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Offline rhalm

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oil pressure drop
« on: January 15, 2018, 01:49:37 PM »
During cranking the oil pressure gauge reads 40 psi. Within a minute of starting the pressure has dropped to zero. If the bike sits for awhile and I begin again, the same thing happens. Does anyone have suggestions on how to start trouble-shooting the problem?
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Offline Keith

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Re: oil pressure drop
« Reply #1 on: January 15, 2018, 07:39:27 PM »
Yes, install a mechanic's oil pressure gauge, and start the engine...see the results.
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Offline Deltarider

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Re: oil pressure drop
« Reply #2 on: January 15, 2018, 11:57:45 PM »
What oil pressure gauge is that? Recently installed? On what bike? How about the oil warning light?
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Offline rhalm

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Re: oil pressure drop
« Reply #3 on: January 16, 2018, 04:30:33 PM »
The bike is a 1973 Honda CB750 Four. The oil gauge is installed on the lower right side of the bike off the main oil galley. Upon immediately starting the engine, the oil gauge reads 40psi and the red light on the handlebars goes out. Within 15 seconds the psi has dropped to zero and the red light is on. I am thinking the oil pump may be faulty, but wonder if there might be a less taxing option to consider? I thank you for your willingness to lend a hand to an "old" new rider
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Offline jgger

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Re: oil pressure drop
« Reply #4 on: January 16, 2018, 04:56:21 PM »
I have heard of the oil lines going to the tank collapsing inside. Or your screen for the oil pick up is clogged. Just a guess or a starting point.
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Offline disco

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Re: oil pressure drop
« Reply #5 on: January 17, 2018, 02:31:05 AM »
Is there enough oil in the oil tank? Sounds like the pump is making pressure but it’s running out of oil supply. Open the oil tank & observe the oil level after you start it.
« Last Edit: January 17, 2018, 02:33:20 AM by disco »
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Offline Kevin D

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Re: oil pressure drop
« Reply #6 on: January 17, 2018, 05:52:32 AM »
Quote
I recently purchased a 1973 CB 750 Four which was thoroughly rebuilt by someone else.

rhalm, I plucked this quote from your introduction thread.
Can you speak to the rebuilders actions?
I wouldn't be running that motor without oil pressure.
Oil pump not too difficult to service - you don't have to pull the engine.
Blocked supply (as mentioned), loose mounting bolts, missing o rings.

.......and Welcome to SOHC4
« Last Edit: January 17, 2018, 09:20:05 AM by Kevin D »
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71 CB750 K1
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———past———
70 SL100/125/150
70 Candy BlueGreen CB 750 K0
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: oil pressure drop
« Reply #7 on: January 17, 2018, 10:37:58 AM »
1. Make sure you fill it with the correct volume of oil
2. Check that the oil screen on your pump is not clogging with fibers, etc due to the rebuild
3. Go from there 
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Offline HondaMan

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Re: oil pressure drop
« Reply #8 on: January 18, 2018, 10:24:02 AM »
Quote from: jgger on January 16, 2018, 04:56:21 PM
I have heard of the oil lines going to the tank collapsing inside. Or your screen for the oil pick up is clogged. Just a guess or a starting point.

This has my vote.
Also: unhook your oil lines at the engine (right lower side) and verify that there are O-rings around the castings that plug the lines into the engine. These are 2.4x12 or 2.5x12 size, Without them, the oil suction line sucks air and the pump stops pumping immediately. I just finished rebuilding an engine that suffered this issue, and it spun all the crank bearings.
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Offline rhalm

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Re: oil pressure drop
« Reply #9 on: January 20, 2018, 11:40:26 AM »
Halm here. Many thanks for the suggestions. I have located a motorcycle mechanic and he will examine the oil issue this week. I'll publish what he discovers.
Ray
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