Author Topic: Dry sump!  (Read 1436 times)

Offline Johnny4428

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Dry sump!
« on: November 22, 2020, 11:43:37 AM »
What controls the amount of oil in the sump of the 750? I drained oil and refilled tank, started up ran for a short while and the oil disappeared completely off the dip stick. Topped the oil up again. Since drained the sump again just to see amount of oil, and took 2 litres of oil out. Is this normal?
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1. Running resto,
1978 Honda CB550K3.
1999 ST1100 Pan European 50th Anniversary.
1975,1980,1984,1986 Honda C90’s
1973 Honda CB750K3

Offline Rob62

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Re: Dry sump!
« Reply #1 on: November 22, 2020, 11:53:27 AM »
Sounds like you may be making it more complicated than it is. The pump controls the oil, all you need to do is fill the tank with the specified amount, run the motor and check that the pump is working (you can see the oil returning to the tank and foaming slightly with the cap removed) and then when its all cooled down re check the level....

Offline Johnny4428

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Re: Dry sump!
« Reply #2 on: November 22, 2020, 12:06:07 PM »
Thanks Rob, I don’t have any experience with these dry sumps other than the Matchless I have, very simple system. Just not convinced the oil was being pumped back to tank! Certainly comes up to oil pressure and circulates in engine.
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1. Running resto,
1978 Honda CB550K3.
1999 ST1100 Pan European 50th Anniversary.
1975,1980,1984,1986 Honda C90’s
1973 Honda CB750K3

Offline Rob62

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Re: Dry sump!
« Reply #3 on: November 22, 2020, 12:09:50 PM »
I dont think you can tell straight after firing up...but once its been running a bit and you look into the top of the tank you will see some foaming as the oil returns....

Offline K2-K6

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Re: Dry sump!
« Reply #4 on: November 22, 2020, 12:31:03 PM »
There's a check valve in the oil pump that prevents the tank running through to fill the engine when it's not running,  that should make the level stay consistent in the tank during normal use. Failure here is similar to the old British bike condition of "wet sumping" which riders checked for if their bike was of this type and had stood for a period of time.

When you change the oil and filter during service on the 750 through,  the initial "fill" to top level on dipstick would drop a fair bit as soon as you start it as it will initially fill the filter housing from this volume,  but shouldn't ordinarily drop below the minimum mark on the dipstick. 

All being normal you should get a consistent "read" of level on dipstick whether it's running or not. Significant variations would suggest you'd need to look further into how it's working.

It's only a significant risk if the level drops so low that there's no head of oil to feed the pump.

Offline K2-K6

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Re: Dry sump!
« Reply #5 on: November 22, 2020, 12:44:12 PM »
You should be able to see a schematic of the oil pump in Ash's manuals for the 750 .

It makes clear the flow pathways and has the "leak stopper valve" usually listed as #3 in my manual.

The whole lubrication schematic is there too, and worth a look.

Offline Skoti

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Re: Dry sump!
« Reply #6 on: November 22, 2020, 02:24:00 PM »
That 'leak stopper valve' once stuck open on my CB750F1 and dumped all the oil from the oil tank into the sump.

I'd returned from a long run and checked the oil tank level the following morning and noticed it was empty, almost shit myself...

But It was easy enough to check the leak stopper in situ by removing the sump and the two 6mm screws on the oil pump leak stopper end cover.
The leak stopper bore had a slight ridge worn in it, presumably at the open position, so I dressed it up with fine wet and dry paper and reassembled it.
It's been OK for the last 5,000 miles or so.


BTW Johnny,
I don't think your sump should normally have as much as two litres of oil in it, but maybe some body who knows for sure will be along shortly to let us know the exact quantity.

 




« Last Edit: November 22, 2020, 02:29:48 PM by Skoti »
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Offline K2-K6

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Re: Dry sump!
« Reply #7 on: November 22, 2020, 02:47:10 PM »
Generally the sump quantity would be less than 500ml and probably aggregated at around 300ml.

It's a general principle of any dry sump system that the scavenge pump capacity exceeds the pressure feed one, else it can't work. The oil tank would be depleated if you rode for a long time with all of the oil remaining in the sump eventually.

Offline Johnny4428

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Re: Dry sump!
« Reply #8 on: November 22, 2020, 05:23:31 PM »
Thanks guys, interesting to learn a little about the lub system. Ran the bike again the day and quite sure there was movement within the oil tank. I was toying with the idea of fettling and running bike next year but too many unknowns! Want to fully restore to as near original as poss so drained oil this afternoon with the view to remove engine for complete strip down. Will post some pics of internals ad I go. Let the fun begin.
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1. Running resto,
1978 Honda CB550K3.
1999 ST1100 Pan European 50th Anniversary.
1975,1980,1984,1986 Honda C90’s
1973 Honda CB750K3

Offline Trigger

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Re: Dry sump!
« Reply #9 on: November 22, 2020, 09:41:14 PM »
Always better to overhaul the oil pump on these old girls, just a few O'rings, a center seal, stopper valve and springs.
The way to check the oil is after a good ride. Pop it straight on the stand and see what level the oil is at. I always have the level about a 1/4 down on the line and if you over fill, it will spray over the rear tyre  :o

Offline Johnny4428

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Re: Dry sump!
« Reply #10 on: November 22, 2020, 10:15:04 PM »
Thanks Trigger!
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1. Running resto,
1978 Honda CB550K3.
1999 ST1100 Pan European 50th Anniversary.
1975,1980,1984,1986 Honda C90’s
1973 Honda CB750K3

Offline MrDavo

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Re: Dry sump!
« Reply #11 on: November 23, 2020, 12:50:20 PM »
You know that your oil is definitely coming back from the engine if it becomes hot!

My CB750 K1 would empty its oil tank virtually overnight when I first got it, the leak stopper valve, like every other bit of rubber on the bike, had turned to stone over the years, they literally fossilize. After looking for replacements on the net, the one place on the planet I found offering all the seals I needed to rebuild my oil pump was Trigger!

Edit: If you think the oil level checking procedure is a faff, on my air cooled (& dry sump) 911, the oil level is checked using a dipstick in the oil tank with the engine running, and hot enough to open the thermostat to the oil cooler behind one of the headlights. The car also has 3 oil gauges (temp, pressure & level).
« Last Edit: November 23, 2020, 03:57:39 PM by MrDavo »
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Offline Andrew-S

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Re: Dry sump!
« Reply #12 on: November 23, 2020, 08:20:19 PM »
Useful thread - my K1 which I bought in Dec 18 had been off the road and dry stored since 2015. I changed the oil and fired it up in Jan 19 and haven't started it since, so the above posts prompted me to check the oil level today which I'm glad to say hasn't dropped at all.  :)
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Offline K2-K6

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Re: Dry sump!
« Reply #13 on: November 23, 2020, 09:00:37 PM »
"Edit: If you think the oil level checking procedure is a faff, on my air cooled (& dry sump) 911, the oil level is checked using a dipstick in the oil tank with the engine running, and hot enough to open the thermostat to the oil cooler behind one of the headlights. The car also has 3 oil gauges (temp, pressure & level).
« Last Edit: Today at 03:57:39 PM by MrDavo »"

That's the correct way to check the level on any dry sump systems ( unless specifically stated otherwise) as it's the "running level that's most critical to it's operation and shouldn't give you false readings. Static and non running, on a well designed system should give the same reading,  with significant difference between the two indicating something isn't functioning as intended.

In this case the variance shows the compromise of leaking stop valve.

Automatic transmissions are the same too generally as the pump and torque converter move the oil in fair volume,  so static measurements can result in too high measurement, in effect giving the opposite of Honda giving under fill when oil changed. 

 

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