updated november 2019
this site is documentation of the work i've done on the Rambler 195.6ci OHV inline six motor. most of these pages cover modifications and analysis well beyond repairing stock motors, but to make an endurance engine out of it i had to resolve a lot of long standing problems that definitely apply to a stock engine.
this isn't a replacement for a Rambler Technial Service Manual. it augments it. quite literally RTFM.
the goal for these mods is endurance, not necessarily increased power output. seriously, if flat-out horsepower is your goal, this isn't the motor for that. endurance means that i can (and do) run this engine at sustained 3000, 3200 rpm, more or less full power, up twisting mountain/desert roads in 100F ambient weather, for hours at a time without a break, and have absolutely nothing go wrong. (example drive; zoom into the wiggly lines). ("Doesn't matter how fast it is, if it ain't running.") so a subset of the modifications/fixes here definitely pertain to stock applications.
Frank Swygert has been a fan and source of knowledge for this motor (and much of AMC) long before me. his knowledge in the old AMC-list, and now the AMC Forum (theAMCForum.com) kept a lot of motors running, and part of the reason i persisted with this thing. so the writing here is mine (except where attributed) but one way or another it's rooted in his earlier work.
this site is documentation of the work i've done on the Rambler 195.6 OHV inline six that powers my rambler roadster. much of the work here is decidedly not stock, and few will bother with hot-rodding such an old motor. but in addition to plain old documentation and information my goal is to build modern levels of reliability and power. while this is a very modest design (putting it nicely), with the dubious distinction of having no performance parts available for it other than the factory two-barrel option ("Power Pak") it has proven to be a reliable engine, with forged crankshaft and connecting rods. most of it's shortcomings are easily overcome.
why "195.6"? Nash engine nomenclature included the decimal, i would guess as part of some long-forgotten "Nash Precision" marketing trope, otherwise, it's sort of annoying. AMC continued it, and that is what appears in service manuals and most internet search results, although enough people call this engine "the 196" to confound searches and identification. annoying or not, it's what all documentation uses so i continue it here.
Thanks to Frank Swygert for much information on this engine and for corrections to these pages.
This section by Frank Swygert:
Nash's economy L-head six was fitted with an overhead valve head for the 1956 model year. (No L-heads were sold for 1956 or 1957, but it reappeared again in 1958 and was available through the 1965 model year.) The 1956 model of the OHV still had the side mount water pump. The front mount pump came in 57.
The original L-head was a 172.6 designed specifically for the first unit-body Nash, the 1941 Ambassador 600. This increased to 184 inches in 1950 for the Statesman, and the new Nash Rambler got the 172.6. 195.6 came in 1952, again for the Statesman. The Rambler got the 184 in 1953, Hydramatic Ramblers got the 195.6 (small wonder -- the Hydramatic was heavy and took a lot of power!). 1952 was the last year for the 172.6, 1954 last year for the 184. All three engines used the same 3.125" bore, strokes were different (3.75", 4.00", 4.25" respectively). This was unusual since the crank and rods were forged -- the usual practice was to keep the expensive forgings the same and alter the cheaper to change block casting. I guess pennies didn't need to be pinched as much then as after the "merger" with Hudson.
if you are going to work on these motors you really need to have a legible copy of the factory technical service manual (TSM). a Haynes or Motors manual is no substitute. the TSM has detailed information you simply won't find elsewhere. for reference, here are the relevant 1961 TSM engine pages, along with the few 1965 TSM pages pertaining to the differences from the earlier motor.
this particular engine has been rebuilt at least three times. twice by me. when this engine was in the 1963 Rambler American 440 Twin Stick hardtop i got in 2005, it had a commercially rebuilt engine in it, .030" overbored. within a year i rebuilt the cylinder head due to sticking valves (old gasoline, foolish mistake).
in 2010 the engine was pulled and i did what i thought at that time was a careful rebuild. many of the successful modifications i made to this engine were done at this time. on this site i refer to this as the "2010 build". in 2014 i again removed the engine, did a cosmetic freshen then installed it in the current chassis, my rambler roadster. in august 2016 i drove the roadster in the LeMons Hell on Wheels '16 Rally, very hard in very hot weather, steep grades in Death Valley, which did some unpleasant things to the bottom end. when i got home the engine was once again removed, torn down, and this time, after careful diagnosis of it's various shortcomings and problems, completed what i call here the "2017 build", by a professional engine builder, Pete Fleming. that turned out to be a great (if expensive) decision as his machine work is impeccable, finding and fixing problems previous machinists either neglected or couldn't see. you get what you pay for.
as of this writing (november 2018) the 2017 build is broken in and has 27,000 fairly hard miles on it -- at a performance level that the 2010 build was not capable of and certainly would not have survived.
what follows is a summary and overview of the work i did. most of it easily applies to stock motors and are mainly the result of testing and measurement. a few problems are hard to solve, mainly oil cooling.
do not let this engine overheat, ever. if the temperature climbs to the high end of the gauge, stop driving or slow to 30 mph/light load to let it cool down. this engine is extremely susceptible to damage from overheating.
when 195.6 OHVs die it is nearly always from overheating, acutely or accumulation of years of prior abuse or neglect. this engine has engineering shortcomings that require attention and one fix, below.
this old, low-output engine paradoxically puts great demand on crankcase oil. i found two problem areas; excessive cam lobe and tappet wear, and crankcase oil overheating due to huge crankshaft journals. with constant (freeway) load at 2500 rpm and up, oil temperature rises alarmingly fast, independently of the engine cooling system. oil overheating is a serious problem not really addressable without invasive mods. more information is in the lubrication section.
i spent a lot of time working out induction systems, and for my fairly heavily modified motor a slightly larger carburetor is indeed an improvement; but otherwise, stock is perfectly fine, and larger/more will make it run worse. assuming you have a good one, which is no small feat in 2019. the castings themselves go bad and many old carbs are not rebuildable. aftermarket, the "Jeep Weber 32/36 DGEV" kit is just great.
my research, and results, tell me that the peculiar head bolt re-torque requirement for this engine is due to the head-cooling engineering issue. the 1/8" hole in the thermostat, or anything that causes slight coolant flow during cold engine start up, is sufficient to eliminate the need to retorque. discussion in the cylinder head section.
but torque-check every time you adjust the valves is not difficult. it does require a torque wrench. just set it to 60 ft/lbs, pull gently. if the tool clicks (or otherwise indicates torque) you're done. the issue isn't whether it's 58 or 60 or whatever ft/lbs; it's whether the bolt has backed out from temperature cycling. if they are all 55 ft/lbs, that's fine, doesn't matter. headgaskets leak and engines fail when some head bolts become loose.
the distributors available are all old and worn. new not available. at these RPMs contact points are fine. i'm always surprised by how crappy and loose people let the wires on the coil get (coil + and -). you should be able to tug hard on those wires. absolutely crimp them with a real crimp tool, not pliers. Pertronix modules are great. chances are your coil is not stock (it's old) and some need ballast resistors/resistance wire, some don't. it matters. but that's all just old-car stuff.
if i were to rebuild a 195.6 OHV engine for a daily driver that i intended to drive long distances with, this is what i would do today: