Some Thoughts On MoPar Flatheads - 1

[grey beard]

What follows are a few of my own observations, made from more than forty five years in the automotive trade. They are offered purely as an aid to those new to flathead engine quirks and differences. Your own experience may vary from mine. This is fine with me. I am still learning a little every day, myself . . . dte

Valves

The valve train is lubricated entirely by the splash effect of the camshaft and valve train. The only pressure feed to the system is to the cam bearings. The oil that escapes the camshaft journals and any splash resulting inside the crankcase from the reciprocating crank mass are the sole source of lubrication for cam followers, springs and valve guides.

Common sensed says that exhaust valves and guides run at a higher temperature than intake valves and guides. Coupled with this temperature differential is the fact that intake guides are subjected to manifold vacuum, (meaning that they tend to suck oil into the guide), while exhaust guides work in the environment of exhaust pressure and heat. These two facts, temperature and pressure, mean that exhaust guides get virtually no lubrication. As a result of this fact, they are one of the more likely components in the valve train to wear out first.

Having said this, a quick look at these engines shows that they, like most automotive engines, sit high in the front. This means that in a splash lubricated valve train, the highest component is also the farthest from the source of splash lubrication – the cam bearings and followers.

Happenstance (and perhaps MoPar engineering) have dictated that the frontmost engine valve in MoPar flathead engines is an exhaust valve – the ones that wears first, anyhow. All this combines to mean that the front valve guide is the hottest, least lubricated and most prone to wear out. Disassembly and inspection of many of these engines have led this writer to believe the front valve guide nearly always exhibits the greatest amount of wear of all the engine guides. Second in likelihood of wear are the remaining exhaust guides, while intake guides rarely if ever show wear. If intake guides do leak, they tend to draw oil into the guide, which tends to aid lubrication. No valve seals are used on flathead engines.

MoPar engines use hardened valves and seats as standard equipment. In this area, these engines are truly overbuilt. When valves show wear, they are invariably exhaust valves. Experience has proven that worn exhaust valves are nearly always caused by worn valve guides. Exceptions to this rule can be a piece of carbon or other debris causing a valve to hang open and burn.

Lubrication Systems

Mopar flathead engines were manufactured at a time when the technology of engine oil was still primitive, by today’s standards. Much of the wear restorers encounter upon disassembly is the result of the poor state of available lubricants. The oil we buy and use today is light years ahead of that available fifty years ago.

Bypass oil filtration systems were never very helpful, but happened to be the only thing available in the forties and early fifties for these engines. The nature of bypass filtration is that likely ten percent or less of the total oil circulated by the oil pump ever gets to pass through the filter. The line that feeds these filters is the smallest diameter steel line used in automotive manufacturing. Even this meager amount of volume allowed to pass through the filter system is shut off during periods of low oil pressure, and only opened for circulation when oil pressure rises above a given pressure point. These bypass filters were optional, for many engines were produced without them.

Full-flow oil filter systems, by comparison, filter ALL oil that is picked up by the pump and circulated inside the engine. Several restorers have performed work-around adaptations for these engines to adapt full-flow filtration to them. This improvement, in this writer’s estimation, goes a long way toward extending engine life. Full-flow oil filtration coupled with modern high detergent oil technology, will allow these already-well-built engines to last much longer between overhauls.

Engine Blocks

Do not be fooled by the small (218/230) cubic displacement of these engines. They are heavy block castings that warm up slowly due to their large mass. The water jacket inside the block is only present in the top several inches of the casting, where the heat of combustion is greatest. On the passengers’ side is the valve chamber, and there is no coolant flow below the level of the water distribution tube, well above the camshaft level. On the driver’s side, the water jacket extends down to the block core plugs and petcock, but the flow is mainly limited to the upper section. The area on the petcock side is typically where sediment and dirt settle inside the block. I have seen these blocks filled with sediment above the tops of the core plugs at the rear. This of course must all be cleaned out as part of any overhaul. Remove all block core plugs and use whatever method you have at hand to make sure everything is clean and free of sediment and dirt.

It is logical to believe that these fifty-plus year old engines may have several hundred thousands of miles on them, in spite of what you want to beleive. Logic further dictates that cylinder heads have been removed several times for valve and piston work during the life of the engine. While the head is off, it is a good thing to check the deck with a straight edge, both for warpage and for distortion. It is not likely that an engine has been overheated sufficiently to warp the entire block casting, but close inspection usually shows some heaving or mushrooming of the deck surfaces around each head bolt hole. I have been successful in removing these distortions with a sharp flat file. Just start at one end and swipe crossways over the deck area. This will reveal high spots around each head bolt hole. These can be filed down to a true flat area with a little diligence. The result is a more precise deck surface against which the head gasket can seat. Most folks know that heads can be safely milled sixty or seventy thousandths to improve compression ratios. Even if this is not important to you, a resurfacing of the head is recommended, just to be sure of a flat surface for the gasket. If you can afford it and your block is at the machine shop for cleaning anyhow, have them resurface the deck a few thousandths to get a true surface. The same advice would not hurt a bit for the manifold gasket surface on the block.

Crankcase Ventilation

Another element of engine technology that has gained vastly from modern engineering understanding is crankcase ventilation. Originally designed only to ventilate the crankcase of fumes and condensation, this system is forced into double duty when an engine begins to wear excessively, for now it also has to handle blow-by products of combustion that have escaped past worn pistons and rings..

Positive crankcase ventilation (PCV) systems were originally mandated with a view toward limiting crankcase emissions. A secondary benefit of the PCV system is its ability to remove much more of the condensation and moisture from the crankcase than was originally possible with the primitive road draft tube that was always open to the atmosphere. Yet another advantage of the PCV system is its ability to disperse any blowby from the crankcase by returning it in the engine.

It is easy to modify these flathead six engines from the original road draft system to the newer, superior PCV system. This is true mainly due to Chrysler’s involvement in military vehicle production during WWII. Many of these military vehicles were equipped from the factory with engines designed to ford streams and run in semi-submerged conditions for short periods of time. One part of these engine sealing systems was the PCV system designed to keep water OUT of the crankcase.

A direct result of this fact is that most military vehicle parts suppliers are equipped to offer the PCV adaptor necessary for this conversion. This writer found one at Vintage Power Wagons. The adaptor is a round, cast metal piece that bolts to the rear of the block in the same spot as the original road draft tube. From this adaptor, 3/8-inch tubing is routed forward and up to the intake manifold. A pipe plug in the center of the intake on the outboard side can be removed and this line connected to it as a vacuum source. In series in this line must be a PCV valve, of the type typically used on any engine of equivalent cubic inch displacement. Because of the closeness of this vacuum line to the hot exhaust manifold, this writer chose to use an all-brass PCV valve, available from the same military source. A PCV system on these engines, coupled with modern oil and a by-pass filter, offer a recipe for extended engine life.

[Johnny S]

Thanks.....this is great

[Don Coatney]

Dave;

Thanks for sharing your well written thoughts. Installing a PCV system is on my to-do list. I am fortunate that my Desoto engine has factory provisions for a full flow oil filtering system. The valve lubricating system has a provision that you did not mention. The piston rods have a small hole above the crankshaft bearing journal that points towards the valves when installed correctly. This hole is designed to squirt oil under pressure on the lower portion of the valves and valve guides as seen in the attached pictures.

[grey beard]

Hey Don,

You are absolutely right - I had forgotten the oil hole in the rods. Thanks for keeping me honest.