Steve Dabrowski
Member
I did a complete rebuild on the engine for my 8N,including grinding crank 0.010" under and installing new Clevite rod and main inserts. Plasti-gaged the mains on reassembly and had about 0.015 clearance , but was lazy with the rods so did not measure them-have done several engines and not had any problems with new bearings and ground crank. So I let it go.
Prior to rebuilding the engine it had not had any oil pressure issues that I recalled and when I took it apart the bearings were standard and had normal wear. But I was going to a lot of trouble so I decided to rebuild my oil pump just in case. I wanted to buy a tool for the bushing but at the time none were available. Bought a rebuild kit and went to work. Kit was manufactured in India. Had the new bushing installed and reamed to fit the new driver gear shaft (0.0005" clearance)at my favorite machine shop. When fitting the gears a couple of teeth were high so I lapped them down until I had an even tooth to body clearance of about 0.002" all around. Assembled it and the engine.
Once it started I noticed the oil pressure was good 35-40 psi at start up but dropped off to around 10-15 after fully warming up. Changed gages three times to make sure that was not the issue, then went from 15-40 to 30 wt oil, with no real change. After a longer hour run the pressure would drop to 9-10 when hot at idle and not get more than 10-13 at half speed. Changed then stretched relief valve spring but no effect.
Decided no option but to look inside and check clearances again, maybe I screwed up trusting the rod clearances. Pulled engine and pan, checked main and rod clearances and found 0.0015"-0.00175" on all except #3 main and #4 rod which were up to 0.002" with slight scoring on the rod journal, but nothing serious-everything really ok and no reason to believe lost pressure came from here.
Rigged up a vacuum set up to see if I could find any leaks in the pump from the pick-up tube and using a brake bleeder pump hooked to the pick-up tube and my finger over the pump's output port pulled 25 in hg and watched it slowly drop away. Put some oil in the rear recess of the drive gear so it would cover the bushing end there and re pulled 25 in hg and it stayed so those components seemed ok.
Removing the pick-up from the pump I rechecked gear to body clearance and still around 0.002". Then I noticed the gears were a bit below the face of the body so I checked this and found they were about 0.007" recessed. Checked the used gasket thickness and that was 0.007" thick so that meant I was running 0.014" end clearance on the gears which is way too much-0.003-0.004 is the norm on almost all gear pumps.
I removed the gears and measured the width and compared to the original gears and sure enough the new are 0.007" narrower. The old gears installed are flush with the face of the pump so clearance is determined by the gasket only.
Ordered another kit from DC and found the gears in it (TISCO) were even narrower (about 0.008") and gasket again 0.007". Ordered three gaskets from CNH and they came in at 0.006 which compressed to 0.005" which was the best clearance I can get with today's manufactured gasket I believe. I would like to tighten it up to .003-.004" and can do that with some kraft paper or, interestingly enough, those 3M yellow sticky back note pad papers (measure 0.0037" thick and very consistent). My only concern is the longevity of the paper in the oil.
To add insult to injury I got a new TISCO bushing tool kit also from DC and when I put it in place, just try the fit, it puts the bushing reamer hole about 0.30-.40" off the center where it should go-so watch out. The other point is the end clearance- it appears all new gears are shorter than original so this should be checked and if necessary mill the face of the pump the bring the gears flush.
My theory on this is that these gears are used on new replacement pumps and are probably flush on those, but the original Ford units were slightly different. The specs shown for the original pump do not specify end clearance for the gears and I suspect that was because Ford made the gears all the same and the gaskets available then were just right-it was not an issue to watch. But now with every third world country making stuff to their own specs it can be a worry.
Prior to rebuilding the engine it had not had any oil pressure issues that I recalled and when I took it apart the bearings were standard and had normal wear. But I was going to a lot of trouble so I decided to rebuild my oil pump just in case. I wanted to buy a tool for the bushing but at the time none were available. Bought a rebuild kit and went to work. Kit was manufactured in India. Had the new bushing installed and reamed to fit the new driver gear shaft (0.0005" clearance)at my favorite machine shop. When fitting the gears a couple of teeth were high so I lapped them down until I had an even tooth to body clearance of about 0.002" all around. Assembled it and the engine.
Once it started I noticed the oil pressure was good 35-40 psi at start up but dropped off to around 10-15 after fully warming up. Changed gages three times to make sure that was not the issue, then went from 15-40 to 30 wt oil, with no real change. After a longer hour run the pressure would drop to 9-10 when hot at idle and not get more than 10-13 at half speed. Changed then stretched relief valve spring but no effect.
Decided no option but to look inside and check clearances again, maybe I screwed up trusting the rod clearances. Pulled engine and pan, checked main and rod clearances and found 0.0015"-0.00175" on all except #3 main and #4 rod which were up to 0.002" with slight scoring on the rod journal, but nothing serious-everything really ok and no reason to believe lost pressure came from here.
Rigged up a vacuum set up to see if I could find any leaks in the pump from the pick-up tube and using a brake bleeder pump hooked to the pick-up tube and my finger over the pump's output port pulled 25 in hg and watched it slowly drop away. Put some oil in the rear recess of the drive gear so it would cover the bushing end there and re pulled 25 in hg and it stayed so those components seemed ok.
Removing the pick-up from the pump I rechecked gear to body clearance and still around 0.002". Then I noticed the gears were a bit below the face of the body so I checked this and found they were about 0.007" recessed. Checked the used gasket thickness and that was 0.007" thick so that meant I was running 0.014" end clearance on the gears which is way too much-0.003-0.004 is the norm on almost all gear pumps.
I removed the gears and measured the width and compared to the original gears and sure enough the new are 0.007" narrower. The old gears installed are flush with the face of the pump so clearance is determined by the gasket only.
Ordered another kit from DC and found the gears in it (TISCO) were even narrower (about 0.008") and gasket again 0.007". Ordered three gaskets from CNH and they came in at 0.006 which compressed to 0.005" which was the best clearance I can get with today's manufactured gasket I believe. I would like to tighten it up to .003-.004" and can do that with some kraft paper or, interestingly enough, those 3M yellow sticky back note pad papers (measure 0.0037" thick and very consistent). My only concern is the longevity of the paper in the oil.
To add insult to injury I got a new TISCO bushing tool kit also from DC and when I put it in place, just try the fit, it puts the bushing reamer hole about 0.30-.40" off the center where it should go-so watch out. The other point is the end clearance- it appears all new gears are shorter than original so this should be checked and if necessary mill the face of the pump the bring the gears flush.
My theory on this is that these gears are used on new replacement pumps and are probably flush on those, but the original Ford units were slightly different. The specs shown for the original pump do not specify end clearance for the gears and I suspect that was because Ford made the gears all the same and the gaskets available then were just right-it was not an issue to watch. But now with every third world country making stuff to their own specs it can be a worry.
