could i be 1st on the list??For a high performance large size nitro or gas engine, .15 cc & larger, a steel connecting rod is best. Since this rod will be a roller type, (bottom end only) with no bushing in the top end & will use the bottom's ID as a bearing surface, the correct selection of an alloy is critical! Another important consideration will be the alloy used for the bottom end roller assemblies retainer! It must have a low weight (mass), high strength, high hardness & wear resistance.
Jim Allen
hi jim, i already knew what the answer was going to be,but i was always told if you don't ask.....Mike,
I hate to disappoint anyone, but there is no list at present.
JA
Very nice piece.It became obvious that the connecting rod needed to be a "one piece design", made of a material that would be 58 Rc after hardening & tempering. Since this connecting rod would have no bushing or roller assembly in the top end, the reciprocating weight is greatly reduced. By not having a roller assembly or a bushing also allows the connecting rod to be at a maximum length which reduces the length of the piston boss areas to a minimum height. Lengthening the connecting rod to its maximum length increases its weight slightly, but the reduction in the amount of connecting rod's angularity is much more important in reducing piston rocking.
As an example, the connecting rod's length in my 15 cc nitro engine is 1.741" with a .902" stroke. The connecting rod's length in my 27 cc gas engine is 2.155" with a 1.102" stroke. The upper end of the bush less, roller less, one piece connecting rod has a wall thickness of .094" with no thrust washers needed giving a mechanically reliable design with very few parts.
After profiling the connecting rod's shape, including the staggered double oiling slots in the bottom end & the single slot in the top end, the rod is ready to be heat treated. Notice the groove in the bottom end that channels any crankcase oil into the slots.
Jim Allen
Note: I'll post better photos from my computer when I return to the shop.
Very well thought out, Jim... I sure wish you had the time to provide theseThe "I" beam part of the connecting rod is .282" wide X .156" thick. The radius at the junction of the I-beam & the upper or lower holes is .8125" (1.625" dia end mill). This end mill profiles the entire outside of the rod. A .1875" ball nosed end mill forms the center section of the I-beam which is .031" thick in the center. The wrist pin hole is .250" ID X .360" OD. The crank pin hole is .4538" ID X .6250" OD. The undercut on the outside of the big end is .031" deep X .156" wide & it also has a radius on the inside corner. The center distance of the two hole is 1.741". After hardening (1760* F; standard oil quench) the S-7 rods are double tempered at 400* F. This heat treatment gives a tensile strength of 315,000 lbs/ square in; a yield strength of 210,000 lbs/ square in; at 58 Rc with a 1" Charpy "V" test of over 224 ft lbs.
This heat treatment gives the strongest connecting rod possible. It also provides the necessary bearing surfaces required for the bottom end roller assembly & the un-bushed upper end.
Completed connecting rods after machining have no sharp inside corners anywhere! All oil slots are .032" wide. The two slots in the bottom end are staggered to each side of the visible undercut. The inside corners of the undercut have a radius also. The undercut lightens the bottom end & forces oil into the connecting rod as it rotates in a groove machined into the crankcase. All connecting rods are guided in the upper end, between the piston bosses (.005") clearance, where the rotational speed is low. Connecting rods should NEVER be guided in the bottom end where the rotational speeds of the crankshaft are very high.
Jim Allen
tim,what do you see with that rod that you are not happy with? i have only run the .12/.21 (S7) rods and never had an issuse..Very well thought out, Jim... I sure wish you had the time to provide theseThe "I" beam part of the connecting rod is .282" wide X .156" thick. The radius at the junction of the I-beam & the upper or lower holes is .8125" (1.625" dia end mill). This end mill profiles the entire outside of the rod. A .1875" ball nosed end mill forms the center section of the I-beam which is .031" thick in the center. The wrist pin hole is .250" ID X .360" OD. The crank pin hole is .4538" ID X .6250" OD. The undercut on the outside of the big end is .031" deep X .156" wide & it also has a radius on the inside corner. The center distance of the two hole is 1.741". After hardening (1760* F; standard oil quench) the S-7 rods are double tempered at 400* F. This heat treatment gives a tensile strength of 315,000 lbs/ square in; a yield strength of 210,000 lbs/ square in; at 58 Rc with a 1" Charpy "V" test of over 224 ft lbs.
This heat treatment gives the strongest connecting rod possible. It also provides the necessary bearing surfaces required for the bottom end roller assembly & the un-bushed upper end.
Completed connecting rods after machining have no sharp inside corners anywhere! All oil slots are .032" wide. The two slots in the bottom end are staggered to each side of the visible undercut. The inside corners of the undercut have a radius also. The undercut lightens the bottom end & forces oil into the connecting rod as it rotates in a groove machined into the crankcase. All connecting rods are guided in the upper end, between the piston bosses (.005") clearance, where the rotational speed is low. Connecting rods should NEVER be guided in the bottom end where the rotational speeds of the crankshaft are very high.
Jim Allen
pieces to us. I have concerns over the con rod in my NR46DD and am already
planning for an alternative.
Thank you-
tim
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