Oil Pump Restoration

[G-Man]

I picked up a heap of engine spares last fall and in one of the boxes was a pile of. oil pumps that had all seen better days. Someone had used the best parts to assemble a good pump and discarded the rest.

It seemed to me a good challenge to restore one of these pumps to its original efficiency (what ever that was) so I did a a little bit of investigation...

Gear pumps lose efficiency as the side clearance and gear tip clearance increases. This is compounded in Honda pumps as the pump sucks up everything that is present in the crankcase and pushes it out to the oil filter. The first thing that a clutch wire or bit of gear tooth, piston ring or dirt meets is the gauze surrounding the pump.


pump with gears by graham.curtis, on Flickr


If it gets past that then it goes straight into those lovely gears in the pump. If you look at the gear teeth and the pump housing you will see the effect of this..


damaged gear by graham.curtis, on Flickr

The housing, being softer material doesn't escape the torture. Check out the deep score in the housing to the left of the drive shaft...

housing close-up by graham.curtis, on Flickr

If you find a good pump body and good gears you can just re-assemble and forget about it.

parts for reassembly by graham.curtis, on Flickr

Just for the challenge - I thought I'd take my worst offender and see if I could bring it back to life. I looked at the lovely Capellini upgrades but, as they readily admit, these only work if you have a perfect pump body to start with. If you pump body is damaged they might improve things a little but they are not a real fix.

What I needed was to re-machine the housing to fit larger gears. I did a 'net trawl to find out possibilities and learn a bit about gear design.

As is often the case, I found HPC Gears just up the road and found some 10-tooth gears that were a little larger than the Honda gears. This is all well and good but bigger gears need to be farther apart - in this case by just over 1mm.

It all sounds dead simple on paper but I actually needed to cut some metal and for that the first thing I needed was some tooling.

G

[G-Man]

I built myself a fixture that could be used in my little Chinese milling machine. This holds the pump body square so that I could do the machining without complicated clamping. Notice the nasty scores in that pump body - the worst I could find......

levelling the pump by graham.curtis, on Flickr

Before I could start any machining, I had to measure the gears, which come as a very wide part. I actually bought two but it is possible to get two gears out of each piece.

big gear by graham.curtis, on Flickr

I made a jig which could be used to measure the new centre distance for the gears.

spacing jig by graham.curtis, on Flickr

And then I could start cutting metal. I worked out that I could go up in width to around 6mm compared with the original pump's 4.5mm. This was necessary to clean up some of the scoring anyway.

machining by graham.curtis, on Flickr

I set up to do the top chamber first and then when this was done, I moved the pump over to do the second, repositioned chamber and its new spindle. Before starting the new spindle I put the side cover back on to get everything lined up. The new spindle is 11mm (compared with 9) so I could re-bore a completely new hole for the new spindle in the existing metal.

The new lower gear spindle is stepped. 11mm for the new bore in the casing then 10mm for the gear and then 9mm where it passes through the outer casing.

New cavity by graham.curtis, on Flickr


G

[G-Man]

Time to put everything together. Because the gears come with a 10mm bore I had to make a little bush for the drive spindle and will need a slightly longer drive pin. Also there will be a bush for the driven spindle in the side casing.

Here is the comparison between a standard pump and my restored one. The final gears worked out about 5.7mm thick compared with the original 4.5mm and the outside diameter 23.4 compared with 22 for the originals.

I'm going to build a little test rig to see if there has been any point to all of this. I have learned a bit during this mod so the next one will be a little simpler..... :-)

Assembled gears by graham.curtis, on Flickr


I realise that this isn't a job for the average workshop but I thought that it would be interesting to look at the possibilities of repairing these old pumps and getting a bit of an upgrade at the same time.... :-)

This setup has been run-in for a little while in my pillar drill and can be seen to pump oil...

G

[R100]

Very impressive work, especially the figuring out.
With things like that "close" doesn't count. Precision is everything.

[G-Man]

R100

Thanks for the comments. Not really an 'economic' modification but the pump was scrap and it made an interesting exercise....

This one has had a few experimental tweaks so the next one (if there is one) will be better.

G

[R100]

R100

Thanks for the comments. Not really an 'economic' modification but the pump was scrap and it made an interesting exercise....
This one has had a few experiment al tweaks so the next one (if there is one) will be better.
G

I haven't done any machining of that level. I have done some resurrections of unobtainable things with hand tools (old Ducati, old Beemer). Took forever, economically ridiculous, but the satisfaction level made it all worthwhile.

[G-Man]

R100

Thanks for the comments. Not really an 'economic' modification but the pump was scrap and it made an interesting exercise....
This one has had a few experiment al tweaks so the next one (if there is one) will be better.
G

I haven't done any machining of that level. I have done some resurrections of unobtainable things with hand tools (old Ducati, old Beemer). Took forever, economically ridiculous, but the satisfaction level made it all worthwhile.

Yes - its just so nice to think that these parts can be rescued.

G