Thread: 101 - Oil Pumps

I would have thought the sole functional difference between the 101 pump and the later pump would be the pump cover and filter head. I'd be taking the 101 pump cover off and inspecting it, a light skim and it should be ready to bolt to the 3.9 front cover. Make sure you have the correct gasket on hand as this controls the clearance of the gears to the cover.

Yes, the 101 springs do sit flat.
Not sure that would improve the situation.

Some random thoughts...
Has the relief valve in the 3.5 pump been checked?
Can the valve be swapped for the one in the 3.9 pump and retest the pressures?


A question for the brains trust...
Could the internals from the good 3.9 pump be fitted into the original 3.5 housing?

Originally Posted by alien

Some random thoughts...
Has the relief valve in the 3.5 pump been checked?
Can the valve be swapped for the one in the 3.9 pump and retest the pressures?


A question for the brains trust...
Could the internals from the good 3.9 pump be fitted into the original 3.5 housing?

The oil pump gears live inside the cavity in the front cover and can only be swapped if the drive shaft and gear depth is the same. The relief valve is part of the cover/filter mount and should be swapped as part of that item. I found some pictures of a 101 engine swap that shows the correct filter mount fitted to a donor engine:

The Neals' 101 engine swap

Looking at the pictures which are pretty small, it seems to me that the oil pump is the same as a normal 3.5/3.9 but there is a "sandwich" on the bottom which has hoses for the oil cooler and a 90degree mount for the filter.
Have you still got that bit?
An old pump can be revitalised with new gears and a new end plate and a clean up of the housing if it is scored. Someone used to do inserts for these long ago.
The 3.9 pump is much the same as a 3.5 pump although the gears are a bit longer, but otherwise it is the same.
Regards Philip A

Have you talked to AJ in Melbourne........he would know whats, what and may have secondhand/new 101 oil pumps.
Using the standard 101 oil pump is a good thing as you get plenty of clearance and to use the standard 101 oil cooler if you want it.
The army had it sorted in the first place.
Yes 101 springs sit mostly flat.

Hi All,

I've spoken to AJ in Melbourne... And here is my current plan:

* Purchase new gears for the oil pump
* Check clearances
* Purchase a second hand case - if my case looks like it is damaged.

The issue (low oil pressure) only started on the 3.9, when my mechanic transferred the oil pump from the 3.5 onto the 3.9. When the engine is cold, it's getting about 30psi (AJ says it should be 50). When the engine idles - it is getting between 0-5psi (AJ says it should be 20+)

Speaking to AJ - it could be all manner of things (oil pickup could be loose, gears are loose or worn, pressure relief value stuck, gasket installed incorrectly, etc).

Speaking to my mechanic afterwards - yes he primed the pump, yes he checked the clearances, yes he checked the pressure relieve value. The engine is not tappety or rattly - and it has only started to loose pressure when we installed the original oil pump from the 3.5

I very much hope (and doubt) that the engine is the issue - because the problem only started when the old pump was installed..

So - buy new gears, possibly buy the second hand casing, and try again...

I'll keep everybody updated.

Cheers,
GG.

Take note
The main thing which governs engine oil pressure is bearing clearances, especially when the engine is hot.
If the old oil pump was working OK in the old motor and the same pump doesn't work to well in the current motor, different bearing clearances would highly likely be a factor.
Oil pressure is not everything.
So long as the oil is available at the bearing is the main thing.
It makes little difference if it is delivered at 5 psi or 80 psi as hydrodynamic wedge action takes the 5000 psi oil load on the bearing surfaces.