[Midlifecrisis42]

The guys helping with the restoration of my 1970 911T have checked the engine compression numbers as follows:

1 - 90

2 - 90

3 - 90

4 - 130

5 - 90

6 - 90

With the following advice..

Scoping the bores shows cleaner edges to the piston tops meaning oil ring issues. the numbers say compression rings as well.
They recommend the motor needs a "Top-End" meaning, everything from the rings out (rings, valve guides, valves, rebuild carbs etc.)

I absolutely don't doubt this is what needs to be done (very well respected mechanic/engineers), however I would like to understand more about compression and what is involved in rebuilding the top end. I've done a search here but can anyone help with more info or suggest a link? I'm a newbie and here to learn.

Thanks