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In-car cam change - '68 GTO


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I am about to swap cams in my 1968 Pontiac GTO. I would like to do it while the engine remains in the car. I have worked on engines throughout my 40 plus years in the car hobby, but only once did I participate in a cam change while the engine remained bolted in its mounts and that was in 1967, my friends 1960 Falcon, in which he stuffed a 289 V-8. This seemed to be straight-forward work, all went well with the Falcon back on the road in a day or two, but I have slept since then... I would like to do the same with the GTO.

The one advantage the Ford had was the distributor location in the front of the engine vs. the rear in the Pontiac. I don't recall any trouble with the oil pump drive, cam gear or distributor either on the way out or the way in. This is just one of the gray areas I have with my Pontiac V-8 - that and the oil pan. There is much information on a cam change but all of it seems geared towards engine out, I have found none on the in-car swap.

So without confusing the issue with more questions, has anyone swapped Pontiac V-8 (389 - 455 family) cams while the engine remained in the vehicle and if so, what can I expect in terms of difficulties ?

Thanks in advance for anyone chiming in on this.

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  • 3 weeks later...

I have done it recently but it was in a '63 Catalina and not a '68 GTO. It took me probably half a day and the most difficult part was reinstalling the snout which the harmonic balancer is attached to. The bolt which attaches it is installed with quite a bit of torque and the best way to break it loose is to place a socket on it with a long breaker bar and then bump the starter with the breaker bar against the front frame fork. My car is standard shift and I had to get a friend to lie under the car with a crowbar jambed into the flywheel teeth, to keep the crankshaft from turning, in order to enable me to put it back on with the proper torque. I had to remove the radiator to have enough room to pull the old cam out and then snake the new one in. As low as the front end is on the GTO I don't know if you will have the room up front even with your radiator removed. Your grill support may be in the way and if so you will have to either remove the entire front end or pull the engine. Then dropping the distributor back in, which turns slightly as it drops all the way down, is just trial and error. It took me a two or three tries to get it down where the rotor was clocked right.

One trick a friend taught me was how to set distributor advance with a multi meter. Set the multimeter to ohms and then attach one terminal to the hot wire going into the distributor, and the other to a good ground, and turn the distributor until you just begin to see resistance, then lock it down fairly tight where you can move it but it was stay where it is. You are now within 2 or 3 degrees of what the timing mark on the hub says and can start the car right up and break the cam in without worrying about messing with distributor advance right at engine start up. Of course you want to set the timing mark on the balancer hub to 6 degrees advance before setting the distributor. And of course you can have set the #1 piston is at TDC before you put the valley pan back on after installing the new cam and lifters.

Be sure to follow the cam manufacturers instructions regarding cam break in using plenty of assembly lube on the lobes and adding the zinc additive to the oil.

It is really a pretty straightforward process.

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