Keith Warren Posted January 21, 2021 Report Share Posted January 21, 2021 (edited) Hi your thoughts on this Having time in lockdown I have taken the sump off while doing the oil change oil pressure was good as pump was replaced with a County one around 10,000 miles ago but removed it to check then compared it with the original and found the holes in the County one to be smaller not sure to open out or should this be OK left has any one else noticed this? Thanks for your thoughts Keith Edited January 21, 2021 by Keith Warren Spelling Quote Link to post Share on other sites
john.r.davies Posted January 21, 2021 Report Share Posted January 21, 2021 (edited) Quote "oil pressure was good " So, NBDF (Not Broke, Don't Fix)! The oilways are much, much narrower, and flow depends on the fourth power of the radius. The difference seen here is insignificant, JOhn Edited January 21, 2021 by john.r.davies Quote Link to post Share on other sites
JohnC Posted January 21, 2021 Report Share Posted January 21, 2021 1 hour ago, john.r.davies said: So, NBDF (Not Broke, Don't Fix)! Best advice anyone will ever give or receive. Quote Link to post Share on other sites
astontr6 Posted January 21, 2021 Report Share Posted January 21, 2021 6 hours ago, john.r.davies said: Quote "oil pressure was good " So, NBDF (Not Broke, Don't Fix)! The oilways are much, much narrower, and flow depends on the fourth power of the radius. The difference seen here is insignificant, JOhn The most important thing is to reduce the end float in the shaft down to 0.0015". This does have a major effect on oil pressure when hot! This always done blue printed pumps. Bruce. Quote Link to post Share on other sites
michaeldavis39 Posted January 21, 2021 Report Share Posted January 21, 2021 Aston are you talking about where the head of pump is sanded down using fine wet and dry on a piece of glass?? Quote Link to post Share on other sites
astontr6 Posted January 22, 2021 Report Share Posted January 22, 2021 11 hours ago, michaeldavis39 said: Aston are you talking about where the head of pump is sanded down using fine wet and dry on a piece of glass?? This where the rotor is placed inside the outer body of the oil pump. Then turned upside down and steel rule is placed across the top and using feeler gauges measure the gap between body and rotors. Some County Pumps that I have seen are bad, in one case 0.012". Yes as you describe above it can be done that way to remove metal from the outer body. Whilst machining the body, you must also make sure that the inner and outer rotors are of identical length or you will have a different end float for each component. Sometimes this work has to be done in a machine shop. This work is sometimes referred to as Blue Printing. Bruce, Quote Link to post Share on other sites
ed_h Posted January 22, 2021 Report Share Posted January 22, 2021 If there is any scoring on the cover of the pump, the straight edge/feeler gage can give a false reading of true clearance. Linishing the cover flat will fix that. Ed Quote Link to post Share on other sites
Keith Warren Posted January 22, 2021 Author Report Share Posted January 22, 2021 Thanks for the advice, outer rotor to pump body is .003” outer to inner rotor .0025” cover plate was in good condition having only done 10,000 miles but gave it a light lapping, end float is .0015 so on the tight side. I have opened the ports out to match the original pump case so ready for fitting. Cheers Keith Quote Link to post Share on other sites
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