Most people install new camshaft seals after they have assembled camshaft covers. They use a special tool (or a PVC pipe) and tap the seal gently into place with a hammer.
This is the most common method.
I have a question about using another method. I'm going to replace my hydraulic lifters. To access them, I have to remove all caps and when I remove camshafts, I can remove the old seals quite easily but what about installing the new seals?
Is it a bad idea to put new seals on camshafts first and put everything back together next? By doing this, I don't even need a hammer and a PVC pipe. I have seen mechanics do it this way like in the following video between 2:24 and 2:48.
https://m.youtube.com/watch?v=yz42qw8c358
The above video is not about my car but is very similar.
I was also thinking about using this method because there is not enough room between the engine and the chassis to use a hammer. If I use this method, I can install the seals much easier. Is this a wrong method? Should I avoid it? Please enlighten me.