updated 03 Dec 2023
(The contents of these sections has been rearranged, but mainly block and rotating parts.)
|cylinder head (valves, head gasket, rockers, springs)|
|block and accessories (block, crankshaft, pistons, rods, covers, pans, balancer)|
|rotating parts (camshaft, tappets, timing sprockets and chain)|
|crankcase ventilation (PCV)|
This site is documentation of information I've collected and work I've done on the Rambler 195.6ci OHV inline six motor. Much of it will apply to the flahead too. These pages cover analysis and modifications to make these engines more reliable they were in their day, mainly but not exclusively cooling system engineering issues, not addressed by AMC until the engine's final years. These pages cover modifications and analysis well beyond repairs,
Keep in mind that considered from the present era this isn't an "American Motors" engine; this is a Nash engine, with Nash part numbers and is based on a motor introduced in 1946. AMC added a hastily-designed overhead valve head to the venerable flathead six (172, 184, then 195.6 cubic inches) in 1958 to squeeze a few more product years out of it. AMC introduced the new AMC six in 1964; that's a great motor, and was available for 40 years. This motor is decidedly not modern.
The year 1965 and it's low standards of reliability are far in the past, when an 80,000 mile engine was considered worn out. These engines are also now 50, 60 years old. Parts and expertise are scarce and expensive. We personally expect more reliability from cars today, too. And finally, modern technology and tools have removed most of the mystery from longevity.
There are suggested modifications to the engine throughout these pages. The goal of these is endurance, not increased power. If flat-out horsepower is your goal, this isn't the motor for that. The modifications vary from simple to invasive. With the more invasive mods endurance means that I can (and do) run this engine at sustained 3000 to 3500 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. (Look at this example drive; zoom into the wiggly lines). Doesn't matter how fast it is, if it ain't running.
The simplest of the modifications and knowledge will prevent failure in street cars in daily-driver service and require no permanent change to the basic motor.
Nash and AMC made continuous small and sometimes large engineering changes, often without changing the part or casting number. As per standards of the era, options and features came and went and often forgotten (E-Stick clutch, various incarnations of "heavy duty", ...). Repair shops swapped and modified parts to keep customer cars on the road, and it is common to find the engine overbored. All of this combines to make precise parts identification difficult. Luckily, blocks and most parts interchange with only minor warnings and issues, the ones I know about documented below.
195.6 engines are short, with only four main bearings. Cylinders are siamesed pairs (no water jacket between cylinder pairs) leaving a very narrow block deck surface that challenges head gasket sealing and requires care in block deck and head machining.
The OHV block retains the old flathead side valve adjustment access covers but there's nothing behind them but pushrod side view. The headbolt pattern sucks. Some of the headbolts draw up from vertical walls and some from horizontal webbing. The bolt pattern and block deck issues make for head sealing issues.
The cooling system is just adequate, but for one very serious flaw: thermostat location. Refer to the COOLING section below for more than most people care to know. It is imperative that some intervention be done on any running motor, even Sunday annual parade cars. These interventions vary from minor to machining-required.
The camshaft is a typical pushrod configuration, chain drive, under a cover on the front of block. The crank damper is typical enough with pulley groove. If original it has already, or is about to, fail, and needs rebuilding (new cast-in rubber). The fuel pump is driven off a camshaft lobe. mushroom cam followers install from bottom, requiring engine removal and inversion for access. The cam follower's very small diameter limits cam profile regrinding, as does the camshaft's very small base circle. The typical helical gear on the camshaft drives both oil pump and distributor, but each has it's own shaft and driven gear -- specifically the distributor does not drive the oil pump. All OHV blocks are drilled for the flathead's distributor location on the right side of the engine, filled with a welch plug.
So-called timing components (crankshaft sprocket, chain, camshaft sprocket) interchange back to 1946, with two variants, 3/4" wide or 1" wide changes and sprocket teeth. I am still researching which was installed when and where.
The cam bearing size was the same from 1941 to 1961, changed in 1961 and 1962, then in 1963 "metered top end oiling" was added (reduces top-end oil) by additional block passages, a slot on the camshaft front journal, additional holes in the front cam bearing, and a second steel line. (The American Interstate highway system came into existence as this engine was getting old, and it wasn't quite up to the task.)
In 1964 the oil pump system changed from by-pass partial filtering to full-flow filtering, on a new pump design. The old system is adequate of you change the oil frequently (fellow AMCer Joe's research found that all of the engine oil passes through the bypass filter in 10 or 30 minutes).
The rocker shaft is lubricated by an external 3/16" steel tube fed from the main gallery, into a hole in the head that feeds the front shaft pedestal (recall this was originally an Lhead motor). In 1958 this received full flow directly off the main gallery. In 1963 the valve train oil feed was from a new casting boss off the camshaft front journal just above the main gallery. The camshaft itself was modified; the front journal had a flat that with each rotation allowed a squirt of oil of approximately 30% of the cam's rotation, to limit total oil to the head. Refer to the oiling section section for details.
Crankcase ventilation was a simple road draft tube in the early years, PCV first in California then national in 1962 (I believe). The draft source (road or PCV) draws from front valve/pushrod access side cover. Air is taken in via the long crankcase oil filler tube dipstick vented cap, and many engines have stamped vents in the valve cover, depending on year and carburetor model. The 1964, 1965 motors have non-vented valve covers and non-vented oil filler neck caps. See the PCV section for details.
Connecting rods remain unchanged from the 1940's through the end of the engine series -- so part numbers would lead you to believe. Unfortunately there are different mass (weight) rods. I personally have had sets with 100 gram differences -- the six rods in the engine were all close, but two different engines had 100 gram differences. Don't assume -- measure.
Another dont-assume-measure item is valve springs. The OHV engine and the Lhead engine valve springs look alike, but the OHV springs are 80 pounds of force on the seat, while the flathead is 40 pounds. Every single spring needs to be checked, I've found mixed springs in engines and once bought new 80 lb springs from Kanter's and received 40 lbs when checked.
Frank Swygert has been a fan and expert and source of knowledge for this motor (and much of AMC) long before me. His knowledge in the old AMC-list, and now the The AMC Forum (theAMCforum.com) kept a lot of motors running, and a large 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.
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.
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.
I have a nice paper copy of the 1965 manual which I've found most useful overall, even for earlier motors. Mainly the differences will be in the oil pump area. For that detail refer to the 1961 manual. The differences from 1958 are quite minimal and for pre-1960, AMC documention is quite skimpy.
|1965 Technical Service Manual|
|Relevant 1961 TSM engine pages|
If someone will scan the 1961 manual I'll index it and put it online for everyone.
The engine in my roadster is not ordinary. It has been my ongoing test bed for some time. It has modifications that make little sense for a street car but in places I've pushed this engine to the breaking point (literally) and get endurance-performance from it that would easily destroy a stock motor. In late 2023 this motor is still working great.
The lessons learned on the roadster's engine definitely apply to a street motor.
This particular engine has been rebuilt at least three times, twice by me. When this engine was in my 1963 Rambler American 440 Twin Stick hardtop (2005) I got it had an older 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.
Here is a brief summary of things that you can do to greatly increase reliability of even the most modest 195.6 OHV (or flathead). Some are easy, some invasive, but the most critical issues, all cooling-system related, are fairly easy.
Absolutely never let this engine overheat, ever. By "overheat" I mean 215 degrees or more. This is a far lower number than the factory TSM suggests is acceptable. I do not let my engines exceed thermostat temperature -- 195 degrees -- by more than 5 degrees or so.
1963 was a long time ago, and the operating manual's suggestion that it's OK to operate this motor at the high end of the gauge, 235 degrees -- it actually says that, in ink on paper -- was bullshit marketing to make people think this engine was competitive in the market. I have measured these things and AMC is flat wrong. This engine overheats the oil at sustained RPMs over 3000 or so (as low as 60 mph depending on the axle) and that radiator is simply too small even new.
When 195.6's 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. It is inarguable fact that when these engines die, it is from running too hot. It's a 1940s motor run on 1960s roads and freeways. Put-putting down the road at 50mph and this motor is working harder than you'd like to think.
This old low-output engine paradoxically puts great demand on lubricating oil. Daily driver service in 2022 makes this old design engine work very hard, and in the extreme service of the roadster engine, when run at high loads consistently above 3000 rpm, engine oil temperature rises alarmingly; that engine has a very large engine oil cooler. lubrication section.
I spent a lot of (foolish but fun) time working out carburetion and EFI solutions and for my fairly heavily modified roadster motor a larger carburetor is indeed an improvement; but otherwise, a small stock-type is perfectly fine, and larger/more will make it run worse. Assuming you can find a good used carburetor, which is no small feat in 2022. The castings themselves go bad and many old carbs are not rebuildable.
My research tells 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.
Torque-checking each 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 or 62 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. Headgaskets leak and engines fail when some head bolts become actually loose. Overheating the engine multiplies this problem hugely.
The distributors available are all old and worn. New replacements are 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. It matters, but that's just old-car stuff.
When I build a 195.6 OHV engine for a daily driver this is what I do:
It was suggested to me that one of those oil changes isn't necessary. My answer is, oil's cheaper than motors. It is settled science that new-engine break in produces wear components that need to be removed ASAP. Break-in is not a place to save money. what, save $50 on a new motor? After 1000 or 2000 miles, the engine will feel "looser" (sliding surface roughness scraped off into the oil) and you'll need to re-do carb idle. ABSOLUTELY DO NOT LET ENGINE OVERHEAT DURING WARMUP!
This website was distilled out of multiple car projects over many years, and a lot of photographs were removed. Some for good reason, but others contain interesting details but don't fit into the narrative. They're all here, below, for what they are worth...
Redundant images here.