Author Topic: Oil pump priming CB750 (Read 9808 times)

Turbogrimace · « **on:** October 05, 2009, 08:02:21 AM »

I had oil pressure in my fresh built 836 and a little while later I dont. I've check the lines, pulled the pump and tore it apart, and check the screen. I cant find anything wrong, other than the oil stopper leaks (common). I read somewhere that you can prime the oil pum by soaking it in oil before you install it. Since my oil stopper leaks, the oil pan is full when the bike has been sitting for a while. This means that the pump is sitting in oil. Could my pump still not be primed? I tried pouring oil down through the tappet cover and then filling the galley and I still didnt get any oil pressure. Lines on the bag arent crossed, and oil used to flow really well. Oye.

Any thoughts? Again, its a 1978 CB750 F bottom end with a K top end. Thanks!

754 · « **Reply #1 on:** October 05, 2009, 09:22:41 AM »

K top end, head & cylinders?
you cant mix those in one application, due to oil drain holes, but can switch head & cyl together.

Turbogrimace · « **Reply #2 on:** October 05, 2009, 10:15:45 AM »

F cases and K cylinders and K head.

754 · « **Reply #3 on:** October 05, 2009, 10:18:49 AM »

Did you try another guage..?

Turbogrimace · « **Reply #4 on:** October 05, 2009, 10:27:41 AM »

I have a gauge hooked up to the sending unit bung. I checked the gauge before I installed it, I've tried the old sending unit, I've even turned it over with my finger over the sending unit bung to see if I could even feel any pulsing.

mystic_1 · « **Reply #5 on:** October 05, 2009, 10:52:58 AM »

Ordinarily oil is fed to the supply side of the pump from the tank under gravity feed, so priming is not needed. The supply intake is not open to the sump so having oil down there isn't relevant to this. See diagram below.

Could your relief valve be stuck open?

I think the best bet at this point is to drop the sump pan and inspect.

mystic_1

Turbogrimace · « **Reply #6 on:** October 05, 2009, 11:12:42 AM »

Where is the relief valve? I was thinking that might be the problem, but I wasnt sure where it was.

mystic_1 · « **Reply #7 on:** October 05, 2009, 11:13:45 AM »

See below.

(Note: FYI these diagrams came out of a Clymer manual circa 1972.)

mystic_1

Turbogrimace · « **Reply #8 on:** October 05, 2009, 11:20:30 AM »

Ok thats whay I thought. I'll check it out and let you know. Last time I pulled it, it seemed fine, but it would hang up now and then.

Turbogrimace · « **Reply #9 on:** October 06, 2009, 11:40:35 AM »

So it's not the pressure relief valve. I pulled the pump and it's fine. The oil stopper leaks, but that just lets oil drain into the pan from the tank. I pulled the filter to see if something crazy was going on in there and the only thing I found was a torn gasket on the filter. I seriously doubt that would cause any issues.

Any other ideas? What could get clogged that would not allow any oil pressure? what else is there to check?

sparty · « **Reply #10 on:** October 06, 2009, 05:44:31 PM »

Quote from: Turbogrimace on October 06, 2009, 11:40:35 AM

So it's not the pressure relief valve. I pulled the pump and it's fine. The oil stopper leaks, but that just lets oil drain into the pan from the tank. I pulled the filter to see if something crazy was going on in there and the only thing I found was a torn gasket on the filter. I seriously doubt that would cause any issues.

Any other ideas? What could get clogged that would not allow any oil pressure? what else is there to check?

After my engine build it took me about 20 minutes or so to build oil pressure in a totally dry engine. Be sure you have a fully charged battery. Us the starter button for 15 seconds on an off until you get pressure. I opened the galley plug on the right side and finally had oil come out. I put the plug back in and used the starter on and off until the oil light went out. It does take some time like I said. 10w oil will flow better. i thought I had a problem at first because the pressure would not build. Also. I think I kept the spark plugs out of the engine. Keep at it, it will happen.

Sparty

HondaMan · « **Reply #11 on:** October 06, 2009, 08:55:39 PM »

You've captured an air bubble inside the pump. It often happens when the cases are sitting upside down for a long time (like on my garage floor), and the oil drains fully out of the pump. It also is an issue after the pumps are disassembled and the seals replaced, then reassembled dry.

Get a pan that is deep enough to hold about several quarts of oil, enough to submerge the whole pump. then turn the gear forward and back while it is submerged, and eventually you will see the burp. Then you will see the old oil (dirty) getting flushed out from inside, and the flow. When you pull the pump out, don't drain it all the way before reinstalling it, because you don't have all the air out, yet. It will finally move the rest out when the engine gets real good and hot, and the bubble is very small.

The hydrostatic head of the tank is not enough to push this bubble out, and it will stubbornly stay in the high-pressure side of the pump, sometimes. The last time I went through this was on the first Hondaman Special, which sat upside-down in my garage all winter while I took the pictures for my book.

Turbogrimace · « **Reply #12 on:** October 07, 2009, 05:38:23 AM »

Thanks Mr. Man. I might give that a try. When I dropped the pump yesterday, I spun it by hand and it was pumping very well. I didnt note any bubbles though.

After I posted yesterday, I noticed that my oil lines...were....um...switched. If I had gotten oil pressure back after switching them, I would have posted in the "stupid stupid stupid" thread again. But I still dont have pressure. It would make sense though that I'd have a lot of air in the pump now because it was originally pulling air from the return tube. Oyeee.

I'll drop the pan again and soak the pump. After I do this, at what point should I get pressure? Should I be able to get a little bit to show on the gauge while kicking? Right now, I've cranked it over for a while and I dont even see any oil moving in the galley.

Turbogrimace · « **Reply #13 on:** October 07, 2009, 05:52:24 AM »

What really bothers me is that I did have oil pressure for a good hour or so of running and then a week later I came back to work on it and had none.

JohnG · « **Reply #14 on:** October 07, 2009, 06:08:07 AM »

I doubt this is it but make sure your oil lines are ok and one did not get
collapsed somehow during the job. Honda had problems for a bit in the 70s with collapsing oil lines (this both told to me by a Honda Rep and also by experience on a second hand 750 I bought). Can't hurt to check!!

How many miles on your pump? At about the 75000 mile mark my pump started doing some really flaky things (I have a pressure gauge). The top pressure was fine (80) but at low RPM alot of weird things would go on with the pressure all over the place including near 0. Finally decided some of the relief mechanism was not working right due to worn components, and replaced the pump with an NOS one.

The new pump took alot longer to develop pressure in than anything from a dry motor. I used a car battery and had the plugs removed. Finally got pressure to my considerable relief.

Hondaman's thoughts on trapped air sound really valuable...

Whaleman · « **Reply #15 on:** October 07, 2009, 06:39:16 AM »

The last time I primed a dry pump I could not get pressure with the starter motor. I tried kicking about 20 times and the pressure came up. I must have dislodged an air bubble. Dan

MRieck · « **Reply #16 on:** October 07, 2009, 06:49:10 AM »

Also....work that bypass relief plunger when it is submerged

Turbogrimace · « **Reply #17 on:** October 07, 2009, 07:22:01 AM »

bypass relief plunger? The relief valve? It was working great, but I'll exercise the whole thing while its submerged.

JohnG · « **Reply #18 on:** October 07, 2009, 07:41:28 AM »

Look on the bright side... you hands aren't gonna rust this winter...

Turbogrimace · « **Reply #19 on:** October 12, 2009, 12:52:48 PM »

Got Earl pressure! I soaked the oil pump in a tub of 20w50 while I spun it by hand in different positions to make sure all of the air was out. When I first started, it was kicking out a ton of air. Once the pump gave me a lot of resistance, I slapped it back in, filled the tank, popped the spark plugs out (no way im kicking against 11:1 CR as many times as was needed), and kicked the crap out of it. I was on the phone talking about secretly painting my brother's CBR Ibis White while I was kicking it and getting a bit discouraged. Suddenly, I noticed my gauge was reading around zero (normally sits way below it), so I started kicking like I was stomping out Hitler himself. Almost 50 psi from just kicking. Now that's what I'm talking about. I started yelling and jumping around after that. Looked like an idiot, felt like a million bucks.

Thanks a lot for the information guys. Thanks Hondman! Now it's onto some carb tuning and a few other odds and ends.

Bob Wessner · « **Reply #20 on:** October 12, 2009, 01:09:22 PM »

How's you leg?

Turbogrimace · « **Reply #21 on:** October 13, 2009, 11:55:09 AM »

I actually busted my shin when I was trying to kick it standing backwards. Feels great. It's a welt of pride

Bob Wessner · « **Reply #22 on:** October 13, 2009, 12:19:36 PM »

Quote

It's a welt of pride

Good one, have to remember it. Glad you got it all squared away.

Turbogrimace · « **Reply #23 on:** October 13, 2009, 01:09:42 PM »

Thanks. Im going home now to slap the carbs back on, set up the magneto, and see what happens when she runs.

HondaMan · « **Reply #24 on:** October 13, 2009, 07:31:01 PM »

Quote from: Bob Wessner on October 12, 2009, 01:09:22 PM

How's you leg?

Bigger.

Mine always gets bigger at that stage of a rebuild.

Seamus · « **Reply #25 on:** October 14, 2009, 04:39:41 AM »

Too late now, but when I was trying to get oil pressure from a rebuilt engine, I pulled off the pan and removed the oil stop valve for a few seconds. (This is there to prevent oil from the tank flowing into the sump, so I guess it will also hold an air lock)
As soon as oill started to flow, I put it back. Replaced the pan and instant oil pressure.

Cheers

Seamus

Turbogrimace · « **Reply #26 on:** October 14, 2009, 05:36:43 AM »

Neat trick Seamus. But my oil stopper already leaked, so there was plenty of oil in the pan when I was working on it.

Seamus · « **Reply #27 on:** October 14, 2009, 02:14:12 PM »

If the stopper was leaking slowley, there would be oil in the pan, but that is not important. The air lock is in the pump and the leak through the stopper will not let that air out. If you actually remove the stopper valve and open up the whole pipe, then the air can move .

Hope this makes sense

Cheers

Seamus

Henning · « **Reply #28 on:** October 14, 2009, 03:18:17 PM »

Problem solved, but I'll chip in anyway for future reference. After having had the motor of my 750 K1 out to do the head gasket, I stored it upside down on the workshop floor for a few days to clean off 35 year old gunk. As guru HondaMan stated, this will drain oil out of the oil pump, and true enough, it kept on leaking oil out of every available orifice, long after I thought it must be empty.

After reinstalling the motor, I couldn't get oil pressure, despite continuous cranking and the onset of mild panic. Then I figured it might have to with oil having drained out of the pump and an air block. So I took it off the mainstand - which you would use when removing/replacing the engine - and put it on the sidestand. Then after a short amout of cranking, Lord Be Praised, I got oil pressure. I guess the air bubble moved enough so that the pump could do its thing. If the sidestand isn't enough, maybe you could lie the bike further down on its side to move that bubble - easier than removing the pan and pump.

- Henning

HondaMan · « **Reply #29 on:** October 14, 2009, 06:16:53 PM »

Quote from: hserrits on October 14, 2009, 03:18:17 PM

Problem solved, but I'll chip in anyway for future reference. After having had the motor of my 750 K1 out to do the head gasket, I stored it upside down on the workshop floor for a few days to clean off 35 year old gunk. As guru HondaMan stated, this will drain oil out of the oil pump, and true enough, it kept on leaking oil out of every available orifice, long after I thought it must be empty.

After reinstalling the motor, I couldn't get oil pressure, despite continuous cranking and the onset of mild panic. Then I figured it might have to with oil having drained out of the pump and an air block. So I took it off the mainstand - which you would use when removing/replacing the engine - and put it on the sidestand. Then after a short amout of cranking, Lord Be Praised, I got oil pressure. I guess the air bubble moved enough so that the pump could do its thing. If the sidestand isn't enough, maybe you could lie the bike further down on its side to move that bubble - easier than removing the pan and pump.

- Henning

Hey, thanks! I'll try that next time, before pulling the pan and pump back out...

JLeather · « **Reply #30 on:** October 14, 2009, 09:03:03 PM »

just throwin' it out there, but Turbo's bike is a Santee chopper. Pretty sure there's no center-stand, only a sidestand.

Turbogrimace · « **Reply #31 on:** October 15, 2009, 05:51:11 AM »

Yeah... No center stand.

But to add to what's already been said, I tried to figure out the best way to get the air out of the pump and the more you lean it to the left (towards the side stand), the more the air comes out faster. So in all, I'd say you could simply lean the bike over really far and it will release the air bubble. I did this a few times with the pump in my hands while it was soaking in a bucket of oil. Same thing should be going on in the engine, so just leave it in the bike and tilt it over. Put some straps on the bars and support it from some rafters and kick away. Or have one of your minions hold it over for you.

Good advice in this thread. I'll bet leaning it over would have done enough to let the bubble out now. It was good practice to take the pump out 5 times though. I can swap the pump in 5 minutes now hahaha.

News:

Author Topic: Oil pump priming CB750 (Read 9808 times)