i have a 98 civic that i put a 99 b18c1 obd2 into this winter, and the other day it got a loud clatter sound on the driver side of the moter, i ran a compresion test and i have about 150 to 160 on the first 3 cylinders and on the fourth on i only have about 100 to 105. i'm looking for any ideas that this might be.

 

If I were you, I would pull the head. Especially with that compression. Check your valves. IMO, It sounds like the your valves had some contact. Hope fully they are just bent and didn't break off and do damage to the piston, if this is it.

 

what do you think about a lifter problem

 

Sounds like bent valves, Your motor does not have lifters, you have lma's and they wont cause a loss in compression.