As seen in Speedboat Magazine’s
August 2021 Issue.
700 SCi Head Gasket
Dear Bob:
I have a Mercury Racing 700 SCI kit. I ran the tank out of gas while under power. I did a compression test that showed 60 PSI on cylinders 4 and 6. The rest of the cylinders tested between 120 and 130 psi.
I took the motor apart and it looks like I just blew a head gasket. Is this a common occurrence? Should I just go back with a stock factory head gasket or is there something better? Is this commonly caused by running the engine out of gas while at full power?
Any information you can provide would be appreciated.
William Katchmar
Yucaipa, CA
Cometic Head Gasket C5760-040
Mercury Racing uses a Cometic multi-layer head gasket. It is the best choice for head gaskets.
Mercury’s part number is 27-811546A03. This is the same head gasket used on the later 525EFI’s, 600SCi’s and 700SCI’s. A similar gasket from Cometic is part number 5760-040.
Cometic Head Gasket and Intake Gasket
Be certain that any head gasket you select is designed for Generation V or VI GM big block Chevy engines. If the gasket is designed for Mark IV engines, the coolant passages are not correct and internal coolant leaks are likely. Many times, if the combustion heat or detonation were severe
enough, it could also have compromised the valves. It is also likely that your cylinder heads will need to be surfaced. You will need to use the correct intake gaskets and other specialty seals, O-rings, and pinch clamps during your re-assembly process. If you prefer to do the repair yourself, I would contact a certified Mercury Racing dealer for assistance or take the boat to one.
Cometic Head Gasket being installed with ARP studs
You may want to install ARP head studs instead of bolts. It is important that the correct stud kit is used. We create the kit from individual ARP parts. Also, the bottom row of studs cannot be too long because they will interfere with the header flange.
It is never good to run an engine out of fuel under load conditions. It is even more of a problem with supercharged engines. The program on the 700SCI monitors fuel pressure and modifies the injector pulse width if the fuel pressure is low. But there is no compensation or guardian for running out of fuel.
Crankcase Evacuation
Dear Bob:
Can you run a crankcase evacuation system from valve covers to wet tail pipes? Thanks!
Dana Mullins
Charleston, WV
I would not advise running a crankcase evacuation system to wet tail pipes. It could result in moisture getting back to the engine if any exhaust back pressure exists. It is also possible that steam would revert after the engine is shut off.
Typically, with dry headers, crankcase evacuation systems utilize a one-way check valve. This type of system might work as long as the point where the vent is placed into the tail pipe is in the dry section of a water jacketed tail pipe. The evacuation tube would have to be placed at an angle and welded in place through both the inner and outer tubes. If you have any signs of water reversion at idle, you may also have moisture entering the ventilation system because of reversion pulses at idle that might cause the check valves to malfunction.
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