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Post by humanshield on Mar 16, 2015 6:27:41 GMT -5
Working on a 50cc scoot with no compression (33 psi)
The scooter was ridden long distance (more than 30 miles each way) daily.
Exhaust valve was was found tight. Taking the top end apart today.
In your experience will I most likely find........
A hole in the piston?
A burned valve?
Damaged rings?
A scored cylinder wall?
OR...All of the above ?
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Post by 90GTVert on Mar 16, 2015 9:54:54 GMT -5
If you want to make a more educated guess before disassembly you'd be better off to add a couple of drops of oil and see if there's much change in the compression test. At 33psi the head needs to come off regardless though, so it's best to check it all over well rather than assume we know what's up.
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Post by Fox on Mar 16, 2015 9:57:49 GMT -5
I'm wondering if he did another test after he loosened up the tight valve. ?
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Post by humanshield on Mar 16, 2015 14:45:55 GMT -5
I'm wondering if he did another test after he loosened up the tight valve. ? Yes. No change. |
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Post by humanshield on Mar 16, 2015 14:48:26 GMT -5
If you want to make a more educated guess before disassembly you'd be better off to add a couple of drops of oil and see if there's much change in the compression test. At 33psi the head needs to come off regardless though, so it's best to check it all over well rather than assume we know what's up. Didnt really expect a definitive answer...just what others have found with these circumstances. For example, how often have other found a hole in the piston etc. About to pull the head off now regardless. |
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Post by Upgrayedd on Mar 16, 2015 15:13:35 GMT -5
Ill take bad valves and cylinder scoring for 600 Alex
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Post by Fox on Mar 16, 2015 15:17:30 GMT -5
I doubt it's a holed piston cause that would yield 0 psi unless it's a pin hole. Most likely you have a bad valve or a clip popped out and ruined the cylinder and piston.
Sometimes the valves look okay to the naked eye but if you spray some WD40 into the intake and exhaust ports it will run out through the bad valve on the dome side.
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Post by niz76 on Mar 16, 2015 18:09:55 GMT -5
I'll take a new top end for $60 Alex!
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Post by humanshield on Mar 16, 2015 22:06:31 GMT -5
Ding Ding Ding we have weiners !!!
Piston was fine.
Rings were fine
Cylinder was fine
Valves for the WIN !!
In true Donut style...here's the resohlooshun
Exhaust seat had carbon buildup on the seat and slight pitting on the valve due to EX valve not fully closing. Was able to get the PSI back up to 70 with a bit of lapping on the exhaust valve but the Intake valve was also leaking and I opted for a different head instead of lapping the intake valve.
Problema solvidado
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Post by Fox on Mar 17, 2015 15:19:26 GMT -5
The lesson to be learned here boys and girls is that the valves should be checked and adjusted regularly to prevent this from happening.
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Post by humanshield on Mar 17, 2015 17:36:23 GMT -5
The lesson to be learned here boys and girls is that the valves should be checked and adjusted regularly to prevent this from happening. Or just install hydraulic lifters like I did and be done with it.  |
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Post by dude on Mar 17, 2015 18:50:46 GMT -5
Does the hydraulic lifters make the cam bigger?
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