Engine Trouble Sudden power loss (solved)

toojung2die

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Everything has been going great with the new motor bike. Every road is a hill around here but there's only one that needs some pedal assist to climb. The engine is on it's second gallon of fuel, still breaking it in. One day out the blue it wouldn't climb that steep hill at all. I checked compression and it's only 60 psi. I don't know what the compression used to be but I know 60 psi ain't good.

Head is torqued to 12 ft/lbs, I check it often. No oil leaking out around the head or jug. So I take off the head, no problems there and the gasket looks good. Next I take off the jug. The cylinder walls look good with some cross hatching still showing. When I inspect the piston and rings the problem is evident.

The top ring locator pin was pushed all the way in and isn't doing its job. The top ring spun so the gap lined up with the exhaust port. The ring is shot and the piston is useless without the locator pin.

IMG_3629.JPG IMG_3628.JPG

I replaced the piston, rings and wrist pin. Assembled it all with new gaskets. The engine started right up and runs great. After a couple of easy 15 minute rides and cool down I tried the hill. The power is back like before the problem. I'll do another compression check after I think the rings have had time to seat.

This engine has a type B, high hole piston. eBay has lots of type A piston kits that include the rings, wrist pin and G clips. Why don't they sell similar kits for type B? I had to buy everything "a la carte". Even so, you have to admit parts for these engines are ridiculously cheap.

Jon
 

Cisco

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Quality Management is divided into Quality Assurance and Quality Control. Quality Assurance examines the manufacturing process to pinpoint where defects might be introduced into a product. Quality Control outlines testing procedures to ensure a defective produce doesn't end up in the hands of the consumer. I guess they skipped that process. :-/
 

Cisco

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Dang my education, I got fired from a job after I tried to explain the Production Equation to the line foreman. Effort alone does not equal production. Effort, directed by efficiency with an emphasis on quality, equals production. He just said to do the job or go home. One of my fellow bench workers said he was amazed that we got paid to turn perfectly good materials into junk. I eventually got moved into a closet, gluing PVC parts together with cyanoacrylate, without any ventilation. He really wanted me to quit. It wasn't long before the boss said that I just didn't fit in. Lucky for me, I got another job working Tech Support for the college (where I've been working, happily for the past 12 years). Too bad, I really liked assembly work. :-/
 

toojung2die

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One of my fellow bench workers said he was amazed that we got paid to turn perfectly good materials into junk.
That statement is a classic. 😁
One of my first jobs out of high school was working quality control on a manufacturing line. I inspected metal parts as they were made on large presses. Sometimes I would have to stop production because the parts were out of spec. The line foreman would blow a gasket because a stopped line meant he wasn't making quota. I'd explain the customer wouldn't accept the defective parts. Without fail the word would come down from above, "Ship it" and production would resume. I wasn't very popular on the production line.

Weeks later the parts would come back as customer rejects. Scrap metal. They'd come to me and ask why I didn't catch the defect. My inspection reports covered my butt. I always wondered why they were paying me to do quality control since they weren't concerned with quality.

I think I know how the piston ring locator pin got damaged. The ring rotated on top of the pin as the piston was inserted into the cylinder. As the ring was compressed into the bore the pin got pushed in. That allowed the ring to rotate in its groove.

Anyone know what compression psi is normal for one of these 80cc engines? My guess is anything over 100 psi is okay. I know the compression is back because I have to pedal fast before letting out the clutch when the engine is warmed up or the back tire skids.
 

Karl Snarl

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Dang my education, I got fired from a job after I tried to explain the Production Equation to the line foreman. Effort alone does not equal production. Effort, directed by efficiency with an emphasis on quality, equals production. He just said to do the job or go home. One of my fellow bench workers said he was amazed that we got paid to turn perfectly good materials into junk. I eventually got moved into a closet, gluing PVC parts together with cyanoacrylate, without any ventilation. He really wanted me to quit. It wasn't long before the boss said that I just didn't fit in. Lucky for me, I got another job working Tech Support for the college (where I've been working, happily for the past 12 years). Too bad, I really liked assembly work. :-/
I don't fit where I work. I make them to much money though. Lol. Smartest guy here is what they call me, I'm the second smallest and the strongest too. If they fired me for not fitting in, they'd lose millions.
 

toojung2die

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That was a reply from @Street Ryderz when I posted the compression of 120psi for my PK80 engine.
I will be happy with 120psi after the rings break in some more. I think 160 psi is overly optimistic for one of these generic CG engines. I'm glad the power is back after replacing the piston. I'll check it again after running a couple of tanks of fuel through it.
 

Karl Snarl

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I will be happy with 120psi after the rings break in some more. I think 160 psi is overly optimistic for one of these generic CG engines. I'm glad the power is back after replacing the piston. I'll check it again after running a couple of tanks of fuel through it.
110-130 is average. 90psi is ok on a stock head. Any lower and you got problems.
 

toojung2die

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The new rings should be close to broken in after a couple of tanks of gas. That hill I used to peddle assist to climb? It climbs without peddling. Compression tested when cold is 92 psi. I don't want to remove the spark plug when hot but if I start the bike too slow on dirt the rear tire skids so I'm sure the compression is higher when hot.

When I took out the chinese plug to do the compression test I replaced it with a NGK BR6HS. It's too long for this head. The electrode tapped the piston and closed the gap. Luckily it didn't cause any damage other than to the plug. Is there a shorter NGK plug for these engines?
 
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