low compression? bad head gasket?

[seapro21]

2001 ox66 200 is being worked on now slowly..
was told so far the fuel pump has a bad diaprham and low compression in one cylinder which possibly could be do to a bad head gasket? the gasket has never been changed.
weird thing is the motor seems to run fine except for a little shake at idle.tops out at 5400 rpm like normal.
heard a tapping noise last trip out which i never heard before which is why i took it the shop. i did clean the o2 sensor like all the directions say before that trip which was the first of the season.

[99yam40]

which cylinder has low compression?

I have heard a bad fuel pump can wash the oil down in the cylinder it gets it's pulse from.
Tapping noise sounds like something worse than cylinder not sealing properly unless it is the fuel pump making the noise some how.

[seapro21]

dont know which cylinder.wednesday hope to have better answers.

[seapro21]

got some news today. low pressure fuel pump had a hole in the diaphragm.
some poppet valve for water flow was stuck open never letting the motor to heat up which was a recall that i didnt know about.not the thermostats.
head gasket needs replacement which caused a small fluctuation in compression in one cylinder .