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Aluminum Connecting Rods


JV Puleo

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There is another little wrinkle to piston design, and that is the offset. By offsetting the wrist pin you reduce piston slap. There are 2 ways to do this, one is to offset the crankshaft sideways relative to the cylinders. The other is to offset the wrist pin in the piston. I believe they knew about this as far back as 1910. Your engine probably has the crankshaft offset, as that is the way they used to do things. On more modern engines they offset the wrist pin. One more thing to check before you start machining.

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Rusty, thanks very much for the interpretation of the chart.

 

The coefficient of expansion has already been calculated by the gentleman who made the piston patterns for me — one of my antique machine collecting friends who is extremely competent at this sort of thing. In fact, the drawings he did for the piston will be the first part I've ever made from a real drawing.

 

The crankshaft is offset 1" from the center line of the blocks.

 

I very much disagree re Sir Henry Royce. I think he had plenty of imagination and he was certainly a competent engineer. There was a great deal more engineering knowledge available then than we commonly think today. He was elected to the Society of Mechanical Engineers long before he was involved in the automobile business, with no formal training aside from an unfinished apprenticeship with the Great Northern Railroad – when still working for Greenwood & Batley, one of the most prominent British machine tool manufacturers. Royce was also very conservative and a meticulous mechanic who insisted on a very high level of workmanship. I'm no engineer either and don't aspire to be one but I am a reasonably competent mechanic with a lifelong admiration for really good mechanical work... thus my admiration for his work.

 

I'm constantly borrowing ideas from other areas so I don't see anything wrong with that.

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Neat thread! :P

 

I've got a 1923 Hupmobile 4 cylinder car,  still running and driving.  But I have always wondered about rebuilding my spare engine with modern techniques and materials. I wonder if tactics like reducing weight of the rotating internal mass, adding some kind of balance weights to the crankshaft, etc, etc, would be worth the cost and time. And then I wonder if you would need to reduce the weight of the flywheel as well? And would it be a mistake to boost compression at all? Would there be any value in larger valve sizes, smoother (slightly larger) intake and exhaust ports? 

 

But then my wiser friends from the old car club are quick to point out that my old touring car cruises easily at 55 mph now. And besides, it's only got 2 wheel mechanical drum brakes, which are external, with wood spoke wheels. They point out that I don't need it to go faster, and it runs fine like it is. Still, I do wonder sometimes...

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When I said Henry Royce lacked imagination that wasn't a crack. I was quoting Henry Royce himself. During his lifetime his cars had no innovations and he bragged about it. Every new feature was adopted only after it proved itself on some other make.

 

Lump about your Hupmobile it would be possible to increase the HP by 50% or more.  Even 100% would not be out of the question. But somewhere around there you reach the limit of strength of the original block crankshaft and connecting rods.

 

I don't know about Hup but a lot of cars in the 20s were hopped up for street and road use as well as for racing. Ford, Dodge and Essex were favorites.

 

Today it seems kind of pointless. Although there are enthusiasts who continue to work on their Model T speedsters, and the like. But if you want to build a Hup 'special' here is the place to run it.

 

http://theraceofgentlemen.com/

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2 hours ago, lump said:

Neat thread! :P

 

I've got a 1923 Hupmobile 4 cylinder car,  still running and driving.  But I have always wondered about rebuilding my spare engine with modern techniques and materials. I wonder if tactics like reducing weight of the rotating internal mass, adding some kind of balance weights to the crankshaft, etc, etc, would be worth the cost and time. And then I wonder if you would need to reduce the weight of the flywheel as well? And would it be a mistake to boost compression at all? Would there be any value in larger valve sizes, smoother (slightly larger) intake and exhaust ports? 

 

 Short answer... yes but I'd do it carefully and not probably not everything that can be done. Certainly lighter pistons and dynamic balancing would be a big improvement. Rather than increase the size of the valves, I'd make sure they were perfectly seated and the guides were tight. I doubt you can add weights to the crank, but they can now be dynamically balanced to a far higher standard than was possible at the time. You can probably raise the compression ratio but not to "modern" levels. With my 1910 Mitchell, I'm not trying to make it faster. I would like to go up most hills without downshifting and, most important, I'd like it to be able to sustain a speed of perhaps 45 or 50 without feeling like it was shaking to bits. I don't plan to drive it that fast - or at least not often - but I'd like to have the capacity to do so if, for some reason, it was needed.

 

Years ago I drove my 1910 REO from Rhode Island to the far end of Long Island. It was an all day trip over secondary roads but in two places I simply couldn't get to where I needed to be without going on the highway for a very short distance. It was early in the morning and traffic was light but I felt it was asking for trouble to do that traveling less than the legally mandated 45mph.

 

I've never found two-wheel brakes to be as dangerous as some would make them out to be. They MUST be properly adjusted and this often means extensive rebuilding of all the metal-to-metal connections so that everything is smooth and straight. It is using them under adverse conditions, such as in the rain, that worries me more. I've had that experience as well. I haven't gotten to the brakes on my chassis yet, but when I do everything is getting new bushings and every other part that shows the slightest wear will be renewed.

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Lump if you wanted to hop up your Hup there are a lot of things you can do without spending a lot of money. The kind of things they did back in the 20s to hop up a car like that.

 

Start by 'blueprinting' the engine. Make sure the crankshaft, bearings, cylinders etc are as they should be. Grind the rods smooth and polish them. Replace the pistons with lighter, higher compression aluminum. Lighten the flywheel as you said. And have the whole reciprocating assembly balanced.

 

Smooth out the ports and fit new valves. You may be able to thin down the valve guides if they protrude into the ports. No need to use larger valves. Do a 3 angle valve job and grind the intake seat to a 30 degree angle.

 

It may be possible to have the camshaft reground by someone who does Model A or similar. You could fit a bigger carburetor and straight through exhaust pipe. In the twenties it was the style to run a straight exhaust pipe down the side of the car, made of copper plumbing pipe. It was said to give an exquisite exhaust note.

 

All this could well result in a 50% horsepower increase with no loss of driveability or reliability. Of course it would really be great if you could find a cheap Hup chassis, and build a speedster.

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A short update on the aluminum rods...

The SAE handbook proved a disappointment although I'm certain it will be useful in the future. I did track down the 7th edition of Heldt's book, published in 1926. I'm hoping that will be more useful. Heldt was so thorough I think there is a good chance he covered them. I am thinking that if I can get specifications for Lynite rods, I could consider the difference in strength between them and the 7075-T6 as a safety factor. I'm not building a racing engine so getting them as light as possible isn't the goal... I just want to be lighter than the originals and, more importantly, balanced. I'm also taking some measurements from the Franklin rod I have and extrapolating them using the maximum explosion pressure generated by the much larger Mitchell pistons. We'll see how the number correlate.

 

Edit: Lump, one of the characteristics of early engines is that they are frequently undercarburated... with smaller intake manifold dimensions than would be optimum. This was to inhibit rpms because the largely unbalanced components would result in severe vibration. If you balance everything, you no longer have the problem they had.

Edited by JV Puleo (see edit history)
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FWIW to help with load design. That Franklin rod you have pictured was original built for use with 3.5 inch aluminum pistons, 4.75 stroke, and 5.1:1 compression. Many owners with tall rear gearing cruise up to 3000 rpm without problems.

 

We haven't run into problems using them with up to .080 over pistons and raising the compression ratio up to 7:1. So far, the rod strength is not the limiting factor - getting close to maxing out the cylinder cooling ability at 7:1 has been.

 

Paul

 

 

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Thanks very much... that is excellent information. I had the bore dimension but not the compression ratio. The fact that you have raised it to 7:1 means that it must have been getting close to the same explosion pressure of the piston I'm working with. I'll post the figures when I've worked them out and solicit more opinions.

 

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Does you 27 SAE hand book list AL65 aluminum alloy ? I know my 28 copy listed alloys, but I can't remember the details. I donated it to the Franklin Club library about 20 years ago.  

 

The Franklin rod drawings of around that time list both the Lynite 25ST and AL65, so they may be the same, or very similar alloy mix ?  If you can find out what AL65 is it may tell you what Lynite 25St is ????

 

Paul

Edited by PFitz (see edit history)
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Actually there is no explosion the fuel air mixture burns.  Of course knocking or pinking is sometimes caused by the mixture burning prematurely, but even then it is not exploding.

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Maximum explosion pressure was defined as the pressure generated when a car was miss-firing and got two or three charges in the cylinder before it ignited. This was probably much more of a problem in 1910 that it would be today but it is still a worthwhile yardstick to predicate the strength of the rod on. I am curious to read the 1926 edition of the book I'm using. By then, some of these figures may have been modified. In 1911 the highest compression ratio envisioned was 5:1

 

PFitz... do you have the cross sectional dimensions of the Franklin rod? I've discovered that my thickness indicator won't open far enough to measure the rod in the center.

 

 

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The beam is 3/4 by 1-1/8  inch. The web joining the two flanges is 3/16 inch thick in the center.

 

As you can likely see on the rod you have, the flanges taper wider from a 3/32 radius at their outer edges to the mid point of each flange, then each tapers narrower as they meet and blend with 1/4 inch radiuses into the web. The web having the narrowest cross section of the rod's beam.

 

Paul

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If that Franklin rod has no taper to the beam is should be a 1929 or earlier rod.

 

If it is a 1930 for the 95 hp, or 31 and later 100 hp engines, it will be slightly thicker in cross section, and the beam tapers slightly from end to end. The web stays a constant thickness and will be 7/32 inch thick.

 

Paul

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Duesenberg Model J originally used aluminum connecting rods (and tubular steel rods on the supercharged versions), but many if not most of the aluminum rods have now been replaced due to failure or fear of failure. Was the reason the increased 4000+ RPM of these engines?

 

Are aluminum rods being used in modern engines? 

 

Looking forward to your information and views.

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I've never heard of a Dusenberg rod failing but I imagine that most owners fear it might - hence changing them. They are commonly used in racing engines and everything on the net is aimed at that market. I've found it very difficult to get any objective information about their suitability for my purposes with the exception of the Franklin enthusiasts who appear, to me, to be better informed about things like this than most. It is quite clear that they will work and that they aren't the "time bomb" some would make them out to be. All that really has to be sorted out are the dimensions.

 

Pfitz... AL65 is not in the 1927 SAE Handbook. They list only alloys 30, 31, 32, 33, 34 and 35 with no mention of the use of aluminum for connecting rods. Of course, these are SAE recommended dimensions and materials and many of the specifications in the 1927 book go back to 1911. If the SAE had not yet studied Lynite or AL65, I can see where they would not have included it.

 

jp

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Maybe you should look up the Stutz rods used in the DV-32 engine. They are always replaced using Packard rods from the late thirties. As far as Duesenberg aluminum rods not failing............there are a bunch of engines and pans that have holes in them. I have seen a failure in person. Today's alloys should preclude strength issues, or what I understand to be the main cause of Stutz and Duesenberg rods, deteriorating metal over time, caused by what I am not sure. Ed

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Thanks Ed. There is no question you have a lot more exposure to D's than I ever have. There are alloys that deteriorate over time. Pot metal is the best known — usually caused by adding lead to the metal - it casts much better but sets up an internal chemical reaction that eventually destroys the item. On the other hand, I can't help but feel that, with big, expensive cars like the Dusenberg and the DV32, most owners aren't just playing safe. I would in a case like that. It may also be that in both cases the rods are just stressed beyond their long term limits where in Franklin engines they aren't. Of course, my engine isn't going to put anything like the stress on the internal components a Dusenberg or a Stutz would so I'm not worried on that score... also, as you say, the new alloys are going to be stronger. I wonder if anyone has ever done an actual metallurgical analysis of a failed rod. I can see why no one would bother but the by not doing we might get a false interpretation of why it failed.

 

jp

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While I am waiting for the 1926  Heldt book, I've done some calculations that appear to be leading in the right direction.

I took the bore and compression figures for the Franklin engine given above by PFitz. Using Heldt's chart, I calculated the area of the cross section of a proposed rod.

I then took measurements from the original aluminum rod and made the same calculations. Based on these, the area of the cross section of the aluminum rod is 1.3 times the cross section of a carbon steel rod for the same bore and compression. Instinctively, at least, this sounds about right but I'll have to keep collecting information. It would be nice to have similar figures for other aluminum rod engines but I think we are on the right track. If anyone knows of a loose (and cheap) Dusenberg or Stutz rod – or would like to let me borrow one to measure – let me know.

 

It is my intention to ignore the added strength of the new aluminum, treating it as an additional safety factor.

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I took another look at your piston photo. It appears that the distance from the wrist pin to the top of the original Mitchel piston is at least 2 inches. Furthermore it probably had a compression ratio of about 4.5:1. If you plan to increase this to 7:1 you will have to make the piston considerably taller.

 

If you use modern rings you will need less than an inch between the top of the piston and the wrist pin.

 

This means you could use a rod that is a full inch or more longer than your original rods, and make the piston to suit.

 

I don't know if you have tried to find replacement rods from another engine. But if you could find rods with the same size bearing the length would not be a big deal provided they were as long as the originals or longer. You would just make the pistons to suit.

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I've no intention of raising the compression any more than 5:1 and I'm not sure even that is possible. I did look for other rods, in as much as I could, but I have never seen any list, modern or old, that lists rods by their size. With a 5" stroke and wide (by modern standards) big ends, it would have been an act of G-d to find one that would work. There was a time when I had lots of parts like that but those went long ago. I don't think you can use a longer rod. The offset of the crankshaft makes the rod come quite close to the cylinder wall on one side. I don't know exactly how much clearance there is but I will be temporarily reassembling a block / crankcase / piston & rod etc to check it before I proceed with making rods.

 

I very much doubt the original compression ratio was as high as 4.5:1. It may have been 4:1 but I'm not even certain "high compression" Buicks were any more than that. Heldt's explosion pressure chart of 1911 only goes to 5:1 which suggests that, at the time, no one even thought of more. In any case, before I dismantled the engine I used a scientific beaker  to fill the combustion chamber with the piston at TDC and get an estimate of its capacity. I also took measurements between the top of the original piston and the exhaust valve directly over it. From these, we were able to calculate the maximum amount the piston could be raised. It is exactly 1/2" and the cast pistons take this into consideration. I seem to remember it was problematical if we could even get to 5:1 compression.

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I saw that myself and wondered about it.

I did find a link to the 1930 Structural Aluminum Handbook with about everything you'd want to know about 25ST. Unfortunately, my ^&*( computer won't cut and paste in firefox and this forum is not readable in Safari. Presumably my version is too old but I'm not buying another computer just to participate n an internet forum. If you google structuralaluminumhandbook as one work, it should come up. I'll try to post a link from my computer at work.

 

EDIT: I just went on line, found a copy and bought it. When I get it I'll be able to compare the appropriate figures between 25ST as used for Franklin rods and  7075 T6. I'm determined to sort this out AND to be comfortable with the rods when I make them.

 

Edited by JV Puleo (see edit history)
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48 minutes ago, JV Puleo said:

 

I did find a link to the 1930 Structural Aluminum Handbook with about everything you'd want to know about 25ST

 

I found it here to read on line. I also downloaded a pdf but it is ghosted; I don't know why.

https://archive.org/stream/StructuralAluminumHandbook/AluminumCompanyofAmerica0002#page/n13/mode/2up

 

I found 25S in Table 1 (a wrought alloy). 25ST is heat treated.

 

49 minutes ago, JV Puleo said:

 

my ^&*( computer won't cut and paste in firefox

 

This is a surprise. I have never had problems and I use only Firefox. My computer is 8 years old. I replaced the power supply when it failed and recently the WLAN card when Windows stopped supporting that model %^&*&^%$

. I do it this way: highlight the URL, Ctrl-C, then put the cursor in the spot in your reply, then Ctrl-V.

 

56 minutes ago, JV Puleo said:

I'm determined to sort this out AND to be comfortable with the rods when I make them.

 

Essential.

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About compression ratios - they were what they were because they were limited by the low octane of the gasoline that was available.

 

Per a Sun Oil Company chemical engineer from that era, up until about 1930 most gasoline was only 57 octane. In 1930 Sunoco came out with "Sunoco Blue", which was 70 octane. Then compression ratios could be raised out of the upper 4:1 range. That is when Franklin increased the rod beam cross section for their new engines introduced in 1930, that were higher compression (5.1:1) and  an increase in horse power over the same CID of their largest engine in 1929. The 1931 engines gained another 5 hp, not by changing the compression ratio but by using a more efficient cooling fan that used 5 hp less while increasing cooling capacity.   To get the 7:1 on a 1930 I had to swap a 31 fan and duct work onto the motor.

 

Even at 5.1:1 there is gobs of room left in the combustion chamber above the pistons before getting near an open valve.

 

To get to 7:1, even starting with the tallest forged aluminum pistons available, it was either have longer rods made (very expensive), or play tricks with shortening the cylinder lengths. Being an aircraft type air cooled motor, with detachable cylinder jugs, (just like rotary aircraft engines) that was the least expensive method with the Franklin.   Other than Helicoiling the wrist pin pinch bolt threads, no other modifications were made to the original lynite rods.

 

Paul

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Fuel octane is a complicated subject. In the 1890s gasoline was a waste byproduct of kerosene refining. They put all the low grade gasoline they could into the kerosene.This is why kerosene of the time had a sharp piercing odor and oil lamps were known to explode. They sold gasoline or benzine for dry cleaning, spot removing, and for gasoline lanterns and stoves. The earliest gas engines were actually designed for no lead, high octane gas.

 

Then cars came in. As they became popular there was more demand for gasoline and less demand for kerosene, as electric lights and gas lights were replacing oil lamps in cities and towns. Therefore kerosene became oilier and so did gasoline as they took more of the low grade gas out of the kerosene and put it into the motor fuel.

 

This led to changes in engine design around 1913. Lower compression ratios, long stroke small bore engines, and hot spots and heaters built into intake manifolds and carburetors to try and vaporize the heavy ends.

 

Until the late 20s this was the story, low grade oily gas of 50 octane or so. Then 2 development came in, the cracking process for getting more gas out of a barrel of oil and the use of tetraethyl lead to improve knock resistance. Octane levels slowly climbed allowing higher compression and more powerful more efficient engines. Long stroke engines were still the rule but not as extreme as in the teens.

 

Your 1910 engine was designed as gasoline quality was reaching a low ebb.

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Well put. I've long realized that.  I've seen a period reference to checking gasoline by putting a drop or two on your hand... the more oiley it was, the poorer it was. I suspect that 1910 was just about the low point.

 

 

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In contrast to the oily gas of 1910 was the very light gas of 1900. I read the reminiscences of an early motorist whose first motor vehicle was a DeDion  tricycle in the late 1890s. One day he came home from a ride and filled the gas tank which held about 1/2 gallon and locked up the garage. A few days later when he went to use it again the gas tank was empty. He forgot to put the cap back on and it all evaporated.

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In 1900 I think the most common use was as a cleaning solution. My mom had a friend whose mother would sent her to the corner gas station for a bucket of gasoline to wash her silk dresses in... this would have been in the late 20s or maybe the early 30s. By then, it was considered a little unusual but older people remembered commonly using gasoline for that purpose at the beginning of the 20th century. I don't imagine the gas of 1928 was actually better than it had been in 1900 for that purpose.

 

I've also known old-time printers who washed their presses down with gasoline.

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I have used gas to dry clean a hat but I used Coleman fuel or Naptha gas. I suppose today's unleaded would work as well.

 

To clean the hat I put it in a 5 gallon pail poured a gallon of Coleman fuel over it and snapped on the lid. Next day swished it around a bit and let it sit for another half hour. Took the hat out and hung it up outdoors to dry. In an hour or 2 it was like new.

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Today's update.

The 1926 edition of Heldt's book was a big disappointment. Not only did I break my own rule and buy a cheap (quality - not price) reprint, aluminum rods aren't even mentioned in it. But all is not lost, because I had the bright idea to search for old technical papers and found one in the SAE Transactions, except that you can't download it anywhere despite being long out of copyright. I've written to the SAE to ask if I can purchase a copy. The wretched google books "snippit view" includes a few lines of a dimension chart comparing aluminum to steel rods. I also have a friend who is a member of the SAE and I've asked him to see if he can get it. It's quite astonishing ow difficult it is to get any real information on this. I also have a 1930 edition of an Alcoa reference that lists the alloy 25ST that was specified for Franklin rods with all of it's salient engineering date so I'm getting close - just not there yet.

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'My mom had a friend whose mother would sent her to the corner gas station for a bucket of gasoline to wash her silk dresses in... this would have been in the late 20s or maybe the early 30s.'

 

Astonishing. I wonder how the dresses smelled afterwards, or whether all the vapour came out??? A bit risky for smokers.

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