Metal chunk in oil

[Scratcher09]

I decided to get started on a 1971 CB350 I've had sitting in my garage for a couple years. It has 7K miles on it. The right cylinder has 155psi cold. The left has none. I am pulling the motor so I can tear into it. As I'm draining the oil, this chunk of metal comes out. Anyone know what it is? The PO told me he had replaced rings and rode it but that it needed a new head gasket. I never put much stock into what I'm told by PO's so I'm not surprised that it needs more than a gasket. Identifying this piece might give me some insight into what will be needed.

 

[Tim]

Aluminum? Steel? Try a magnet.

Doesn't look like any internal part I've seen. Seems smooth for a part of the case casting.

 

[Scratcher09]

It steel. Has a shiny gunmetal finish--almost like hematite. Has me puzzled.

 

[Scratcher09]

Just figured out the piece is magnetic. It is a magnet.

 

[my-79-750-k]

PO probably didn't want to spring for a magnetic drain plug and glued a magnet to the original plug... LOL

 

[Scratcher09]

This might have something to do with the lack of compression. Looks like it had been rebuilt recently like the PO said. The cylinder walls look fresh and looks like a new KA Performance cam chain tensioner. Crank spins freely and chili dear wall looks and feels smooth. Will I need to do anything other than replace the piston and rings and gaskets?

Looks like chewbacca may have been right. PO must have put that magnet on the drain plug.

 

[Brodie]

Jesus, look how scoured the piston skirt is. Never mind the hole in the top that shouldn't have gone back in at all.

I imagine that the PO couldn't find the $ for new pistons so he bolted it back together and sold it off.

Since you are that far into the engine look at doing the much needed oil mods. PJ has a thread on what needs to be done.

Check the bore size of both cylinders. It has been know for a PO to bore 1 side and not the other.

Depending on how the cylinder walls look you should be able to get new piston and rings. There is a big bore mod using Suzukis GS pistons if you are interested.

 

[teazer]

Something odd there. It could just be a result of the detonation and overheating, but the holed piston looks much newer than the other one which appears to have a heavy carbon deposit. Maybe the PO replaced one piston for some reason and screwed up jetting or timing and melted the new piston after very few miles.

Either way the motor has to come apart to be flushed out. Bits of that piston will be in the crank, under the windage tray and in the transmission probably.
Fortunately, they are easy motors to work on and only two cylinders. The biggest PIA is drilling out the rivets on the windage tray to see what horrors are lurking beneath.

When it's apart, be sure to power flush the rocker arms and camshaft too, to remove any debris from that or prior issues. Same with the oil pump and transmission shafts. If you don't have a parts washer with kerosene or similar solvent cleaner, you could use a couple of cans of WD40 or possibly some diesel in a spray bottle, or kerosene. Not acetone or MEK or similar solvents.

That strange part looks almost like the tip of the clutch adjusting camp but it's on the outside or perhaps part of the kickstarter ratchet pawl.

 

[Scratcher09]

When teazer says flush out the motor, is he suggesting to open up the bottom end? I've never gone into a bottom end so I'm worried about that.

 

[adventurco]

When teazer says flush out the motor, is he suggesting to open up the bottom end? I've never gone into a bottom end so I'm worried about that.

I would. Who knows where scraps of that piston have made it to. Splitting cases is more intimidating than anything, it's really not that complicated or difficult once you get into it. Take a lot of photos and make notes of where everything goes, use the parts fiches as reference. May as well replace the oil seals while you're in there. Grab a tube of yamabond or Hondabond for resealing them.


Sent from my iPhone using DO THE TON

 

[irk miller]

Brodie's mod suggestions are for a 360, not a 350. He might be confused on which model your bike is. Also, kerosene is the best stuff ever.