Flat head combusti&#111;n chamber

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Posted: Mar/25/2021 at 11:25am

Thanks… Interesting process… I wonder if anyone actually tried it ...if so maybe they could post their experience

I need to run this by my brother… 60 years of Marine diesel engines ..outboard motors and tractors

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Posted: Mar/25/2021 at 9:34pm

43n, I wasn't too precise with the depth measurements. It's rough in there, and I was standing in front of the bench with a hand caliper. A better job would require sitting down and a depth tool that is vertical, placed carefully, etc.

Given that there's no underhangs, greasing it up with vaseline and pouring in plaster of paris or dental casting stuff (that stuff is very useful) then you'd have a positive model to measure.

I really want a flathead! I'm hoping the 1960 AMerican two-door wagon I'm gonna look at soon has one. Chances are its dead though.

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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Posted: Mar/25/2021 at 11:49pm

TomJ:… Your photos were priceless ..couldn’t find anything like them anywhere

I generally grease the head surface and use an acrylic plate with a hole and a burette of water to find the cc… Same for the gasket… Blocks are more of a problem especially if it’s relieved but anyway the calculated compression ratio often falls below the advertised compression ratio

A plaster 3-D model of the combustion chamber would be intriguing to analyze

This combustion chamber is really strange… The curved end over the piston rather than the traditional straight cut squish pad about halfway across the piston…?

What is with the deep bowl or dish where the spark plug is located?… Actually a dome when it’s inverted and the engine is running

The deep relief’s almost down to the top piston ring?

Maybe through trial and error they were onto something?

..Extra turbulence… Especially at part throttle ?

We know these engines gave outstanding fuel economy

… I know they could measure airflow back then however today it’s all about swirl and tumble And direct injection

two door wagon… Yes!… Good luck

Noticed a Rambler Engine on Tucson FB Marketplace for $100

The good news:oil pan cylinder head with spark plugs water pump motor mounts flywheel distributor all seem intact

The bad news: it’s been outdoors for years The carburetor hole and the exhaust ports are open to the atmosphere… Doesn’t rain much in Tucson but you have to assume water got into it

Has a PCV valve that should help date it...newer than say 1963??

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Posted: Mar/26/2021 at 5:14am

That small area over the valves then a larger area over half the piston has to induce swirl. The intake charge comes in the small area then is pushed over to the top of the piston where it expands... I don't see any way NOT to induce swirl!

The flat-head six gave good economy (and low performance) because it's a long stroke small bore engine. Almost all 40s and earlier engines are. Compression was low. The first flat-head of this design is thew 172.6 1941 Nash Ambassador 600 engine. 3.125" bore, 3.75" stroke, 6.70:1 compression, 75 hp @ 3600 rpm. It would reach 3600 on a test stand, but only about 3200 in the car -- in gear going down hill. so you never got up to 75 hp, more like 65 usable.

The long stroke and small bore make it a great tractor motor. Along with a low geared rear axle (4.10 was standard with the three speed manual -- very few high speed roads in the 40s!) there was plenty torque off idle to get the car moving. I don't know what the top speed of the 2600 (and some change) pound car was, but at 3000 rpm with 26.5" diameter tires and 4.10 gears, it would be traveling 57.7 mph. I'd say 55-60 was tops. Most people hardly used first gear unless taking off from an incline or loaded down. The typical form of driving was to start in second then go to third once up to speed (30 or so). Typical speeds were 40-45 on most roads, and most rural roads were dirt with lots of potholes. I grew up on dirt roads... 30-35 is more like it. The low speeds helped gas mileage a lot!

Frank Swygert

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Posted: Mar/26/2021 at 10:00am

This has been an interesting and enjoyable thread to follow.

Within the aspect of bore spacing it seems a flathead potentially allows for larger valves since they are not confined to the the width of the narrow bore of the similar OHV engine.

Regarding the notches in the block I too question that like 43n did. If the flow volume was needed why not just put it in the head? I have lightly notch blocks (OHV) in the past to increase flow around the valve. Others do this for (larger) valve clearance. In the flathead it would seem that rounding over the edge of the cylinder (above the top piston ring, on the valve side) would have helped flow rather then having the channel cut in the block and still retaining the sharp edge the mixture needs to flow over.

Another though that comes to mind is that in a OHV engine the flow spills over all 360 degrees of the valve. In the flathead the flow on the intake side would seem to predominately come over the 180 degrees closest to the bore since that is the direction of the draw. I'd think that lift would be a significant performance increase given that the flow is outputting roughly half the valve area (see crude drawing).

As to the spark plug indent it might better displace the flame front??? The early Honda CCVC engines actually had a small, rich mixture, secondary chamber that was ignited, then burned into the much leaner primary chamber.

The thing I find most interesting about this discussion is the AMC flathead was (to my knowledge) the last flathead ever offered in an American (and maybe any) car. Seeing one in a 1965 American caused me to double take the first time I saw one.

Edited by wittsend - Mar/26/2021 at 10:40am

'63 American Hardtop

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Posted: Mar/26/2021 at 9:28pm

I'm not convinced there was much, if any, hydrodynamic modelling or design done. It all looks like someone was winging it.

Lheads are cheap to make. Good observation though that side valves would provide room for bigger valves, but it wasn't done on this motor. Also the pocket for it would once again increase chamber volume. And at these RPMs and fill rates, small valves are likely just fine.

There's a lot of even-recent work on flatheads, so these things are knowable, though none of it was done on ramblers as far as I can tell! Side valve is side valve... I bet some grouchy old flathead Ford boards would have a lot of information on how they behave and how to make them better.

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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Posted: Mar/26/2021 at 9:40pm

43n wrote:

This combustion chamber is really strange… The curved end over the piston rather than the traditional straight cut squish pad about halfway across the piston…?

What is with the deep bowl or dish where the spark plug is located?… Actually a dome when it’s inverted and the engine is running

The deep relief’s almost down to the top piston ring?

I think the combustion chamber is really BAD, lol. Squish at least makes sense. All I know about it is casual reading, and the semi-obvious way it works (i'm sure dominated by subtleties I kow nothign about. A quick google of flathead squish shows a lot of lore and discussion.

I think the dish around the plug is oooold low compression leftover design, plus manufacturing convenience. Weren't the first versions of this motor around 7:1?

The water jacket is pinched to zero there; there woudl have to be a big dish on the top, or one on the bottom, for the top iron to meet the bottom iron, so they did both. (On OHVs the valve is in a head pocket.)

I too wonder about the deep 1/8" dead space around the piston crown, down to the top ring. It seems like it's there to keep the top ring cool -- I'm guessing here -- since clearly gases won't burn well there! The thin gas section in contact with the moving wall and piston would suck a lot of heat out.

(The OHV has the same awful wide dead space, but also the terrible pop-up wedge. From my studying of the chopped-up cylinder head I'm pretty sure the pop-up wedge's purpose is to make room for the intake trough -- clearly money savings over performance. THere is nothing "good" about the trough other than cost and compactness.)

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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https://images.app.goo.gl/yDF661oeUDPZ4Rwr5

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Posted: Mar/26/2021 at 9:49pm

...but maybe the spark plug dome is more squish! It's hard to second-guess hydrodynamical stuff....

via googling "flathead engine squish area", select IMAGES

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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