Cylinder head

03 jun 2022

This section covers the head, head bolts/studs, intake trough, valves, rockers, exhaust ports and mods, and pistons. head oiling, camshaft and especially lifters, valve springs and related are mentioned.

carburetion now has it's own section.

Overview



Cylinder head cooling

There is a serious engineering flaw in the cylinder head design that is a major source of failure and other problems with this engine. As serious as it is, there are two fixes, one easily doable in your driveway. Please refer to the COOLING SECTION for details.

Retorquing

The factory technical service manual for these engines has the peculiar requirement of cylinder head retorque schedule of check every 4000 miles, and re-torque every 8000, done while the engine is hot. This is just plain weird, and I am convinced this was due to the head expansion/thermal cycling problem designed into the head. In 1965 the cooling system was modified to solve this, the fix is easy to apply to earlier heads when the head is off. See the COOLING SECTION for details. With cooling system mods the retorque seems to no longer be required; my annual check now consists of setting the torque wrench to 60 ft/lbs and simply checking for loose fasteners. Not even one fastener in an improved engine has budged in over 10 years. I consider the problem identified and solved, but since valve adjustment needs to be looked at every other year or so, I check torque then.

Trough intake

The head has a trough intake, adequate and short short paths to each sylinder, with one 90 degree turn each from carb to valve. Combustion chamber is a popup wedge. The trough has clever Nash anti-reversion wedges that make for excellent fuel distribution, at least.

Some of the intake ports are paired/siamesed, some are not. Front to rear, the intake pattern is I-II-II-I. Fuel mixture is evenly distributed to the end cylinders, often a problem on inline sixes. Between cylinders 2 and 3 (and 4 and 5), adjacent to the second head stud from the front of the engine, you will see within the right hand trough wall a ramp-shaped protrusion cast into the trough. It pinches mixture flow at that point -- it is an anti-reversion device, preventing back-flow of intake mixture pulses. All six plugs burn to the exact same color.

The trough is covered with a cast aluminum plate, a very handy design for hacking induction. It's flat, easy to fabricate from scratch.

Valves

The valve setup is common enough, valves in the head with umbrealla seals, springs and retainers, and serrated keepers (3-groove intake, 2-groove exhaust). Valves are operated by pushrods and adjustable rockers on a rocker shaft. Lubrication is handled by a pressurized rocker shaft, fed through the rocker stands from the head. The head casting is fed pressurized oil at the front fo the block by an external line. There are early and late versions of the top-end oiling; see the lubrication section for details.

Valve springs should always be measured for height and tension, especially for this engine -- the OHV and flathead versions have identical-looking springs, but OHV springs are 80 pounds of force at the seat and the L-head engine only 40. In 2010 I purchased new springs from Kanter and in 2017 found that they were all 40 lbs.

Rocker shaft assembly

The rocker shaft assembly is straightforward and reliable. The shafts wear and new ones are not available. I've had no trouble with the rockers nor the adjusters. New adjusters are available.

The rocker shaft can't be inverted to wear the other side, as oil ports are milled into it to lubricate the bottom (loaded side) of the rocker.

For what they're worth, here are some rocker assembly movies taken while I was adjusting the valves.





Improvements



Head studs, not bolts

Most of the following are improvements to the cylinder head or it's attachment and sealing, useful only when the head is off and apart. Even if you are doing a freshen on a dead-stock motor you should consider some of these improvements.

In 2010 I replaced all of the old head bolts with studs, nuts and washers designed for this job, from ARP (Automotive Racing Products). These are so superior to bolts, relatively inexpensive, and so easy to do that I recommend this for even the plainest stock engine (such as the 195.6 OHV in my 1960 American Super wagon).

Head to block sealing is a very weak area of this engine. There is a single source for headgaskets, Best Gaskets (the 195.6 OHV gasket is part number 527G), of the old metal-sandwich construction. It needs a very flat surface and unlike modern gaskets, sealer. (I've found through experience that Permatex #3 works best, though copper sealant is shown in some photos here).

Here are some pics of the studs installed in the lab. this is the 2010 build.

Studs are superior to bolts for this application. When a head bolt is torqued, it remains twisted along it's length, due to friction in the threads and under the bolt head. Any transverse motion in the head (caused by thermal cycling...) backs out the bolts. With studs, all of this friction is at the top of the stud, which remains un-twisted. Quality and tolerances are better too.

Since ARP doesn't make a "kit" for this motor and my application isn't particularly stressful on the studs, I simply picked their stock parts from the catalog. There are three different stud lengths. They are coarse threaded at the block end and fine threaded at the top. Twelve-point nuts, machined washers and ARP lube was used. Part numbers are below.

Item ARP part number Quantity Location
Stud, 7/16" x 5.75" AP5.750-1LB 6 Through trough plate
Stud, 7/16" x 5.5" AP5.500-1LB 4 Head ends
Stud, 7/16" x 4.5" AP4.500-1LB 5 Under valve cover
7/16"-20 Nut APN12-1 15  
7/16" ID non-chamfer washer APW1316N 15  
Assembly lube n/a 1 Thread lubricant

ARP recommends three torque/release cycles before final use. I read and followed their recommendations exactly. I did this with the head on the block but no gasket since those are a one-time crush. The third cycle I let set overnight. Final assembly, with the headgasket and sealant, was torqued in a spiral patttern in three stages, to 70 ft/lbs. (AMC recommends 60; ARP recommends 75.) See elsewhere on this site for engine-breakin procedures. After final assembly with gasket in the car I measured stretch on one stud at .012" when torque increased from 20 ft/lbs to the rated 75 ft/lbs. Thanks to David Forbes for the measurement suggestion.

Upon every retorque each nut rotated the exact same amount. This was good, because two end nuts will not accept a socket when the rocker shaft is installed; I used a box-end wrench and extender and turned them the same rotational angle as the rest did with the torque wrench. (i'v never found a 12-point box end crows foot socket.)

The stock head bolts penetrate the block exactly one inch. Placement isn't that great, at least to my novice eye; some are along casting side walls, and some are in the middle of horizontal spans. Headbolt spacing is wildly uneven, but there's nothing to be done about that. Here are pics of the stock bolts and their protrusion through a section of a junk head:




Port work

On my 2010 build I did a heavy cleanup of the ports and combustion chambers with a Foredom tool and a big bag of abrasive rolls. For 2017 the head got a little more improvement by the builder including some proprietary valve seat and pocket work. I've never done this before; I claim no authority but man, were these ports awful. It would be hard to not improve (except for cutting through into the thin castign metal over the water jacket).

The best thing that can be said about this head is that the trough design keeps the ports short and relatively straight. However there was (is) substantial protrusion and sharp corners, and heavy valve shrouding. I was able to clean up a lot of that, but the 195.6 OHV cylinder head dissection revealed a lot of thin areas that precluded a better job. Nonetheless I think it's much improved.

The third retorque, at 1000 miles, zero rotation. It appears that stud stretch and headgasket crush is complete. [in 2010 i wrote:] I will continue to check it at intervals, but hopefully the need for constant retorquing is over [in 2018 this seems true].

Some of the intake ports are paired/siamesed, some are not. Front to rear, the intake pattern is I-II-II-I. this confounds port injection fuel-injector layout. throttle body injection would be adequate anyway.

exhaust ports and manifold

the exhaust side of the head is overall not too terrible, with the sole exception of the carb-heat provision in the center siamesed ports. in 2010 i equalized exhaust ports to make them all equal.

Head having (milling)

It is common to mill cylinder heads to clean up surfaces, or to raise compression. There's nothing unusual about this head in any way, but everything has limits... and the owner of this engine found it the hard way. I bought this newly-built engine for cheap because it had a slight rap, which turned out to be pistons just kissing the combustion chamber. Too much metal had been removed, an estimated .050". I don't have a hard limit to give you but it would be easy to derive from this knowledge and these photos showing precisely where the least-clearance is.

If you decide to mill a head (or deck) for more than clean-up, be sure to use clay to determine how much room you have. At this great age I would not make assumptions about prior work done -- measure.






head installation

To install the cylinder head onto the block, use guide studs, don't drop the head onto the sealant-coated gasnet adn slide it around to locate the holes. If you're using the recommended ARP studs, install one in each end of the block and use those as guides, then install the studs. If you're useing stock bolts then get lengths of threaded rod or chop the heads off long bolts to use as guides.

Assembly

Apparently at the factory the bodies were set over the engine and transmission assembly on the line. Preventing easy insertion from above is the front welded-in cross-brace, just behind the radiator top tank. Mine had long ago been hacksawed out, as is common. With it out of the way top-insertion is relatively easy.

I've installed engines without the head attached and with head and complete transmission. the latter definitely requires that the hoist have a load-shifting trolly and a lot of finesse.


other images

Below are photos taken for thi page over the years, some are redundant, but some aren't, and have no succinct place in the page, but might have interesting tidbits. These photos are of three or four engines, in no particular order; 2010, 2017, the 1960 American's '65 motor, and a cylinder head freshen.





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