Home Documentation and manuals 195.6 OHV Engine Front suspension Rear suspension Brakes How-To's Case studies Other My cars


cylinder head

01 mar 2020

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. 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.

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 cylinder head dissection revealed a lot of thin areas that precluded a better job. nonetheless i think it's much improved.

carburetion

carburetion now has it's own section.

trough plate

the head has a trough intake, adequate and short short paths, with only 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.

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.

it has an interesting advantage in that it delivers perfect mixture distribution to all cylinders, a problem on long inline sixes. if you click on the picture above, 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 trough plate, a very handy design for hacking induction. It's flat, easy to fabricate from scratch if necessary.

carburetion now has it's own section.

valves

Be careful with valve springs. Used springs may be partially collapsed from age. Each spring needs to be checked at least for height. Flathead and OHV springs look the same, but flathead springs are 40 lbs at the seat, and OHV springs are 80 lbs. In 2010 i purchased new springs fro 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.

head oiling is accomplished by the rocker shaft itself being pressurized, via the front-most stand, up through a port in the head, which is fed by an external steel line. There are early and late versions of the top-end oiling; see the lubrication section for important details.

the rocker shaft can't simply 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.

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 installation

head sealing

this engine is known for head gasket failure and subsequent external coolant leaks, water in the oil, usually preceded by chronic overheating issues. see the cooling section for a simple fix to this problem.

before i had worked out the cooling issue i also replaced all of the head bolts with studs from ARP. after my experience with them here i will probably replace bolts with studs in all future engines.

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

head installation was actually a bit of an adventure. i did not want to drop the head on the sticky gasket and slide it around to find the bolt holes. my plan to install two studs and use those as guides was foiled by the fact that the thermostat pod needs to be fit under the from fender brace.

the solution was simple. i placed the gasket on the block, carefully aligning the holes by eye. i used the engine hoist and a chain bolted to the rocker shaft bosses to lower the head within an inch of the block, but not touching. i ran a couple of head studs down a front and a rear hole, aligned the head with one hand while i installed a stud with the other. then i could just lower the head onto the gasket and block and install the other studs.

head gasket prep and installation

i was very paranoid about head sealing. the block deck and head surface were double-checked for flatness [2018: or so i thought; see the head section] and immaculately clean and degreased. the gasket got three light coats of permatex copper, both sides, and i brushed on permatex copper around the steam holes. i bevelled holes in the head and block, though there was no sign of thread pulling, but what the hell.

the gasket was coated and allowed to more or less fully dry between coats. i assume that once in place, the solvents in the gasket cement are difficult to evaporate. the final coat was slightly tackier, and with the brushed-on spots around the holes (i mainly did that so that the micro-surface in those areas would be wetted with cement) i'm quite certain it was tight steel-cement-gasket-cement-steel sandwich.

2017 note: the head leaked anyways, between siamese pairs. likely due to the crappy deck surfacing.

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 added a bolt-in internal triangular brace between the inner fenders and firewall to replace it.

i've installed engines without the head attached (2010) and with head and complete transmission (2017). the latter definitely requires that the hoist have a load-shifting trolly.

ARP recommends three torque/release cycles on new studs. for the 2010 assembly, and before operation, I did four, without the headgasket, since that gets a one-time crush. I left the third torque to set overnight. 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.

The studs were bottomed in the block and snugged up with an allen key two-finger tight, assembled with ARP hardware and lube and torqued in three stages to the rated 75 ft/lbs. I did not start it until the next day.

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.)

these same studs were used in 2017, and the builder used his own method of assembly.

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, and that is utterly negated by the cooling system fix and ARP studs.

in 2018 i am still running the ARP studs installed in 2010, and other than initial break-in my annual torque-checking has revealed zero need for retorquing. without the thermal-cycling problem there is no need to retorque.

my annual check now consists of setting the torque wrench at 60 ft/lbs and simply checking for loose head nuts. none have loosened. since i have to remove the valve cover annually for valve adjustment (nearly unnecessary) this takes little effort.

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].

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

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:




other images