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How many hours between overhauls?

He He - That is a loaded question.

Know an operator from a few years back that was running seismic, 7 days a week. We were going through whatever that straight line crossed. He had better than 4000 hours on his motor (on a alumitech built airgator, 14' slider hull). I know that motor was turning 4900-5000 quite a bit. Was the second set of head when the motor went. We didn't stay working if we could get the job done and the boat down the line. He also owned his boat versus running a company boat.

If it wasn't running he wasn't getting paid.

Got a friend over here that just place his second crate ZZ4 in his boat in less than 14 months.

Know a fellow in the Galveston area with a decked over Palm Beach. Has gone through 2 sets of cylinder and mag drive gear broke and a few other items. That boat has less than 700 hours on.

Both of those guys have money to play.

I say that is hard to call, it depends on the boat and mainly operator.
We have had Buick 455s w/reduction units run in excess of 4,000 hours, many of which were hard use - 1000# payload hours. These engines are built tight to begin with then well maintained. Max RPMs at 4200. Our biggest problems have been valve wear from running unleaded gas, and temperature.

Because of high temps we have had detonation tear a couple of engines apart. Due to this we have switched to larger, aluminum radiators. When we opened these engines up they show little cylinder or bearing wear and would have continued to run reliably till the valve seats died. The next engine we build up will have hard seats that were not available a few years ago.

You are a pretty analytical guy. I'd like to hear your reasons for going with the Buick.

Don't know how many hours on my motor have a 350 chevy that i've ran for 3 years hard.I bought it from a buddy that ran it for who know how long still runs good. just put a box on it will see how long it lasts now.
Analytical doesn't do much good unless the analysis is sound:) but you asked for it, so here goes.

Our first engine was a direct drive Buick since we had a high torque, low rpm cam developed specifically for airboats. It worked like a charm. We ran this on a heavy plywood hull for a couple of years while we built up an aluminum hull using a 455 buick again and cogged belt reduction unit (Airboat Drive Units - CH3). I suspect the primary reason we stayed with the buick was because of weight - they weigh less than the 454s. Also, early on we found a good reduction ratio / prop combination that worked well and didn't want to fix something that wasn't broken. We are building another boat this winter and again using the Buick 455 because we know what to expect from it, and we have yet to have anyone show us something that will outperform it.

If someone were to show us thrust/fuel consumption curves on a powerplant with better performance, that looked like it might have some durability we might consider a change, but haven't seen any convincing evidence yet.
Yea CC - most those 350s do alright and I like them. My friend over here has most money than sense. It ain't the motors, it is him.
Mark's overhauled my o540 in 1981 and after many hard running seasons, it continues to perform just fine. Never had a jug off. Will probably outlive me.
Cylinder head temp max in summer 325
Oil temp max in summer 180
Use 100 LL aircraft fuel
Cooling shroud made by Mark's (runs noticeable hotter without)
Winter time cyl head temp average 250
Winter time oil temp average 140
Mostly dry marsh running @ 2400 rpm's with max @2800rpm's
Use Shell Aero 100

You are running that O540 the way Lycoming designed it to run: Cool heads, warm oil, and don't spare the horses. It probably will outlast you.

Jim :lol:
Hogman and any other that have CHT gauges.

How are the gauges set up?

Do you have one on the control console?

How many jugs do you have a probe on?

Used to have one that had enough wire to reach all of them, found the hottest under normal running and left it attached there. The gauge was attached to a home made panel. Crude but it worked. Looking for better ideas. Drool at those multi cylinder gauges but will have to win the lottery first.
Installed the cyl head temp sensor to the cylinder that would run the hottest as informed by an aircraft mechanic.
Installed it on top of the console with a separate alum bracket.
My console is different than most. It's set up like a center console bay boat with windshield and dash. Sorta sissy but it keeps me from catching pneumonia in the cold humid winters here which is when most running and hunting takes place.