SOHC.co.uk Forums > CB750
Engine full of fuel and seized up
Trigger:
As Oddjob says, pack the pump.
You should not try to turn the engine on the starter motor until you have oil pressure up or you will damage the shells. Lets hope you put bearing guard on the shells when yo assembled the engine ::)
allankelly1:
--- Quote from: MrDavo on November 17, 2020, 06:18:25 PM ---After a complete failure to get any oil pressure in my CB750K1 engine after I rebuilt it, a worried query on here sent me off to Boots to buy a tub of generic Petroleum jelly (it doesn't have to be Vaseline by brand).
I took the oil pump apart and packed it with the stuff, then tried again. Instant success! Oil appeared in the oil gallery at last, then in the cambox. I believe some old American V8s use the Vaseline technique as a matter of course to get their oil pumps started. The jelly simply dissolves into the oil, and wont damage or block anything. One wonders if Honda did something similar at the factory, I recall reading that they came primed with some sort of fishy oil that had to be replaced before use, the ex Honda workshop guys on here may be able to confirm that.
There was also a very sad thread on here from a member who put all his effort and money into a rebuild, then started his CB750 up without checking for oil pressure. the result was a beautiful rebuilt bike with a freshly ruined motor. :( As I remember it he was too disheartened to pull the engine to do it all again, and sold the bike 'as is' for someone else to fix.
--- End quote ---
Yes packing the pump with Vaseline is standard practice when building Rover V8 engines so the pump can prime itself
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K2-K6:
As already noted above, vaseline method is good.
Also if you want to observe for initial flow, the pump goes straight to the oil filter housing which you can look at without the filter on to see if you've any output at all. As soon as you can see it coming through that pipe you know the pump head is operating and filled with oil.
If present there, it will have to fill the housing then go through the filter to enter the feed galleries via the centre of the bolt.
If you take the oil filter housing off and it's dry, then it confirms the pump is air locked.
PJM47:
Ok thanks, I did read about the vaseline truck but I wasn’t sure. Should I be able to get oil pressure or at least oil coming out the filter hole just turning it over on the starter? or am I better off waiting til I can fire it up properly.
K2-K6:
You won't get pressure, but it's got to go thtough there first to get to the rest of the engine.
So if nothing comes out at all, then you'll never get pressure anywhere.
You've literally got to see it delivered through there, then that confirms the pump is pumping oil. Put the filter assembly back on and it should then fill and deliver through the whole system.
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