Good afternoon folks,
I have a bit of a confusing predicament with my latest project motor. I have a 2014 Mercury 25 hp EFI tiller that starts super easy on pull start and electric start, and runs relatively smooth at idle. I did a compression test and top cylinder is at 200 PSI and bottom 2 cylinders are at 120 PSI each. Adding oil to cylinders didn't really boost compression numbers at all. I then performed a leak down test and all cylinders showed minimal leakage like no more than 5%. When cylinders were pressurized, I could hear just the slightest hiss from the oil cap (indicating slight blowby to my interpretation). I heard relatively the same amount from each cylinder and it really didn't sound like much.
WHat could be going on here? I may be missing part of the process, or just missing something obvious, but I am stumped. Y'all have any suggestions as to what I could look at next? I've borescoped the cylinders and they don't look bad. Still have good cross-hatch and not really any signs of scoring. Pistons are a bit icky, but not horrible. Haven't done sea trials as I am rebuilding the lower unit and waiting on shipping for parts.
TL
R I have 2 cylinders with 80 PSI lower than the highest Piston on compression readings, but all cylinders have less than 5% leakdown values.
I have a bit of a confusing predicament with my latest project motor. I have a 2014 Mercury 25 hp EFI tiller that starts super easy on pull start and electric start, and runs relatively smooth at idle. I did a compression test and top cylinder is at 200 PSI and bottom 2 cylinders are at 120 PSI each. Adding oil to cylinders didn't really boost compression numbers at all. I then performed a leak down test and all cylinders showed minimal leakage like no more than 5%. When cylinders were pressurized, I could hear just the slightest hiss from the oil cap (indicating slight blowby to my interpretation). I heard relatively the same amount from each cylinder and it really didn't sound like much.
WHat could be going on here? I may be missing part of the process, or just missing something obvious, but I am stumped. Y'all have any suggestions as to what I could look at next? I've borescoped the cylinders and they don't look bad. Still have good cross-hatch and not really any signs of scoring. Pistons are a bit icky, but not horrible. Haven't done sea trials as I am rebuilding the lower unit and waiting on shipping for parts.
TL
R I have 2 cylinders with 80 PSI lower than the highest Piston on compression readings, but all cylinders have less than 5% leakdown values.