almost overhaul

kub6040

Well-known Member
Well as the heading goes I almost overhauled a 8n and lost oil pressure in the process , what did I over look.
 
Front mount .007 main clearance , pulled the spring in relief valve to gain a little tension on the valve ? New gears and bushing in oil pump.
 
(quoted from post at 01:00:12 11/15/15) Will that cause 10 pounds of oil pressure idling? 20 wide
open ?

Ideally main bearing clearance should be close to .001-.002 and as Mr. Geiger says .005 is the wear limit. That would be good pressure with that much clearance. Playiing with the the oil pressure relief spring won't fix low oil pressure. The valve doesn't doesn't even crack until close to 50 PSI. You need to correct the bearing clearances if you want to get decent oil pressure.

TOH
 
I am assuming that you put in new main bearings. Provided that you put in the correct ones, your oil pressure should have at least stayed the same even if your tolerances are to high. With new bearings the tolerances should be less than they were with the old bearings. If you didn't replace the main bearings, the oil pressure should be the same as it was before, if something else isn't wrong. I would be more inclined to think you have an oil pump issue, if in fact, the oil pressure is actually low. Have you checked the pressure with another gauge?
 
(quoted from post at 13:09:50 11/15/15) I am assuming that you put in new main bearings. Provided that you put in the correct ones, your oil pressure should have at least stayed the same even if your tolerances are to high. With new bearings the tolerances should be less than they were with the old bearings. If you didn't replace the main bearings, the oil pressure should be the same as it was before, if something else isn't wrong. I would be more inclined to think you have an oil pump issue, if in fact, the oil pressure is actually low. Have you checked the pressure with another gauge?

I'll bet a LOT that the oil pressure gets measurably better if the main and rod bearing [b:14181e9af4][u:14181e9af4]clearances[/u:14181e9af4][/b:14181e9af4] are all brought back into specification.

TOH
 
(quoted from post at 16:53:11 11/15/15) Yeh, and probably the ham fist oil pump job to,with less oil pressure than before,

Indeed. The fact that it was assembled with .007 main bearing clearance doesn't bode well for the rest of the job :roll:

TOH
 
OK, let's just back up a bit here... Did you look at the size markings on the old bearing inserts (could have been .001' or .002", or .003" or .005" US), or mic them as to thickness vs the new ones you installed?

Reminds me of a poster I have hanging in the shop "If It Ain't Broke We'll Fix It 'til It Is!".

Sometimes, despite even our best attempts, that's what happens.

And, if one does not check the basics, like bearing markings, or measure them, it is even more likely to happen!

And, it seems it DID!
 
(quoted from post at 18:26:58 11/15/15)
(quoted from post at 13:09:50 11/15/15) I am assuming that you put in new main bearings. Provided that you put in the correct ones, your oil pressure should have at least stayed the same even if your tolerances are to high. With new bearings the tolerances should be less than they were with the old bearings. If you didn't replace the main bearings, the oil pressure should be the same as it was before, if something else isn't wrong. I would be more inclined to think you have an oil pump issue, if in fact, the oil pressure is actually low. Have you checked the pressure with another gauge?

I'll bet a LOT that the oil pressure gets measurably better if the main and rod bearing [b:3275ed9de6][u:3275ed9de6]clearances[/u:3275ed9de6][/b:3275ed9de6] are all brought back into specification.

TOH
I'm sure it would, but that was not my point.
 
Ok folks I got oil pressure fixed I hope loading it for work tomorrow , ran it 2 hours today with good for me oil pressure 25-45 hot and 40+ cold so I am happy . I will try not to embarrass myself by asking oil pressure questions when on a budget , just hoped since this is a 8n that I may have overlooked something .
 
(quoted from post at 23:22:24 11/20/15) Ok folks I got oil pressure fixed I hope loading it for work tomorrow , ran it 2 hours today with good for me oil pressure 25-45 hot and 40+ cold so I am happy . I will try not to embarrass myself by asking oil pressure questions when on a budget , just hoped since this is a 8n that I may have overlooked something .

I wouldn't worry about embarrassing yourself by asking questions. People who are afraid of that sort of "embarrassment" go through life learning very little ;-)

So what did you do to get the pressure back up? Your new numbers are "factory fresh" pressures.

TOH
 
(quoted from post at 19:27:36 11/22/15) TOH , thanks I had the crank turned and used appropriate
bearings .

You are more than welcome. The much maligned N-series oil pump seems to have become the whipping boy for just about everything these days. Amazing how much the oil pressure drops when the main clearances open up just a few thou....

TOH
 

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