Post by Deleted on Dec 13, 2008 18:59:14 GMT -5
So I finally got the oil pump shaft bore bushing mod done (delayed due to busy-ness not laziness). This is a long post, so get your popcorn now. I would not normally post so many pictures, but due to the somewhat mythical status of the bushing mod I went into detail. This method represents one of many ways that this modification can be done. The tooling used in this procedure is beyond the resources of the average person. I think it could be done very well in a do-it-yourself situation with a decent drill press, jig, guides, proper drill bits and reamers, test indicator, and C-clamp, dry ice, etc... I plan on exploring that method at a later time, and would ask that any questions pertaining to that method be asked in a new thread.
Problem Summary:
The oil pump rotor shaft bore in the aluminum crankcase plate wears out and tapers creating an eccentric rotation of the rotor itself.
Solution:
Bore out the rotor shaft bore and re-bush to the proper bore size.
I had my 3 crankcase plates Jet Washed at the local machine shop for $5.00 US each. When I got them back I was able to see the considerable wear in the shaft bore that was not apparent before the cleaning. The scoring in the shaft bore was, qualitatively speaking, approximately 3 to 5 times worse than the scoring on the steel rotor. I imagine that the worn aluminum particles pack in the grooves like a hard paste, giving the illusion that the bore is not worn. I measured a taper of between (.002"-.004")/in. in the three c. plates I have.
I looked for an Oilite bushing for this application, but due to the unusual ID size (.491"/ 12.47 mm) I was not able to locate one. Machining an Oilite bushing smears the surface pores of the bushing thereby negating the Oilite characteristics.
I went with bearing bronze. I ended up using finished bushings (.375" ID/.625" OD .75"L) that I bought at Mcquire Bearing ( for Portland peeps) for ~$3.00 ea. I also bought a 14" stick of .625 bronze for $9.00 at Alaskan Copper and Brass (again for Portlanders) as a back-up. The measured OD of the bushings ranged from .6273"-.6277". The measured OD of the stick of bronze was ~.637". The bushing below right is bored to final ID.
The measured OD of the new oil pump rotor shaft is .491". With references from my instructor at Clackamas Community College (CCC) we determined that a .0006" slip fit with the bushing would be adequate.
I bored the bushings on a horizontal lathe using a small offset boring bar. Using .001" plug gauges I bored the ID until the .491" gauge fit easily within the bore, but the .492" did not fit at all. I then inserted the rotor to make sure it spun freely.
The work on the crankcase plate all took place on a vertical end mill. First we measured (using a height gauge, test indicator, and surface plate) the gasket surface of the oil pump for parallelism with the gasket surface of the back of the plate to see if we could just bolt the crankcase plate to the table of the end mill (sorry I forgot to take pics). All 3 of my plates were within .0005", which was close enough for me.
The first crankcase plate was bolted to the table and the oil pump gasket surface was measured again to see if the table of the endmill was off. The dial face in the pic was not yet zeroed, so that wasn't the actual reading.
In this case the table was off, so I dialed in the head of the endmill.
After the datum was accurately established, the bore had to be centered under the head using the test indicator, once again. I am showing all of this to emphasize the importance of accuracy in this regard. If you re-bush the shaft bore axially or angularly off-center from the drive...well it doesn't take too much imagination to see the problems that would create.
So after patient and meticulous centering, the bore was opened up by first plunging a .5" center-cutting endmill and then a .613" center-cutting endmill.
This is the .613" bore:
The final bore diameter was created using a small offset boring bar and adjustable boring head.
The final bore was .001"-.0013" smaller than the outer diameter of the bushing. According to thermal expansion coefficients this interference fit will be good up to 400-525 degrees F, respectively. If you want a larger interference fit I would recommend the hot/cold strategy...freeze or dry ice the bushing and warm the (whole) plate. Dry icing alone would probably be adequate. There is always lock-tite and other methods if your are leary of the fit.
Final bore before bushing:
The bushing was pressed in place using the quill of the endmill. The plate was shimmed underneath for support. A .75" roughing endmill was installed backwards in the collet and the bushing was gently yet firmly pecked into place.
The only thing left was to mill (.75" center-cutting) off the bushing material that extended out the back of the plate.
MANY THANKS TO BOB DELGATTO AND MARK SCHMIDT AT CCC FOR HELPING ME WITH THIS, LETTING ME USE THE FACILITIES, AND FOR THEIR GENERAL AWESOMENESS. SUPER SOLID FAVOR. THANK YOU! AND ON BEHALF OF THE JUSTY COMMUNITY, THANK YOU.
Problem Summary:
The oil pump rotor shaft bore in the aluminum crankcase plate wears out and tapers creating an eccentric rotation of the rotor itself.
Solution:
Bore out the rotor shaft bore and re-bush to the proper bore size.
I had my 3 crankcase plates Jet Washed at the local machine shop for $5.00 US each. When I got them back I was able to see the considerable wear in the shaft bore that was not apparent before the cleaning. The scoring in the shaft bore was, qualitatively speaking, approximately 3 to 5 times worse than the scoring on the steel rotor. I imagine that the worn aluminum particles pack in the grooves like a hard paste, giving the illusion that the bore is not worn. I measured a taper of between (.002"-.004")/in. in the three c. plates I have.
I looked for an Oilite bushing for this application, but due to the unusual ID size (.491"/ 12.47 mm) I was not able to locate one. Machining an Oilite bushing smears the surface pores of the bushing thereby negating the Oilite characteristics.
I went with bearing bronze. I ended up using finished bushings (.375" ID/.625" OD .75"L) that I bought at Mcquire Bearing ( for Portland peeps) for ~$3.00 ea. I also bought a 14" stick of .625 bronze for $9.00 at Alaskan Copper and Brass (again for Portlanders) as a back-up. The measured OD of the bushings ranged from .6273"-.6277". The measured OD of the stick of bronze was ~.637". The bushing below right is bored to final ID.
The measured OD of the new oil pump rotor shaft is .491". With references from my instructor at Clackamas Community College (CCC) we determined that a .0006" slip fit with the bushing would be adequate.
I bored the bushings on a horizontal lathe using a small offset boring bar. Using .001" plug gauges I bored the ID until the .491" gauge fit easily within the bore, but the .492" did not fit at all. I then inserted the rotor to make sure it spun freely.
The work on the crankcase plate all took place on a vertical end mill. First we measured (using a height gauge, test indicator, and surface plate) the gasket surface of the oil pump for parallelism with the gasket surface of the back of the plate to see if we could just bolt the crankcase plate to the table of the end mill (sorry I forgot to take pics). All 3 of my plates were within .0005", which was close enough for me.
The first crankcase plate was bolted to the table and the oil pump gasket surface was measured again to see if the table of the endmill was off. The dial face in the pic was not yet zeroed, so that wasn't the actual reading.
In this case the table was off, so I dialed in the head of the endmill.
After the datum was accurately established, the bore had to be centered under the head using the test indicator, once again. I am showing all of this to emphasize the importance of accuracy in this regard. If you re-bush the shaft bore axially or angularly off-center from the drive...well it doesn't take too much imagination to see the problems that would create.
So after patient and meticulous centering, the bore was opened up by first plunging a .5" center-cutting endmill and then a .613" center-cutting endmill.
This is the .613" bore:
The final bore diameter was created using a small offset boring bar and adjustable boring head.
The final bore was .001"-.0013" smaller than the outer diameter of the bushing. According to thermal expansion coefficients this interference fit will be good up to 400-525 degrees F, respectively. If you want a larger interference fit I would recommend the hot/cold strategy...freeze or dry ice the bushing and warm the (whole) plate. Dry icing alone would probably be adequate. There is always lock-tite and other methods if your are leary of the fit.
Final bore before bushing:
The bushing was pressed in place using the quill of the endmill. The plate was shimmed underneath for support. A .75" roughing endmill was installed backwards in the collet and the bushing was gently yet firmly pecked into place.
The only thing left was to mill (.75" center-cutting) off the bushing material that extended out the back of the plate.
;D
;D ;D
;D ;D
MANY THANKS TO BOB DELGATTO AND MARK SCHMIDT AT CCC FOR HELPING ME WITH THIS, LETTING ME USE THE FACILITIES, AND FOR THEIR GENERAL AWESOMENESS. SUPER SOLID FAVOR. THANK YOU! AND ON BEHALF OF THE JUSTY COMMUNITY, THANK YOU.