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Post by gingel on Jan 20, 2013 5:59:31 GMT -5
Hi,
I have a 125cc 4t scooter, and i have a strange problem.
if i don't start the scooter for 2 days, then sometimes there will be
no compression.
If i push the kick start, then it has no resistance, you feel that there is no compression.
But after i try to start the engine a few times, with full throttle, then it starting
to come back to life, and after that it's working ok.
Anyone know, why after 2 days without starting the engine, this is happening?
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Post by richardthescooter1 on Jan 20, 2013 8:33:01 GMT -5
Have you rested the compression? if not take spark plug our and hold your finger or thumb over the hole and crank the scoot, it should push you finger out.
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Post by gingel on Jan 20, 2013 8:59:45 GMT -5
Last time i tested the compression was a few months ago.
it was around 135 psi.
Now it's starting ok, and you can feel that there is compression when
you push the kickstart.
I just wonder why after 2 days without starting the scooter, it sometimes losing the compression,
but after i start it with full throttle it's getting compression back
and working ok.
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Post by snugglebunny on Jan 20, 2013 10:03:15 GMT -5
hmm strange
i would like to read what the rest of the mechs say
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Post by scootnwinn on Jan 20, 2013 10:59:48 GMT -5
What seals the rings fully is a film of oil coating the rings. What kind of oil do you use perhaps it isn't holding after 2 days is it fresh are you using any addituves that might make it less viscous?? That's the only way intermittant compression is possible that I can think of...
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Deleted
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Post by Deleted on Jan 20, 2013 11:55:02 GMT -5
Are you sure the engine is truly freewheeling and it's not just the kickstart failing to grab, because they'll do that, these kickstart mechanisms don't always engage gears. As to why it would do it after some days, perhaps your foot loses the touch, I don't know but why not try the electric start and see if the results replicate?
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Post by skuttadawg on Jan 20, 2013 12:11:07 GMT -5
You do know that a 4T has 4 cycles , intake , compression , power and exhaust ? So it will have compression during kicks and not so at other cycles . Always gentle kick to get to the compression cycle then push down a lil firmer but be easy as they are so wimpy they break unlike motorcycles where some required one to man kick it
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Post by gingel on Jan 20, 2013 14:40:42 GMT -5
What seals the rings fully is a film of oil coating the rings. What kind of oil do you use perhaps it isn't holding after 2 days is it fresh are you using any addituves that might make it less viscous?? That's the only way intermittant compression is possible that I can think of... I use the same oil since this scooter was new. Motul 10w40 . I replaced the oil about 1200 miles ago, but this happend also before i change the oil. I never used any additives, not in oil or in fuel. This scooter has 55,000 miles on it, and engine was never rebuild (only carb was replaced). Are you sure the engine is truly freewheeling and it's not just the kickstart failing to grab, because they'll do that, these kickstart mechanisms don't always engage gears. As to why it would do it after some days, perhaps your foot loses the touch, I don't know but why not try the electric start and see if the results replicate? The kickstart is ok. i always use the electric start, but when this no compression problem occur, i tried the kickstart, and then i saw that there is no compression. After that, i use the electric start with full throttle, then it starts to come back to life. After the engine started again i turned it off, and i checked the kickstart again, and compression was back. You do know that a 4T has 4 cycles , intake , compression , power and exhaust ? So it will have compression during kicks and not so at other cycles . Always gentle kick to get to the compression cycle then push down a lil firmer but be easy as they are so wimpy they break unlike motorcycles where some required one to man kick it Yes, i know that you have to push the kickstart gently, until you feel it's firm. When this compression problem occur, i never get this firm feeling. The engine just spin very easy. I mainly use the electric starter, so my kickstart is still ok. |
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Post by skuttadawg on Jan 20, 2013 14:43:49 GMT -5
How many miles are on it ? Does it smoke or burn oil ? Had the valves adjusted ? New rings and sparkplug can often do wonders
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Post by gingel on Jan 20, 2013 14:49:06 GMT -5
How many miles are on it ? Does it smoke or burn oil ? Had the valves adjusted ? New rings and sparkplug can often do wonders It has 55,000 miles on it. i need to add about 100-150ml of oil every 600 miles (1000km). No smoke. the spark plug was replaced about 1000 miles ago as part of a service that i did to the scooter. At the same time i also checked the valves, and if remember correctly, only the exhaust valve needed to be adjust. |
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Post by skuttadawg on Jan 20, 2013 14:59:00 GMT -5
55,000 miles  New rings time |
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Post by qwertydude on Jan 20, 2013 15:14:00 GMT -5
55,000 miles? Wow that's now officially the highest miles I've seen on a GY6 engine. You sure this isn't kilometers?
Time for new rings. Or better yet new piston, cylinder and rings.
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Post by gingel on Jan 20, 2013 15:16:04 GMT -5
55,000 miles New rings time Yes, 55,000 miles. and besides this problem which occur not alot, it's running great. So do you think it's the rings? if the rings are the problem, shouldn't it be a constant problem? I just want to understand why it's happening only after the scooter was not started for at least 2 days? and how it's fixing itself, after starting it with full throttle? |
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Post by skuttadawg on Jan 20, 2013 15:16:25 GMT -5
Maybe a typo as 5,500 sounds more realistic to me . I have 13,500 and still running strong
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Post by gingel on Jan 20, 2013 15:19:02 GMT -5
55,000 miles? Wow that's now officially the highest miles I've seen on a GY6 engine. You sure this isn't kilometers? Time for new rings. Or better yet new piston, cylinder and rings. Yes, i'm sure it's 55,000 miles. my Odometer is in KM, and it's around 91,000 KM. The scooter is made by SYM. |
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Post by skuttadawg on Jan 20, 2013 15:23:00 GMT -5
Awesome !!! I would think a new piston and rings would help
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Post by Moat on Jan 20, 2013 16:19:32 GMT -5
May be a valve sticking - a few days allowing just enough rust to form on the stem(s) to cause it to hang up. With that many miles, it wouldn't surprise me that the stems and/or guides were rather coked/carboned up, and on the verge of sticking to begin with. Was the weather at the time the bike sat humid/wet/rainy by chance?
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Post by qwertydude on Jan 20, 2013 20:50:52 GMT -5
That's different Sym engine that's about average. Since it's Sym you probably just need new rings at most new rings and piston. If you take it apart and the ceramic coating on the cylinder isn't flaking off, just put in the new rings and or piston. Don't sand the ceramic coating, usually when you put new rings you scuff up the cylinder with scotch brite or sandpaper, but not on a ceramic cylinder. Generally with these ceramic cylinder the cylinder never really wears out, it's always just the rings and or piston.
I wouldn't get the new cylinder kit then just rebuild it and keep riding. The Sym engines are built like tanks. I have no doubt you have 55,000 miles.
Also as said by Moat when replacing the rings do check and clean the valves if necessary they could be coked up too.
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Post by Deleted on Jan 21, 2013 2:45:11 GMT -5
Oh heck with that many miles maybe start saving for a new gy6 or an entire new scooter as it could be giving you signs that it won't last much longer, but I would just keep doing whatever you've been doing and DRIVE it, I wouldn't even try to fix that engine, maybe something's wrong with it and maybe it isn't, might not last another 100 miles and it might do another 5 or 10 thousand, who knows, start saving your money, that's what I would do.
Oh, and one more thing...
600 miles is the oil change interval...
Why add oil at this point?
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Post by lovemy2strokes on Jan 21, 2013 5:20:49 GMT -5
Well I highly doubt its the rings if you get compression sometimes and not others. Its a one way street with rings. Valves on the other hand is what I imagine is the problem. There may be some crud on the seats or the springs are weak. But definitely doesnt sound like rings.
55k miles is a lot and congrats for making it that long! You should take a picture and post it. My highest KM is 45k on a kymco zx50. Nothing is original on the engine at all though on that one.
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Post by leo on Jan 21, 2013 5:36:57 GMT -5
Well I highly doubt its the rings if you get compression sometimes and not others. Its a one way street with rings. Valves on the other hand is what I imagine is the problem. this is my opinion as well. a valve stem that is bent just enough to cause intermittent hanging. i assume that these valves also rotate while in operation which causes the hanging to be intermittent. |
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Post by gingel on Jan 21, 2013 5:45:17 GMT -5
May be a valve sticking - a few days allowing just enough rust to form on the stem(s) to cause it to hang up. With that many miles, it wouldn't surprise me that the stems and/or guides were rather coked/carboned up, and on the verge of sticking to begin with. Was the weather at the time the bike sat humid/wet/rainy by chance? Last time it happned it wasn't raining. it's not always do that problem. there are sometimes when i don't start it for more than 2 days, and when i start it, it's ok. I wouldn't get the new cylinder kit then just rebuild it and keep riding. The Sym engines are built like tanks. I have no doubt you have 55,000 miles. Also as said by Moat when replacing the rings do check and clean the valves if necessary they could be coked up too. You are right about that, i didn't think this scooter will last so much miles. I'll think about replacing the rings, and overhaul the head (valves, springs etc..). could be a nice project :-) But maybe i'll wait, just to see how much miles can it do more ;D (it's not far from 100,000 km) Oh, and one more thing... 600 miles is the oil change interval... Why add oil at this point? The company that import SYM in my country, recommend to change the engine oil every 2400 miles (4000 KM), and they recommend to use an half synthetic oil. I think the manufacturer says to use mineral oil, so they recommend to change it every 600 miles (1000 KM). I always used Motul half synthetic oil type for scooters. BTW, if you use a full synthetic oil, can you increase the interval of oil change? Thank you all for the answers and ideas of why this problem occur.  |
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Post by gingel on Jan 21, 2013 8:46:59 GMT -5
Well I highly doubt its the rings if you get compression sometimes and not others. Its a one way street with rings. Valves on the other hand is what I imagine is the problem. There may be some crud on the seats or the springs are weak. But definitely doesnt sound like rings. 55k miles is a lot and congrats for making it that long! You should take a picture and post it. My highest KM is 45k on a kymco zx50. Nothing is original on the engine at all though on that one. If i'll open the head to replace parts, i should already replace the rings, right? |
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Post by lovemy2strokes on Jan 21, 2013 9:37:38 GMT -5
You can take the head off with out taking the cylinder off. You should do an easy test on the valves also once you get it off. Turn the head on its side and fill the port up with oil and see if it leaks out the valve. Im guessing its probably going to be a leaking exhaust seat.
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