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

[Superhawk996]

Used T4 mystery pump.

Heres a caution to anyone buying a used T4 pump for resue. You need to open them up and make sure it has the right parts inside before you use it.

I do want to note that I've bought several pumps off the forum here as well as e-bay for cores and to understand the variance in these pumps. I don't hold anyone at fault for a pump that isn't 100% OEM. That is a chance you take collecting core pumps.

Previously in this thread I ran across a pump that appears to have been rebuilt with non-OEM parts. I suspect that across 50 years in service, folks have decided to swap in T1 parts occasionally.

We'll here is another case study.

First clue is that the idler shaft is sitting way too deep in the face plate housing. OEM pump from GA000099 on the right for comparison.



Likewise, on the inside of the pump, there isn't enough of the idler shaft exposed to engage with the housing counterbore properly. The engagement would only be about 3mm where as the OEM pump is about 6.7mm.




When I took this pump apart, it was clear that someone had been inside before me. The washers under the nuts on the OEM pumps are a very thin wave washer. On this pump, they were conventional washers.

It seems to be that this is either a misbuild of the pump at the factory or someone has swapped in an idler shaft from some thing other than a T4 pump. I suspect T1, because so many of the guys that played with T4 engines back in the day also played with the VW T1's from the Bug too. Well at least I did! Why would someone swap in a T1 idler shaft into a T4 pump? (IMG:style_emoticons/default/confused24.gif) Your guess is as good as mine.

In the case of this mystery pump, it had some mild scoring of the pump body from pumping chunks and/or rust at some point. The comparion on the right is the pump housing from Engine GA000099 that was low mileage and had a pump in pretty good shape.



I've seen worse, and this one (on left) is likely fine but the scoring of the housing and the gear set will reduce pump efficiency. How much is yet to be determined and is the reason I will eventually build a test setup to measure these pumps.

Here again is a comparison of the this gear set (left) with some scoring of the gear OD vs. GA000099 which is pretty free of scoring on the OD of the gear.



Bottom line to all this. Before you try to resuse a used T4 pump, at least open it up and make sure what you have are the right OEM parts in there and that things aren't too torn up. And like any T4 pump, the idler shaft should be pinned to prevent movment.

[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.

[Nogoodwithusernames]

Another thing to keep an eye out for is the small nuts holding the housing together actually have threaded inserts from the factory (don't know if true of all years though?) that I believe act almost as lock nuts. I noticed that when doing my 1.7 rebuild for my VW and got that answer on my STF thread. (In sig) Might be another indicator of a pump being opened/worked on previously.

That CNC pump is pretty.