Aluminum Rods

[Guest Industrialdeere]

A dropped the oil pan on my 1926 Stutz today, and my rods are aluminum. I was told that this can be a problem. Apparently they tend to break. How often does this happen? How big of a concern is this? Should I run out and get steel rods? Limit speed? Pray alot?

Thanks,

Steve

[jrbartlett]

I have no knowledge of Stutz aluminum rods, but do know about such rods used in Duesenbergs. The Model J originally had aluminum rods. They were known to fail occasionally. Virtually all (if not entirely all) have been changed out, and were back in the day. The factory came out with tubular steel rods and many of the original rods were replaced during the '30s. In the modern day, those engines with aluminum rods were frequently retrofitted with Carillo custom-made rods. As for whether you should change yours may depend on whether you have purely a show car or a driver.

[RU22]

Hi Steve

The rods are OK as long as you don't rev the car

Also if the previous owner drove the car with respect too

Problem is there are very very few cycles between cracked and broken.

There is an old racer's trick ...... push the rods side to side if they move easy the bearings are pretty much OK

[Guest Industrialdeere]

RU22,

Thanks for the response. I will try that out. The vehicle has 55k miles and spent most of its life in various museums. Before that it was vanderbilt car that was probably chauffeured quite a bit. I did not find debris in the pan and the rods seemed properly oiled. There was quite a bit of sludge.

[RU22]

When I got my Speedster it had sat years in a warehouse .... there was honest 3 inches of gray milky crap in the sump. I checked and cleaned it and thought..... can't get worse so started and drove it. It was OK no more water in the oil...... glad I didn't start it!

Clean it all and enjoy your ride but remember you don't have a ''high speed ride '' there.

[Ivan Saxton]

I have written this before, but it always seems difficult to find past information cold when you are new with a question.

Stutz conrods are not aluminium, but duralumin, a high duty alloy. Apart from J Duesenberg as JR says, Pierce Arrow also used them for the Model 81 for one year before they dropped it and the last big T-head six and introduced the straight 8.

There are two problems that can arise with the duralumin rods.

At that time the best and most reliable big end bearings were thin layer of tin-based alloy poured into the the conrod on a tinned surface. Tin will alloy with aluminium ( and duralumin), but the surface oxidizes and becomes unreactive very rapidly in the air. It is possible to "tin" these reliably by bringing the rod or cap to temperature just above the melting point of tin, and scratch-tinning the surface with pure tin. The new bearing of suitable grade babbit alloy can then cast at suitable temperature and with skill and tecnique to wet the tinned surface to become a perfectly bonded bearing. With skill and care this can then be bored concentrically with the bore of the rod. Then if you tap the rod or cap with a small hammer, you can get some indication of the bonding by the tone of the ring. I believe there is a technique to determine exactly the bonding, but I do not know what it is or how to access this. The durability and success of the bearing will depend on the percentage of the bond. In preparing original conrods for tinning, I have sometimes found it possible to peel out the original babbit with a pocket knife.

The Stutz instruction book says that you should tighten the big end bolts with a spanner 6 inches long. There were probably no torque wrenchs then, or if so, they were not in general use. When you tighten the conrod bolts in a steel rod, you will find that the bolts stretch slightly within their elastic limit. Unfortunately, duralumin is much softer than steel that it crushes . The conrods where this is greatest risk are those of the 1929 M Series and L6 Blackhawk with a six cylinder version of the same engine. The steel caps on the conrods of these mean that there is about 40% of the height of duralumin to absorb the crush of the tightened bolts. I have a number of these conrods on the shelf which are cracked at "ten oçlock" and "two oçlock "where the bolt heads have embedded themselves.

So, there are two ways you can break a rod. The result of a crack is obvious.

If the bearing layer completely detaches, it can jam on the journal and bend the rod till mit strikes the side of the crankcase. Some lowerr primate re-metalled the conrods foran owner here without tinning, and just made locking holes in the surface with a drill. It bend conrods and punched one hole in the crankcase.

Long ago in ACD Newsletter, Jerry Gebby described the process of replacing the poured bearings of his SJ Duesenberg with ( I think) a pair of bearing inserts side by side. He was a very good engineer of long experience, and drove his car when people still drove them , with a heavy foot. There are two bearing inserts that you can use in these Stutz rods. One is Bedford truck, and the other is an International truck bearing.

There is another way that you can get a reliable babbit bearing in these conrods. This is with Metco Spraybabbit onto a bond coating of Metco 405 nickel-aluminide, which alloys with considerable exotherm as it is sprayed by wire-feed gun onto the cleaned, prepared surface.

Paul Freehill sold me an incomplete 1928 DV32 engine DV30004 that previous owners had ratted for parts. There had been an incomplete set of original Stutz steel conrods in this that Paul had sold to Ernie Toth jnr to make a complete set in one of his engines. I believe Stutz knew that they also had problems with main bearing cap strength. The centre main bearing cap was up-graded between my BB engines 91845 and 92335 in early 1928. Geoff Ringrtose in Sydney found the centre main bearing cap had broken when the engine developed a knock on a club run. I cannot remember the exact engine number without checking the records, but it is close to #91845. In DV3004, (engine casting date June 27, 1928), The main bearing caps are massive; probably 3 to4 times as strong as production previously. My guess is that the Black Hawk which raced Weymann's special 8 litre Hispano Suiza at Indianapolis probably blew up because that centre main bearing cap failed, reduced the oil pressure, and eventually conrods bent and broke.

[Guest Industrialdeere]

Ivan. I can't thank you enough for the effort and extensive knowledge that you have shared. Thanks, very much. Steve

[Otahuhu]

As a solution you should check out to replace the orginal duralumin rods with Packard Model 356 steel rods. If you go this route you can still have run bearings or if you are going to race the car you can grind the crank down to suit shell bearing

Even after testing my orginal rods through a certified aircraft motor shop I replaced these with the Packard rods with run bearings. Yes the motor is balanced and runs well

[stutzl6]

Steve I got 356 packard rods in my 29 blackhawk turned shaft down .125 but strocked it ..100 of and inch. have run for 7 years . Iam doing a M and the shaft turned only .020 In sted of turning it again I bored the packard rod larger and had them rebattited . If you need any Stutz rods i have many.used . Have new valves in stock SS for your motor .

[alsancle]

I am also using the steel Packard rods in my 28 bb engine. This is what George Holman recommended to me. We have not fired the engine yet.