Brass Metal shavings on top of the piston

[Lukasz]

Hello,
I was checking compression today, and, whilst having the spark plugs out, I also checked the cylinders with a camera.
I found metal shavings, looks like brass, on top of two pistons. One of them looks like its ground the shavings.
The worse cylinder (attached photo) has only 120psi, all the others are close to nominal 150-ish psi.
Any idea what this might be? I am worried and should I be worried? There were also traces of oil mixed with coolant in the air box breather enclosure. There is a separate topic for that. Thank you.

 

[MaxMidnight]

Not something I have seen before.
If it was an item that entered through the inlet then I would have thought only one cylinder would be affected?
There are brass or bronze components in the crank case but would there be sufficient blow-by past the rings to allow it to migrate into the cylinder?
It's strange that whatever has got in affected two cylinders. Was the one with low compression affected?
Can't think of anywhere that brass would come from. There are brass items in the carb but none that could have made it into the inlet.
As far as I can recall the butterfly screws are steel?

I would do a cylinder leakage test to establish where you are losing compression which will give an area of the engine to investigate.
May also be worthwhile dropping the oil to see if there is evidence of brass there.

 

[Lukasz]

Hi, thank you for your reply.
Yes, the low compression cylinder is the one with most shavings found.
I have drained the oil and found no evidence of metal there. Carbs were re-built and cleaned recently, no issues there, I also checked the butterflies - all screws are in place.
I have hoovered the filings out for now, ordered a mirror for my endoscope to see the upper portion of the head and the valves.
Looks like the leakage would be a good idea, I will find a local mechanic as I have no idea how to do it

Many thanks

 

[Coastal Grey]

Hi, thank you for your reply.
Yes, the low compression cylinder is the one with most shavings found.
I have drained the oil and found no evidence of metal there. Carbs were re-built and cleaned recently, no issues there, I also checked the butterflies - all screws are in place.
I have hoovered the filings out for now, ordered a mirror for my endoscope to see the upper portion of the head and the valves.
Looks like the leakage would be a good idea, I will find a local mechanic as I have no idea how to do it

Many thanks

Dr. Google is your friend

 

[Parminio]

The only thing I can think of that is brass that could have wound up down there is somebody was messing with the carbs while they were sitting on the bike and dropped a jet or something down the intake manifold.

There is one other possibility but I highly doubt it: If memory serves, the valve guides are made out of a knickle / bronze alloy and has the appearance of a dark brass. You may have one coming apart.

 

[Radioguylogs]

You feel confident it is brass and not discolored aluminum?

 

[02GF74]

What about the bushes for the spindle in the Vboost. And the single itself, what are they made from?

There are brass parts in the carbs such as jets, the main needle runs in a brass tube, could that be bent or incorrectly fitted to be rubbed on the tube?

It would not harm removing the cabs and having a look inside.

Did you collect the metal from the cylinders.?

 

[02GF74]

Just to add, you said 2 cylinders were affected - do those cylinders share the same Vboost manifold?