[phoenixpnr]

I am working on a 57 347.
First question is, why are there "vents" on the exhaust side of the head to the intake valve guides, that have corresponding grooves on the intake valves?

Why are the openings into the block closed at the timing cover? If you run coolant into the cyl heads and then out the intake, is the engine really getting cooled?

Are there any overheating issues on the engines that use the transfer tubes from the timing cover to the heads?

Any insight would be appreciated!

[Jack Gifford]

Both of your first two questions are best answered in the Pontiac shop manual. Until I (or you) get around to looking at the manual, here's what I recall-
1) The intake guide vent passages were an attempt to reduce oil consumption ("positive" stem seals hadn't yet been developed).
2. The total capacity of the cooling system was "normal", with no inherent problems. The main justification Pontiac gave for the reverse cooling was to allow valve seats simply cut into the "native" head material (the water distribution tubes were an important aspect of this reasoning). A secondary reason was the faster heating of the crankcase (coolant transferring combustion heat to the block) to hasten evaporation of sludge-causing vapors from the crankcase.

[phoenixpnr]

Originally Posted by Jack Gifford

Both of your first two questions are best answered in the Pontiac shop manual. Until I (or you) get around to looking at the manual, here's what I recall-
1) The intake guide vent passages were an attempt to reduce oil consumption ("positive" stem seals hadn't yet been developed).
2. The total capacity of the cooling system was "normal", with no inherent problems. The main justification Pontiac gave for the reverse cooling was to allow valve seats simply cut into the "native" head material (the water distribution tubes were an important aspect of this reasoning). A secondary reason was the faster heating of the crankcase (coolant transferring combustion heat to the block) to hasten evaporation of sludge-causing vapors from the crankcase.

Oil consumption? Was the "extra" oil supposed to drain out of those vent tubes?
It just seems to me that if the guides get a little loose, there is an awful dirty vacuum leak!

[Jack Gifford]

No oil out, just eight "vacuum leaks", as you noted.

[pfilean]

And as I recall the problem the holes to make a vacuum leak to the valve guides that was supposed to bleed off vacuum so oil wouldn't get sucked down the guides was a fix that didn't fix much and a lot of the heads had the holes plugged by dealer mechanics.

[Safari Larry]

Originally Posted by phoenixpnr

Why are the openings into the block closed at the timing cover?

I don't know but it may have something to do with casting of the block. Those holes were used in later years (1960 and later) for pumping water from the water pump into the block. So another possibility is that the holes were in the design to allow for either reverse or non-reverse cooling.

If you run coolant into the cyl heads and then out the intake, is the engine really getting cooled?

Yes. Coolant enters the heads through the water distributing tubes which direct cooling water to the hottest parts of the engine, at the exhaust valves. Ports in the front of block lead directly to intake side of water pump. That creates a low pressure inside the block which causes some of the cooling water to be "sucked" into the block. During warmup prior to thermostat valve opening, all water circulates through the block resulting in quick block warmup.

Originally Posted by phoenixpnr

Are there any overheating issues on the engines that use the transfer tubes from the timing cover to the heads?

I assume you are referring to the tubes inside the heads. Pontiac calls those tubes "water distributing tubes". No reported cooling issues that I know of. It worked quite well. The shop manual has a pretty good description of the cooling. See also Pontiac Engine Cooling.

[phoenixpnr]

Thanks for clearing all that up!
I am so accustomed to later style engines, that I wondered if it was a design that was ineffective and there for changed in the later years.
In reality, it probably just saved money on production costs

[pfilean]

A lot of the plugged holes in castings were there to hold the mold core. Yes a lot are called freeze plugs because they may pop out and save the block when freezing but they were originally intended to hold the mold core.

[phoenixpnr]

Originally Posted by pfilean

A lot of the plugged holes in castings were there to hold the mold core. Yes a lot are called freeze plugs because they may pop out and save the block when freezing but they were originally intended to hold the mold core.

Considering how these era engines are cooled, I am guessing that the front holes in the block were used as core holes. Rather then plugging them like the side ones, they used the timing cover instead?

[pfilean]

Since some of the early engines had "reverse' flow the block holes in this situation were probably for core support but came the flow return that went past a thermostat to the radiator. Would need an old picture of the original engine configuration to convince myself that was the way it went.

[Safari Larry]

Originally Posted by pfilean

Since some of the early engines had "reverse' flow the block holes in this situation were probably for core support but came the flow return that went past a thermostat to the radiator. Would need an old picture of the original engine configuration to convince myself that was the way it went.

See the link I gave earlier for those old pictures and an explanation of water flow through the block for reverse flow (1955-59) and "conventional flow" (1960 and later) engines.

Those large holes in the front of block identified by you as "core support holes" (good info!) were sealed off in the reverse flow engines by the timing cover. In the "conventional flow" engines those holes were matched to water output ports in the front cover and used to deliver water from the water pump into the engine block. Reverse flow engines pumped water into the heads and later conventional flow engines pumped water into the block through those holes.