Ol Pump

I completed working on my 48 8N oil pump and reinstalled the engine and started it up and ran it for a couple of hours today. Result was that by eliminating the excess end clearance that came from the new replacement gears that are 0.007-0.008" thinner than the original along with the 0.007-0.008 thick gasket that comes in the kits I gained back 10-15 PSI hot oil pressure.

I re-installed my original pump gears which are flush with the pump face and used a gasket that I got from New Holland which was a couple of thousands thinner than comes in the TISCO pump kits. I further compressed the CNH gasket to about 0.005" thick before installing it. I plasti-gaged the end clearance and ended up with .004-.005 all said and done.

Now at cold start up I have 45 PSI, after warm-up it runs about 35 PSI at half throttle and after a couple of hours drops to a steady 27-30 PSI, where as before after that time it would be around 12-15 PSI. Hot idle is now 18-20 PSI where before it was about 8-10 PSI.

Lesson in this, two fold. First keep a record of pressure before pulling the engine apart and don't fix it if it ain't broke. Second, if you replace the gears be sure they are flush with the face or plan on milling the pump face so they are, then get a good thin gasket from CNH or cut one from paper so you end up with 0.003-0.005 maximum end clearance on the gears. It is a big deal and the 0.014" clearance you will get using the gears and gasket in the rebuild kit will result in low pressure.

I agree ...Good Work...

####### Chinese junk!

Wonder if silicone glue would hold up as a gasket in the oil pump. That would remove the gasket thickness completely. I use it on things like trumpet housings etc and have great results.

Lots of modern engines use silicone totally on non compression locations.

Zane

I considered it, but worried that it might squeeze into the gear chamber. If the gear faces are flush with the housing the gasket then controls the clearance. Others have indicated they have had success in using paper products so there are kraft wrapping papers that are 0.003" and the yellow sticky back note paper that 3M makes also measures 0.0035" and I believe that would do the trick.

(quoted from post at 11:05:24 07/06/15) I considered it, but worried that it might squeeze into the gear chamber. If the gear faces are flush with the housing the gasket then controls the clearance. Others have indicated they have had success in using paper products so there are kraft wrapping papers that are 0.003" and the yellow sticky back note paper that 3M makes also measures 0.0035" and I believe that would do the trick.

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This isn't a tough sealing job. I'd paint a thin coating of Permatex Aviation Gasket Maker on the sealing area of the body, dispense with the paper gasket, and sleep like a baby. In fact I have done exactly that in the past.....

TOH

There is a product called bedplate sealer made by Permatex for sealing between two machined surfaces. It's an anaerobic sealer and they are proud of it. I have half of a tube left from an engine job I did a couple of years ago. It looks like cherry jelly.

(quoted from post at 22:10:40 07/06/15)

(quoted from post at 11:05:24 07/06/15) I considered it, but worried that it might squeeze into the gear chamber. If the gear faces are flush with the housing the gasket then controls the clearance. Others have indicated they have had success in using paper products so there are kraft wrapping papers that are 0.003" and the yellow sticky back note paper that 3M makes also measures 0.0035" and I believe that would do the trick.

Click to expand...

This isn't a tough sealing job. I'd paint a thin coating of Permatex Aviation Gasket Maker on the sealing area of the body, dispense with the paper gasket, and sleep like a baby. In fact I have done exactly that in the past.....

TOH

Click to expand...

I have ran across quite a few oil pumps that did not use a gasket I also paint'em with Aviation Gasket Maker when I run into this...

Permatex 51813

I would have been concerned then that I had too little clearance-although if it doesn't bind after assembly it might be ok, but things tend to grow some with the heat so that might not be the best test.

I'm ok with the clearance I have-it resulted in the pressure meeting the 27 PSI hot quoted in the original owner's manual.

Since one cannot find any real clearance specs on the pump (probably because the Ford Motor Company made the parts to fit correctly and the gaskets there was no need for a spec to the world-if you
rebuilt it you used Ford parts and they fit right-no issues!) I'll go out on a limb and say to try to get less than 0.003" tooth to housing clearance, ensure the rotating gears are flush with the face of the
housing and try to achieve 0.003"-0.004" end clearance.

(quoted from post at 20:28:48 07/06/15) I would have been concerned then that I had too little clearance-although if it doesn't bind after assembly it might be ok, but things tend to grow some with the heat so that might not be the best test.

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I'll go out on a limb and say to try to get less than 0.003" tooth to housing clearance, ensure the rotating gears are flush with the face of the
housing and try to achieve 0.003"-0.004" end clearance.

Click to expand...

The thermal expansion of the parts is linear and affects the opening depth as well as the length of the gear. In other words they are similar metals (iron/steel) and for all practical purposes everything grows and shrinks at the same rate. If .003 or less clearance at room temperature is OK with the gear tip to housing I would expect the same of the end clearance.

TOH