with an SF, SG and SL? I currently use SF.
AnswerRon, do you notice oil smoke when you accelerate after idling for a few minutes? Does it smoke when you are coasting down a long grade in gear? These are both situations were there is a high manifold vacuum produced and encourages oil consumption, especially past the valve stem seals, which are now over 20 years old. I bought a CBX six (engines are similar in design) back in the late 80s and had to replace the stem seals on a bike that only had about 12k miles on it. Air cooled engines run hot in traffic when air flow is limited or non-existant. This high temperature condition is brutal on valve stem seals and on oil, in general.
At highway speeds, oil temperature drops and the engine manifold vacuum readings are reduced, as well, so consumption is reduced. My bet is that you need a fresh set of valve stem seals installed. If the bike has periods where it sat for a long time with old oil in it, the piston rings may be sticking in the ring lands, especially the oil rings and expanders. I hope you are using something like 20-50 wt oil, especially if you live in a hot climate. As mentioned in the stories below, do NOT use oils that are labeled FUEL EFFICIENT, which may include your SF brand. Try SG instead...
http://homepages.paradise.net.nz/~hasl/oillinks.htm
http://www.yft.org/tex_vfr/tech/oil.htm from that list of links mentions SF and SG oils in motorcycle applications.
Bill Silver
