Mercruiser420
Petty Officer 3rd Class
- Joined
- Nov 24, 2015
- Messages
- 92
Greetings fellow boaters,
I wanted to share my 470 rebuild with everyone who may be interested. Hopefully it will be helpful. I will do my best to be as clear as possible.
The boat is a 21' 1977 (pre-alpha) Fiberform Cuddy cabin, with a 1986 Mercruiser 170 but with the 70s exhaust manifold (cast iron) and larger coupler as I didn't want to switch my entire setup to alpha 1 so I kept the exhaust and heat exchanger from the original 1977 motor.
So a few months ago cylinder 3 decided to die on the way back from the Elizabeth islands, in the middle of Buzzards Bay earlier in the summer. I was doing about 3200 rpm when I heard the dreaded "engine damage" noise then the engine died. Fortunately, the other 3 cylinders were enough to get it restarted and I was able to limp home on cylinders 1,2 and 4 only.
Got home safely, started the engine and flushed the system with freshwater and while it was running (very rough) I pulled every ignition wire to see which one(s) made a difference and concluded cylinder 3 to be the bad one. So I performed the following tests:
Ignition/spark test = Pass. All 4 firing.
Compression test = Fail. 145 psi, 140 psi, 30 psi, 145 psi
Conclusion: low compression and the horrific metal crunching noise I heard can only mean that I need an engine/rebuild.
And the tear down begins...
I wanted to share my 470 rebuild with everyone who may be interested. Hopefully it will be helpful. I will do my best to be as clear as possible.
The boat is a 21' 1977 (pre-alpha) Fiberform Cuddy cabin, with a 1986 Mercruiser 170 but with the 70s exhaust manifold (cast iron) and larger coupler as I didn't want to switch my entire setup to alpha 1 so I kept the exhaust and heat exchanger from the original 1977 motor.
So a few months ago cylinder 3 decided to die on the way back from the Elizabeth islands, in the middle of Buzzards Bay earlier in the summer. I was doing about 3200 rpm when I heard the dreaded "engine damage" noise then the engine died. Fortunately, the other 3 cylinders were enough to get it restarted and I was able to limp home on cylinders 1,2 and 4 only.
Got home safely, started the engine and flushed the system with freshwater and while it was running (very rough) I pulled every ignition wire to see which one(s) made a difference and concluded cylinder 3 to be the bad one. So I performed the following tests:
Ignition/spark test = Pass. All 4 firing.
Compression test = Fail. 145 psi, 140 psi, 30 psi, 145 psi
Conclusion: low compression and the horrific metal crunching noise I heard can only mean that I need an engine/rebuild.
And the tear down begins...
