What is the grey sludge in my cylinder?

[GAJ]

well that was going to be my question until I took apart my HPI 5.9 and found 1/3 of the piston skirt missing.
What could have caused this failure? There is no evidence of any debris in the crankcase, is it possible that the skirt was just sucked into the cylinder? The bearings are clean and smooth operating, is it safe to reuse them?
Thank you.

 

[WoodiE]

The bearings are clean and smooth operating, is it safe to reuse them?

I wouldn't, I'd replace them as well while you're at it.

 

[DXtreme1]

I second this. What may appear to be smooth operating by cranking it by hand will nowhere be close to simulating what the bearings experience on load running at 32k and up rpm. You can check at Fast Eddy bearings they're top notch quality for a great price. I highly recommend them.

I wouldn't, I'd replace them as well while you're at it.

 

[cbaker65]

well that was going to be my question until I took apart my HPI 5.9 and found 1/3 of the piston skirt missing.
What could have caused this failure? There is no evidence of any debris in the crankcase, is it possible that the skirt was just sucked into the cylinder? The bearings are clean and smooth operating, is it safe to reuse them?
Thank you.

The greying could be caused by not enough lube in the fuel causing to much friction on the piston ,
also ,do to a worn sloppy rod in which can get stressed out during break-in period ,some people actually
replace the rods shortly after break-ins!...

 

[GAJ]

Thanks for the responses. Engine is a couple of years old, I had just switched to 30% nitro as LHS was out of 20%. I was tuning at the time, maybe went too far, although I had smoke and temps under 260. I did think she was real responsive to the throttle, then she died. Time for a new engine.. Is an LRP 30 enough for a Savage XL?

 

[DXtreme1]

Sometime an engine will make its peak power right before it grenades. They do not always slowly show signs that it's about to break. 30% has less lubricants and more nitro. As far as power it is relative to matching the right gearing for the motor that you choose. For these bigger MT you need one with gobs of torque or else it will feel lazy and heavy. With the right gearing and pipe combo most motors .28 and up with high torque specs should be good.

Thanks for the responses. Engine is a couple of years old, I had just switched to 30% nitro as LHS was out of 20%. I was tuning at the time, maybe went too far, although I had smoke and temps under 260. I did think she was real responsive to the throttle, then she died. Time for a new engine.. Is an LRP 30 enough for a Savage XL?

 

[olds97_lss]

Yeah, running too lean/hot will cause the piston to kind of crumble. Then the pieces bang around inside the engine and get powdered, then you end up with oil/fuel/aluminum sludge in there.

 

[Certified Mike]

When it 'powders' alum Def turns a gray color. Its most likely what has happened in this case. The other thing that comes to mind is possibly water mixing with the oil in the fuel. Water and oil turns funky colors as well.
If you take a little of the gray material and spread it across a white piece of paper, you'll be able to determine what is in it pretty easily.

 

[GAJ]

When it 'powders' alum Def turns a gray color. Its most likely what has happened in this case. The other thing that comes to mind is possibly water mixing with the oil in the fuel. Water and oil turns funky colors as well.
If you take a little of the gray material and spread it across a white piece of paper, you'll be able to determine what is in it pretty easily.

Thanks Mike, definitely not water contamination. I have put an old Nitrostar 25 in the XL, so at least I am up and running.