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Post by ralphie on Apr 6, 2009 7:14:15 GMT 11
I have just rebuilt my 4JB1T bighorn motor. Crank grind, bearings, new rings. It runs sweet, but I have noticed the oil pressure is down to 10PSI when hot at idle. I have fitted an external pressure guage so it is not read from the dash. I have taken the motor out and checked the bearings. They seem to be good. Also have checked the oil filter housing pressure by pass valves, pressure valve that feeds the oil cool lines the squirt under the pistons. I now have the motor strapped to a pallet and am test running it before I put it back as it is not the easiest thing to get out. Any one got any ideas.  |
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Post by geeves on Apr 6, 2009 16:48:47 GMT 11
A bit more info please
Whats pressure like at idle and 2000 cold
Whats pressure like at 2000 hot.
What temperature is hot.
That idle pressure is not very different to the reading I get off the factory guage on mine once converted. It may be just that your guage isnt perfect.
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Post by mulover on Apr 7, 2009 13:56:26 GMT 11
The pressure may be a little low as everything should be clean and near new after the rebuild maybe?  |
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Post by James W on Apr 7, 2009 18:48:07 GMT 11
Pressure should be high after an overhaul... new bearings, new oil etc... usually is the highest you will ever see. But, you have done and checked everything I would have done.
If the oil pressure is lower than before overhaul then something is really wrong and does need to be found.
Was the oil pump overhauled?
I have a simular problem with a 3 ton vintage diesel I have done some work on.... the workshop manual has a test procedure to using regulated compressed air to pressureise an oil tank and feed it into the oil galleries of the engine. There then is a specific drip rate for a weight of oil from each big end, main crank etc.... will need a big drip tray for the job. You don't have known drip rates but maybe you might find oil squirting from somewhere it shouldn't?
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Post by Yarno on Apr 7, 2009 23:00:56 GMT 11
I thought the crank was nitrided and shouldn't be ground, not that this would be the problem but would make the crank less resistant to wear.
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Post by ralphie on Apr 9, 2009 19:31:43 GMT 11
Thanks everyone for you suggestions. I like the Idea of pumping oil into the galleies. Migh try that this weekend. Oill pressure when cold at idle seems to be great. 80 psi. Oil pressure when hot at idle, ie Operating temp 80 odd deg, 10 psi. Have also heard that the cranks were nitrided but hey why can you get undersized bearings. Oil pressure before overhaul was great. I never had an external pressure guage on it, but the dash guage was approx 200 kpa when hot. The motor ran a big end bearing on No 3 that is why I pulled the motor down.
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Post by geeves on Apr 9, 2009 20:02:32 GMT 11
Dash guage is kg/cm2 not kpa
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Post by blondininz on May 2, 2009 20:37:38 GMT 11
Take the plate off the oil pump and see if there is any wear marks as when the oil gets hot it will lose pressure.
You can fix this buy getting 1200 wet and dry sand paper and putting it on a dead flat surface like glass and sand with a bit of kero.
This will stop any bypass of oil in the pump...
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Post by Yarno on May 3, 2009 10:53:42 GMT 11
I pulled apart my engine for rebuild yesterday and when I took the filter/cooler part off a steel ball fell out and have no idea where it goes (will have to have a good look later), but if you have lost this it may have something to do with it.. I can't seem to find it in the manual either.
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Post by Benzev on May 7, 2009 23:07:11 GMT 11
It's probably part of the pressure relief valve! If this is open(i.e. no check ball) your oil pressure would be negligible! Another possibility for low oil pressure in these engines is when the rockershaft has been installed the wrong way around leaving the large oil hole down the wrong end!
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