The Verdict- Why my inline went out after two trips?

[Black Max]

I recently rebuilt my 1978 90hp inline 6. The first time I took it to the water it ran as good as new, but the second trip she completely died out.<br /><br />I tore the powerhead down today and found number 2,3, and 4 piston scuffed. It looked like excess heat on these cylinders caused the pistons to expand, thus scuffing. I realised that behind the small cover behind the exhaust baffel plate had a small port hole near the top of the motor that was oxidized shut and I didn't realize it when I was putting the powerhead back up. I think this caused an air pocket near the upper cylinders which then cooked the gasket making it have the consistency of a potato chip. Seems the gasket then blew and dumped water into the top four cylinders. <br /><br />The powerhead wasn't damaged and I am almost ready to put it back up. Is there anything else I can do while the motor is apart to make sure the motor is reliable this time? Any one had this happen before?

 

[Silvertip]

Re: The Verdict- Why my inline went out after two trips?

Were the carbs rebuilt during the engine overhaul? Did you determine what killed the engine the first time? If an engine dies and is then rebuilt and the original cause not corrected you run the risk of getting to do the job again. New thermostat & water pump installed? Carbs set too lean.

 

[Clams Canino]

Re: The Verdict- Why my inline went out after two trips?

Add too much advance or overpropped? to the list.<br /><br />Use midgrade gas too.<br /><br />-W

 

[Black Max]

Re: The Verdict- Why my inline went out after two trips?

Yes, the carbs were completely rebuilt along with water pump and every single odd and end on the motor. The previous problem with the engine was due to the commom loss of compression in cylinder 3. The current powerhead is a completely different one than the one that had a bad cylinder. It appears that the the heat and water cut off lubrication of the cylinders making metal to metal heat buildup. I was running a 21 pitch prop on a 16ft Bassboat. The same prop I ran on my 85hp for 6 years. Everything was set up by a certified outboard mechanic with nearly 38 years of experiance (My wingman).<br /><br /> Clams I just hope this time around I can keep this inline on the water (where it belongs) for good. I feel lost in the 1970's when I'm running the river with old Merc's and I love it.

 

[Black Max]

Re: The Verdict- Why my inline went out after two trips?

Any oil suggestions this time around? I was running the new Quicksilver 2-stroke synthetic with premium fuel, to try and keep the motor free of carbon build up.