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Issues with an 0540


Well-known member
Hey guys, first time poster here on Southern Airboat and I have an issue with an 0540 I just had mounted on my first boat. First off, let me say that this site and the advice contained within has been a huge help for a newbie like myself. I plan to add some of those red stars above my username shortly.

I recently purchased a 300 upstack off of another boat, and at the time of purchase the engine sounded good, has decent oil pressure (5o-55 lbs. cold idle), and was priced right.

After mounting the engine, overhauling mags, and adding new headers we fired her up to discover it had a stuck valve. I immediately took the boat to an A/C mechanic who performed a leak down test and a valve job on the appropriate cylinder. The leak down test revealed that I only have good compression on 3 cylinders. :( I don't remember exactly but I think the readings were 70, 68, 60, 48, 45, and 30. Not really a big deal because I don't mind having a top end job done. But, here is where I run into a problem. When the mechanic pulled the cylinder he said he realized the engine is not a true 300 angle valve because it lacks some kind of injector for the high compression pistons. He believes I would be better off to sell the engine and start over than to overhaul the top end and tear into the lower end to install the injectors. Apparantly what I have is a 260 case and 300 jugs? Anybody have any advice, could I put on 260 jugs and be done with it? I would prefer to salvage/fix what I have.

Thanks again SA and regular contributors who make this such an excellent site!
What you have is fine. Don't change a thing. Actually that is the motor everybody in the glades here prefers. I am building one of each right now. A large journal and a small journal 300. The 260 lower end is lighter. It has smaller rods and a smaller diameter crank. It does not have the piston cooling nozzles. My younger customer wants a light fast boat, The 68 year old customer does not care about weight and feels he wants a large journal motor. I personally like the 260 narrow deck lower end with the angle valve cylinders. It sounds like he is trying to talk you into a lot of unneeded work. However A/C guys only know how to build them by the book. So in his eyes what you have in a basket case. In our eyes it is a preference. He may not be trying to get in your pocket, but if so don't let him.
Mike, thank you for volunteering the information. That certainly puts my mind at ease. I was led to believe by the a/c mechanic that it would be an unreliable setup without the cooling nozzles. I didn't mention that he was trying to sell me one of his engines.
I noticed some parts of interest to me on your e-bay store and will be contacting you soon.
Thanks again for the info. Guys like yourself, Waterthunder, and others on this site who freely help greenhorns such as myself is what makes this site such a valuable asset to the airboating community. (IMO)