Hey all!
I have a buddy of mine that has a D16 that has no compression on #4 and its low on #3(sorry I dont know the numbers across the board). I don't know much about piston engines, he sent me some pics and it looked alright to me, but I'm just a rotary guy so I only know some basics.
If anyone has some ideas of what would cause this that I can bounce back to him, please let me know. Thanks!

pistons look like this
#4
#3 on the right.

 

Before taking the head off, a leakdown test should have been conducted.

Make sure the valves close all the way when the cam is turned to the TDC for that cylinder.

 

Tell your buddy to make an account and post.