Topic: Drilled Gear Shaft for Oil Pump

[Ellz10]

Just curious how many of you, if any, have taken the liberty of drilling holes in the gear shaft of your oil pump to shave weight and perhaps create less drag?

I noticed on some of the older diagrams/microfiches that the gear is already drilled, but I have yet to encounter one in person that presents itself that way.

I figured that while I have the pump apart, might as well ask and see if doing this little modification would benefit.

[Don R]

 I always wonder what was Honda thinking when they made a change, cost savings or lack of a performance benefit? 
  I'd say if you have not lightened the flywheel and crankshaft, gotten lighter rods, light cam chain sprocket,  or drilled the clutch basket there are far bigger rotating weight savings that you are already missing. I doubt even an engine dyno could measure the weight savings of the oil pump gear. All that said, if it gives you a good feeling go ahead and do it.
  I'm inspired to look through my pump collection to see if any gears are lightened.

[Jerry Rxman Griffin aka MuthaF'er]

My only concern would be creating an out of balance situation

[Ellz10]

I always wonder what was Honda thinking when they made a change, cost savings or lack of a performance benefit? 
  I'd say if you have not lightened the flywheel and crankshaft, gotten lighter rods, light cam chain sprocket,  or drilled the clutch basket there are far bigger rotating weight savings that you are already missing. I doubt even an engine dyno could measure the weight savings of the oil pump gear. All that said, if it gives you a good feeling go ahead and do it.
  I'm inspired to look through my pump collection to see if any gears are lightened.

I've done all you mentioned, save the lighter cam chain - or maybe I did, seeing as I went with a Tsubaki Cam chain.

I've got a few pumps laying around so I'm gunna go ahead and drill this one and see how she operates.

My only concern would be creating an out of balance situation

In what way are you thinking? 🤔

[Don R]

 rock on brother. I was trying to say cam gear. Some are significantly lighter than the solid ones.

[Ellz10]

rock on brother. I was trying to say cam gear. Some are significantly lighter than the solid ones.

So a little update, or rather a conclusion, insofar that I have NO IDEA what these gears are made of, because I cannot for the life of me get even a scratch to penetrate the surface. I tried a tap, the drill press, a step-drill bit, no dice.

It's got to be some sort of hardened steel.

[Jerry Rxman Griffin aka MuthaF'er]

I can't say that the gear is rotationally balanced but probably better than taking a solid center gear and manually drilling it out. Like any other rotational piece it is best to have in a balanced state whether that be a crankshaft, charging rotor, rods, etc. Better balance gives better operational results  ie smoother longer life span

[calj737]

rock on brother. I was trying to say cam gear. Some are significantly lighter than the solid ones.

So a little update, or rather a conclusion, insofar that I have NO IDEA what these gears are made of, because I cannot for the life of me get even a scratch to penetrate the surface. I tried a tap, the drill press, a step-drill bit, no dice.

It's got to be some sort of hardened steel.

A good quality carbide bit, drill press, slow speed, proper cutting fluid. Will go right through.

[simon#42]

I would think very carefully before doing this . The gears might not be drilled any more for a reason . It could be that the gear cracked or that having more inertia was easier on the pump or pump drive . Also drilling it will create more drag in oil not less . There are much better areas to save reciprocal weight if that’s what you are after .

[MRieck]

There is no gain on the rotational piece...make one out of Ti or something else light.