The CB750 is the only SOHC/4 model with a dry sump. As a result, the oil change process is more involved than just removing the sump bolt since you need to drain the oil tank as well.
Excellent set of instructions posted by Jonesy:
Here’s how I do it (FWIW…)
- Start up bike and let it run for about 10 minutes. This warms up the oil and gets things roiled up inside, but not so hot you’ll burn yourself. This helps lets the oil pick up crud and let it drain away with the oil, rather than having it settled out and stay in the engine.
- After the bike is warmed up a bit, shut it off and put it on the center stand.
- I start with the oil tank first. I remove the sidecover and temporarily undo the rear brake light switch to get it out of the way. I also crack the filler cap. Have a drain pan ready and remove the plug. I have a piece of aluminum that I bent into a small trough to keep the oil from running all over the frame.
- After the tank is drained, replace and tighten the plug. Proceed on to the oil pan plug and drain the oil from there. Again, replace and tighten the plug.
- With the oil pan plug out, kick the engine over a few times to pump out the remaining oil
- Lastly, remove the oil filter housing. If all the parts are in the housing, there is a thin washer between the oil filter element and the spring. This likes to stick to the filter and before you know it, you’ve thrown it away. (This is probably why 90% of them are missing)
- In other words, when you remove the innards, don’t lose it!.
- Wash out any sludge or particulates that have collected in the oil filter housing. Take a good look at what’s in there, as any sizable bits of metal might be a warning that something’s on it’s way out. In some cases it’s worthwhile to drop the oil pan to give it a good cleaning and look for any signs of trouble.
- If you bought an oil filter kit that includes new O-rings, fit the small O-ring on the oil filter bolt and seat the big O-ring in the groove of the filter housing. Apply a bit of clean oil to the oil filter bolt O-ring to make it easier to reinsert into the housing.
- With the bolt back in place, reassemble the oil filter housing with the spring first, then the washer and finally the new filter. Reinstall the filter on the engine, being careful not to overtighten the bolt.
- Reinstall the sidecover over the oil tank and put the brake switch back in place.
- Fill the oil tank with 3 quarts of oil. According to the owner’s manual, the oil level will settle into the correct range when the engine is started. So far, I’ve found this to be true.
- I like to hit the starter a few times with the emergency stop switch off to circulate the oil into the empty filter housing before running the engine. After doing this, fire up the bike and make sure the oil light goes out in a few seconds.
Again, this is how I like to do it. It doesn’t HAVE to be done this way, but I hope it’s helpful.
If you happen to want or need to drop your oil pan (I obviously don’t know how familar you are with these bikes), just a heads up to keep track of what holes the different bolts come from; they do vary in their length.
If you happen to need the torque specs for the different bolts:
OIL TANK DRAIN PLUG – - – - – - 24 FT LBS (ideal median)
CRANKCASE DRAIN PLUG – - – - – - 24 FT LBS (ideal median)
OIL FILTER HOUSING BOLT – - – - – - 20 FT LBS (ideal median)
OIL PAN BOLTS – - – - – - – 7 to 10 FT LBS (pick your median)
On an older bike you will probably have a lot of gunk sitting in the bottom of the oil tank.
After you have drained the oil put a screwdriver down there and see what you bring up stuck to the tip, and use a flashlight to have a look inside the tank. If it is a mess down there I recommend you pull the tank off the bike and clean it out properly.
Although the torque on the oil bolt is listed at 20 ft-lbs: for many years, I’ve only tightened them to (snug + 1/8 turn). This works out around 7-8 ft-lbs on a T-wrench. I’ve always done this because the oil filter housing distorts and locks that $%#*! bolt in something awful, often causing its destruction the next time around.
…just some experience. It won’t leak if your large o-ring is new…