GaJeff
Petty Officer 2nd Class
- Joined
- Jul 9, 2012
- Messages
- 149
I have a 1981 merc 120 that I tore down for a rebuild. This engine starts up with no problems at all and would idle fine. I put a vac gauge on it to see whats going on because it started to have a bit of vibration in it. Well the vac gauge was jumpy at 19 so I did a compression test. I have about 65psi on all cylinders. Thats when I decided it was time for a rebuild.
My base timing was always around 15* but thats where it ran happy and strongest so I knew that something was always wrong but it just ran to good. It has been like that for the past two years I've owned it. So ive been riding on borrowed time anyways.
I tore it down and found most of my teeth on the cam gear worn and chipped, thats got to be my timing issue. My number 4 had a ring about halfway down the wall from where it was sitting before I got it. Also my head gasket looks to have been leaking compression between 2 and 3. Number 1 looked just fine, im sure something is wrong being it was about 65psi too.
Anyways, the cam gear is aluminum, it felt brittle to me. Maybe because its 30yrs old maybe because its aluminum. When I build this motor is my replacement gear going to fail? Are these gears known for chipping? Is there a better gear out there for this? Im sure since it's gear to gear timing there has to be a weak point to prevent major damage in the event of a failure, but is this common? Or do I need to look for something else like maybe a lifter causing the binding or valve sticking? I tend to think that number 4 may have been stuck and when it was started beforeI bought it there may have been damage then.
Jeff
My base timing was always around 15* but thats where it ran happy and strongest so I knew that something was always wrong but it just ran to good. It has been like that for the past two years I've owned it. So ive been riding on borrowed time anyways.
I tore it down and found most of my teeth on the cam gear worn and chipped, thats got to be my timing issue. My number 4 had a ring about halfway down the wall from where it was sitting before I got it. Also my head gasket looks to have been leaking compression between 2 and 3. Number 1 looked just fine, im sure something is wrong being it was about 65psi too.
Anyways, the cam gear is aluminum, it felt brittle to me. Maybe because its 30yrs old maybe because its aluminum. When I build this motor is my replacement gear going to fail? Are these gears known for chipping? Is there a better gear out there for this? Im sure since it's gear to gear timing there has to be a weak point to prevent major damage in the event of a failure, but is this common? Or do I need to look for something else like maybe a lifter causing the binding or valve sticking? I tend to think that number 4 may have been stuck and when it was started beforeI bought it there may have been damage then.
Jeff
