Author Topic: 1978 CB750K — Post 836 OIL PRESSURE - Seems bad :(  (Read 264299 times)

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Offline SKTP

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Re: 1978 CB750K — Post 836 OIL PRESSURE - Seems bad :(
« Reply #1450 on: May 04, 2025, 12:56:00 PM »
I just removed my pipes and drained the oil (cold).

I got 450ml from the side tank

and 1850ml from the engine plug and oil filter.

EDIT: another 100ml from the oil-pan

This is 2.4 liters (or 2.53605 quarts)

I am wondering if a low oil level has been the cause of all of my problems? But I am thinking this is a average amount of oil when draining the bike...there's got to be a bunch of oil still in the motor..correct?

« Last Edit: May 04, 2025, 03:21:13 PM by SKTP »
1978k rebuild thread http://forums.sohc4.net/index.php?topic=68423.0
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Offline SKTP

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Re: 1978 CB750K — Post 836 OIL PRESSURE - Seems bad :(
« Reply #1451 on: May 04, 2025, 03:20:37 PM »
Oil pump is out and I am returning to Ken at Cycle-x. He is going to test it for me.

There was some black "gaskety?" grit in the pan and one sliver of non-magnetic metal. Nothing of note in the oil filter cover.
1978k rebuild thread http://forums.sohc4.net/index.php?topic=68423.0
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Offline HondaMan

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Re: 1978 CB750K — Post 836 OIL PRESSURE - Seems bad :(
« Reply #1452 on: May 04, 2025, 07:58:32 PM »
While rare, I have seen the tunnel warped where the Overpressure Relief valve lives. This makes it sort of oval, and then the piston sticks slightly open in it. The tunnel cane be re-bored, though, to make it round again. I have 2 in my "to be rebuilt" box of pumps that are like that, and they both caused the majority of oil in the tank to drip into the cases - faster when hot, slowly when cold, much like an old Bonneville 650 twin would do.

It happens mostly because the metals used were not really intended to last 50 years...
« Last Edit: May 08, 2025, 08:10:48 PM by HondaMan »
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Offline PeWe

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Re: 1978 CB750K — Post 836 OIL PRESSURE - Seems bad :(
« Reply #1453 on: May 04, 2025, 09:11:51 PM »
2.4L should not be dangerous too low.
I refill with ca 2.9L at an oil change with new filter.

I have leaned the bike to the right when it had stopped dripping and a little more came out.

If 0.5L short. Oil level should be visible on the stick, maybe half.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
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http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline BenelliSEI

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Re: 1978 CB750K — Post 836 OIL PRESSURE - Seems bad :(
« Reply #1454 on: May 06, 2025, 05:31:10 PM »
When looking for “debris” open the folds of the paper oil filter element. The glitter usually ends up deep in the “V” part.