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outbush24
50cc nipper
Joined: 03 Sep 2009
Posts: 20
Location: orange nsw
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 Posted: Sun Sep 13, 2009 8:21 am Post subject: thumpstar problems |
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Hi guys im new on here and am currently working on my 125cc thumpstar, i have only ridden my bike half a dozen times and it stopped one afternoon after giving it a good flogging. Once it stopped i tried to kick it over and it had lost most compression, kick starter goes down with minimul resistance. Any ideas?
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ForeverThreeWheels
The Day Starts With OZATV !
Joined: 18 Nov 2008
Posts: 1742
Location: Maitland
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| Posted: Sun Sep 13, 2009 7:37 pm Post subject: |
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Sounds like the rings may be flogged out or the head gasket could be blown or maybe just the plugs loose. 
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wa5
Big Bore, Stroked & Bling +
Joined: 06 Nov 2007
Posts: 446
Location: Port Stephens
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| Posted: Sun Sep 13, 2009 11:27 pm Post subject: |
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| thrown a cam chain maybe? |
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outbush24
50cc nipper
Joined: 03 Sep 2009
Posts: 20
Location: orange nsw
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| Posted: Mon Sep 14, 2009 7:15 pm Post subject: |
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I stripped the whole motor down and i cant figure out what the problem is, cam chain was on rings seemed ok. Any other ideas?
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wa5
Big Bore, Stroked & Bling +
Joined: 06 Nov 2007
Posts: 446
Location: Port Stephens
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| Posted: Mon Sep 14, 2009 10:25 pm Post subject: |
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| could the cam chain have skipped a few teeth, check the top of your piston, is it possible it kissed the valves? and they are not seating correctly in the head? |
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outbush24
50cc nipper
Joined: 03 Sep 2009
Posts: 20
Location: orange nsw
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| Posted: Tue Sep 15, 2009 3:19 pm Post subject: |
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I checked the piston when i had the engine apart it seemed fine, i also rotated the cams a couple of times and the valves seemed to open and close ok. Do you think it could be possible for the timing to be out and the valves to not hit the piston? Thanks for your input guys as im used to 2 strokes
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doorslammer
Roostin Away
Joined: 24 Jul 2007
Posts: 902
Location: Northern WA
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| Posted: Tue Sep 15, 2009 3:34 pm Post subject: |
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do the kickstarters on these run through the gearbox, then throught the clutch and to the crank?
maybe there's something wrong with the clutch or gearbox.
i know thats how it is with the pit bike i used to own
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01 Banshee
Never take life seriously. Nobody gets out alive anyway |
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outbush24
50cc nipper
Joined: 03 Sep 2009
Posts: 20
Location: orange nsw
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| Posted: Tue Sep 15, 2009 4:52 pm Post subject: |
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I'm not too sure how that side of things are with the kickstarter, but now that you mention it the kick starter goes down with ease but when i put it in gear it still locks up the rear wheel when i try to push it??
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feralkid
The Day Starts With OZATV !
Joined: 29 Oct 2007
Posts: 1567
Location: North Western Victoria
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| Posted: Tue Sep 15, 2009 5:07 pm Post subject: |
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Does the kick starter acctually turn it over like if it is in gear and you kick it will it move forward?
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"If in doubt go flat out"
"Nothing worth having is easy to get" |
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outbush24
50cc nipper
Joined: 03 Sep 2009
Posts: 20
Location: orange nsw
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| Posted: Wed Sep 16, 2009 8:46 am Post subject: |
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Thanks feralkid, i put it in gear and put the front wheel against the shed wall and pushed the kickstarter down and the back tyre spun so i guess the kickstarter is ok. Maybe the timing is out in the top end.
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PeteW
Moderator
Joined: 09 Feb 2006
Posts: 1877
Location: Doreen, Vic
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| Posted: Thu Sep 17, 2009 2:33 pm Post subject: |
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with the piston at TDC there should be an obvious mark on the cam sprocket that points to the top of the engine. make sure that it is lined up properly.
have you got the facility to measure compression?
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outbush24
50cc nipper
Joined: 03 Sep 2009
Posts: 20
Location: orange nsw
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| Posted: Thu Sep 17, 2009 9:02 pm Post subject: |
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Thanks petew, i will try the timing again tomorrow. From what i can remember there wasnt any marks on the camshaft sprocket but i will pull it apart and check it again. Thanks for your help.
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outbush24
50cc nipper
Joined: 03 Sep 2009
Posts: 20
Location: orange nsw
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| Posted: Thu Sep 24, 2009 10:29 pm Post subject: |
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Hey guys sorry to keep this thread going for such a long time, today i reset the timing and left the side case off the flywheel and the cover off the cam sprocket and kicked the bike over and they didnt move while kicking. I tried roll starting the bike and it pretty much did the same thing. Is it fixable or should i just pay $299 for a new motor?
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