1936 Nash OHV I6 Pistons

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1936 Nash OHV I6 Pistons

Post by Daniel Jones »

Are custom pistons available for the smaller bores and tall pin heights typical of older engines? I've got a 1936 Nash Ambassador with OHV I6 (3 3/8" bore x 4 3/8" stroke = 234.8 cubic inches) that I inherited more than a decade ago and I'm starting to consider my options for the restoration. According to my Motor Manual, the engine originally had a compression ratio of 5.7:1 and made 93 HP @ 3400 RPM with a single barrel Stromberg carburetor. Appears to have a 7 main bearing bottom end with insert bearing, pressurized lubrication, forged crank and rods, cast aluminum pistons (with Invar strut) with 4 rings (2 compression and 2 oil). Intake valves are 1.75" diameter and exhaust are 1.625". After 1937, the Nash OHV 6 had the intake manifold integral to the head and a semi-cylindrical exhaust log that clamped to the head but mine has conventional bolt on intake and exhaust manifolds. The cylinder head has a multi-piece rockershaft arrangement and the shafts have circumferential groove with the rocker arms are held in place by spring-loaded ball bearings. Head retention is by long studs which may have been in the engine for 87 years so have me worried. The twin spark plugs per cylinder are nearly horizontally placed and there are dual coils and points with a twin bladed rotor. Distributor cap looks like it belongs to a V12. I believe the twin ignition went away in 1942. Over the years, compression and power increased with the larger bore (252.6 cubic inches) 8:1 compression LeMans Dual Jetfire version making making 140 HP @ 4000 RPM through dual Carter side draft carbs. If I need to rebuild the engine, I'd like to increase the compression via domed pistons. Any leads on a piston manufacturer that could make such a piston would be greatly appreciated. I don't think camshafts are available so I'd be looking at a regrind. I believe the Super and Dual Jetfire engines got a bit hotter camshaft but, even if I could find one, I'm not sure it is backward compatible to my engine or not. Transmission appears to be a Warner T212 with an R1 overdrive. Anyone familiar with the T212? My internet searches haven't returned anything relevant.
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Re: 1936 Nash OHV I6 Pistons

Post by frnkeore »

The bore diameter is the same as a bored Ford FH. They have slightly domed pistons and Ross makes lots of Ford FH pistons.
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Re: 1936 Nash OHV I6 Pistons

Post by MichaelThompson »

My first call would be to Egge pistons. They make their own and may be able to make a custom set for you.
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Re: 1936 Nash OHV I6 Pistons

Post by MichaelThompson »

By the way the pistons made for an Ardun may fit the bill. I’ll bet you can get them in 3 3/8” + .030”
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Re: 1936 Nash OHV I6 Pistons

Post by PackardV8 »

The good news is that Nash is one of the stronger engines of that era. Kanter Auto Parts still has pistons in their catalog. However, don't take it to the bank as they do a lousy job of updating the catalog and the website. Many parts shown are vaporware.
Daniel Jones wrote: Mon Jan 02, 2023 10:16 pm Head retention is by long studs which may have been in the engine for 87 years so have me worried.
And well you should be! Those studs rust tight. Sixty years ago, I was replacing a burned valve in the 1952 version of that engine. The head wouldn't come loose, so I hooked a hoist to it and lifted the front of the car off the ground without loosening the head. I knocked the center out of a spark plug and screwed in a air line quick disconnect and put 150 PSI in each cylinder. Of course, it leaked out about as fast as I could move from hole to hole. It was one of the more difficult shadetrees I've ever done. Start two weeks ahead with Kroil or other penetrant.
Daniel Jones wrote: Mon Jan 02, 2023 10:16 pmNo camshafts are available so I'd be looking at a regrind. I believe the Super and Dual Jetfire engines got a bit hotter camshaft but, even if I could find one, I'm not sure it is backward compatible to my engine or not.
My local guy has cam masters going back to the Stutz Bearcat. Decide what you want and he's the one who can grind it for you.
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Re: 1936 Nash OHV I6 Pistons

Post by Daniel Jones »

> By the way the pistons made for an Ardun may fit the bill.

Ooh, the domes on those look promising. I've not seen a 1934 to 1937 Nash OHV combustion chamber yet but the period advertisements touting the twin ignition suggests it is basically a cylinder. Trim the dome to get the desired compression and allow for spark propogation (from both sides).

> They have slightly domed pistons and Ross makes lots of Ford FH pistons.

The pictures of the Ardun pistons I saw are also Ross. I'll be giving them a call once I'm a little further into this project.

> My first call would be to Egge pistons.
> Kanter Auto Parts still has pistons in their catalog.

I'm under the impression Kanter's pistons are from Egge and their gaskets are from Olsons. There's a set of Thompson Nash Ambassador OHV 6 pistons (p/n 737 +0.030") and rings on ebay at the moment. At $250 (or make offer), it might be worth it to buy them as a back up plan but, if I'm rebuilding this engine, I really want more than stock compression.

> My local guy has cam masters going back to the Stutz Bearcat. Decide what you want and he's the one who can grind it for you.

Excellent!

> The good news is that Nash is one of the stronger engines of that era.

If it wasn't, I'd probably already be onto Plan B (AMC/Jeep 4.0L fuel injected I6 and a T5 5 speed). Since Nash became AMC it would keep the engine in the family.

> Start two weeks ahead with Kroil or other penetrant.

Kroil is the stuff my dad used to use. On things like the Nash cylinder head where gravity can assist, torch heat plus candle wax might help too.

> screwed in a air line quick disconnect and put 150 PSI in each cylinder.

I thought about backing off the acorn nuts and cranking it over to let the compression pop it loose.

I pulled the rockershaft assembly over the holidays. When I removed the valve cover, my heart sank as everything up top looked to be covered in a thick layer of rust but what looked like rust turned out to be the remnants of whatever material (felt, leather or ?) was fastened to the inside top of the valve cover to drip oil down on the valvetrain. It had turned to dust and stuck to the oil residue. I vacuumed and scraped and blew everything out. Besides that, there was very little gunk in the rocker area so perhaps my dad cleaned the head years ago. Some rust on a few of the springs but those will get changed out anyway. I was surprised to see the rockershaft consists of three interlocking shafts with 4 rockers each. One set of 4 rockers were frozen to the shaft but I sprayed carb cleaner down the oil holes and then submerged the assembly in EvapoRust and got them to loosen up. The shaft is pitted but doesn't appear worn on the bottom. I'll replace the ball bearings and see if polishing the rockershaft helps any. The hold down bolts don't have any grade 8 markings (only marked with a "1" on top) but still look good.

Thanks guys! I appreciate the input.
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Re: 1936 Nash OHV I6 Pistons

Post by jred »

Kanter has their brand of pistons (rebuilders choice)

In the last couple of years I've gotten at least 10 or more kits from them,, 161 Willis flat head a couple of Studebakers a 331 Cadillac and some other's,,

The rebuilders choice pistons are as nice as some of egge's and I use both with no problems,,

Just ordered a set for a Burtz model a from Egges we'll see how good those look and work,,

If they Egges and Kanter don't have them you will probably need a set of customs from some like Auto/Race Tec..
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Re: 1936 Nash OHV I6 Pistons

Post by RCJ »

With 4 ring piston , if you were going to leave a ring out which would it be?
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Re: 1936 Nash OHV I6 Pistons

Post by PackardV8 »

Long strokes have more friction. If having custom pistons made up, use modern thinner three-ring pack.
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Re: 1936 Nash OHV I6 Pistons

Post by Daniel Jones »

Egge doesn't list pistons for the Nash 6 but Kanter does list them for later Nashes (mine has a different ring pack but I'm not sure if there are any other differences yet. In any case, rings and pistons are $827.37 for a set. I'd certainly pay the delta for custom high compression pistons with a modern ring pack.
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Re: 1936 Nash OHV I6 Pistons

Post by jed »

I have a 1959 Studebaker side valve 170 cid 6 cyl. I checked on pistons from Egge. They were something like $500. More than I wanted to spend. So I got in Wiseco and JE piston book and started looking. I knew the stock dimension and wanted something close. Jack said that block could be bored .100 no problems. I found a piston .070 over bore. .020 to tall on the deck height. and the pin was .130 to big. Some machine work necessary but all manageable for a cheep replacement piston. Summit sells them for $75 for a set of 4. I need 2 sets.
Point is take some time look around or have Ross or some other manufacture make some.
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Re: 1936 Nash OHV I6 Pistons

Post by Daniel Jones »

Thanks for the replies guys. I found some documentation from Nash that it's safe to bore the 3 3/8" block to the 3 1/2" bore of the later 252.6 inch Nash OHV 6 engine. Also, the Nash club store sells the larger bore pistons for a reasonable sum ($330) but they don't have the matching rings. One of the Nash Healey guys is finishing up a rebuild of his engine and was unable to find a ring set from the usual suppliers. He ended up piecing together a partial set of rings but ended up re-using his original "U-Flex" oil rings (he didn't bore his block). If I end up needing new pistons, I will definitely get custom ones made with a modern ring pack. That said, my plans have changed on this build. As luck would have it, a 1956 LeMans Dual Jetfire OHV 6 came up for sale semi-locally last week. I rented a truck and made the 440 mile round trip and it's now on the stand in my garage. Included in the deal is a Borg Warner T-86 3 speed manual and R-10 overdrive.

The LeMans Dual Jetfire engines are fairly rare and were developed for the Nash-Healeys but only 506 of those were made. Initially, in 1951, the Nash Healeys used the smaller bore 234.8 cubic inch OHV 6 with dual SU carburetors. Sometime in 1952, they switched to the larger bore 252.6 cubic inch engine with dual Carter YH-2369S carburetors for 140 HP which was used through 1954, the final year of Nash-Healey production. The Dual Jetfire was also optional in 1953 through 1956 Ambassadors, though most were equipped with the single carb Super Jetfire engine. 1956 was the last year of production and the only year with 12 volts and was rated at 145 HP @ 4000 RPM and 230 lbs-ft of torque at 2000 RPM versus 93 HP @ 3400 RPM for my 1936. I'm not sure how many of the LeMans Dual Jetfires were installed in Ambassadors in 1956 but I bet it wasn't very many since an optional Packard V8 was introduced a year earlier. Unlike my twin ignition 1936 engine, the 1956 has a single spark plug per cylinder which makes the distributor caps and rotors much cheaper (and still available from NAPA and RockAuto). The 1956 also has the notched exhaust pipe type manifold that clamps to the head and wraps around the front, exiting on the opposite side of the engine. The one on the engine is solid enough but Waldrons makes replacements in T304 stainless steel. BTW, I found correspondence between Sig Erson (then shop manager for Isky Cams) and a Nash Healey racer that mentioned Nash cams are steel instead of cast iron.

The seller said the guy he bought the car from claimed the engine had been rebuilt in 2005 and has less than 10K miles on it since then but he had no way of verifying it. The seller did claim it held good oil pressure, doesn't use oil and, after he rebuilt the carbs, ran great, getting 21 MPG on trips. He noted the carbs are very sensitive to float level setting. In addition to the carbs, the water pump and generator have been rebuilt and he supplied a new-in-the-box fuel pump to replace the one on the engine that still pumps fuel but no longer provides vacuum for the wipers, along with some spare ignition parts. From what I see so far, the signs are encouraging. I popped the valve cover off and it's spotless up top with the valve springs appearing new without any oil residue or surface rust. Unlike my 1936, the 1956 version of the Nash OHV 6 did away with the fiber rocker arm oil wicks but is still an adjustable shaft rocker design. I think I'll purchase some gaskets, pull the side cover, drop the oil pan to check the rod and main bearings and snake a borescope down the spark plug holes. Then I'll build an engine run stand, do a leak down compression test, fire it up and see how it sounds. If all seems well, I'll paint and detail and call it good enough for installation in the 1936 Ambassador. The fact that it's 12 volts is a bonus as I intended to convert from 6V anyway. I'll probably replace the unshrouded fixed blade metal fan with a pair of electric fans, install the largest Magnaflow stainless steel muffler that will fit, along with an MSD multi-strike ignition, and maybe duct cold air from a remote air filter to the carburetors. That should preserve as much of the power as is practical. I'm unfamiliar with the Carter YH carbs but they were also used on the Corvette inline 6, turbocharged Corvair and marine applications. It appears the needles, seats and main metering jets are interchangeable with more common Carter AFB.

The seller had his 1956 Nash converted to a carbureted Ford 302 V8 with a 3 speed, along with a 9" Ford differential. He lamented the lack of overdrive so I left him with a Tremec T-150 (Ford 3 speed top loader with Laycock De Normanville overdrive). He had a top loader 4 speed there and, though the T-150 was out of an AMC application, we verified the input shafts are the same and bolted it up to a Ford bell housing. If he wants to, I think he could swap the overdrive over to the 4 speed (extra points for using an aluminum SROD case). I got the Borg Warner T-86E 3 speed and R10 overdrive in exchange. Though I'm hoping the Dual Jetfire will bolt directly to the T-212 transmission and R1 overdrive in my 1936, the T-86E and R10 are Plan B if there is some sort of bell housing or crankshaft bolt pattern difference. I won't be able to use either the T-86E or R-10 directly though. This T-86E is set up with side levers for column shift whereas my car is floor shift and the R10 output is for a torque tube. I'm told you can unbolt the top cover and bolt on a floor shift from another T-86. I've got one here I'll try. Also, the output of the overdrive is for a torque tube instead of my conventional driveshaft. AFAIK, there's nothing wrong with my the T-212 transmission and R1 overdrive in my 1936 Ambassador but I can't find any information, much less a parts source for either. The R1 is the first version of the Warner overdrive. There's a whole bunch more info on the R10 including rebuild manuals. The factory repair manuals are much more detailed for the 1956 engine, transmission and overdrive too.
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Re: 1936 Nash OHV I6 Pistons

Post by PackardV8 »

Congrats on finding the last, latest, greatest of the Nash OHV 6s. Should be perfect for your application.
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Re: 1936 Nash OHV I6 Pistons

Post by Daniel Jones »

Thanks Jack. I'm excited. After I've got the Dual Jetfire running and in the chassis, I'll probably get the 1936 engine running too.
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Re: 1936 Nash OHV I6 Pistons

Post by Flo »

Although this might not be relevant for this particular case anymore, I want to add:
I had custom pistons done by JE several times for such vintage applications.
I always started off with finding off-the-shelve rings in a more modern dimensions. 2 compression, one oil, nothing crazy, soemthing like 5/64" or 1/6".
Then had JE make the pisotns according to all the domensions I wanted. For a set of 6 it was somethhing like $700 including pins. Not "cheap", but great quality and a major leap forward.
The weight savings takes load off of the rod, bearings etc. Strong forging, less friction from the rings. I thought this was well-invested.
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