Re: 60 HP Yamaha ??
while testing compression on a two stroke can give an indication as to overall cylinder sealing abiliy two strokes of modern outboard designs require both primary and secondary compression.
if the rings leak on the secondary side it forces hot combusting,not just combustion, gasses past the rings,past the piston skirts,eating off the lubrication and eroding metal on the way, into the crankcase area.
as the reeds are trying to seal the crankcase we just contaminated the incoming air,fuel and lubrication mix with spending and spent gasses.
thats why two strokes dont lose compression over a long period of time.
they tend to die suddenly and violently.
have seen scuffed cylinders show perfect compression after the head gasket was replaced only to destroy themselves due to the gasses blowing past the scuff marks.
I started doing this work as a proffesional when I was about 15 years old.
so far I have been a fairly accomplished machinist.
probably on of the few posting here thats ever run a boring bar or a crankshaft grinder or a valve faceing or seat machine.
I also did 6 years with the United States Navy as a firecontrolman in the navies advanced electronics field.
was medically retired as an E5.
for the past 20 years I have had my own shop doing my own thing and in past years have been factory certified for warrenty repair and service on Force,Mercury,Mariner,Suzuki,Tohatsu,Honda, Volvo and Mercruiser.
I am currently one of about 50 Yamaha Master technicians in the US.
you can look it up on the Yamaha website under training.
I am the one from Joes Marine in Wanchese NC.
for years the backbone of my living wages was from OMC products altough I never went to school for any of it.
I do still own quite a bit of specialty tools for OMC stuff until about 2002.
Do I waste to much time here? probably but I do get to help folks occasionally and I do try to wade through the internet wives tales.
most manufactures DO NOT post numbers and usually when they do its with a disclaimer to look for pressure variations rather than specific numbers.
and some Yamaha outboards wont even do that.
most V6 2 strokes from yesteryear had about a 15 PSI difference from top to bottom designed into it.
most 3 cyl motors back in the late 80?s to the mid 90?s had the same 15 PSI variation designed into the engine.
cant tell you how many folks have pulled heads only to find nothing wrong as this variation isnt published you just have to know about it,OR do a leakdown test.
never heard of any factory tester actually checking compression,most did not even check timing, thats why we PDI things.
and yes I have talked with many testers from OMC and merc. some are actually instructors for yamaha now.
but you will find,warm or cold, the PSI variation doesnt change much at all.
if its blown up cold its just blown up and will be when warm.
kinda like when you pull the plugs and they are covered with water or Aluminium throw off.
I am NOT sticking my compression tester on that hole.
I will use my snap on bore scope and take pictures or video of it,I will leak down test it and usually pull that head and have a close look.
I already know mechanical damage has occured just a matter of finding out how much.
I dont work on many 1959 jonnyrude twins nor many 1968 4cyl mercs.
most of what I deal with is offshore with V6 and V8 twins and they have to run correctly.
