GLV305 Compression question
Posted: Wed Oct 09, 2019 4:32 pm
Hello All,
I have recently picked up a 1978 17' Lancer Stinger with a GM based 305 motor. (1977 according to the block casting numbers).
According to the last owner, he was told when he bought the boat in 2012, that the boat was sitting for a couple of years before he bought it because the owner was advised that one of the cylinders was low on compression and he didn't want to fix it. My seller didn't do anything to the boat prior to my purchase either.
As I'm sorting out my new boat, I did a dry compression check across all cylinders and sure enough, number 5 is sitting at 100 pounds with all the rest at 140, 150 and numbers 3 & 8 at 160..! So, I shoot some 30 weight oil into all the cylinder (three squirts each from and oil can then turn the motor over a few revs before the next compression check...) and then check the numbers again... Number 5 builds right up to 150 but now, #8 and #6 dive down to 120... What gives?
First where do I begin with #5 is the building pressure from the oil a sign of rings or top end problems? And,
numbers 6 & 8...? Could I have blown the head gasket by putting the oil into the cylinders?
I have recently picked up a 1978 17' Lancer Stinger with a GM based 305 motor. (1977 according to the block casting numbers).
According to the last owner, he was told when he bought the boat in 2012, that the boat was sitting for a couple of years before he bought it because the owner was advised that one of the cylinders was low on compression and he didn't want to fix it. My seller didn't do anything to the boat prior to my purchase either.
As I'm sorting out my new boat, I did a dry compression check across all cylinders and sure enough, number 5 is sitting at 100 pounds with all the rest at 140, 150 and numbers 3 & 8 at 160..! So, I shoot some 30 weight oil into all the cylinder (three squirts each from and oil can then turn the motor over a few revs before the next compression check...) and then check the numbers again... Number 5 builds right up to 150 but now, #8 and #6 dive down to 120... What gives?
First where do I begin with #5 is the building pressure from the oil a sign of rings or top end problems? And,
numbers 6 & 8...? Could I have blown the head gasket by putting the oil into the cylinders?