Reading valve color

LOUD MOUSE · Post by **LOUD MOUSE** » Sat Oct 16, 2010 10:50 pm

I see/saw what looks as new pistons with not much running time (underside shows not much high temp running time) and skirts don't show a lot of BLACK (aluminum to cylinder) scoring.
I do think from the black/carbon on the tops that both were RICH on the gas/fuel adjustment.
SO I'm not sure where the noise and seizure came from as yet cause I don't see any signs of crank or piston/cylinder problems. ..............lm

teazer wrote:Piston 1 has a small but easily seen stain under the crown. Not bad, but it's stained. Piston 2 has a slight discoloration. In neither case is it serious or a sign of an overheating problem.

At higher mileages, most pistons will have some build up on the lower surface, but my understanding was that these hadn't done many miles. Either way, it's not a problem and the top surfaces look fine.

teazer · Post by **teazer** » Sun Oct 17, 2010 9:46 am

Agreed.

LOUD MOUSE · Post by **LOUD MOUSE** » Sun Oct 17, 2010 10:03 am

What bothers me is "why are the piston tops so black (Rich?) and one side of the head shows what should to me show a Hot/Lean/Mistimed valve area"!. ...........lm

LOUD MOUSE wrote:I see/saw what looks as new pistons with not much running time (underside shows not much high temp running time) and skirts don't show a lot of BLACK (aluminum to cylinder) scoring.
I do think from the black/carbon on the tops that both were RICH on the gas/fuel adjustment.
SO I'm not sure where the noise and seizure came from as yet cause I don't see any signs of crank or piston/cylinder problems. ..............lm

teazer wrote:Piston 1 has a small but easily seen stain under the crown. Not bad, but it's stained. Piston 2 has a slight discoloration. In neither case is it serious or a sign of an overheating problem.

At higher mileages, most pistons will have some build up on the lower surface, but my understanding was that these hadn't done many miles. Either way, it's not a problem and the top surfaces look fine.

nander · Post by **nander** » Sun Oct 17, 2010 11:44 am

I had recently adjusted the valves and I wonder if I overtightened that exhaust valve. So, the valve got hot recently while the pistons had accumulated the carbon over some time. And that valve appears to leak now, if it didn't before.

Could that misadjustment of the valve have caused the motor to lock up?

The spark plugs looked good.

And LM, your observations are accurate. I probably have less than 2k miles since the motor was re-ringed and honed. Also, looking back, the break-in of the motor probably wasn't optimal. After the rebuild, I spent a lot of time with it just idling as it took me forever to get the carbs tuned and synced.

Here are a couple of other things I found when I took the motor apart, that may or may not be of concern: the clutch push rod appeared a little bent and one of the three screws on the back of the starter clutch had worked itself halfway loose.

Thanks for everyone's insight.
nander

LOUD MOUSE · Post by **LOUD MOUSE** » Sun Oct 17, 2010 1:40 pm

Ya can check the valve adjustment even now.
Did the screw contact the starter sprocket. .................lm

nander wrote:I had recently adjusted the valves and I wonder if I overtightened that exhaust valve. So, the valve got hot recently while the pistons had accumulated the carbon over some time. And that valve appears to leak now, if it didn't before.

Could that misadjustment of the valve have caused the motor to lock up?

The spark plugs looked good.

And LM, your observations are accurate. I probably have less than 2k miles since the motor was re-ringed and honed. Also, looking back, the break-in of the motor probably wasn't optimal. After the rebuild, I spent a lot of time with it just idling as it took me forever to get the carbs tuned and synced.

Here are a couple of other things I found when I took the motor apart, that may or may not be of concern: the clutch push rod appeared a little bent and one of the three screws on the back of the starter clutch had worked itself halfway loose.

Thanks for everyone's insight.
nander

teazer · Post by **teazer** » Sun Oct 17, 2010 10:13 pm

As I understand it the bores were honed and fitted with new rings. How clean were the pistons when they went in? Some carbon, or shiny and clean? If the crowns already had a carbon film, that explains things.

If the bores were not broken in properly it is possible that there was oil getting up to the top end. Inspect the rings and see if there is an even shiny wear ring around each ring. If the oil rings have spots where they are not making contact with the bores, that would be an issue.

Tat burned valve is in all probability a tight (zero running clearance) issue. If it was tight when cold and ran out of clearance, hot burning gasses would be torching it.

That loose screw could be an issue if it shows signs of rubbing and/or there are signs of it rubbing on the nearest surface.

A bent pushrod might be a minor issue. Look for signs that it has rubbed at the bends.

nander · Post by **nander** » Mon Oct 18, 2010 11:04 am

Teazer: The transmission shafts all spin freely and look to be ok. I don't know the age of the pistons. I had the motor rebuilt many years before I actually put the bike together and ran it. I remember getting new rings for the rebuild, but I think the guy who did it used the existing .25 over pistons.

Piston skirts: so some scoring is normal on used pistons? Can they be smoothed with 1000 grit and refitted or must they be replaced?

Valve clearance: The .004 feeler gauge was nowhere to be found at the time I loosened the adjuster. However, by hand I could tell that the cooked valve was noticeably tighter than the other three.

Starter clutch: The loose screw is backed out to the point where it must have been in contact with the sprocket. It looks like the sprocket prevented it from coming out completely. I'm not very familiar with this mechanism, but it would be right in line with my kinda luck for a single halfway backed out screw to bind up the whole motor. Is that possible?

Thanks,
nander