Aluminum Connecting Rods

[JV Puleo]

Finding worthwhile period information on this subject is proving a real challenge. Aside from the Franklin rod I already have, I've yet to locate any others to measure. I have found a 1922 article by Laurence Pomeroy. At the time, I believe he was working for Alcoa with the job of finding ways to increase the use of aluminum in automobiles. It would seem impossible that no one in the SAE wrote a paper on the necessary dimensions of aluminum rods so I will continue to pursue that thread while looking for some other rods to measure.

 

 

Edited July 21, 2017 by JV Puleo (see edit history)

[PFitz]

47 minutes ago, JV Puleo said:

Finding worthwhile period information on this subject is proving a real challenge. Aside from the Franklin rod I already have, I've yet to locate any others to measure. I have found a 1922 article by Laurence Pomeroy. At the time, I believe he was working for Alcoa with the job of finding ways to increase the use of aluminum in automobiles. It would seem impossible that no one in the SAE wrote a paper on the necessary dimensions of aluminum rods so I will continue to pursue that thread while looking for some other rods to measure.

 

 

 The answer may not be in the automotive field, but in another growing industry of that time - the aircraft industry.

 

As far as that Franklin aluminum rod, there is sort of a connection to aircraft engines. Next to the aircraft industry of that era, Franklin was one of the biggest users of aluminum.  Plus, they were so very design-wise connected to aircraft engine design that  their two top engineers later formed the very successful small aircraft and helicopter engine company - Aircooled Motors - when the Franklin started to fall on hard times in the early 30's.  

 

You may have better luck with early aluminum rod design by searching for info on early aircraft engine design ???? 

 

Paul

Edited July 21, 2017 by PFitz (see edit history)

[JV Puleo]

I am certain you are right about that. Fortunately, by the 1920s the SAE encompassed aircraft design so a lot of the papers they published were on that subject. I asked them to search under "aluminum connecting rod dimensions." I should have added "aluminum connecting rod design." (and will do shortly).

 

Somehow I sense I'm getting closer to an answer. I suspect that it will be something close to a 1:1.3 ratio between carbon steel and the best aluminum available in the 1920s and deduced from the Franklin rod. I am going to re-read the Pomeroy paper now... I only glanced through it today when I downloaded it.

 

jp

Edited July 21, 2017 by JV Puleo (see edit history)

[JV Puleo]

The only hard ratio re stiffness I found in the Pomeroy paper was 1:1.44 and this was in reference to the dimensions of the big end. It is, however in keeping with the general estimate expressed through out the paper that aluminum components can be made to weigh half that of iron and steel. Part of this comes from the observation that manufacturing requirements precluded making the steel components as light as they could theoretically be made. Also, I have to remember that Pomeroy was writing in December of 1922, at the very beginning of the the period, although it is clear that some aluminum rods were already in use. It is very likely that the aluminum being made in 1930 was stronger and we know that the modern alloys are stronger yet. The material I have is 7075-T6511, an alloy was developed by the Japanese and used for air frames. It was a secret until the end of WWII.

[JV Puleo]

On 7/12/2017 at 1:39 PM, Rusty_OToole said:

Why don't you fit shell bearings while you are making new rods? Everybody else goes to great expense to change their old babbit bearings to shell bearings and you can do it for free. In fact it would be easier than babbit and a lot cheaper.

 

I have been reconsidering this suggestion. I am not certain that the crankshaft stiffness issue has much bearing on connecting rods and there is no doubt it would be much easier. The only  question I have is, how do I find a suitable bearing? I have never seen a bearing catalog that lists them by size. Is there such a listing? Everything I have ever seen is in relation to what it fits. (Not that I've even looked at one in the last 30 years. It has been a long time since I had the bottom end of an insert bearing car apart.)  Also, the crank pins are small by modern standards and quite long... it looks to me as if you would have to use 2 bearing in each rod... then, what do do about the thrust sides... does aluminum make a suitable thrust surface? The original bearings had Babbit thrusts.

 

Oops... I should have looked at the Franklin rod that is sitting on the table next to the computer. It looks as if the aluminum was perfectly adequate for a thrust surface.

Pfitz... do you happen to know what the thrust clearance was in the Franklin engine?

Edited July 21, 2017 by JV Puleo (see edit history)

[PFitz]

Yes, shell bearings can be looked up by size. You can call 315-655-8812, ask for Pat, or Mike, and give them the crank journal diameter and width.    If there are shell bearings available they can get them. Plus, they've rebuilt countless Franklin engines and may be able to give you more info on aluminum rods.

 

For rod/journal side clearance, because the Franklin engine bases are  aluminum with a forged steel crank,  the rods have a lot of side clearance to be able to float to allow for the differences in thermal growth. I'm not sure of the exact side clearance, offhand, and I can't find a drawing for the spec for that rod you have, but, on the V12 the drawing I found, it calls for .004-.012 side clearance on the rod (two rods on each journal). I do know it's enough that you can easily move the rods sideways on the journal by hand. So much that it would lead someone with more modern engine experience to think there's too much side clearance. But it's that way on at least their 1920's and 30's engines and it works out fine.  Again, Franklin wasn't worried about keeping high oil pressure, just oil volume.

 

FYI.

Even though spun babbitt has better heat transfer, Franklin went to shell bearings with their aluminum rods in '31, and replacement rods for '29.

 

I noticed that they used the term "duraluminum rods" on their bearing drawings, if that helps in your search.

 

Paul

Edited July 21, 2017 by PFitz (see edit history)

[JV Puleo]

Thanks. The figure I have is .020 to .025 so that is pretty much in keeping with Franklin's practice.

Duraluminum was one of the better known alloys and, more to the point, the exact composition and strength is easily found. The rods on this engine will have to work with splash lubrication. At best, oil pressure will be quite low. I should be able to get sufficient volume, but it will only go directly to the main bearings. I am also dealing with an aluminum crankcase and steel crank so the situation is similar. Tonight I'll be going through the index of SAE technical papers in the hope of finding one dealing specifically with connecting rods... there are over 8000 papers, starting in about 1902 so that may take a few hours.

[JV Puleo]

I googled duraluminum, only to find that it was the earliest "hard" alloy. Apparently, the name became a euphemism for a hard, aged aluminum so it isn't clear what alloy is being referred to. I jut got my copy of the 1930 Structural Aluminum Handbook and, in looking through it, I'd guess that 25ST was what was meant.

 

[JV Puleo]

Here is what I have found so far. The figures for 1035 steel come from the 1927 SAE Handbook. 1035 is a carbon steel with the same carbon content as mentioned by Heldt in his 1911 text. Unfortunately, the alloy numbering system wasn't invented in 1911 so we cannot be certain what other elements were included but it seems likely that, by 1927, the steel was slightly better than it was in 1911. Heldt gives an approximate tensile strength of 70,000 lbs./sq. in. and 1035 is listed at 83,000 lbs/sq. in.

 

The 1920s Franklin rods were made from Alcoa 25ST. The figures for this alloy come from the 1930 Alcoa handbook on Structural Aluminum and are confirmed by a 1927 SAE paper on manufacturing aluminum automobile components.

 

The figures for 7075-T6511, being modern, are easily found and are simply from one of the many internet engineering sites.

 

 

In his 1922 article on the use of lightweight reciprocating parts, L.H. Pomeroy uses a ratio of 1:1.44 (carbon steel to aluminum) in determining the thickness of the bottom end of a connecting rod. My own figures, based on the central portion of a late 20s Franklin rod were 1:1.3. With that in mind, I've started making drawings of a rod that has a bottom end configuration similar to Pomeroys and a cross sectional area of slightly more than 1:1.5 based on a carbon steel rod for the bore and compression ratio of the Mitchell engine using Heldt's formula from 1911 (which is identical to the formula he used in the 1927 edition of his book). I have purposely ignored the difference in strength between 25ST and 7075-T6511, treating this as an additional safety factor. My goal here is to halve the weight of the rods. I am not building a racing engine and do not have to run risks to get the rods as light as possible. I am still not fully pleased with this and have some inquiries out to see if I can find someone more adept at engineering math to run the figures for me as a "second opinion."

Edited July 26, 2017 by JV Puleo (see edit history)

[Rusty_OToole]

Another point worth considering. The typical I beam rod is made with flat edges and indented sides, this is a matter of manufacturing convenience in forging. Theoretically the I beam should go the other way with flat sides and indented edges. The most expensive racing rods are made this way. If you are machining the rods from the solid it may be possible to make them this way.

[JV Puleo]

You are certainly right there and that is the plan. Most people don't realize that the conventional shape of a connecting rod was determined by the forging process rather than a scientific assessment of what would be strongest. There is also no reason for them to taper from bottom to top... straight (which is much easier to machine) is every bit as good. I read this in the Heldt book, but then noticed that Simplex connecting rods (see The Old Motor web site) are machined all over, straight and are grooved exactly as you recommend.

 

Oh... and it is easier to do them that way.

Edited July 26, 2017 by JV Puleo (see edit history)

[Rusty_OToole]

In the old days there were engineers who believed splash lubrication was superior to pressure. Hudson for one, Buick and Chevrolet also stuck with splash long after others went to full pressure. The limitation seems to be high speed use. Beyond a certain point only pressure lubrication will cool and lubricate a plain bearing. This was around 50 - 55 MPH on a Chev. Keep to 50 or below, it would have a long life. Try to drive over 60 and engine life would be measured in days or possibly minutes. I suppose it would depend on the rubbing speed of the bearing in other words the diameter of the shaft times RPMs. So, don't plan on revving much more than a stock engine but within that limitation the light weight rods and pistons should give you a peppy smooth running engine.

[Spinneyhill]

I wonder if that would be the full story? The dipper removes and splashes some of the oil in the trough so it takes a little time to refill the trough. Is there a limiting time between dips for effective lubrication? Once revs get above some level, perhaps there is not quite a full trough for the dipper so lubrication is reduced?

Edited July 26, 2017 by Spinneyhill (see edit history)

[JV Puleo]

I don't know what sort of rpms a later engine like a 50s Chevy turned at 60 mph but I am certain it was a much lower number than this engine. If my calculations are correct (and in this case I am certain they are) the Mitchell would be traveling at 63mph if the engine was turning 2,000 rpm. It is geared very high, obviously to take advantage of low end torque. Displacement is just short of 300 cu. in. in 4 cylinders. From other aspects of the construction, I estimate that something in the neighborhood of 40 mph was the most that could reasonably be expected when new and, at that speed, it probably felt as if it would fly to pieces any second. On dirt roads in rural Wisconsin this may hardly have been noticed. I'm striving for 40 to 45 as a comfortably speed and possibly a little more if absolutely necessary with the added advantage of long bearing life and smooth operation.

 

There does not seem to have been any attempt to balance the reciprocating parts and both the rods and the pistons are exceptionally heavy, even by the standards of the time.

 

EDIT... I'm certain the 50s engine turned at a much HIGHER number than this engine....

Edited August 1, 2017 by JV Puleo
typo (see edit history)

[Spinneyhill]

Maybe the very heavy flywheels helped to deaden out of balance reciprocating components?

[JV Puleo]

I have heard that before and I suspect they may have thought so at the time but I really wonder. The heavy flywheel is a holdover from steam and stationary engine practice. A very heavy flywheel, if out of balance, could only exacerbate the problem. Most heavy flywheels I've seen have balancing holes drilled in the rim but true dynamic balancing was beyond them. They did do static balancing but probably the best solution was a "machined all over" flywheel. My car does have that but it has been fooled with, as all of the timing marks are missing, so I don't really know what it was like new. Flywheels with integral multiple disc clutches were a special problem when they incorporated fan blades because it was impossible to machine those all over. My 1910 Model R REO had that type of flywheel. I was only in my 20s when I owned that car and I've learned a lot since then. It had an effective top speed of perhaps 40 at most - though it was advertised as being able to go quite a bit faster.

 

An addition... this engine didn't have dippers but did have a fairly large hole in the lower end of the connecting rod bearing and smaller oil holes in the upper half.

I don't know if my assessment of the REO engine is fair. That was the only engine I've ever sent to a "professional" – someone that came highly recommended by people I presumed knew what they were talking about. He may have been just fine with a mid-30s car but was in over his head with a 1910 car. Although I didn't fully appreciate it at the time, he did some real bone-head things that, today, make me shudder. It was that experience that spurred me into doing my own work.

Edited July 26, 2017 by JV Puleo (see edit history)

[Spinneyhill]

Just looking in Machinery's Handbook 1943 for "connecting rod", for another topic. The aluminium it gives as commonly used for con. rods for automotive engine is S.A.E. Std No. 27, Type 2 Alloy. It "is esp. adapted to forging because of its excellent hot-working properties."

 

The alloy is Cu 3.9 to 5.0%; Mn 0.5 to 1.1%; Si 0.5 to 1.1%; aluminium min. 92.0%. The min. tensile strength for forgings is 55,000 psi and the yield strength is 30,000 psi. The elongation is 2" at 16 percent. The shearing strength is about 35,000 psi for the heat-treated condition.

[JV Puleo]

Thank you. That's interesting. My newest SAE reference is 1927. I hadn't even thought to look at Machinery's Handbook although I have 2 copies... one of which is 1939 (purchased in a used book store in Cheltenham - it was likely someone's reference for all of WWII). Those figures seem relatively consistent with the 25ST that I found referenced in two or three articles published by the SAE in the 20s.

 

I'm holding back on starting this project, although I did buy some grade 8 bolts. I'm giving this one quite a bit more planning than I usually indulge in because the exact sequence of machining operations is critical. Invariably, I change something in the course of a project but I'd like this one to be a bit better planned. Also, I have some work to do on my house that simply can't be put off any longer. It gets very cold in New England during the winter and unless I fix a few things, it will be just as cold inside my house as outside.

[Rusty_OToole]

The limiting factor of bearings is the rubbing speed. This is a function of bearing diameter and rotating speed. Pressure fed bearings are cooled as well as lubricated by the flow of oil and can stand higher revs.

 

I know Chevs of the forties were best kept below 50. My father owned a straight eight 1947 Hudson Commodore Eight with a splash lubricated engine and habitually drove at 70 mph. By 1951 the engine was shot. He traded it on a new Chev hardtop which wasn't half the car. The point is, splash fed bearings will last a long time but must be kept below the critical speed. Above a certain speed they wear rapidly and burn out.

 

It also occurs to me that all the splash lubricated motors had poured babbitt bearings long after pressure fed motors went to the cheaper shell bearings. Wonder if this is significant.

Edited August 17, 2017 by Rusty_OToole (see edit history)

[JV Puleo]

Rusty,

Do you have any idea what RPMs the Hudson (or Chevy) was turning at 50? The car these rods are for would be doing 63MPH at 2,000 RPM. Short of outright racing, that's pretty fast for a brass car... faster than I'd be inclined to. I'm guessing that a fast cruising speed would be in the area of 1,500 to 1,800 RPM. Connecting rod journal size was severely limited by the oil of the period not being able to hand the surface speed of a larger diameter, which give us the "bent hairpin" cranks. I suspect that by the 50s the oil had improved, the cranks journals could be bigger and the speeds could be higher. I still wonder about using inserts on splash lubricated rods but this seems to have been done successfully quite a bit now and is probably worth trying. This car should have pressure to the mains and splash for the rods if things come out as I plan.

[Rusty_OToole]

A quick check revealed the Chevs developed max HP at 3400 - 3600 depending on year and model. Hudson 4000 - 4200. So, they must have been safe at those speeds although for how long I don't know.

 

 Both had scoops on the bottom of the rod. Hudson had a pan with troughs that the scoops dipped in, above the oil pan. Chevrolet had little pipes that shot a stream of oil where the scoop could catch it as it came around.

 

The Chev lubrication system explained. The engine part begins at 5:30, the rod bearings at 7:30.

 

Edited August 17, 2017 by Rusty_OToole (see edit history)

[JV Puleo]

That's about what I thought. Those engines ran at twice the speed of mine so I don't think the splash rod lubrication is an issue.

[JV Puleo]

23 hours ago, Spinneyhill said:

Just looking in Machinery's Handbook 1943 for "connecting rod", for another topic. The aluminium it gives as commonly used for con. rods for automotive engine is S.A.E. Std No. 27, Type 2 Alloy. It "is esp. adapted to forging because of its excellent hot-working properties."

 

The alloy is Cu 3.9 to 5.0%; Mn 0.5 to 1.1%; Si 0.5 to 1.1%; aluminium min. 92.0%. The min. tensile strength for forgings is 55,000 psi and the yield strength is 30,000 psi. The elongation is 2" at 16 percent. The shearing strength is about 35,000 psi for the heat-treated condition.

 

I looked this up in my 1939 copy where it adds that "the commercial designation is 25S." I believe the "T" refers to heat treatment, which makes sense. So this is further confirmation of what was being used for con rods.

[herm111]

Here are some more Aluminum Rods, and Mains again, that we done not to long ago.

 

Thanks,

 

Herm.   KohnkeRebabbittingService.com

 

 

 

 

Edited September 13, 2017 by herm111 (see edit history)

[herm111]

On ‎7‎/‎11‎/‎2017 at 2:01 AM, JV Puleo said:

The aluminum rods in the 20s were Lynite, an Alcoa alloy. I believe they were cast – or at least they look as if they were cast. Franklin and, I think, Dusenberg were also early users. I have one of the Franklin rods in the shop to look at. I don't know what the strength of Lynite was but it apparently deteriorates over time. (Nevertheless, most Franklins must still be running with aluminum rods...at least I've never heard of them being regularly replaced.)  I don't have my figures in front of me, but I seem to remember that the tensile strength of 7075 is comparable to that of the mild steel forgings commonly available in 1910. Of course, tensile strength isn't the only salient feature that has to be considered but it is certainly a good starting point.

 

 

 

On ‎7‎/‎12‎/‎2017 at 7:50 PM, JV Puleo said:

 

I have all, or at least most of the fixtures needed to Babbit the shells. They came free with my align boring machine — neither of which I've ever used so I still have to figure that out. I've done a lot of lathe boring so I'm not particularly intimidated by that part of the job.

A Lynite Rod, you can cast Babbitt into the rod. The Rod also can be tinned.

T Aluminite Rod can not be Tinned, and the Aluminum runs directly on the crank like some lawn more engines.

Some gas engines have stamped on the rod what it is made of.

 

Herm.     KohnkeRebabbittingService.com

[JV Puleo]

Beautiful work Herm.

I'm curious about the Babbit shells you show. Are they removable Babbit connecting rod bearings? I have seen original main bearings made that way but never rod bearings.

[PFitz]

Very nice work on those Franklin main caps and rods, Herm.

 

A lot of modern engine shops won't babbitt directly onto Lynite rods the way Franklin did. 

 

The reason  that Franklin did that was their engineers said it gave better bearing heat transfer to the rod than an insert could.

 

Paul

[JV Puleo]

Herm,

 

A question for you... can you Babbit and bore rods from the crankshaft measurements? I'm thinking of having you do the rods, but don't want to ship the crank which I can have ground and balanced locally. I'd have an accurate and uniform crank measurement to work from. The rods I am thinking of will have bronze inserts. There are actually two sets... the rods I am making for myself and another set I'm working on for a friend where I am using rods that fit, but are not original to the engine in question. I will have to make inserts in order to reduce the inside diameter to match the crank (which is already ground).

 

jp

 

Edited September 14, 2017 by JV Puleo
Added a question. (see edit history)

[herm111]

On ‎9‎/‎14‎/‎2017 at 8:34 AM, JV Puleo said:

Beautiful work Herm.

I'm curious about the Babbit shells you show. Are they removable Babbit connecting rod bearings? I have seen original main bearings made that way but never rod bearings.

Just found your post now, Mr.JV.

 

The main shells are solid Babbitt. They are out of a 1923  Franklin. The rods are poured solid.

 

Thanks,

 

Herm. 

[herm111]

On ‎9‎/‎14‎/‎2017 at 9:46 AM, PFitz said:

Very nice work on those Franklin main caps and rods, Herm.

 

A lot of modern engine shops won't babbitt directly onto Lynite rods the way Franklin did. 

 

The reason  that Franklin did that was their engineers said it gave better bearing heat transfer to the rod than an insert could.

 

Paul

That's always true, Mr. P. F.

 

thanks,

 

Herm.

[herm111]

On ‎9‎/‎14‎/‎2017 at 10:04 AM, JV Puleo said:

Herm,

 

A question for you... can you Babbit and bore rods from the crankshaft measurements? I'm thinking of having you do the rods, but don't want to ship the crank which I can have ground and balanced locally. I'd have an accurate and uniform crank measurement to work from. The rods I am thinking of will have bronze inserts. There are actually two sets... the rods I am making for myself and another set I'm working on for a friend where I am using rods that fit, but are not original to the engine in question. I will have to make inserts in order to reduce the inside diameter to match the crank (which is already ground).

 

jp

 

Yes, we do it all the time, as long as  the measurement is correct, it will fit.

 

Babbitting inserts in a rod, is not a good idea. We pour them solid, and an insert has to be 100%,  a true fit with its rod shell backing, or it will fracture. If the bronze shell is not up against the shell, the crank pushes the insert back, and forth, into the shell, and the Babbitt will brake from the tinning, and you can't stop it.

The Factory can make it work, as they machine both sides of the bearing, and it is true. But when pouring an old insert, they can warp a little, and all that we can true is the inside. We can pour them, but can not Guarantee.

Mains are all right, as there isn't the shock of a Rods up, and Down. The mains just hold a shaft that just turns in a cicrle

 

Since Friday, a Guy, in one of  his posts, stated that any kind of THICK  Babbitt in a bearing will Fail.

Boys, that is just NOT True. It never has been, and never will be. This lie has been perpetrated by many people that heard it from some one else, or a bearing gone bad from countless other things, and they picked the wrong reason.

 

Thanks, Herm.

[JV Puleo]

Herm,

 

I'm quite aware of the problems of fitting the bronze insert and, while I admit to being a "hobbyist,"  I suspect I am far better equipped to do this sort of thing than the average hobbyist. See my thread in the Restoration sub-forum on the "1910 Mitchell." I would make the inserts with a .001 to .002 pinch and bore the inner surface with the insert torqued up in the rod. There won't be any shims. My rods are going to be 7075 aluminum which I understood from your previous posts Babbit metal won't stick to. In any case, they won't be old... they'll be new. It's my practice to work on a job until I get it right... even if I have to do it over two or three times though I realize that isn't a luxury that is enjoyed by people who are in business.

 

I have another job that actually calls for those thick Babbit bearings. This would save me the effort of making the bronze inserts (a tricky job at best). When I get to that point, I'll contact you.

 

Cheers,

Joe P.

Edited September 20, 2017 by JV Puleo (see edit history)