Hello Jim, I'm interested.It is very difficult to use any Titanium alloy as a connecting rod material in a miniature two cycle engine! If your interested, I'll explain why from actual experience.
6AL4 V Titanium does work in smaller size engines. Since Titanium alloys are not bearing materials it will be necessary to provide a suitable bearing surface in the upper & bottom ends. Titanium alloys also have very poor thermal conductivity, therefore any heat developed in the bushed ends of the rod remains there causing the rod to close down on its crank or wrist pin. Henry Nelson & I were able to get the bushed bottom ends of Titanium rods to survive at RPM's beyond 24,000 by running a bottom end clearance of more than .0065". Titanium connecting rods that used any type of roller assembly in the bottom end also did not work with drawn cup bearings or machined roller bearings because it is impossible to hold whatever type of hardened bushing that can be used without distorting the bushing. A great deal of time went into determining that the best material for a connecting rod in a larger size engine is hardened & tempered STEEL!Hello Jim, I'm interested.
What about 7068 Aluminum? Its supposed to be just as strong as Titanium without the BS of machining Titanium (or its thermal properties).
EDIT: I found this on Wikipedia (yeah I know for whatever its worth but....) "Primarily developed for ordnance applications, alloy 7068 is now being used or considered for markets like the aerospace and automotive industries (valve body and connecting rod applications)"
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Jim Thanks for the info. I do have one question though. In the above you talked about holding roller bearing assemblies but then said it couldn't be done without distorting the bushing. Did you mean without distorting the bearing? Is the distortion a result of running the engine, or when fitting it to the rod...... Titanium connecting rods that used any type of roller assembly in the bottom end also did not work with drawn cup bearings or machined roller bearings because it is impossible to hold whatever type of hardened bushing that can be used without distorting the bushing.......
Ti is not that difficult to machine. Slow spindle speeds, heavy feed rates and keep everything cool. I've been using the same solid carbide roughing end mill to make connecting rods ( and other parts) for more than a decade.
For what it's worth, the 7068 is almost unobtainium. I had an RFQ for some 7068 parts a while back, and ended up finding some after some considerable searching. I eventually found it on eBay, tracked down the seller and bought it direct. I could only buy the drops they had left over from purchases made by military contract MFRs, and only if those drops weren't potentially sought by those MFRs (these drops were what was on eBay). I still have most of what I bought, and I hold it fairly close to the chest.
Titan Racing Components
Model Machine and Precision LLC
The answer to this is definitely yes Rudy. The size of the engine in question will make a difference as to what works & what will not work. No one has ever calculated or attempted to calculate what effect the displacement, coupled with the engine's RPM has on this fact! However, after thousand of hours of testing, what we found is that loose needles can work when the RPM's are below 24,000 in .45 to 1.00 cu in engines. The RPM limits are much higher in .21 to .45 cu in engines, even when Titanium rods were used. What happens in any loose, unguided needle assembly is the helix angle of the needles in relation to the axis of rotation increases with the rotational speed of the assembly. Look in any needle bearing catalogue & it can be easily seen that guided needles have a much higher rotational RPM than unguided needles. However, loose full complement needles can carry a larger load.Jim, did you ever use loose needles in your steel con rods??