Unusual conrod wear pattern

[Kez]

I have a new 12mm crank K&B .21 that I bought over 20 years ago. Only ran it for the first time last year. After the first runs, I tore down the engine and noticed the conrod had unusual wear pattern. The conrod big end that faces the PTO has a crescent shaped polished pattern centered at about 5 o'clock position. The wear mark is pretty wide..starting at about 3 o'clock to 8 p'clock.

The PTO surface that contacts the conrod showed normal wear but that is expected being steel.

At first I thought the crankcase was machine out of square. I bought a new crankcase. Put in a new conrod and the same thing happened. I called MECOA but they said the warranty would not cover this engine even though I never ran it.

Has anyone experienced this problem? What is the cause? And how to fix this?

I can take photos of the conrod if my description is not clear.

Thanks,

kez

 

[carlnoki]

photos are worth a million dollars.

always include photos if possible so others can see the problem.

thanks

 

[Geraghty]

I have a new 12mm crank K&B .21 that I bought over 20 years ago. Only ran it for the first time last year. After the first runs, I tore down the engine and noticed the conrod had unusual wear pattern. The conrod big end that faces the PTO has a crescent shaped polished pattern centered at about 5 o'clock position. The wear mark is pretty wide..starting at about 3 o'clock to 8 p'clock.

The PTO surface that contacts the conrod showed normal wear but that is expected being steel.

At first I thought the crankcase was machine out of square. I bought a new crankcase. Put in a new conrod and the same thing happened. I called MECOA but they said the warranty would not cover this engine even though I never ran it.

Has anyone experienced this problem? What is the cause? And how to fix this?

I can take photos of the conrod if my description is not clear.

Thanks,

kez

The crankpin and wristpin bronze bushings in the rod are not parallel to each other....that is what is causing the crescent shaped wear pattern...

While the motor is running the connecting rod is walking back towards the pto disc causing the scuffing.....

In my 35+ years of doing this I have maybe seen 5 production conn rods from the factory with perfectly parallel rod end bushings....

PS:That is "any motor manufacturer" not just K&B......

 

[Kez]

I have a new 12mm crank K&B .21 that I bought over 20 years ago. Only ran it for the first time last year. After the first runs, I tore down the engine and noticed the conrod had unusual wear pattern. The conrod big end that faces the PTO has a crescent shaped polished pattern centered at about 5 o'clock position. The wear mark is pretty wide..starting at about 3 o'clock to 8 p'clock.

The PTO surface that contacts the conrod showed normal wear but that is expected being steel.

At first I thought the crankcase was machine out of square. I bought a new crankcase. Put in a new conrod and the same thing happened. I called MECOA but they said the warranty would not cover this engine even though I never ran it.

Has anyone experienced this problem? What is the cause? And how to fix this?

I can take photos of the conrod if my description is not clear.

Thanks,

kez

The crankpin and wristpin bronze bushings in the rod are not parallel to each other....that is what is causing the crescent shaped wear pattern...

While the motor is running the connecting rod is walking back towards the pto disc causing the scuffing.....

In my 35+ years of doing this I have maybe seen 5 production conn rods from the factory with perfectly parallel rod end bushings....

PS:That is "any motor manufacturer" not just K&B......

Thanks Rod. I figured it was not the case out of square after replacing mine and still having the same problem. I will try another rod.

I do not understand why it is so difficult to get the two bushings to be parallel. If they machine the rod on a milling machine and bore the two holes without changing the set up that should be square?

kez

 

[Geraghty]

I have a new 12mm crank K&B .21 that I bought over 20 years ago. Only ran it for the first time last year. After the first runs, I tore down the engine and noticed the conrod had unusual wear pattern. The conrod big end that faces the PTO has a crescent shaped polished pattern centered at about 5 o'clock position. The wear mark is pretty wide..starting at about 3 o'clock to 8 p'clock.

The PTO surface that contacts the conrod showed normal wear but that is expected being steel.

At first I thought the crankcase was machine out of square. I bought a new crankcase. Put in a new conrod and the same thing happened. I called MECOA but they said the warranty would not cover this engine even though I never ran it.

Has anyone experienced this problem? What is the cause? And how to fix this?

I can take photos of the conrod if my description is not clear.

Thanks,

kez

The crankpin and wristpin bronze bushings in the rod are not parallel to each other....that is what is causing the crescent shaped wear pattern...

While the motor is running the connecting rod is walking back towards the pto disc causing the scuffing.....

In my 35+ years of doing this I have maybe seen 5 production conn rods from the factory with perfectly parallel rod end bushings....

PS:That is "any motor manufacturer" not just K&B......

Thanks Rod. I figured it was not the case out of square after replacing mine and still having the same problem. I will try another rod.

I do not understand why it is so difficult to get the two bushings to be parallel. If they machine the rod on a milling machine and bore the two holes without changing the set up that should be square?

kez

I am confident the aluminum rod beam is square but I am sure the manufacturers take the rod out of the CNC to press in the bronze bushings and then ream them to size in a separate processes.....

I have a fixture to check the rod for alignment then I straighten and clearance the bronze bushings when I blueprint a motor.....

 

[dizzy dean]

thanks rod,

robin and i, were talking about this the other day. we were wondering how you did such procedures <_<

now we know

tim