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ETC-Era Pontiac Marine Engines

Arn Landvoigt brought this subject to me severalyears ago after having come across a Pontiac split-head 6 cylinder converted by Gray Marine for use ina 1931 Chris Craft. Gray Marine built engines foryears, but began converting automobile engines in1927. So far, Arn has identified 4 split-head six con-versions from Gray; the 6-27 from 1927, the 6-40from 1927-28, the 6-41 from 1928 and the 6-63 dat-ing from 1931-32.

He recently sent me a link to an E-bay auction of aKermath Sea Chief Eight, which was based upon thePontiac straight 8. I did a bit of research and Ker-math used Pontiac L-head straight sixes and eightsfor marine conversion, apparently under the SeaChief name, although this name was also applied toengines from other companies as well.

The seller in this recent auction provided 74 pho-tographs of the engine and I found them to be quiteinteresting. I am somewhat familiar with marineengines, having been trained on a wide variety ofthem in the Navy. I also owned a 26’ Lyman forseveral years powered by an inboard Chevrolet 350V-8 conversion from Crusader Marine.

The primary changes from automobile to marineuse involve the cooling system and addition of a wa-ter-cooled exhaust manifold. Since the boat is float-ing in an unlimited supply of water, marine enginescan be water cooled without the use of an automo-tive type water to air radiator. This is especially truefor fresh water applications. Marine engines have a“raw” water pump that brings in cooling water fromunder the boat. It is a centrifugal type pump withan impeller, just like an automotive water pump. Itis usually mounted low, under the boat’s waterline,so the pump housing will always be full of water. Ifmounted above the waterline, the suction sideneeds a check valve so the pump does not loose itsprime. The raw water pump has sufficient capacityto provide cooling water for the engine cooling sys-tem plus the exhaust manifold; any extra water isdumped into the exhaust pipe where it connects tothe manifold and flows out with the exhaust. This isa one-pass system, all of the water is discharged outthe engine exhaust after flowing through the engine.

Generator/starter side of Gray Marine engine,the flywheel housing is on the right.

Carburetor side, note the crankcase breathertube just in front of the carburetor flame ar-

restor. The fuel pump is also shown. Thetransmission is on the right.

The raw water pump & pulley below the har-monic balancer. The hose under the genera-tor is the suction line. The v-belt drives thegenerator and raw water pump, the enginewater pump has no pulley and did not turn.

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Salt-water applications can be done the sameway, but quality marine conversions will utilize sometype of water to water heat exchanger because salt-water is very corrosive. Automotive engine conver-sions typically use a header tank system that keepsthe raw water separate from engine cooling water.The engine cooling system is sealed and water circu-lates to the sealed side of the header tank and backagain. The raw water side of the unit dischargeswater to the exhaust manifold for cooling. It mayalso have a dedicated overboard discharge pipe, ifextra cooling capacity is necessary.

Since engines are more efficient when running atoperating temperature, marine conversions are fit-ted with one, and often two thermostats. The ther-mostat works just as it does in an automobile, re-stricting the flow of water until its design tempera-ture is reached. During low speed or at economycruise RPM, minimal engine heat is generated andwater flow through a single thermostat is sufficient.But unlike automobiles, boats can be operated athigh speeds for hours on end. In marine applica-tions, engines are also rated for maximum continu-ous RPM, at these high speed and power levelsmuch more heat is generated, whereby the secondthermostat will open and increase the flow of cool-ing water. In applications where salt-water is actu-ally circulating in the engine, lower temperaturethermostats are used to help minimize corrosiondamage.

There can be another significant difference whenautomotive engines are adapted for marine use, es-pecially for installation in smaller pleasure boatswhere the engine is under the deck. The crankshaft

will be much closer to the bottom of the boat if youtake power from the front (timing case) of the en-gine. The engine / transmission unit is narrowenough to fit deep between the stringers (hull struc-tural members that run fore & aft, parallel to thekeel). The conversion company would design itsown housing to cover the timing case and mountthe transmission. A coupler would be needed toconnect the crankshaft to the transmission, whichwould possibly include a torsional damper since theoriginal harmonic balancer was probably unsuitable.The automotive water pump could be replaced withappropriate hose connections, the raw water pump

Kermath Sea Chief 8 water outlet, you canjust see “outlet” by the hose nipple.

You can barely see the raw water pump dis-charge line at the lower left of the balancer.

The fitting on the timing cover mounts a cableto drive a tachometer. Raw water enters theexhaust manifold at the other end, at this endyou can see the fittings that connect to the en-

gine water pump. The raw water pump pro-vides the circulation, the engine pump serves

as a hose connection and directs the water intothe distribution tube. The cooling water is be-ing warmed by the exhaust before entering the

engine. Knowing what a cylinder head lookslike under the Pontiac thermostat housing, andnoting how short this water outlet is, I doubt

this engine is fitted with a thermostat.

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would provide the necessary circulation and oftenthe generator would be converted to a geared orchain drive on the redesigned timing case for ulti-mate durability.

Since power is taken from the front, an enclosedflywheel housing is needed, usually fitted with rub-ber cushioned mounts that lag bolted on the top ofadjacent stringers. The starter can be mounted highand dry, away from bilge water and accessible forservice. Some conversion companies installed a pul-ley on the flywheel hub and mounted a belt drivengenerator on the housing as well.

Inline engines were typically fitted with an updraftcarburetor, by mounting it under the manifold a verylow profile could be maintained. It was not uncom-mon for marine engines to have dual carburetors forincreased power. A mechanical fuel pump was typi-cal, but likely to be inverted for access to the sedi-ment bowl and fitting connections.

Crankcase ventilation was needed but the auto-mobile road draft tube was unacceptable in the en-closed engine bay of a boat. Typically the originalvalve chamber (side) covers would be replaced, onefitted with an inlet breather and the other fitted witha metal outlet tube that would rest directly on thecarburetor flame arrestor. Air rushing into the car-buretor would create a suction on the ventilationtube and draw fumes from the crankcase.

Arn and I would appreciate hearing from any ofyou that have additional information regarding non-automotive applications using Pontiac engines.

The bright object is the top of the fuel pump,the dirty square is the flame arrestor. Thecarburetor is a single barrel updraft unit.

Thanks to this shot of the cylinder head castingnumber, we know this is a 1950-51 engine.

The distributor, octane selector and plug wiremanifold are stock Pontiac units. Note the

unique oil fill tube and sealed fill cap.

The engine water pump, casting No 511244

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The photo at left is tilted to the left, it shows theback of the block and head. The lower left corner isan aftermarket oil filter and connecting tubing. Justto the left of where the tubing disappears is a hoseand clamp, it is the raw water connection to the ex-haust manifold. The large rounded piece above thehose connection has lettering on it, but even greatlyenlarged I could not make any sense of it.

To the left of the hose connection and letteredcomponent is what appears to be a tube, possibly acrankcase vent from the rear side cover. Unfortu-nately the engine was sitting next to a wall, so therewere no good photos of the carburetor side of it.

The photo below was taken looking down, itshows the top of the oil filter, the exhaust pipe witha cooling water connection and the top of the trans-mission with engine I.D. tag and finally the starter.

The bottom photo shows the starter, cables andelectric solenoid switch. This starter has a Bendixdrive as opposed to Delco type shift solenoid.

The Kermath company was a well respected namein marine engines. They introduced the Sea Wolf se-ries in 1926, which featured a single overhead cam-shaft; hemispherical, 4-valve combustion chambers;and a 12 spark plug, dual ignition system. It dis-placed 648 cubic inches and was rated for 150 horse-power @ 1,800 RPM. By late 1929, this engine hadgrown to 678 cid and 225 horsepower.

The fine print on the tag recommends S.A.E 30 insummer and S.A.E. 20 in winter. The valve clearancespecification was .010 on the intake and .012 for theexhaust. I would have liked to know if the Kermathserial number was the same as the number Pontiacstamped on the engine block. The Code on the tag isPEBM 7. I wonder if PEBM stood for Pontiac EngineBlock Marine. We will probably never know.