Ouch

[David Ashcroft]

Delete

 

[David Ashcroft]

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[David Ashcroft]

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[Michael Costanzo]

Good point Danny so I wonder why these manufacturers do things like this to begin with . A new boater would be **** out of luck with one of these new engines without proper guidance . Meanwhile car engines run and run . Closest thing to perfection for me has been the CMB VAC 91 , run a few tanks and hammer it . Of course it's no longer produced LOL .

tommy,i would pre head the heads like i do my high end on-road car engines.makes a huge difference in the life span of the rod and entire motor.i just changed out the rod on my .12 NR after 5+ gallons of fuel!! moron's are telling me you need to change the rod after 1 gallon break in?? PS an i beat the **** out of this .12 at 42,000 rpm's!!! (JP Modified) don't like the french people too much,but this guy build's some fast motors!!

 

[Tom Foley]

Then they should come with a spare rod for this purpose if that is required .JMHO

 

[Michael Costanzo]

Then they should come with a spare rod for this purpose if that is required .JMHO

well the changing the rod after 1 gal is non sense. because the p/s fit is so tight and is such a precision fit,is what makes it such a top notch (long lasting) engine.remember the italian motors are the cream of the crop and i guess they expect all modeler's to know how to break them in?? happy holiday's Tommy from the IRS...

 

[Jim Allen]

There can be many reason why an aluminum connecting rod, made of aluminum (2024-T351, 7075-T651), that is used in smaller size engines (.21 cu in, .45 cu in), may fail. What we have found with our.45 cu in pylon racing engines operating in the 29,000 to 32,000 RPM range is that the total radial clearance becomes "CRITICAL" as the RPM increases! Connecting rods set up with .001" to.002" total radial clearance will fail at RPM's beyond 32,000, no matter what alloy is used for the bushing! In depth testing, with various B-1 & B-2 bronze alloys, that had precisely honed to size bottom end holes, proved that insufficient clearance will cause bottom end connecting rod failure. The clearance that seems to work the best is .003" to .004". I'm not sure what process is being used in manufactured engines but the final honing to size must be done after the bushing is pressed into the rod.

The size of the crank pin, the bushing's total area & the engine's RPM will determine the amount of heat developed in the bottom end. One reason that aluminum works well is because of its high thermal conductivity & its high expansion rate. This allows the bushing & rod to expand as the heat increases. If this does not happen in a sufficient amount, the bottom end will run with less & less clearance as the RPM increases. Connecting rod failure is around the corner!

Steel type roller rods cannot be compared to aluminum because all the parts involved are made of steel!

Jim Allen

 

[David Ashcroft]

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[Michael Costanzo]

There can be many reason why an aluminum connecting rod, made of aluminum (2024-T351, 7075-T651), that is used in smaller size engines (.21 cu in, .45 cu in), may fail. What we have found with our.45 cu in pylon racing engines operating in the 29,000 to 32,000 RPM range is that the total radial clearance becomes "CRITICAL" as the RPM increases! Connecting rods set up with .001" to.002" total radial clearance will fail at RPM's beyond 32,000, no matter what alloy is used for the bushing! In depth testing, with various B-1 & B-2 bronze alloys, that had precisely honed to size bottom end holes, proved that insufficient clearance will cause bottom end connecting rod failure. The clearance that seems to work the best is .003" to .004". I'm not sure what process is being used in manufactured engines but the final honing to size must be done after the bushing is pressed into the rod.

The size of the crank pin, the bushing's total area & the engine's RPM will determine the amount of heat developed in the bottom end. One reason that aluminum works well is because of its high thermal conductivity & its high expansion rate. This allows the bushing & rod to expand as the heat increases. If this does not happen in a sufficient amount, the bottom end will run with less & less clearance as the RPM increases. Connecting rod failure is around the corner!

Steel type roller rods cannot be compared to aluminum because all the parts involved are made of steel!

Jim Allen

so jim what your saying is the larger size motors from the factory with alum rods should have the clerance opened up some? is there enough room for this? PS,in all the 20 years of running N/R .21's in my on road cars i have never lost a rod. 30%nitro and 9-11% oil.mostly byrons fuel.

 

[Jim Allen]

Michael,

I can only speak in general terms because there is no way to tell what alloys engine manufacturers are using for connecting rods or their bushings. When you examine the size of crank pins in large size nitro engines with aluminum rods you will not see a crank pin larger than 7 mm (.2756"). Larger size pins & bushings can carry larger loads but they will also generate more heat.

JA