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]

T4 Mystery Pumps -- The plot thickens

Recently bought a couple more used T4 pumps for futher investigation.

One had an idler shaft that was recessed pretty deeply. The other (right) had an idler shaft that was peened as preventative measure to keep the shaft from moving.

I'm going to compare these to the low mile, OEM pump that came out of GA000099 (center) which shows virtually no wear and is the closest thing I have to a baseline of what the OEM pump should be.



On the pump (far left) with the deeply recessed idler shaft, this is the third I've seen this way. The other two, I belived to have been some sort of Type 1 pump parts swap. This was primarily because one of them clearly had a diferent set of pump gears vs. any others I've seen come out of a T4 pump to date.

The idler shaft has a slight protrusion behind the gear that sticks out. This is by design. It goes into the counter bore in the pump housing. This is the feature of the T4 pump that puts the idler gear into double shear vs. a Type 1 pump in single shear.

So after measuring all three pumps, it was very curious to me that all three pumps have EXACTLY 6.59mm of idler shaft protrusion behind the idler gear.



If someone had messed with the idler shaft and replaced it with a different (shorter) shaft, I'd expect some variation in this protrusion length. I saw that variation in one of the previous pumps. In that case, there was barely enough of the idler shaft sticking out to engage the counter bore.

(IMG:style_emoticons/default/idea.gif) Hmm. Now I'm starting to think that VW actually changed the T4 pumps somewhere along the way to address the possibility of the idler shaft getting pushed out into the cam gear. (IMG:style_emoticons/default/WTF.gif) Anyone else have T4 pumps that you've seen with the deeply recessed idler shafts? If so please feel free to post info here to confirm or deny this possibility.

Otherwise, these two pumps look pretty resonable to what I'd expect from a used T4 pump. Some mild scoring of the main housings was evident from pumping some usual garbage. On the whole, both pumps should be completely serviceable after pinning the ider shafts. The one thing that I see as a downside to the short ider shafts is that it will be much more difficult to pin the idler shaft since there is less of it to work with w.r.t how much shaft is engaged in the housing.

The other curious thing about the pump on the left is that the driven gear has the drive shaft with the drive tang counter sunk to the end of the driven gear. In the past, when I've seen this I had assumed that it was the result of swapping in T1 parts. Now I'm not so sure. (IMG:style_emoticons/default/confused24.gif)

As a couple final items of note, both these pumps had OEM washers and nuts unlike a couple of the earlier pumps. Sample size of T4 pumps is now 10 including the CNC Samba pump previously reviewed.