In a month or so I will be taking my Z out of storage. I plan to rebuilt/upgrade the top end but before doing so I want to make sure the bottom is still OK. The motor is completely original (LG4) with 140000KM. Last year before storing it started using quite a bit of oil (the rear main seal is leaking and I suspect the valve seal are leaking to). Beside the rear main seal that need to be change what should I do to know if the bottom end doesn't need to be rebuilt (compression check?).

 

If you are going to pull the motor apart anyway, you would be much further ahead if you simply freshened the bottom end. New rings, bearings etc. While apart, check clearances, and bore diameter as well. This will tell you if you need to go any further...

Have fun.