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Hello all! This is my first post and I wanted to share my experience in troubleshooting (with Don Moyer's help!) sticking intake valves. I just bought this Islander 32 about 6 months ago and my scenario was this; every time I came out to the boat it wouldn't start, and a quick compression check always revealed zero compression in all cylinders. All 4 intake valves would be stuck wide open. Sometimes they would be stuck quite hard, but squirting MMO in thru the spark plug hole and tapping them down with a punch would always get them freed up.
It would then start, but usually ran rough for a few minutes until the engine heated enough to melt the residual carmelized goo that was sticking my valves, then it ran perfectly smooth, like flipping a switch. It would run great all day, then the next morning, zero compression again, and I would have to repeat the process.
Don instructed me that sticking intake valves are usually caused by elevated back pressure in the exhaust. We thought the valves might clear themselves out if we corrected the back pressure issue. So I drilled and tapped my hot section just aft of the flange and took back pressure readings with a digital gauge. It would fluctuate a bit, but it was mostly between 1.5 and 2.7 PSI, just borderline high. I then removed my entire hot section and waterlift muffler to check for any restrictions. All was free and clear, then I blew air thru the discharge hose with a shop vac, all was clear. I did notice that this exhaust system had a really high loop in the discharge side (over 34 inches) and the higher the snorkle of water you are trying to push out, the higher the back pressure. I read in the forum that 18- 20 inches is plenty, so I lowered the loop and took another reading. More normal this time, 0.8 - 1.7 PSI
The valves may have eventually cleared up, since I believe that I corrected the root cause. But I decided to remove the head and valves, so I could evaluate and have a baseline to start from if they start sticking again.
I pulled all 4 intake valves and found SEVERE deposits of carmelized goo on not only the valves but it also had the intake ports caked up really bad.
So I guess the moral of this long winded story is that, it would seem that even moderately high back pressure can, over time, gum up your intake valves until they are as bad as mine were.
After hours of cleaning the intake ports, valves and guides, I put her back together and all was buttery smooth. Started on the first crank!
Time will tell if my problem returns, but I believe the severe gunk on my intake valves was years of build-up.
Special thanks to Don Moyer for helping me troubleshoot what initially was a very bizarre problem engine that would run perfect one day, then have zero compression the next day!
It would then start, but usually ran rough for a few minutes until the engine heated enough to melt the residual carmelized goo that was sticking my valves, then it ran perfectly smooth, like flipping a switch. It would run great all day, then the next morning, zero compression again, and I would have to repeat the process.
Don instructed me that sticking intake valves are usually caused by elevated back pressure in the exhaust. We thought the valves might clear themselves out if we corrected the back pressure issue. So I drilled and tapped my hot section just aft of the flange and took back pressure readings with a digital gauge. It would fluctuate a bit, but it was mostly between 1.5 and 2.7 PSI, just borderline high. I then removed my entire hot section and waterlift muffler to check for any restrictions. All was free and clear, then I blew air thru the discharge hose with a shop vac, all was clear. I did notice that this exhaust system had a really high loop in the discharge side (over 34 inches) and the higher the snorkle of water you are trying to push out, the higher the back pressure. I read in the forum that 18- 20 inches is plenty, so I lowered the loop and took another reading. More normal this time, 0.8 - 1.7 PSI
The valves may have eventually cleared up, since I believe that I corrected the root cause. But I decided to remove the head and valves, so I could evaluate and have a baseline to start from if they start sticking again.
I pulled all 4 intake valves and found SEVERE deposits of carmelized goo on not only the valves but it also had the intake ports caked up really bad.
So I guess the moral of this long winded story is that, it would seem that even moderately high back pressure can, over time, gum up your intake valves until they are as bad as mine were.
After hours of cleaning the intake ports, valves and guides, I put her back together and all was buttery smooth. Started on the first crank!
Time will tell if my problem returns, but I believe the severe gunk on my intake valves was years of build-up.
Special thanks to Don Moyer for helping me troubleshoot what initially was a very bizarre problem engine that would run perfect one day, then have zero compression the next day!
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