As part of the work involved in a long-running
project 3.6 engine rebuild, I decided that I wanted to use a 911-style engine-mounted oil cooler rather than get involved with adding a new centre-mounted cooler up front. This engine will go in a G50 Carrera which already has the fender-mounted front cooler so I don’t anticipate any cooling issues for street use.
Fitting the oil cooler requires the following issues to be addressed:
1. Camshaft P/S drive boss
2. Thermostat
3. Top oil connections (in and out of cooler)
4. Bottom oil connection (oil pump supply)
5. Air ducting
Because the power steering pump drive usually occupies the space where the oil cooler fits, this must all be removed. Unfortunately, the drive boss on the end of the RH camshaft also pokes into this space and will need to be cut off flush with the end camshaft bearing journal. I got John at Dougherty Cams to do this for me while he was doing a DC-21 regrind for me.
I will plug the hole in the camshaft housing with the standard steel plug (93010516100).
A standard 911 thermostat will fit as a direct swap for the blanking plate that is used on 964, but the thermostat won’t work until the oil passages to/from the oil cooler are opened up.
Another related issue in this area is relocation of the oil temp and pressure switches/sensors. I haven’t looked at this in detail yet, but I don’t expect any problems here if I use the top breather housing from a 911 engine.
For some unknown reason, only the front oil passage between thermostat and cooler is correctly drilled and machined to take the usual rectangular seal but the hole is plugged. Drill and tap the plug so it can be pulled out.
The rear passage is not drilled or machined for the seal. I haven’t done this yet but it will be a relatively simple machining operation – just annoying that one passage is machined and one not – go figure!
I burnt off a few brain cells figuring out the best way to adapt the bottom oil cooler connection.
The problem is that there is precious little space in this area to work with and machining the crankcase to suit the rectangular standard 911 seal just won’t work because there isn’t enough metal there to start with.
The only real option was to modify the 964 fitting (to which the original inlet oil pipe attaches). The length of this fitting must be reduced considerably so it loses the 30mm hex. Fortunately, the 17mm bore of the fitting lends itself to being cut to an internal 17mm hex so that the fitting can be tightened with an allen key or allen socket.
A visit to the local seals specialist turned up an ideal O-ring size. The diameter of the recess in the oil cooler is 26mm, so that was a starting point. The ID of the O-ring was constrained by the size of internal hex that I planned to cut in the fitting. A standard section diameter of 2.62mm gave me enough room all round so I ended up with an O-ring 26 OD x 20.8 ID x 2.6 dia. I could have gone with a fatter O-ring but the resulting smaller ID would have meant machining the fitting with a flat face and doing away with the spigot that provides the O-ring with internal support. Because this is a suction line, I prefer to have the O-ring supported on the inside.
Maintaining correct compression of the O-ring is critical so it is important to machine the fitting to suit the actual dimensions of your cooler, crankcase and the aluminium sealing washer. See A and B dimensions below. The squash on a 2.6mm Viton O-ring should be 0.5 to 0.6mm.
I guess a few pictures and drawings might help.
Ducting air into the cooler was a major piece of work timewise.
Really, the processes are all quite simple, it’s just time consuming – especially if you are learning as you go!
I decided to follow the same general shape as the ducting on a 911 engine. I considered using a standard 911 duct at the oil cooler end and just making up the extra piece to adapt it to the 964 shroud, but in the end I decided to make a whole new duct from the fan to the cooler as the 911 part didn't fit the 964 shroud very well.
I built up the shape I wanted using foam blocks and filler, then used this as my mould for laying up the fibreglass duct. I had hoped to be able to get the part off without damaging the mould so I could make up one or two spares, but unfortunately that didn’t go to plan. At least I have one good part that I can reproduce a mould from if I really need to make another duct.
Continued ...