Type 4 oil pump rebuild, Comparison of OEM vs. Samba CNC pump Options

[Superhawk996]

Playing with the idea of what it will take to rebuild a type 4 pump.

The pump that came out of my 2.0L engine is trashed from pumping rust. Both the gears and the housings are seriously scored.



I figured I'd roll the dice and see what might be on Ebay. Took a gamble and bought a used pump hoping I might get some core parts that are useful.



I did end up with a good housing outer. However, the gears are pitted and it the inner housing plate either has a serious casting flaw, or some sort of galvanic corrosion that pitted it. I always struggle with this kind of thing. It really would have minimal effect on the pump and it probably worked OK for a lot of years. However, I'd just like to know that it is perfect going before going into a engine.





It looks like new inner plates are available but at a cost of $150+.

I decided that since I have a donor "scrap" pump, I have nothing to lose by experimenting with machining it.

[Superhawk996]

Time to light up an old thread. I continue to build my Type 4 oil pump collection with the firm belief that the Type 4 oil pump is the way to go for a Type 4 engine.

A while back I acquired one of the CNC Type 4 pumps that was offered on the Samba. I'm finally going to get around to posting a comparion to the OEM pump. In addition, I'll compare it (later on in a separate post to this thread) to a mystery type 4 pump that demonstrates why you want to open up a T4 pump before you use it blindly.

As mentioned previously my final intent is to build a fixture that will let me objectively evaluate T4 pump pressure vs. volume curves. This is still a long ways off since I'll need to machine a fixture as well as buy a flow meter which can get pricy.

Anyway . . . . here we go.



The Samba pump is very nicely done. The main problem I ran into with it is that I thought it would be a duplicate of the OEM pump. It is almost perfectly close in all regards except one. The gear set is 30mm. Doh!



vs. OEM 24mm gearset.



Both gears are the same diameter.



This can be a pro or a con depending on intended use. It will be great for an external oil cooler setup. Otherwise, it will be pumping more oil and sapping more horsepower to drive than the OEM pump. It can be argued that the increased flow will provide better oil pressure when hot, but, there is also such a thing as too much oil pressure. I'll set that aside for now.

You'll notice the housing face plate for the Samba pump is different than the OEM pump in order to accomodate the 30mm gear set. The OEM face plate is flat. The Samba pump has been counterbored in order to fit the 30mm gear into the same space. All machine work on the Samba pump appears to top notch but I haven't done a deep dive on clearance between the pump gears and the pump housing. For the moment, I'm assuming that since it is CNC'd its good. It certainly looks good.

I also notice that the driven shaft is recessed deeper in the driven gear.



Looking at the amount of engagement that the idler shat has with the housing. It is about the same as OEM.

OEM is 6.76mm



Samba is 6.33mm



For me, the fact that the idler gear is in double shear is a big plus for the T4 pump.

Of course the major design flaw with the T4 oil pump is the fact that the idler shaft isn't pinned into the face plate. If the engine is overheated, the difference in thermal expansion between aluminum and steel can create the opportunity for the idler shaft to get pushed outward in the housing toward the cam gear. The easy fix is to pin the idler shaft. This should be done with any reused T4 pump and would also need to be done with the Samba pump.

Here is the comparison of the OEM housing to the Samba housing.

OEM



Samba



And finally, here is a comparion of the exterior of the pumps.