• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

74 sohc oil stuck in tank??

Curtis87

CB750 Enthusiast
Messages
40
Reaction score
0
Points
6
Location
Ontario Canada
Hi guys i have a 74 hasnt run in decades. Dropped the drain plug and filter and drained the oil. When i filled up the oil tank it just sat in the tank, its not going to the bottom end. I even cranked the engine over a few times. I pulled the oil lines off and they are not clogged? Whys this happening?
 
Its not supposed to go the bottom. Its a dry sump motor. Oil is sucked out of the tank sent through the engine and drain to the pan where it is pumped back to the tank.
 
Its not supposed to go the bottom. Its a dry sump motor. Oil is sucked out of the tank sent through the engine and drain to the pan where it is pumped back to the tank.
So i had only put one quart of oil into the tank and the oil from the pan was drained. Does the bike need to be running to get the oil to start pumping out of the tank then? Like i said i kicked it over a few times and i didnt want to run it with only one quart of oil in it. I even cranked the engine over with the starter to get it to cycle, DOES IT MAKE A DIFFERENCE IF MY SPARK PLUGS ARE CURRENTLY REMOVED? i forgot to mention that....?
 
The bike needs to be running to correctly add oil. Put three quarts of oil into the tank. Using the starter button with the engine stop switch in the off position, crank the bike over a few times to cycle some oil into the engine and filter housing. Then start the engine and make sure the oil light goes out after a few seconds. If the light does not go out, immediately stop the engine. If the light does go out, run the engine for about a minute, then shut it off and let it sit for 15 minutes. Next, check the oil level in the tank using the dipstick with the bike upright and top off the oil level in the tank to the correct line on the dipstick. Do a thorough check for oil leaks anywhere such as drain plugs, filter housing, oil hoses, and anywhere on the motor. I check my oil level with the dipstick before every ride, it only takes a second.
If the oil in the tank is not cycling into the engine, you could have a clogged oil port, or the oil pump could be bad. Your oil pressure switch could also go bad, causing the oil light to stay on, even when the oil pump is properly pumping oil to the engine. If you are in doubt about any of this, and you don't have much experience, I would recommend you take the bike to your local Honda service department. You can ruin an engine rather quickly by running it with no lubrication.
There is a lot more information on oil change procedures here on the forum, just search the topic you are looking for. Hope this helps some. Good luck with your bike, let us know how it goes!
 
Last edited:
The tank will hold the entire spec of 3.7 qts of oil but most start with 3 and start it and run for a minute or so. then shut off and let sit for a couple minutes then check level. It will take a lot of kicking to get the oil pump to pump. Even just spinning with the starter will take a while...especially after sitting for so long. Put a full 3 quarts in the tank and crank it for a bit then start it up. Pull a couple of valve caps on the valve cover and watch for oil splash... it will take a bit for oil to get to the top end but you will see oil splashing around. The oil level should go down in the tank a bit when running but it should never be empty. If it runns empty then you have an air lock in the scavange pump and will have to do some addition things if it comes to that point.
 
Thanks to both you guys! It worked well, I managed to get the bike running but it was rough, couple of issues the petcock on the tank is leaking terribly all over and the spark plug wires are damaged as well. I will be taking the engine out (1974) to put in my (78) cb750. I did notice a bit of smoke from the right hand side exhause but not the left, probably a number of reasons that could be. I.E, not firing properly or bad plugs?
 
Could be your bad spark plug wires causing one or both right side cylinders not to fire. Could be a lot of other things too though. Replace your plugs and wires, points and condensers, and check your coils for starters. Do everything you would do for a 5000 mile service using the factory Honda service manual. Wouldn't hurt to clean and rebuild your carburetors too.
The first thing I would do though is fix your leaking petcock! It would be a shame to spark a fire and watch all your hard work burn to the ground. You can buy a rebuild kit for your petcock pretty cheap, or a new one with a new tank gasket isn't very expensive either.
Glad to hear your coming along and actually got to hear it run! Sometimes it's almost like winning the lottery to hear that noise the first time!...lol! Good luck and keep us posted. Start a build thread if you haven't already!
 
Ya thanks, it was great haha.. That's enough playing around though I will be pulling the motor, not going to worry about that petcock as I have a 78 bigger tank in good working order, I will have to buy a fuel "T" though to split the lines since the 78 tank only has one fuel line. My plan is to buy carb rebuild kit, new coils, new wiring harness and all. Since I'm putting the engine into my 78 cb750 should I buy the 78 wiring harness instead of the 74 just so the controls wire up?
 
Get the wiring harness for the frame you are using. The motors all have the same connectors but the harness is different from year to year.
 
Be sure and buy a "T" fitting with a big enough inside diameter. If the inside diameter is too small it will restrict flow to the carburetors. My personal preference is to use a metal "T" instead of a plastic one so I don't have to worry about it breaking or ethanol fuel affecting the plastic. For that matter, I try to never run ethanol fuel in my bike anyway.
 
Back
Top