Small Engines (Lawn Mowers, etc.): john deere head gasket, automatic compression release, john deere stx38

Question
Hi there
I have a john Deere STX38 that has a sever loss of power and I checked the compression and it was low so I decided to replace the head gasket but the problem is it is an over head valve and I was wondering if I have to set the timing or adjust the rocker gap and what the gap should be or anything like that
the mower is a john Deere STX38
with a kohler command 13 hp
family SKH398U1G2RB
model CV13S
displacment 398
serial 2706711192

thanks for the help
Derek

Answer
Is the service manual link below for your engine?

http://www.kohlerengines.com/onlinecatalog/pdf/tp_2339_d.pdf

These engines are equipped with an automatic compression release (ACR) mechanism. Because of the ACR mechanism, it is difficult to obtain an accurate compression reading. As an alternate, use the
leakdown test described in the repair manual.

Let me know if this helps.
Eric