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An ugly truth raised its ugly head today.
If you've been following the trials of engine # 178848, you'll know that it was running GOOD, then running BAD, then I replaced the carb which made it run GOOD again, but only at idle. Under load I can only get 900 RPM, though no doubt thanks to a freshly-cleaned hull, shaft and prop, I still can do 5.5 mph as measured by my GPS.
So today I did a compression check, and the results are grim. I don't know off the top of my head (OTTOMH ) the actual firing order, but taking the cylinders from the flywheel end back to the shaft end as cylinders 1-4, I got the following results:
Cylinder# Test 1 Test 2 Test 3 Test 4
1 105 105
2 105 105
3 10 10 10 10
4 10 10 15 10
After I performed tests 1 and 2 on cyls. #3 and 4, I squirted five or six blasts of MMO into the cylinder top as recommended by the manual, then ran the engine at ~1200rpm for 15 minutes and tested again. I got the same results on cyl. 3, but cyl 4 showed 5 lbs improvement on test 3, then dropped back to 10 lbs on test 4.
By the book, this indicates head gasket failure. But I'm not seeing any of the other failure symptoms: water in the oil, water or oil in the cylinder, etc. When I look into cyls. 3 and 4 with a mirror and light, all I see is piston top, slightly sooty. And now scented with the lovely wintergreen scent of MMO.
What I've done right now: after I did compression tests 3 and 4 on cyls 3 and 4, I squirted another six blasts of MMO into the clyinder as recommended by the manual, and left it to simmer for a few days.
I just find it hard to believe the head gasket failed because of the engine sitting from mid-July to mid-September, when I finally got the carb problems worked out. It was running great up until then, and I really think that I'm looking at a valve/piston ring-related problem.
What other troubleshooting steps can I take at this point that might let me figure out whether it's the valves/rings or a head gasket?
Thanks!
If you've been following the trials of engine # 178848, you'll know that it was running GOOD, then running BAD, then I replaced the carb which made it run GOOD again, but only at idle. Under load I can only get 900 RPM, though no doubt thanks to a freshly-cleaned hull, shaft and prop, I still can do 5.5 mph as measured by my GPS.
So today I did a compression check, and the results are grim. I don't know off the top of my head (OTTOMH ) the actual firing order, but taking the cylinders from the flywheel end back to the shaft end as cylinders 1-4, I got the following results:
Cylinder# Test 1 Test 2 Test 3 Test 4
1 105 105
2 105 105
3 10 10 10 10
4 10 10 15 10
After I performed tests 1 and 2 on cyls. #3 and 4, I squirted five or six blasts of MMO into the cylinder top as recommended by the manual, then ran the engine at ~1200rpm for 15 minutes and tested again. I got the same results on cyl. 3, but cyl 4 showed 5 lbs improvement on test 3, then dropped back to 10 lbs on test 4.
By the book, this indicates head gasket failure. But I'm not seeing any of the other failure symptoms: water in the oil, water or oil in the cylinder, etc. When I look into cyls. 3 and 4 with a mirror and light, all I see is piston top, slightly sooty. And now scented with the lovely wintergreen scent of MMO.
What I've done right now: after I did compression tests 3 and 4 on cyls 3 and 4, I squirted another six blasts of MMO into the clyinder as recommended by the manual, and left it to simmer for a few days.
I just find it hard to believe the head gasket failed because of the engine sitting from mid-July to mid-September, when I finally got the carb problems worked out. It was running great up until then, and I really think that I'm looking at a valve/piston ring-related problem.
What other troubleshooting steps can I take at this point that might let me figure out whether it's the valves/rings or a head gasket?
Thanks!
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