Carbon Ring Wear Limit

[markdsr]

I have a 96 Challenger with a 787 that I just rebuilt. The motor runs great. There seems to be no power until you hit 6000 rpms then it flies. I noticed that the carbon ring is very sloppy. The id of the ring is 1/2 bigger than the size of the shaft. Could this be a problem? This was the same situation before I locked up the motor.

 

[Dr Honda]

The ID of the ring is much bigger than the driveshaft, so it can move around. Most of the time it will not look aligned.

There isn't really a wear limit. When you get bad cavitation though it... it's time to change it.


Most of the time, it will look fine from the outside, but when you remove it... one edge will be worn more than the other.

 

[markdsr]

Thank you Tony. Does that sound like a cavitation issue to you? The boat moves slowly at 2 to 3m rpm, From 3 to 5500 there is no additional forward thrust. At 6000 it snaps your head back. You can throttle back to 5300 and cruise all day but if you throttle back under 5000 it dies. I didn't measure the wear ring to impeller clearence but it looks very close and no signs of damage. Since I just rebuilt the engine I didn't go above 6000 rpms yet. Your comments please.

 

[Dr Honda]

Yes... It sounds like cavitation. But... it sounds more like a wear ring, or impeller. Normally with a carbon seal, you don't go anywhere until you throttle back a little to get it to seal up.

But... honistly... if you have bad cavitation... change both.

 

[markdsr]

Yes, good advice, as long as I have to take it apart anyway I'll change everything.