Compression Question

Discussion in 'Outboard Maintenance' started by Glock2710, Jun 6, 2013.

  1. Glock2710

    Glock2710 Wishing I was on the water!!!!!

    I am looking at buying a boat with a 1997 80hp yamaha. The compression check is 101-100-99 top to bottom. Should I have any concerns with these numbers being slightly low? They are all close so that is pretty good but I thought I would ask here from some with more knowledge than me.
  2. Brett

    Brett > PRO STAFF <

    Less than 2% compression difference between high and low cylinders is good.
    The values you read may be affected by the gauge. I have one compression gauge
    that reads consistently 10-12 psi lower than my other two. I expect to read 110 psi
    on an older motor. Anything above 110 is gravy.  :)

    btw, if I get a sub 100 psi reading, it usually means
    I forgot to make sure the intake was wide open, before testing. :-[ ;D

  3. Capt Dan Medina

    Capt Dan Medina Well-Known Member

    I've got a 96 75 HP yam I... compression is the same... runs great...