'12 50 2T not starting - has power, fuel, spark and low compression; Worn rings?

[netlag]

Engine seemingly died over the weekend as after 10 mile run. Stopped for a drink at store and started back up okay. Paused for two minute idle and the the engine cut off. Tried to start again and nothing. Checked the usual suspects  such as battery, gas, oil, and spark and found all available. Just not igniting. Fact that it would turn, but not ignite led me to believe deeper issue might be at hand as engine has 12k mileage.

Had time to test it again today. Double checked battery, fuel, oil, and spark. All tested as available.

Stumped, so chose Internet research instead. The results lead me to understand that the issue could be depleted piston rings.

Couple phone calls lead me to learning from a mobile mechanic guy that Engine Restore might cure same, so planned to try that. Also, figured that the result would be the same as the wet/dry compression test technique I just researched.

Tested three times:

30 psi (dry)

90 psi (wet)
 
Figured 90 psi was close enough to make a determination that the rings were shot as the motor was not igniting at that psi either

Also, during the compression buildup tried test firing with the plug in place to see if any difference igniting would happen. Nothing did.

Anyways... compression was back at 30 psi after leaving it sit for 30 min break.

At this point I am planning to do a full-top end rebuild with BBK parts if I am going to bother with the rings.

Although, thought to ask the forum if anyone has had like issues.

Please share similar results, or symptoms including or not including worn rings.

Thanks.

[Chris0381]

What would cause the rings to wear so prematurely ? At 12k, a good quality scooter is nicely broken in.

Have you taken apart the head (4 bolts) and looked inside for scoring of the cylinder walls etc ?

My only assumption is at some point, the scooter was running with improper lubrication.

Also, where do you buy a good compression tester at a good price. It stands to reason to test compression at least 1-2x a year to see if its creeping down. It didn't go from 90 to 30 overnight wo improper lubrication and I doubt that normal wear and tear for such a quality engine.

Are you going to do any exhaust valve porting with the BBK ?

[netlag]

Yes, this is the same motor that had the oil injector issue. Although there was a slight burble earlier in the day and of course this instance. Engine had been running fine since replacing the injector earlier last week.

Besides this, had assumed that there was going to be some damage to cylinder wall, and piston from earlier use, as I purchased it used with 11k a few months back. Also, it was run hot twice before the injector was diagnosed and premixing was utilized until the injector was placed. Have not pulled the head as of yet, but just expecting the worst. That is why I figured to just replace cylinder toi.

Not sure of any testing perfirmed outide of what I have done. As to the quality of the guage I am using... it looks like Harbor Frieght, but mine is free rental from Autozone. If it is inaccurate, atleat it is consistently inaccurate. It gave thw same reading when I pulled it off before and after test to ignite.

I have zero experience for port and polish. Would be great to get extra flow; although, I dont have a flow bench to check for improvement. Also, not changing exhaust any further atm. So, unless head is available already finished... will probably pass on it this round.

[netlag]

Has anyone noticed any deals on 70-BBK for the KF10AA?

Found the 70cc Malossi BBK for 139. Sounds like good deal to me... Suppose I should plan on upjetting the stock carb to around 90-94?

[netlag]

Not sure if I should bother with the BBK for the moment.

Looking at the head and gasket; cylinder and piston, and piston rings themselves... I don't see any glaring issues. Slight wear on top of piston and one small discolored looking line on side of piston.

Have not had time to put a gauge between the cylinder wall and rings, but they feel snug when manually running the piston through the cylinder.

Even the lower gasket looked ok, even though it seemed to be permatex vs fiber.

Wondering what I am missing. No reason to invest another 200.00 in the wrong direction.

[Chris0381]

Have you checked the reed valves?

Also.

I think the throttle has to be held wide open when kicking the motor for the compression test.

[netlag]

Have you checked the reed valves?

Also.

I think the throttle has to be held wide open when kicking the motor for the compression test.

Not as yet for reed valves. Was at full throttle during compression test.

[netlag]

reeds looked great.

[netlag]

Hrmmm. Put it back together this morning figuring that I would start diagnostics again.

Was delayed in doing it the other day as I lost a wrist (circlet) somewhere the the day before.

Managed to find a correct size donor pin at a local shop. Figues it would have a larger gap. Desperation setting in...decided to lesson the gap manually even with the likelyhood of possible failure. Click. Hurrah!

Worked my way back through leaks, air, gas, and spark while placing the components back.

Full tank gas; and carb was fully operational when placing it.

Could not recall what level of spark the spark plug displayed last test. Pulled both ends and thought to reset the connections just in-case.

Left the air chamber for last to put back on.

Squirted some raw gas past the auto-choke and sure enough it gurgled.

Another squirt and it was running again.

Suppose somewhere in the build-back corrected the no-start condition.

Thanks to all those that commented. Suppose I am back to this scoots mod thread I started.

[Chris0381]

Have you read thru this ?

http://forums.everything2stroke.com/archive/index.php/t-29368.html

[netlag]

Don't recall reading that one. Sounds familiar scenario though. While frustrating, glad that it was experinced as this and that troubleshooting info will make future episodes easier to diagnose.