Having seen rods heated at an automotive machine shop in a Sunnen rod heater, I always wondered about the purple/blue coloration left on a rod after assembling it. On line investigation turned up this: "Heat the steel to temperatures from 400 to 800 degrees Fahrenheit, to produce oxidation colors. At 480 degrees F., the steel turns brown, at 520 degrees, it turns purple, at 575 degrees, it turns blue and at 800 degrees, it turns grey." It would seem that the less heat imparted to the rod, the better.........but I realize millions of rods have been assembled with the Sunnen heater with apparently no disasterous results. Anyway I found this video on line with a simple jig for insuring the rods are centered on the pins and easy assembly. . I got an old Cadillac rod out of my stash and a compatible piston pin. I placed the rod lightly in a vise and pointed my Propane torch at it for about 15/18 seconds at which time the pin slid easily into/thru the rod. Then I pointed my infrared heat gun at the rod and it showed only 400 (or less) degrees. Thats well below any coloration temperature. When I finish a couple of current projects, I think I will make me a jig for rod assembly. The idea is to be able to push the pin further than where it will be when centered. Then the rod is held against one piston pin boss and the pin is inserted till it hits the stop. A few seconds to cool and then the rod/pin is locked in the correct location to be centered in the piston. The stop is adjusted to allow for using the boss to locate the rod on the center of the pin. Anyway,thought maybe a few of you might want to build your own. Experiment with an old rod and pin first before you try the new ones. Now if I can just find a cheap way to make a rod/cap grinder................
I've always wondered what heating the rods does to the strength of the rods. Way back in my industrial mechanics days, I was sent to a bearing company's tech training tolearn the proper method of installation for what was essentially a giant wheel bearing set, worth in 1973 dollars about $2000 a set. 4 sets had been installed by all the wrong methods and were trash. At that time we used an induction heater that in mere moments (probably 60-90 seconds) would turn the bearings brown,thus even that destroying the bearings. The bearing company wanted no more than 350 degrees fahrenheit, with 300 degrees preferred. And they recommended an oil bath heater. I never used the heater I had at the time for rods, but it seems like that method would be ideal. I used an oil with a relatively high flash point and an electric heater that looked like an industrial version of a crock pot. I think it might have been heat treating oil??? It took a bit to get to temperature, but once there it took only 4 or 5 minutes to get a bearing set to temperature. It could be set to 300 degrees on its controls and would only vary by a few degrees when a bearing was immersed in the oil. BTW these bearings fitted onto a shaft that was about 6 inches in diameter and the od of a bearing cone was approximately 9 to 10 inches, so lots of steel. I can imagine putting a whole engine worth of rods in at once and going for coffee. When you get back, viola, rods at 300-350 degrees uniformly heated and more importantly not locally overheated. Oh and already lubricated to ease assembly. I don't have pictures of the setup unfortunately, but I bet a google search would find one, or a good alternative, a commercial deep fat fryer, just change the oil before you do your turkey at Thanksgiving...
What about putting them in the oven? Would take longer that immersion in liquid, but we all have an oven in the kitchen.
What I like about the oil immersion method is the uniform consistent heating. Ovens cycle to maintain heat, as would the oil bath, but the oil would dampen the potential for spikes in temperature. As my brother-in-law the professional chef has said many times, you really have to know your oven to get even heat so as not to over or under cook stuff. From my 2nd career as an engineer, and my first position at a research firm doing research on how things break, I know that the grain structure of metals can be affected with heating and cooling. And the temperature history of a structure can tell a story of the reason for failure. Of course a rod sees temperature swings in use, and could exceed the temperature used to assemble the components, however the pin will also see an increased temperature, so the shrink fit should still exist. So take these thoughts as suggestions for what they are worth. The oven method is after all what a Sunnen device is and has worked for what, a century give or take a decade or 2...
Dave G, I really like the info you posted. I agree that heating oil to a consistent temp and putting the rods in would be more controllable. I do think I would only want to put the rods halfway in, so the end I'm handling wouldn't be at full temp. I am going to put some thought into this before I decide which way I want to go.
Glad to help. PM me if you want to getinto the metalurgy more. I'm really just a hippy nerdy type at heart... And remember, change the oil before turkey dinner
I just use the sunnen rod heater we have at the school, works fantastic! Sent from my iPhone using H.A.M.B.
How would you maintain the rod temp when taking it out of the oil? Or is the pin put in with everything in oil? Just curious.
I know with our rod heater you don’t have a lot of time to get the pin in, I’ve had more than one stop part way together, then you have to press the pin back out and start over. Sent from my iPhone using H.A.M.B.
Like above you have to move quickly to get the pin in before temperatures stabilize between the rod andthe pin, and the shrink fit grabs hold. Then its to a press and if you are lucky you get it in place without ruining the piston. The original post details his fixture to make alignment and final position happen in one fell swoop. Pro shops have a commercially made fixture that sets all those up for you so no FUs. I like chicken nuggets and fries... before of course.
Back in the 70's when I started with the sprint cars, a drag racer showed me the "heat the rod" trick for installing piston pins. Did this on all my race engines. The rod ends did turn colors, but I never had a failure. I ran some of those pistons and rods for years.
Back in the days when I worked a at company building dynamometers, that weighed from a low, 19 pounds to a high, 20 tons we used the hot oil method, as well as a 6 foot by 6 foot hot box. The hot oil method was messy, but it worked. On the larger dynamometers the shaft diameters were well over 1 foot, and the bearing were huge too. If you want to see the dynamometers I mentioned, look up Kahn Dynamometers on the internet.
The Jalopy Journal
