I never thought about doing it with the cams on, to be honest. I don't think it can be done. I dont know how you could remove the rocker arms and then the retainers with the cams on.

The problem is that the retainers "Stick" inside of the top piece. You need to tap the top of the compressor with a hammer to get that out/loose. Then you can pull those off. I don't see how you can remove the rocker arm with the cam on (I've tried!) and then the retainers and springs to get at the old seals. MAYBE if you have hydraulic ball studs or turn the mechanical ones down?

Edit: Oh, and the valve being at TDC should be sufficient. The problem is that the exhaust valve's stem is thicker, so that you can only push the retainer down so far (it's tough to get the keepers out - I suggest a magnetic tool). Actually since I have one sitting on my desk I can show you - this is all the room you'll have to work with. First, exhaust. Second, intake.

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