Crank is blacked

[MedicWild]

Tearing down my 2nd motor for rebuild and noticed A LOT of build up and blackening on the left side of the crank/piston push rods. I got this motor thrown in as part of a trade a few years ago. It was reported to have been in a fire (not sure if the bike itself or in a surrounding shed. The stator and point wires were slightly melted but still intact enough where I think the heat wasn’t too intense.

Could this blackened side of the crank be just burnt oil? I plan on replacing the crank bearings on this one as it as some lateral play in the push rods. Complete tear down, clean, and rebuild. Just wondering if I should be looking into anything else or if anything can shed light on this finding. Thanks in advance!

 

[Jan_P]

I would inspect the chain tensioner plastic for heat damage
Cant se anything on the outside --possibly fine
Some play is OK
The small end con rod hole can be worse and below
Splitting the crank is a big expensive job here - best avoided
Possible better find a replacement
There are inspection routines in On line manuals

It can be a high mileage motor .. The piston skirts wear can show more
and there can be piston size markings on top

 

[gggGary]

Stuck rings, severe blow by? Just a guess.

 

[MedicWild]

I would inspect the chain tensioner plastic for heat damage
Cant se anything on the outside --possibly fine
Some play is OK
The small end con rod hole can be worse and below
Splitting the crank is a big expensive job here - best avoided
Possible better find a replacement
There are inspection routines in On line manuals

It can be a high mileage motor .. The piston skirts wear can show more
and there can be piston size markings on top

This is great insight! Thank you! The cam chain guide shows no major wearing at all really. So that was a surprise. I split the case on my last build (pics) so i am not too shy about it (for better or worse). I am worried about what is lurking in the bottom case. The oil plugs came out horribly plugged up. Oil was like rubber.

My pistons are both 0.50 so that means I need to step up my new rings to +0.50 rings right? My last build was still stock rings so that is a new area for me to learn.

I will looking into more wear areas in the up coming days.

 

[Jim]

Stuck rings, severe blow by? Just a guess.

Agree. looks like blow by to me too.

 

[MedicWild]

Agree. looks like blow by to me too.

Would that indicate the need for larger rings? The pistons are stamped 0.50 currently

 

[Jim]

Have a look in Tech. There's a top end buildup thread that explains all this.
The short answer is it's not that simple. An elongated, tapered or otherwise bad bore, worn pistons beyond the skirt clearances needed.... stuck rings as Gary pointed out... lot's of variables need to be checked and addressed. Too many to answer if the rings are worn. Yes they are, but what else is going on in there... it all needs checking and measuring.

 

[MedicWild]

Have a look in Tech. There's a top end buildup thread that explains all this.
The short answer is it's not that simple. An elongated, tapered or otherwise bad bore, worn pistons beyond the skirt clearances needed.... stuck rings as Gary pointed out... lot's of variables need to be checked and addressed. Too many to answer if the rings are worn. Yes they are, but what else is going on in there... it all needs checking and measuring.

Gotcha. I will check that thread out. Also sounds like new sleeves, pistons, and rings would solve this…?

 

[Jim]

And to be perfectly blunt, leaving gouges in the piston while removing the carbon ain't helping. That one is dangerously close to being tossed. Put your sharp edged metal scrapers away.

 

[MedicWild]

And to be perfectly blunt, leaving gouges in the piston while removing the carbon ain't helping. That one is dangerously close to being tossed. Put your sharp edged metal scrapers away.

View attachment 336710

Copper wire brush actually but I will keep it away from now on haha thank you.

 

[Jim]

Also sounds like new sleeves, pistons, and rings would solve this…?

No, you can't know the answer to that until you disassemble, clean and measure everything. Until then, it's all opinions and guesses.
If I had to guess, definitely rings... probably pistons and no idea on whether the sleeves are good or not. It's simply a matter of tearing it apart and having a look.

 

[MedicWild]

No, you can't know the answer to that until you disassemble, clean and measure everything. Until then, it's all opinions and guesses.
If I had to guess, definitely rings... probably pistons and no idea on whether the sleeves are good or not. It's simply a matter of tearing it apart and having a look.

The micrometer and gauges are coming out tomorrow. Thanks. I will update

 

[Jim]

Cool. We get some numbers, we can figure out which way is north... and how much the trip will cost.

here's that thread btw.
https://www.xs650.com/threads/xs650-top-end-buildup.52041/