Intake Manifold Replacement

I admit to being a wuss and booking a garage to refit the intake manifold in order to fix the oil leak under the dizzy, I was quoted 5 hours = couple of hundred quid. I thought this isn't too bad really, already have the parts so I said ok. The bloke at the garage asked who built the car and was surprised when I said self-build and I wanted something as straightforward as a manifold gasket replacing.

That got me thinking and I later rang the garage back to cancel, having decided to do it myself. Armed with knowledge from all corners of the internet I got to work. First job, get some supplies from the kitchen, this could be a 4 cuppa job:

Then jack up the car ready to drain the coolant - its too low to get a bucket under otherwise.

I forgot how much I bloody hate draining the coolant, I always get it everywhere as the only way I can do it is to pull off the bottom rad hose as I my radiator doesn't have a drain plug. Anyway, that done, on with the job - disconnect coolant hoses from the inlet manifold, namely the thermostat and heater connection.

Next, all the connections from the carb. Fuel line, vacuum line, throttle return spring bracket, throttle cable.

Labels on all ignition leads

Note position of rotor

Position of distributor housing, complete with marks from previous distributor removal just to confuse things.

I removed the intake bolts and checked that they are all the same length so didn't have to note where they all came from.

Now remove the intake, the lovely sound of sealant coming unstuck. I had to get a long screwdriver in the front end and gently pry it apart but once the seal started breaking I could lever it up just by getting my hand in the carb inlet hole in the top. Quick look in the engine to see if anything has dropped into the valley, looks ok (paper towels stuffed everywhere immediately after taking this picture)

Here's the manfold with the old gasket stuck on. Its a rubber/metal type with lots of rtv all over. The end with the round hole (dizzy end) is where the leak was. There was no obvious break in the seal (assembled with RTV on the front and rear walls) but the sealant peeled off very easily and was saturated with oil on both sides so clearly the seal had been broken at some stage and once the oil has a small path through then its game over. 

To get to this stage had probably taken about 2 hours but that includes jacking the car up which takes a good 20 mins or so as I've only got one hydraulic jack and one scissor jack to get it on axle stands. I had also stopped for 2 cups of tea. The next stage is probably the most time consuming - cleaning everything.

I started off by going straight in with a stanley blade and most of the rubber gasket came off easily. The RTV bits at each end peeled off in one go but left a very thin film behind that even a blade couldn't remove and I didn't want to get any deep scratches in the machined surface of the manifold. I gave everything a good soaking in brake cleaner and found some fine wet & dry, 360 grit and 1200 grit. I went at it with the 360 and finished with the 1200 and it came up looking nice. One final wipe with brake cleaner on a cloth and half an hour or so later had nice clean gasket surfaces. I stuffed paper towels in all the runners to stop debris getting in then got a hoover with brush attachment to pick up the little flecks of silicone that were stuck to the casting.

The heads on the engine cleaned up nicely just with brake cleaner and a blade, no RTV had been used on the cylinder head side of the old gaskets so it was very easy to clean it up. The china walls front and back of the block did need a bit of 1200 paper just to get the thin film of sealant off. Again paper towels were stuffed everywhere and anywhere to stop dirt and debris spreading.

Got a nice picture of one of the inlet valves, I'd never seen any SBC valves before. I knew they were big but good heavens they are about the same diameter as my cup of tea!

Clean and tidy ready for reassembly.

The replacement gasket I bought was an Edelbrock 7201 which comes with exhaust crossover restrictors (not needed) and a replacement distributor gasket. The instructions recommend gasgacinch on the cylinder head side only, RTV around the water ports (extreme left and right holes on above picture) and RTV on the front and rear block china walls. So that's what I did. I ignored lots of the internet where people have done it differently "for years with no problems" and followed the instructions to the letter.

I painted gasgacinch on the gasket (cylinder head side only - the side without the black silicone bead embedded in the gasket) and on the cylinder head. Gasgacinch only holds the gasket in place for fitting, it doesn't do any sealing so there's no need to ladle it all over like gravy on your sunday roast. Just a thin smear then leave for 5 minutes before mating the gasket to the head.

Top tip here: loosen or even remove the rocker covers. Luckily I dry-fitted the gaskets to make sure everything lined up and the rocker cover gaskets stopped me getting the inlet gaskets in exactly the right place.

The RTV needs to cure for 15 minutes until you can touch it without it sticking to your fingers. Just enough time for a cup of tea and some biscuits.

Then confidently place the manifold down flat and level and don't move it too much once its down. Bolts in and torque tighten to 25lb.ft (34Nm) in two stages starting with the central bolts, then front, then rear. The centre ones are a pig to get to with my torque wrench even with a universal joint on my 1/4 drive.

All that remains is to refit everything that was taken off before.

Tada!

Oh and refill the coolant. I know my cooling system takes exactly 9 litres to halfway up the header tank. On my Dax I have found the best way is to unbolt the header tank and balance it on top of the carb, nice and high to get some rho*g*h going on, then just fill, fill fill, occasionally squeezing the bottom hose (lowest point), you can hear the system burping air. I don't know if this is the same for other cobras as some are plumbed differently. There are no other bleed points in my system apart from the small take-off just after the thermostat housing, which is the highest point of the system.

Filling went ok on this occasion, previously I have started the car with the header cap off if I suspected some air was still inside and let it burp the air locks out that way. Another good way I've found is to pull the heater return hose off which gives a good route for escaping air.

When I eventually found the car keys I started it up, it was a bit reluctant but of course the fuel bowls were completely empty and the inlet tract dry as a bone so after two or three pumps on the throttle then hold the throttle halfway while cranking it finally caught. Through all the escapades with this car I've learned not to worry when smoke billows out the engine bay, this was just a bit of oil on the headers that I dripped on when removing the dizzy, and spilled some coolant too which got burned off. As soon as it idled on its own (no choke of course) which pleasingly was about 15 seconds holding it at 1500rpm, I hopped out and got a torch and had a good look at the front and rear block wall seal. I had cleaned it all up to make it easy to spot new leaks. I've seen a trick with flour to show up leaks but makes a mess so I just relied on my 550 lumen bike light. A careful inspection showed nothing so I went for a drive, 30 miles or so. Got it nice and hot, got the revs up and inspected again with the torch when I got back. No obvious leaks so it looks like its good! I'll keep an eye on it of course but the next job now is to clean up the sump and bellhousing which are covered in oil. I didn't see any point cleaning them until I knew the leak was gone.

Total time from opening the garage door with tools in hand to starting the car and rolling out = 6 hours. If I was to do it again I reckon 4 hours is just about possible.