Finding new way's to leak oil

[robber57]

What concerns me a little bit is that your piston is completely covered in black but the valves appear to be covered in ash and no black carbon, meaning: you have low compression and oil leakage but apparently still high combustion temperatures and screaming hot valves.
It doesnt add up...

It also suggests that you may want to replace the valve seals (little green seals under the spring), the cost is minimal and these rubbers are in direct contact with the hot valve stem.

[breaknwind]

My spark plug was white and didn't show signs of burning oil, maybe running lean? I type slow.

[robber57]

Yeah, just thinking out loud:

an air leak causes lean burning and high combustion temperatures which may cause wear/pitting on the valves which cause compression loss???

There seem to be several options on the cause...

[breaknwind]

Don't know, what's up?

[robber57]

Other scenario: the oil scraper got stuck ,carbon build up make the valves leak, this causes leaking of hydrocarbons (fuel) in the exhaust, the O2 sensor sees this,the ecu regulates the fuel amount to a lower threshold.

Its difficult to keep cause and effect apart, is the lower compression a cause or an effect(result) from another defect?

I would suggest to first check the valves and then decide if further action is necessary.

If you want i can take some photos from the head although mine is now completely clean and beside the wear on the valveseats there is not much to see.


For now: zzzzzzzzzzzz, its 3 am over here and i am nodding

[breaknwind]

Preliminary valve test shows OK. I'll check it again Monday because I'm using a oxygen tank from work that I brought home with a modified nozzle. I used it to blow the dirt and dust off the injector before I removed it. Wouldn't fuel also leak through a bad valve? Maybe I could put fuel in the manifold and see if its leaking out(yes I know that fuel evaporates). Maybe set it on a clean rag and check it in about an hour. This test is new to me because I did the wet test(using a syringe I squirted oil in the cylinder) and the compression went up a little over 10 lbs. usually indicating ring blow by. I'm curious about ring gap placement and how it affects compression and oil management. Could be an assembler was new at it or having a bad day(like my leaking crankcase seal). About running lean, I wonder if the O2 sensor is clogged, could unburned oil in the exhaust be confusing the ECU? I'll have to read about testing it later(that sucker costs $92 ). This is both enlightening and annoying .

[Taos]

Another thing you might look at is ,over here in canada we have a problem with 2008-2010 Honda accords with there fuel mixture causing the piston rings to seize to the piston from carbon built up, we're reprogramming the ecu and replacing pistons and rings on low kilometre cars (as low as 20,000kilometers) this maybe is a case on a scooter that has been modified for running richer to produce more power,also in canada our fuel is not the best and honda recommends top tier fuel ,this fuel will keep combustion area a lot cleaner( less carbon) and keeps injector also cleaner I have seen the results from some of our customers with 200,000.00 kilometers on there cars using only top tier fuel, this will help with keeping the rings free as no carbon in ring grooves or on valves or top of piston, normally the first to seize to the piston is the oil rings,then the engine starts using more oil then you see more carbon forming (its a snow ball effect)

[breaknwind]

http://www.dansmc.com/leakdown.htm
Shure do wish I read up on leak down testing before I disassembled the motor. Now if the compression is still low I can figure it out. Too bad I'll waste a head gasket if the compression is still low. I'll still use Robber's valve check Monday.

[robber57]

For another leak test on the cylinder you can easily use the old head gasket, if you would use some sealant i am pretty sure it will even run without any problem (although probably not for a long time).
The sealant/plastic layer on the headgasket should be removed, i am not sure but i think if you leave it in paint thinner or stripper for several hours it will probably(hopefully) rub off easily.

Also: your idea of the rings been placed poorly from factory is imho not correct, piston rings rotate, the placement of the rings when installing at 120 degree increments is just to make sure the rebuild engine will start and dont loose to much compression but once it is running the rings will start to rotate slowly which is good thing as this rotating ensures that rings, groove and cylinder will wear evenly.
If rings would not rotate there wouldn't be any necessity for ring pins in two stroke pistons which keep the rings in pace so the ring slot cannot run in a port and break.

Valves also rotate but this is engineered on purpose in the construction of valvestem,spring and underlaying disks: http://www.youtube.com/watch?v=nsa6kq-qqIE

Another view of this amazing engine where you can clearly see the valves turning: http://www.youtube.com/watch?v=vcyT18qk8ls