Author Topic: Finished oil tank cb750 (Read 25186 times)

VTEC · « **on:** December 13, 2011, 10:17:50 PM »

Hey guys can some one explain what this line? i planing on building custom oil thank and was wondering if i can plug this not use it? The engine is cb750 76k

Eddie · « **Reply #1 on:** December 14, 2011, 04:06:17 AM »

yeah, you plug that and you'll have oil shootin out all over the first time you rev past 5-6K...

VTEC · « **Reply #2 on:** December 14, 2011, 06:08:18 AM »

Ok guys wasn't exactliy sure what it was. I'll leaw it a lone

Hinomaru · « **Reply #3 on:** December 14, 2011, 12:33:24 PM »

VTEC, you can plug the rear crankcase fitting, but only if your custom oil tank has a means to vent. The oil tank cutaway pictured in your post does not show a vented design, this means that excess oil can only be relieved from the oil tank overflow to the rear crankcase fitting.

The crankcase is designed to flow from the rear crankcase oil fitting then up to the valve cover which vents vapors and blow-by to the atmosphere. This is easily checked by blowing air into the rear crankcase fitting.

VTEC · « **Reply #4 on:** December 20, 2011, 11:06:15 AM »

Hey guys how much oil fits in original tank?

This what I'm going after

And here's my progress

gnarlycharlie4u · « **Reply #5 on:** December 20, 2011, 11:47:41 AM »

oh wow that looks GREAT!
Good job so far.

It's been said but I'd like to reinforce that you CAN plug the rear case vent but your oil flow may suffer because of it. I'd keep it. it's only a small, short line to run anyway.

CB750K4 · « **Reply #6 on:** December 20, 2011, 12:46:32 PM »

3.5 qts?

When I change oil, I put three qts in the tank, run for short time then top off with forth quart. Been doing that since I bought it in 1974, never any problems.

Duke McDukiedook · « **Reply #7 on:** December 20, 2011, 12:52:40 PM »

Quote from: CB750K4 on December 20, 2011, 12:46:32 PM

3.5 qts?

When I change oil, I put three qts in the tank, run for short time then top off with forth quart. Been doing that since I bought it in 1974, never any problems.

+1.

ANVkevin · « **Reply #8 on:** January 10, 2012, 05:38:28 PM »

May be obvious but, I assume the lower crankcase vent should be routed into the tank at a level higher than the full level of the tank. Correct?

MCRider · « **Reply #9 on:** January 10, 2012, 05:58:00 PM »

Quote from: ANVkevin on January 10, 2012, 05:38:28 PM

May be obvious but, I assume the lower crankcase vent should be routed into the tank at a level higher than the full level of the tank. Correct?

If you maintain the original purpose, no. The original setup has the crankcase vent (misnomer as you'll see) entering the oil tank below the level of the oil. That is because there is a pipe right there that travels up the inside of the tank and terminates in the condenser bulb at the top. Hence whatever is in that pipe never touchesthe pool of oil.

So if fumes travel up the pipe, dribbles of oil travel down the pipe and enter the crankcase through what we are are calling the breather. Those droplets of oil are deposited on a sheet metal pan about the size of a matchbook, and used to feed the chain oiler.

If you are doing away with the chain oiler, and just need a terminus for the crankcase hose, then yes you would want it above the oil level.

Hinomaru · « **Reply #10 on:** January 10, 2012, 07:05:00 PM »

Quote from: MCRider on January 10, 2012, 05:58:00 PM

If you maintain the original purpose, no. The original setup has the crankcase vent (misnomer as you'll see) entering the oil tank below the level of the oil. That is because there is a pipe right there that travels up the inside of the tank and terminates in the condenser bulb at the top. Hence whatever is in that pipe never touchesthe pool of oil.

So if fumes travel up the pipe, dribbles of oil travel down the pipe and enter the crankcase through what we are are calling the breather. Those droplets of oil are deposited on a sheet metal pan about the size of a matchbook, and used to feed the chain oiler.

If you are doing away with the chain oiler, and just need a terminus for the crankcase hose, then yes you would want it above the oil level.

MC, did you know that the chain oiler was eliminated on the K6, which is what the OP has? This chain oiler delete change resulted in a new crankcase design and new crankcase part number. The K6 oil tank also lost the condenser bulb and open vent hose to the atmosphere. With the new K6 design, any excess oil in the tank is returned to the engine via the lower crankcase vent fitting. Remember how an overfilled KO-K5 oil tank deposited oil out the upper oil tank vent hose and made a serious mess? I sure do.

(click images for a larger view)

KO to K5 oil tank design:

New K6 oil tank design:

ttr400 · « **Reply #11 on:** January 11, 2012, 06:35:42 AM »

So on the pic of the K0 to K5 design, the lower pipe is connected to the rear of the crankcase, does the top pipe vent to the atmosphere? just making sure.

Kevin

MCRider · « **Reply #12 on:** January 11, 2012, 06:53:12 AM »

Quote from: ttr400 on January 11, 2012, 06:35:42 AM

So on the pic of the K0 to K5 design, the lower pipe is connected to the rear of the crankcase, does the top pipe vent to the atmosphere? just making sure.

Kevin

On the K0-5, yes.

MCRider · « **Reply #13 on:** January 11, 2012, 06:58:40 AM »

Thanks Hino! That clears things up. I need to remember my "expertise" or experience at least, tapers off quickly after the K2. So as not to mislead.

I see from the cutaway of the later tank, the overflow is completely contained inside the tank.