Hot-rodding the Nash/Rambler 195.6 overhead valve six

or other engines in the family

08 Feb 2012

new 28 May 2010

It seems like no one but me loves this engine. Too bad for everyone else, because it's a fine thing. It is the very end of a long Nash six evolutionary line, with an overhead valve cylinder head added by AMC in 1958 to squeeze more power from the old engine. Aftermarket performance parts were and are rare -- Offenhauser made a two-carb intake trough cover (think "manifold") for the aluminum version. (The "big" Nash six and the flathead got multi-carb setups and aluminum heads.) The cast iron 195.6 OHV, as far as I know, has no -- zero -- performance parts designed for it, ever.

But I love underdogs, and to be honest, it's the only engine (other than the flathead version of this motor) that "fits in the hole". And I took the abundance of ignorance about it as a challenge.

Thanks go to Frank Swygert for lots of information on this engine and for corrections to these pages.

Brief history

This section by Frank Swygert:

The 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 -- Hydro 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. Guess pennies didn't need to be pinched as much then as after the "merger" with Hudson.

Background

This is an incredibly rugged and long-lived engine. Nearly all problems with it stem from "old car" syndrome -- "it's an old car, just slap rings and gaskets innit" and wonder why it only lasts another... decade or two. Of the four engines I gathered and disassembled for this build, three had been rebuilt at least once and one showed convincing signs of two full rebuilds (.060" over pistons, etc.) Three had died from headgasket-related problems and one had a ventilated block (and a previously repaired cylinder head).

If you run any engine long enough, something will fail. These engines tend to get leaky headgaskets, the root cause of which I have figured out, and have an easy fix for.

Mine got water in the oil.

Joe found this car in northern California; a friend of his was going to part it out, and Joe convinced him it was worth saving. It had been found sitting beside a house for nine years, history prior to that is lost to the dusts of time. Joe hauled it down to me here in Los Angeles in 2007. I got it running and in the months that followed I gunked up the valves and bent some pushrods running it on old gas left in the tank (don't do that). I cleaned out the tank (amongst many other fixes) and rebuilt the cylinder head. The engine was painted gold, and had a tag riveted to it that said "REBUILT... POWER PAK". The car had one of those old-fashioned gas station service stickers in the door jamb; the car had 65,000 miles in 1975. When I got it it had 69995 miles. I don't think the odometer had rolled over, the rest of the car didn't have that much wear. My guess is that the rebuilt motor was installed after that. It was bored .040" over.

I then proceeded to put another 20,000 miles on the thing, and I did not baby it. I commuted 100 miles/day to work on the notorious 405 freeway and did one vintage rally of some 500 miles. In February 2010 mayonnaise appeared on the dipstick...


I pulled it and did a full, bottom-up rebuild. I knew back in 2007 that this day was coming so I'd gathered junk motors for parts and information. I bought an NOS rebuilt shortblock from eBay that got me a lot of new-in-1975 hard parts including pistons.

Besides a proper rebuild, I wanted to solve or at least address some of the shortcomings of this engine: the "head sealing" problem and partial-flow oil filtration. The latter worked out straightforwardly and the former uncovered, and I think, solved once and for all, a very old design flaw in the cylinder head cooling system. And none of this extra work cost any real money (eg. it's "Rambler mentality" compatible).

I ended up hot-rodding the engine a bit more than initially planned. Everything worked out great and two years later it's sorted out and running great.

Here are the major sections of the build that were out of the ordinary in some way:

Overview

The pages below detail the work done, but as overview, here's a summary of what I did to the motor.

Full teardown, and bottom-up rebuild. Very few "wear parts" were re-used or pulled from other motors, and all of those were hot-tanked, media blasted and magnaflxed where appropriate.

Block, head, crank, rods and pins and related are of course used parts. The block was honed only; the bores had almost no taper, but the pistons were somewhat scuffed, and the rings were ancient. New .030" over pistons and rings. New bearings, .010" over rods .020" over mains. Rods, pistons and pins were static balanced within a gram or so and the piston crowns polished.

195.6 OHV "RV" cam grind,
from Doug Galvin
Specs at .050" lift
Centerline 108 degrees ATDC
Lobe separation 108 degrees
Duration 202 degrees
Peak valve lift 0.39"

A new [reground] camshaft and new bearings were installed. This was an "RV" type grind bought from Doug Galvin. New (or refinished, unknown) followers. Though this was a 1963 block with the camshaft-timed top-end oiling (the slot in the front cam bearing that meters oil to the head) the head oil was plumbed from the main gallery, and the rocker assembly got full pressure oil, as the bypass filter was removed. The "blueprinted" oil pump provides more than enough oil for this. A new timing chain and gear set was installed.

Valves and springs are new parts from Kanter. New bronze valve guides were installed, and the casting was machined to accept Chevy-type valve stem seals instead of the old umbrella seals. A three-angle valve job was done. The other valve train parts (rocker shaft, rockers, pushrods and keepers etc) were select used parts.

Piston crowns were polished mirror smooth, with the goal of minimizing heat retention in combustion chamber parts. The heads were more or less pocket ported, not to increase volume but to knock down the huge number of flashing intrustions and sharp edges. The very rough casting inside the combustion chamber proper was smoothed with 80 grit abrasive rolls. My sliced-up head (link below) revealed that the unfortunate large intrusion between intake and exhaust valve pockets contains water jacket so I did no more than de-sharpen the edges for fear of weakening them.

The intake trough had flashing de-sharpened but was left otherwise alone. The anti-reversion pinchpoints were left as-is. The intake trough cover plate (that mounts the carburetor and serves as "manifold") was radically blended and smoothed to the Weber carburetor adapter and the bore opened up somewhat. A Weber 32/36 DGEV progressive secondary two-barrel carburetor replaces the ancient Carter WCD that reliably starved the main jets in every hard turn.

Exhaust-wise the engine isn't too bad stock, except that the center siamese exhaust port (cylinders 3 and 4) is very oddly shaped, with a near U-turn that causes exhaust to blast the roof/floor beneath the carb. This was boxed in with 1/4" steel plate to be the exact same size and shape as the other two ports. The exhaust manifold had the choke stove removed and protusions blended. The exhaust system consists of 2" pipe into a side-by-side turbo muffler, and exits in front of the rear wheel. It is approximately 70" long with three bends totalling no more than 110 degrees.

The cylinder head mating surface and the block deck were carefully made flat with a relatively fine surface. ARP studs replace the old head bolts with a new torque spec.

A small but critical change was made to cylinder head coolant flow. I am confident that this fixes a major design flaw in this engine. This incredibly easy mod and the reason for it is described below.

For reliability, the main oiling system was modified for full-flow filtration. A new pump cover was made, and the pump body modified for oil to exit out the cover through a carefully chosen filter, then into the main gallery. I experimented with "blueprinting" the oil pump and reducing the end clearances for increased flow; this certainly worked, but caused problems later; I've since replaced the pump body with stock clearances and have more than adequate oil volume and pressure.

The distributor has been removed and replaced with a Ford EDIS 6 ignition, controlled by a MegaSquirt Lite Junior controller. I ran a "hot-rodded" stock distributor for two years; both systems are described below.

Work detail

Previous work

Before the performance build, I'd done a number of smaller things along the way, some which were investigation for the build. Slicing up the junk cracked cylinder head, for example, had countless positive effects, not just for porting and such but for fitment and all sorts of 'what-if's.