Additional rod information

[Jim Allen]

During the development of the retainers for my steel connecting rod; Carl Dodge completed testing of a roller rod assembly for his control line .21 speed engine. This engine normally turns 42,000 rpm in flight. If a propeller should break during the flight, the engine rpm will go beyond 50,000; breaking any aluminum connecting rod. Carl solved this rod breaking problem by using a titanium rod with a hard steel race in the bottom end & a bushing in the top end. The retainer for his rod is machined from beryllium copper which is fully hardened. The diameter of the rollers used is .0312. The unique feature of Carl's rod is that there are 3 rollers in each retainer window; not one, as would be found in a standard roller assembly!

In roller assemblies that are not caged, a helix angle will be developed by the rollers as they rotate that will be increased as the rpm increases. This helix angle in uncaged assemblies at high rpm's will cause high friction & high heat to develope causing the assembly to fail. Caging rollers will reduce the load that can be carried, but will increase the operating rpm.

My roller assembly was modified from 13-.0627 dia. individually caged rollers in each retainer window to 16-.0627 dia. dual caged rollers in each retainer window. The crank pin dia. remained at .3281. The retainer material between roller windows was reduced from .030 to .027 at the roller center line. This final assembly has increased wear resistance; increased load carrying capabilities & has been tested at rpm's of 38,000 with no failures.

 

[Ian Inverarity]

Jim,

Very interesting info! Have you measured if there is a performance difference between using caged and crowded needle roller bottom ends?

Also from what you say the main benefit of caging the rollers is holding them 'straight'? Could this also be achieved by making a retainer with, say, 2 or 3 large windows for the rollers, ie minimal reduction of bearings from a crowded setup, and still holding the needles 'straight'? This should only slightly reduce the load capacity from a crowded setup.

Ian.

 

[Jim Allen]

Jim,
Very interesting info!    Have you measured if there is a performance difference between using caged and crowded needle roller bottom ends?

Also from what you say the main benefit of caging the rollers is holding them 'straight'? Could this also be achieved by making a retainer with, say, 2 or 3 large windows for the rollers, ie minimal reduction of bearings from a crowded setup, and still holding the needles 'straight'? This should only slightly reduce the load capacity from a crowded setup.

Ian.

108561[/snapback]

​

Ian,

I tested both caged & full complement roller assemblies. Full complement assemblies failed once rpms reached 25,000 for extended periods. Caged assemblies continued to function even for extended periods beyond 35,000 with no failures. Initial failures of full complement assemblies would be the blueing of the rollers; the crank pin; & the bottom end of the connecting rod. Continued running in this condition would give a final failure where the rollers are ground away to almost nothing because they have been softened due to excessive heat.

If you examine the limiting speeds given in any roller bearing catalogue for full complement & caged roller assemblies of the same size, it can easily be seen that caged assemblies can run 4 to 5 X faster than full complement assemblies. Basic dynamic load ratings are less than 50% greater for full complement assemblies.

One problem that occurs with increasing roller count per window is the weakening of the cage. My original cage had 13 windows compared to the 8 windows presently used. The 8 window cage weighs .8 gm & the 13 window cage 1 gm. The 8 window cage is definitely weaker, but roller count increased 23% from 13 to16 rollers. It would appear that roller assemblies can be built to accept present loads but must be caged for high rpm applications.

I am presently looking at the possibility of using ceramic rollers in place of the steel rollers. SAE paper #931561 shows that ceramic rollers have 1/2 the crushing strength; & 1/4 the bending & breaking strength of steel rollers. Their bearing friction torque & skew force are less than steel rollers. Their life is 1.7 X that of steel rollers & they have a smaller temperature rise. Will they make the engine turn faster? Maybe yes; maybe no; test,test----------test again.

Jim

 

[Richard Dahlheimer]

Jim,
Very interesting info!    Have you measured if there is a performance difference between using caged and crowded needle roller bottom ends?

Also from what you say the main benefit of caging the rollers is holding them 'straight'? Could this also be achieved by making a retainer with, say, 2 or 3 large windows for the rollers, ie minimal reduction of bearings from a crowded setup, and still holding the needles 'straight'? This should only slightly reduce the load capacity from a crowded setup.

Ian.

108561[/snapback]

​

Ian,

I tested both caged & full complement roller assemblies. Full complement assemblies failed once rpms reached 25,000 for extended periods. Caged assemblies continued to function even for extended periods beyond 35,000 with no failures. Initial failures of full complement assemblies would be the blueing of the rollers; the crank pin; & the bottom end of the connecting rod. Continued running in this condition would give a final failure where the rollers are ground away to almost nothing because they have been softened due to excessive heat.

If you examine the limiting speeds given in any roller bearing catalogue for full complement & caged roller assemblies of the same size, it can easily be seen that caged assemblies can run 4 to 5 X faster than full complement assemblies. Basic dynamic load ratings are less than 50% greater for full complement assemblies.

One problem that occurs with increasing roller count per window is the weakening of the cage. My original cage had 13 windows compared to the 8 windows presently used. The 8 window cage weighs .8 gm & the 13 window cage 1 gm. The 8 window cage is definitely weaker, but roller count increased 23% from 13 to16 rollers. It would appear that roller assemblies can be built to accept present loads but must be caged for high rpm applications.

I am presently looking at the possibility of using ceramic rollers in place of the steel rollers. SAE paper #931561 shows that ceramic rollers have 1/2 the crushing strength; & 1/4 the bending & breaking strength of steel rollers. Their bearing friction torque & skew force are less than steel rollers. Their life is 1.7 X that of steel rollers & they have a smaller temperature rise. Will they make the engine turn faster? Maybe yes; maybe no; test,test----------test again.

Jim

108570[/snapback]

​

Hi Jim, would titanium be a good material to use for a .21 size crankshaft? Thanks for all of the interesting info. Richard

 

[Jim Allen]

Jim,
Very interesting info!    Have you measured if there is a performance difference between using caged and crowded needle roller bottom ends?

Also from what you say the main benefit of caging the rollers is holding them 'straight'? Could this also be achieved by making a retainer with, say, 2 or 3 large windows for the rollers, ie minimal reduction of bearings from a crowded setup, and still holding the needles 'straight'? This should only slightly reduce the load capacity from a crowded setup.

Ian.

108561[/snapback]

​

Ian,

I tested both caged & full complement roller assemblies. Full complement assemblies failed once rpms reached 25,000 for extended periods. Caged assemblies continued to function even for extended periods beyond 35,000 with no failures. Initial failures of full complement assemblies would be the blueing of the rollers; the crank pin; & the bottom end of the connecting rod. Continued running in this condition would give a final failure where the rollers are ground away to almost nothing because they have been softened due to excessive heat.

If you examine the limiting speeds given in any roller bearing catalogue for full complement & caged roller assemblies of the same size, it can easily be seen that caged assemblies can run 4 to 5 X faster than full complement assemblies. Basic dynamic load ratings are less than 50% greater for full complement assemblies.

One problem that occurs with increasing roller count per window is the weakening of the cage. My original cage had 13 windows compared to the 8 windows presently used. The 8 window cage weighs .8 gm & the 13 window cage 1 gm. The 8 window cage is definitely weaker, but roller count increased 23% from 13 to16 rollers. It would appear that roller assemblies can be built to accept present loads but must be caged for high rpm applications.

I am presently looking at the possibility of using ceramic rollers in place of the steel rollers. SAE paper #931561 shows that ceramic rollers have 1/2 the crushing strength; & 1/4 the bending & breaking strength of steel rollers. Their bearing friction torque & skew force are less than steel rollers. Their life is 1.7 X that of steel rollers & they have a smaller temperature rise. Will they make the engine turn faster? Maybe yes; maybe no; test,test----------test again.

Jim

108570[/snapback]

​

Hi Jim, would titanium be a good material to use for a .21 size crankshaft? Thanks for all of the interesting info. Richard

108585[/snapback]

​

Richard,

Titanium alloys 6AL-4V; 3AL-2.5V; 5AL-2.5SN; 7AL-4MO & others are not bearing materials. Therefore a crankshaft made of these alloys will need a seperate hardened crank pin for bushed or roller rod operation. Heavy press fits (.0013) in soft materials such as titanium or aluminum do not work. Shrink fits work best on alloys like these; but in the case of titanium the mean coefficient of thermal expansion is low (5.2). This makes titanium a very poor conductor of heat & when heated it does not dissipate that heat.

If your intention is to lighten the crankshaft assembly; drill a hole through the crank pin & drill the depth of the threaded hole in the front of the crankshaft to the area where the rear main bearing sets.

Titanium alloys are about 1/2 the weight of steel alloys.

Jim

 

[Richard Dahlheimer]

Jim,
Very interesting info!    Have you measured if there is a performance difference between using caged and crowded needle roller bottom ends?

Also from what you say the main benefit of caging the rollers is holding them 'straight'? Could this also be achieved by making a retainer with, say, 2 or 3 large windows for the rollers, ie minimal reduction of bearings from a crowded setup, and still holding the needles 'straight'? This should only slightly reduce the load capacity from a crowded setup.

Ian.

108561[/snapback]

​

Ian,

I tested both caged & full complement roller assemblies. Full complement assemblies failed once rpms reached 25,000 for extended periods. Caged assemblies continued to function even for extended periods beyond 35,000 with no failures. Initial failures of full complement assemblies would be the blueing of the rollers; the crank pin; & the bottom end of the connecting rod. Continued running in this condition would give a final failure where the rollers are ground away to almost nothing because they have been softened due to excessive heat.

If you examine the limiting speeds given in any roller bearing catalogue for full complement & caged roller assemblies of the same size, it can easily be seen that caged assemblies can run 4 to 5 X faster than full complement assemblies. Basic dynamic load ratings are less than 50% greater for full complement assemblies.

One problem that occurs with increasing roller count per window is the weakening of the cage. My original cage had 13 windows compared to the 8 windows presently used. The 8 window cage weighs .8 gm & the 13 window cage 1 gm. The 8 window cage is definitely weaker, but roller count increased 23% from 13 to16 rollers. It would appear that roller assemblies can be built to accept present loads but must be caged for high rpm applications.

I am presently looking at the possibility of using ceramic rollers in place of the steel rollers. SAE paper #931561 shows that ceramic rollers have 1/2 the crushing strength; & 1/4 the bending & breaking strength of steel rollers. Their bearing friction torque & skew force are less than steel rollers. Their life is 1.7 X that of steel rollers & they have a smaller temperature rise. Will they make the engine turn faster? Maybe yes; maybe no; test,test----------test again.

Jim

108570[/snapback]

​

Hi Jim, would titanium be a good material to use for a .21 size crankshaft? Thanks for all of the interesting info. Richard

108585[/snapback]

​

Richard,

Titanium alloys 6AL-4V; 3AL-2.5V; 5AL-2.5SN; 7AL-4MO & others are not bearing materials. Therefore a crankshaft made of these alloys will need a seperate hardened crank pin for bushed or roller rod operation. Heavy press fits (.0013) in soft materials such as titanium or aluminum do not work. Shrink fits work best on alloys like these; but in the case of titanium the mean coefficient of thermal expansion is low (5.2). This makes titanium a very poor conductor of heat & when heated it does not dissipate that heat.

If your intention is to lighten the crankshaft assembly; drill a hole through the crank pin & drill the depth of the threaded hole in the front of the crankshaft to the area where the rear main bearing sets.

Titanium alloys are about 1/2 the weight of steel alloys.

Jim

108591[/snapback]

​

Jim, yes the reason i thought about a titanium crankshaft, was for the weight difference, over steel. The weight difference is impresive. I thought having the crank and rod made from titanium, and a forged aluminum piston, just might make for an ultimate .21. I was checking out the RBPRODUCTS web site, and i see they are building a .21 engine with a forged piston. (E1005-RC) is the engine with the forged piston. If i may ask, what type of induction is used with the Carl Dodge .21 speed engine mentioned above? Thanks again, Richard D.

 

[Jim Allen]

Jim,
Very interesting info!    Have you measured if there is a performance difference between using caged and crowded needle roller bottom ends?

Also from what you say the main benefit of caging the rollers is holding them 'straight'? Could this also be achieved by making a retainer with, say, 2 or 3 large windows for the rollers, ie minimal reduction of bearings from a crowded setup, and still holding the needles 'straight'? This should only slightly reduce the load capacity from a crowded setup.

Ian.

108561[/snapback]

​

Ian,

I tested both caged & full complement roller assemblies. Full complement assemblies failed once rpms reached 25,000 for extended periods. Caged assemblies continued to function even for extended periods beyond 35,000 with no failures. Initial failures of full complement assemblies would be the blueing of the rollers; the crank pin; & the bottom end of the connecting rod. Continued running in this condition would give a final failure where the rollers are ground away to almost nothing because they have been softened due to excessive heat.

If you examine the limiting speeds given in any roller bearing catalogue for full complement & caged roller assemblies of the same size, it can easily be seen that caged assemblies can run 4 to 5 X faster than full complement assemblies. Basic dynamic load ratings are less than 50% greater for full complement assemblies.

One problem that occurs with increasing roller count per window is the weakening of the cage. My original cage had 13 windows compared to the 8 windows presently used. The 8 window cage weighs .8 gm & the 13 window cage 1 gm. The 8 window cage is definitely weaker, but roller count increased 23% from 13 to16 rollers. It would appear that roller assemblies can be built to accept present loads but must be caged for high rpm applications.

I am presently looking at the possibility of using ceramic rollers in place of the steel rollers. SAE paper #931561 shows that ceramic rollers have 1/2 the crushing strength; & 1/4 the bending & breaking strength of steel rollers. Their bearing friction torque & skew force are less than steel rollers. Their life is 1.7 X that of steel rollers & they have a smaller temperature rise. Will they make the engine turn faster? Maybe yes; maybe no; test,test----------test again.

Jim

108570[/snapback]

​

Hi Jim, would titanium be a good material to use for a .21 size crankshaft? Thanks for all of the interesting info. Richard

108585[/snapback]

​

Richard,

Titanium alloys 6AL-4V; 3AL-2.5V; 5AL-2.5SN; 7AL-4MO & others are not bearing materials. Therefore a crankshaft made of these alloys will need a seperate hardened crank pin for bushed or roller rod operation. Heavy press fits (.0013) in soft materials such as titanium or aluminum do not work. Shrink fits work best on alloys like these; but in the case of titanium the mean coefficient of thermal expansion is low (5.2). This makes titanium a very poor conductor of heat & when heated it does not dissipate that heat.

If your intention is to lighten the crankshaft assembly; drill a hole through the crank pin & drill the depth of the threaded hole in the front of the crankshaft to the area where the rear main bearing sets.

Titanium alloys are about 1/2 the weight of steel alloys.

Jim

108591[/snapback]

​

Jim, yes the reason i thought about a titanium crankshaft, was for the weight difference, over steel. The weight difference is impresive. I thought having the crank and rod made from titanium, and a forged aluminum piston, just might make for an ultimate .21. I was checking out the RBPRODUCTS web site, and i see they are building a .21 engine with a forged piston. (E1005-RC) is the engine with the forged piston. If i may ask, what type of induction is used with the Carl Dodge .21 speed engine mentioned above? Thanks again, Richard D.

108597[/snapback]

​

Richard,

Carl uses a standard rotary valve in his bar stock motor. This tuned piped motor has several unusual features: the depth of the transfers in this motor are very shallow (.050); the tranfers are also "tepee" shapped from the bottom to the windows in the liner; the center line of the cylinder is angled 1 or 2 degrees to the intake valve side of the motor to prevent the rod from walking off the crank pin; the head is cone shapped with no squish band; a titanium roller rod with beryllium copper retainer is used & a parabolic pipe is used. Henry Nelson chromes Carl's liners, but Carl hones all his liners himself.

Jim