bad compression

[football004800]

Alright so i have a gemini 1989 bass boat. i bought it used and i have ran it this summer about every weekend. now it has a 1992 yamaha motor p150tlrq and it has low compression in one cylinder. on the left side the compression numbers(from top to bottom on all 3 cylinders)read 110 108 and 83 and on the right side the all read 112. so i am asumming something is wrong. now the boat seems to run pretty decent, it only hits about 4200rpm. so im missing alot of speed and im sure its cost me alot of gas. it is sumtimes hard to start after sitting awhile, but once started it will run good all day, motor sounds good. so im only 15 years old, i can do motor work its just i dont know how to even begin from here. I am going to have to do the work and pay for the parts so taking it to a shop is out of question. From what i have read its either the head gasket, intake valve, exhuast valve or piston rings. now how can i figure out what it is? also if its a valve can someone help show me witch vavles and what will alway need to be replaced? i plan to buy of boats.net for the watever i need. im just very confused and whatever any info any body has has to help me, thanks for the help

 

[99yam40]

Re: bad compression

2 stroke motors do not have valves so that would eliminate them.
More that likely you have a ring/piston problem, due to running lean cylinder or overheating,
but it could be a head gasket blown or broke /stuck ring but not as likely
you need to inspect top of piston and the cylinder wall to see what kind of damage there is.
I would not keep running it or piston could come apart

A Yamaha service manual is a must have if you plan on working on this motor yourself

 

[football004800]

Re: bad compression

i plan on taking a more in depth look today, and yeah after i watched a 100 videos on how motors work and the difference between 2 and 4 stroke motors i found out there was no valves. Now i do plan on getting a service manual here soon, but if i take the head off, will i have to put it to a certain torque win i put it back on. sorry if that was confusing, im good at fixing things bad at explaining things

 

[99yam40]

Re: bad compression

Yes there is a procedure for torquing the bolts in the manual and you cannot reuse the gaskets

 

[football004800]

Re: bad compression

if it is pistons is there a way i can remove them without disasembleing the hole motor?

 

[Bondo]

Re: bad compression

if it is pistons is there a way i can remove them without disasembleing the hole motor?

Nope....

 

[football004800]

Re: bad compression

well is there any way for me to figure out if its the piston before i take off the head...EDIT: alright i put some oil into the spark plug hole. it went from 83 compression to 90. does this sound like a head gasket? i didnt have the correct tools to open it up. if i replace the head gasket is there any other cheap things i should replace at the same time?