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billjam billjam is offline
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Join Date: Aug 2007
Location: Perth, Western Australia
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How to fit scavenge pump to SC camshaft

I spent some time looking at this today and have found that the solution is quite simple IF you don't want an air-pump.
As Mike suggested, bolting the scavenge pump directly to the camshaft housing is the way to go but there are a few things to watch out for. I took a bunch of photos (before and after) so anyone wanting to fit SC cams and delete the air-pump drive can follow what I have done.

Deleting the air-pump drive housing and mounting the scavenge pump to the camshaft housing will move the scavenge pump closer to the engine by 48mm.
This means that the oil suction pipe from the turbo needs to be shortened by about 48mm (cut and braze or silver solder, or use hose and clamps to rejoin pipe after cutting).
The oil pipe from scavenge pump to tank needs to be bent rearwards to new pump location (see photos).
This pipe will interfere with the sheetmetal however a simple notch is all that is required.
Deletion of the air-pump drive housing leaves a large gap in the sheetmetal above the scavenge pump. It is fairly simple to fill this gap with a small panel.

The SC camshafts that I am using (left 930.105.147.9R, right 930.105.148.9R) have 5mm dia holes at 25mm centres in the end of the front journal.
These holes are the correct size to tap M6 but the camshafts are too hard to tap with ordinary high-speed steel taps, so my preferred option of screwing in a socket-head cap screw got canned. I didn't want to risk breaking off a tap in the end of the camshaft so I have opted to use 5mm roll pins (25mm long).
The roll pins need to protrude 10mm (+/- 1mm) from the end of the camshaft to fully engage with the cross pin in the oil pump shaft.
If you wanted to use solid drive pins, I am sure that this would work just as well. Obviously, they would need to be a tight fit in the 5mm holes and they might benefit from having a drop or two of Loctite just to be sure.
It would be interesting to know what type of drive pins were used in older 930s (without air-pump).

A potential problem area to watch for is the clearance between the end of the pump shaft and the end of the camshaft. After allowing for the gasket (0.5mm), I had about 0.2mm interference here. Grinding 1mm off the end of the pump shaft fixed this and gives a reasonable operating clearance.

I hope this explanation and the following photos are useful to others planning to take the same route.
Thanks for your input Dave and Mike.

1988 Carrera - 3.6 engine (with ITBs, COPs, MS3X) and a whole set of turbo body panels waiting in the attic.
Day job ...
Memories: '68 912, '72 911T, '80 911SC, '84 911, '85 930, '86 930, '87 911
Old 11-16-2008, 05:55 AM
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