218 flat six max RPM

[Plymouthy Adams]

yeah, its stock, but stock to what....lol

[FarmerJon]

I would doubt that there is any real way to know what was actually done to his race engines, but there were a lot of tricks used to get "stock" engines to perform. 

Careful blueprinting and balancing of the rotating assembly is key to high rpm durability, then and now. 

Picking the ideal factory parts was also a big help.

Look at the variety of minor differences in factory engines. You might find that truck engines have the same number on the rods, but beefier bolts, or a slightly better timing set, or a cam that had slightly more duration.

 

Guys also found many ways to straight up cheat, like acid porting manifolds. 

 

 

[Matt Wilson]

14 hours ago, Loren said:

From what I've read in the early days of NASCAR stock meant stock.

So that would mean the Pettys used Plymouth rods and rod bolts. The forging numbers were right there for all to see.

Assuming they were stock, and if 5200 RPM is even remotely close to what that engine was running, then that's impressive.  I realize it may not have been 5200 for the entire 500 miles, but even if the average was in the mid- to upper 4000's, then it's still impressive. 

 

I would imagine some careful checking of weights was done to ensure good balance and maybe some polishing of the bolts to remove nicks and such, which could be stress risers where fatigue cracks could start (since bolts might be less visible to judges or inspectors who would be inspecting the parts). 

 

Regardless, it's kind of mind-blowing to run a long-stroke engine continuously at such speeds.  I also realize it's probably the shortest stroke of all the DPCD flatheads, but still a long stroke by today's standards, for sure.

 

Interesting story about Smokey Yunick too.  I imagine every team was doing what they could to get around the rules without getting caught.

 

Speaking of high-rpm driving, I was taking with George Asche a few years ago, and he described a time when he and some buddies drove his flathead six at an estimated 4000 - 4500 RPM continuously for something like 8 or 9 hours while on a trip out west.  This was back in the early 50's, I believe, when they were practically just kids.  I'm pretty sure he said it was either a 251 or a 265 and it had the stock bottom end, but some other mods to increase the power output.  He says there was no sign of any engine issues after the trip was finished.  Again, kind of mind-blowing.  With my luck, if I were to try something like that, it would instead be engine-blowing.

[D35 Torpedo]

I'd say the major player in rpm limit would be the pistons. If they are cast iron, then they are pretty heavy. A guy could lighten them. Can anyone offer up some piston tech. Like what years were iron, when did they go to ali, and are there any common piston swaps?

[TodFitch]

13 minutes ago, D35 Torpedo said:

I'd say the major player in rpm limit would be the pistons. If they are cast iron, then they are pretty heavy. A guy could lighten them. Can anyone offer up some piston tech. Like what years were iron, when did they go to ali, and are there any common piston swaps?

Huh? When did Chrysler put cast iron pistons into the L-6 engine? My '33, the first year for the L-6, came from the factory with cam ground aluminum pistons and it seems highly unlikely that Chrysler would have back tracked on that item for cost savings.

[D35 Torpedo]

32 minutes ago, TodFitch said:

Huh? When did Chrysler put cast iron pistons into the L-6 engine? My '33, the first year for the L-6, came from the factory with cam ground aluminum pistons and it seems highly unlikely that Chrysler would have back tracked on that item for cost savings.

I don't know what/who gave me the idea. This is why I asked for any info regarding pistons. Maybe someone else can shine more light on the topic. 

[Matt Wilson]

1 hour ago, D35 Torpedo said:

I'd say the major player in rpm limit would be the pistons. If they are cast iron, then they are pretty heavy. A guy could lighten them. Can anyone offer up some piston tech. Like what years were iron, when did they go to ali, and are there any common piston swaps?

Most of the Dodge/Chrysler flathead engines had aluminum pistons.  I've never heard anyone on these forums, or other forums, talk about anything but aluminum pistons. 

 

Also, I have four factory or Army manuals, and they seem to indicate that nearly all of the engines came with aluminum pistons.  The only place I have seen an exception to that is in the Chrysler Six Cylinder Industrial Engine manual, from the early or mid-50's, which lists the industrial versions of the 218, 237 and 251 as having cast iron pistons, but oddly, it lists the industrial version of the 230 as having aluminum pistons.

 

My other manuals all state that the pistons are aluminum.  These include: 

 

-1942 manual TM 9-808 covering repairs of the 3/4-ton Dodge WC trucks used in WWII, which were equipped with the 230.

 

-1948/49 Dodge Truck Shop Manual (civilian vehicle manual), covering all sizes of trucks, which were fitted with the 218, 230, 237, 251, 282 and 331 cid engines.

 

-1952 Army 3/4-ton truck manual, TM 9-1840A/TO 19-75B-15, covering the M37 and M43 trucks, which were fitted with the 230 engine.

 

I've never heard of cast iron pistons in any truck or car equipped with these engines.  The only place is in those industrial engines, but not in any road vehicle or off-road vehicle.

Edited August 16, 2023 by Matt Wilson

[D35 Torpedo]

1 hour ago, Matt Wilson said:

Most of the Dodge/Chrysler flathead engines had aluminum pistons.  I've never heard anyone on these forums, or other forums, talk about anything but aluminum pistons. 

 

Also, I have four factory or Army manuals, and they seem to indicate that nearly all of the engines came with aluminum pistons.  The only place I have seen an exception to that is in the Chrysler Six Cylinder Industrial Engine manual, from the early or mid-50's, which lists the industrial versions of the 218, 237 and 251 as having cast iron pistons, but oddly, it lists the industrial version of the 230 as having aluminum pistons.

 

My other manuals all state that the pistons are aluminum.  These include: 

 

-1942 manual TM 9-808 covering repairs of the 3/4-ton Dodge WC trucks used in WWII, which were equipped with the 230.

 

-1948/49 Dodge Truck Shop Manual (civilian vehicle manual), covering all sizes of trucks, which were fitted with the 218, 230, 237, 251, 282 and 331 cid engines.

 

-1952 Army 3/4-ton truck manual, TM 9-1840A/TO 19-75B-15, covering the M37 and M43 trucks, which were fitted with the 230 engine.

 

I've never heard of cast iron pistons in any truck or car equipped with these engines.  The only place is in those industrial engines, but not in any road vehicle or off-road vehicle.

Thanks for digging up all that information. You pretty much put that topic to rest. I wonder if they are an alloy or straight up aluminum. So if the pistons are not the limiting factor to rpm, it will be the rods or rod ratio. Are these engines prone to spinning rod bearings?

[Loren]

Ford ditched cast iron pistons with the Model T last built in 1927. The Model As all had aluminum pistons.

Chevrolet kept them until 1953 or 4 as I recall. General Motors sold the tooling to Toyota and that engine came back to America in the Land Cruiser.

Chrysler had engineers who were wise to the problems of reciprocating weight and had moved to aluminum pistons early.

 

The issue is really about long vs short stroke. The fuels that were available during each automotive era had a lot to do with the design of the engines.

The war changed the thinking about compression ratios and fuel octane. High torque slow speed engines were desirable before the war and high horse power high speed engines became possible afterwards.

The metric that limits long stroke engines to low rpm is piston speed.

During the travel of the piston up and down, it has to speed up from a dead stop at the bottom and the top of the stroke to a peak speed in the middle, slowing back down to zero. That peak speed in the middle of the stroke is what limits the engine's rpm.

A long stroke engine will have a higher piston speed than a short stroke engine of the same displacement at a lower rpm.

Thus the advantage of Over Head Valves is better breathing at higher rpm and higher compression, all made possible with better fuel. A short stroke ( smaller than the bore ) went along with it. There was a time when engine data pages included piston speed as a specification. Now days most engines are short stroke and piston speed isn't even mentioned anymore.

[D35 Torpedo]

But there are plenty of big blocks, with big strokes, turning big rpm. So I don't think piston speed is the limiting factor. I use to remember what speed most pistons fly apart at. Think it was something like 33 feet per second. Edit googled it. 3500 fpm or almost 60 fps. Yeehaw thats a cast piston. Quick math 4.25" stroke at 4000 rpm is travelling 2800 fpm

Edited August 16, 2023 by D35 Torpedo

[Matt Wilson]

9 hours ago, D35 Torpedo said:

Thanks for digging up all that information. You pretty much put that topic to rest. I wonder if they are an alloy or straight up aluminum. So if the pistons are not the limiting factor to rpm, it will be the rods or rod ratio. Are these engines prone to spinning rod bearings?

No problem. 

 

One manual says the pistons are made of an aluminum alloy and another manual says "special aluminum alloy."  Pure aluminum is rather soft and weak, generally considered no good for structural applications.  It pretty much has to be alloyed (combined) with other elements (mostly other metals) to have decent strength.

 

I've heard of people spinning bearings in these engines, but I don't know that they are particularly prone to it.  A couple of folks who said they've spun bearings said that there were warning signs ahead of that, meaning knocking noises, and I seem to recall one of those gentleman, who visits this forum, saying he was too young and ignorant to realize what was going on before catastrophe struck. 

 

If the engine is in good shape and maintained well, then I'm told it will do ok at higher rpms for extended periods.  Mind you, for most people, higher rpms are 3000 -3200 or so.  I've read about a number of folks who say they cruise at those speeds often.  When I was driving my Power Wagon with a 230, I didn't have a tachometer or a good working speedometer, but I think I was cruising at close to 3000 rpm some of the time.  I ended up tearing down the engine for reasons not related to speed, and the bearings, crankshaft, pistons, rings all looked fine.

 

As for much faster speeds, it seems they will do it, but I wouldn't do it.  Too much risk for me.

 

But for some more interesting reading, you can do a Google search on Hudsonator, and you should come up with another example of some high-speed engine usage, discussed on forums (mainly on H.A.M.B., I think).  The guy and his father used to use a Dodge 230 in tractor pulls, about 20 years ago.  (Despite his forum name, he isn't only into Hudsons.) He said it would reach engine speeds of 5500 - 6000 rpm (for short bursts) without failure.  He said they had to do some oil system mods, like cross-drilling the crank, but otherwise, it sounded like it was fairly stock, except for mods to gain more power, of course.

 

Here's also an article by a gentleman who drove his early 50's Desoto with a 251 (later converted to a 265) all over the U.S., towing a heavy trailer and cruising at 3200 rpm or more, all day long, and his engine lasted pretty well (for back then), about 85,000 miles before the first rebuild, and then another approximately 85,000 miles.  It's a long read, but interesting.  He was meticulous about his documentation, just as he was with his maintenance.

 

https://www.allpar.com/threads/the-1951-desoto-suburban-long-term-owners-report-of-a-truly-noble-motor-car.236556/

 

I just find this stuff interesting because, for so many years, I heard people say that these engines wouldn't tolerate high rpms, meaning anything beyond around 2500 (some people recommended even lower speeds than that), but as time has passed, I've read and heard more and more stories about people who don't baby their engines nearly that much and the engines are doing fine, unless the engine is pretty worn out to begin with, or there is poor maintenance involved.

Edited August 16, 2023 by Matt Wilson

[kencombs]

14 hours ago, D35 Torpedo said:

But there are plenty of big blocks, with big strokes, turning big rpm. So I don't think piston speed is the limiting factor. I use to remember what speed most pistons fly apart at. Think it was something like 33 feet per second. Edit googled it. 3500 fpm or almost 60 fps. Yeehaw thats a cast piston. Quick math 4.25" stroke at 4000 rpm is travelling 2800 fpm

Agreed,  stroke does effect the max rpm, but lots of others things do too.  Probably the most significant is the weight of the rotating and reciprocating pieces.   Starting and stopping a long cast or steel rod is hard on everything.   That's also why chevy 216/235 with iron pistons were so tough on soft babbit rods.

[kencombs]

15 hours ago, Loren said:

 

Chevrolet kept them until 1953 or 4 as I recall. General Motors sold the tooling to Toyota and that engine came back to America in the Land Cruiser.

 

I still remember the first Toyota engine that I worked on.  Everything looked like a Chevy six.  Clearly the Japanese studied the Stovebolt very carefully before building it!   But it is not a copy as nothing interchanges.  General head bolt placement for instance, looks like the Chevy, but the actual measurements are not the same.   That one out of line head bolt has stymied many a shade tree mechanic.   We sold more than one head to replace those  damaged by using chisels or such to force a 'stuck' head off the block.  Bolt still in place!

 

I think GM stayed with cast iron on all the 216s, but switched to aluminum on the babbit versions of the 235.   All full pressure sixes had aluminum pistons.  Lots of them had the cast pistons replaced with aluminum at rebuild time.   And usually without any balancing, a testament to the great inline six configuration.  Sure couldn't do that with a V8!

[D35 Torpedo]

I went to a car show this last weekend. I met up with a bunch of others going to the same show, mostly corvettes....the show was far away so we hit the highway. Well....we were doing 80 mph down the transcanada highway for a good hour. The guys were surprised the ole girl did as well as she did. Rpm calculator says the engine was turning around 3600 at 80mph.

Edited August 17, 2023 by D35 Torpedo

[Matt Wilson]

54 minutes ago, D35 Torpedo said:

I went to a car show this last weekend. I met up with a bunch of others going to the same show, mostly corvettes....the show was far away so we hit the highway. Well....we were doing 80 mph down the transcanada highway for a good hour. The guys were surprised the ole girl did as well as she did. Rpm calculator says the engine was turning around 3600 at 80mph.

Wow, what engine do you have in it?  Even though there seems to be a good amount of evidence that these engines will do it without much ill effect, I don't think I'd have the guts to do it.  I'm too afraid that my engine would end up as one of those few that didn't handle it.

[D35 Torpedo]

1 hour ago, Matt Wilson said:

Wow, what engine do you have in it?  Even though there seems to be a good amount of evidence that these engines will do it without much ill effect, I don't think I'd have the guts to do it.  I'm too afraid that my engine would end up as one of those few that didn't handle it.

I don't know a lot about it. It was apparently rebuilt in 2000 and was never ran. I broke it in as a percaution. The material in the oil backed up that statement. The engine is stamped D35 aswell as the car. So 25" 218 with unknown over bore. When I compression tested it, it was 125 accross the board. But I forgot to open the throttle. It has a E7T2 ball and ball.

[FarmerJon]

Engine condition is a huge factor in what is "safe" for these old engines.

A half sludged up, 1960 sears rebuild with 75k miles on it is not going to survive the regular use that a factory fresh one would happily tolerate.  

3600 rpm is not abusing these engines (when they are in good condition)They are well designed, built and balanced from the factory (unlike many of their competitors of the time)

Just because they make more noise on the highway than your prius doesn't mean they are going to implode. 

 

As a note, Torpedo's 25" 218 should have a high-speed durability advantage over a US 23" 217, due to how the rods are paired.

 

Years ago, "Moparsled" on the HAMB built a 23" 230 for a dragster, and ran it several pulls on a dyno. He was spinning 5000+, making around 170hp at 4800 rpm or so. 

On tear down he did have some concerning bearing wear, but found that machine shop had not properly sized and aligned the main journals of the block, and quite possibly had left contamination in some of the assembly. He also noted that he was running NO oil filter.

[Matt Wilson]

11 hours ago, D35 Torpedo said:

I don't know a lot about it. It was apparently rebuilt in 2000 and was never ran. I broke it in as a percaution. The material in the oil backed up that statement. The engine is stamped D35 aswell as the car. So 25" 218 with unknown over bore. When I compression tested it, it was 125 accross the board. But I forgot to open the throttle. It has a E7T2 ball and ball.

One thing I'd like to mention, and maybe you've already addressed this, is that you need to be sure to re-torque the head bolts after the engine warms up the first time after a rebuild, and again after 500 miles (and some manuals may specify different internals and I would say it doesn't hurt to do it a few times).  If you overlook that, then there is a high likelihood of blowing a head gasket.  If you haven't done it yet, then I think it's a good idea to do it soon - better late than never.

 

I only bring this up because you said you didn't do the rebuild and don't know much about the engine, and it could be easy to overlook this crucial piece of the post-rebuild maintenance for these engines.

Edited August 17, 2023 by Matt Wilson

[wallytoo]

i'm one of the guys that spun a rod bearing in my flathead (truck 237)  but it wasn't the fault of the engine, just the rebuilder (me).  forgot to clean the oil passages after getting the block back from the machine shop, and after the first start, immediately made noise at #2.  pulled the pan, cleaned up the crankshaft as best as i could, added a new insert, and ran it for about 4 years.  pulled the pan about once per year and cleaned that #2 journal/insert.  put about 7k miles on it, too.

 

the last straw (or ****) was the 3-ton load of horse manure i was bringing back (the third trip of the day) from 40 miles away.  going up a steep hill, dropped into 3 high (from 4 low), rpms hit 3200, and that bearing really started screeching.  drove it another 6 miles with it screaming - it was already cooked anyway, and i had a spare 251 in the garage.  well, it finally spit the cap, slammed the rod, and stopped the rotating mass.  pretty loud noise.

 

 

 

 

i installed a tach in the truck - a 1.5-ton - and i regularly run it at 2900 to 3100 rpm.  both the original 237, and now the 251.  the p-15 picnic crowd from last year saw how well my truck goes along on the twisty, hilly roads, too.  having the 2-speed rearend is what makes it driveable on modern back roads.  i wouldn't drive it on the interstate, since 55mph is at 3100 rpm, and i can't hold that speed up any big hill.

 

[D35 Torpedo]

Tell me more about paired rods. I did retorque the head and checked it again. Maybe ill check it one more time.

[D35 Torpedo]

6 minutes ago, wallytoo said:

i'm one of the guys that spun a rod bearing in my flathead (truck 237)  but it wasn't the fault of the engine, just the rebuilder (me).  forgot to clean the oil passages after getting the block back from the machine shop, and after the first start, immediately made noise at #2.  pulled the pan, cleaned up the crankshaft as best as i could, added a new insert, and ran it for about 4 years.  pulled the pan about once per year and cleaned that #2 journal/insert.  put about 7k miles on it, too.

 

the last straw (or ****) was the 3-ton load of horse manure i was bringing back (the third trip of the day) from 40 miles away.  going up a steep hill, dropped into 3 high (from 4 low), rpms hit 3200, and that bearing really started screeching.  drove it another 6 miles with it screaming - it was already cooked anyway, and i had a spare 251 in the garage.  well, it finally spit the cap, slammed the rod, and stopped the rotating mass.  pretty loud noise.

 

 

 

 

i installed a tach in the truck - a 1.5-ton - and i regularly run it at 2900 to 3100 rpm.  both the original 237, and now the 251.  the p-15 picnic crowd from last year saw how well my truck goes along on the twisty, hilly roads, too.  having the 2-speed rearend is what makes it driveable on modern back roads.  i wouldn't drive it on the interstate, since 55mph is at 3100 rpm, and i can't hold that speed up any big hill.

 

I love how the 25" was mostly reserved for big trucks, and then Chrysler Canada went and stuck them into little cars like mine. An overdrive would be nice, or even a small diff ratio. It currently has 3.73s. 

[TodFitch]

6 minutes ago, D35 Torpedo said:

Tell me more about paired rods. I did retorque the head and checked it again. Maybe ill check it one more time.

On the shorter 23" block the center of the rod bearing is slightly offset from the centerline of the rod. When installed the offset on one rod is forward or backward depending on which cylinder (thus “paired”). On the 25" block the rod bearing center is in line with the centerline of the rod.

 

There is some thought that the offset on the rods on the shorter block may cause some issues at higher RPMs so the bigger block engine could be more durable than the shorter block engine. It has been enough decades since I took my statics and dynamics classes that I don’t feel qualified to give an opinion.

[D35 Torpedo]

2 minutes ago, TodFitch said:

On the shorter 23" block the center of the rod bearing is slightly offset from the centerline of the rod. When installed the offset on one rod is forward or backward depending on which cylinder (thus “paired”). On the 25" block the rod bearing center is in line with the centerline of the rod.

 

There is some thought that the offset on the rods on the shorter block may cause some issues at higher RPMs so the bigger block engine could be more durable than the shorter block engine. It has been enough decades since I took my statics and dynamics classes that I don’t feel qualified to give an opinion.

Oh that's interesting. I guess it depends how the bearing is loaded. How is it located relative to the piston? If it isn't centered on the piston, I could see the lack of symmetry applying thrust load to the bearing. 

[Matt Wilson]

Todd's description of the pair rods is good.  Here's an image to help too.  Rods #1 & 2, #3 & 4, and #5 & 6, respectively, are "paired."  The easiest ones to see are #3 & 4, but you have to look somewhat carefully.  They are mirror images of each other.  You can also see the offset pretty easily in rod #1.

[Matt Wilson]

37 minutes ago, wallytoo said:

i'm one of the guys that spun a rod bearing in my flathead (truck 237)  but it wasn't the fault of the engine, just the rebuilder (me).  forgot to clean the oil passages after getting the block back from the machine shop, and after the first start, immediately made noise at #2.  pulled the pan, cleaned up the crankshaft as best as i could, added a new insert, and ran it for about 4 years.  pulled the pan about once per year and cleaned that #2 journal/insert.  put about 7k miles on it, too.

 

the last straw (or ****) was the 3-ton load of horse manure i was bringing back (the third trip of the day) from 40 miles away.  going up a steep hill, dropped into 3 high (from 4 low), rpms hit 3200, and that bearing really started screeching.  drove it another 6 miles with it screaming - it was already cooked anyway, and i had a spare 251 in the garage.  well, it finally spit the cap, slammed the rod, and stopped the rotating mass.  pretty loud noise.

 

 

 

 

i installed a tach in the truck - a 1.5-ton - and i regularly run it at 2900 to 3100 rpm.  both the original 237, and now the 251.  the p-15 picnic crowd from last year saw how well my truck goes along on the twisty, hilly roads, too.  having the 2-speed rearend is what makes it driveable on modern back roads.  i wouldn't drive it on the interstate, since 55mph is at 3100 rpm, and i can't hold that speed up any big hill.

 

Wow, what a mess!  I'm sorry to hear that it went south like that.

 

What was the motivation behind annually cleaning the insert and journal?  Did you see that there was more than the desired clearance when you took it apart that first time (after the knock during the first run)?