I brought a cg125 in Coventry last week and we took it for a test ride and all was well.
I then rode it to London, Yes it took me three hours. I took it top top gear and pinned the throttle back and sat on the motorway all the way home.
Well now there is a rattle at the top end.
What could it be? Maybe being thrashed for three hours did not do it much good. But I got nearly 70mph out of it! well it was a steep hill!
Do you think I might have bent a valve slightly? there seems to be no loss of power, I think any way? So the valves might be fine? maybe an adjustment would be nice.
BUt it rattles, so I am thinking cam chain. Maybe the tensioner needs to be looked at? Does the cg125 have a cam chain tensioner? If so where is it?
Am I right in thinking that a 04 model, the one with electric start would still have tappets and not be shim under bucket. Are there any 125's with shim under bucket?
If it is the cam chain it would be easy to replace no? Just make sure I use new gaskets. But just check the tensioner first.
any advice is appreciated.
CG125s don't have a cam chain - the cams are gear driven and sit below the cylinder, and actuate the valves vie push-rods and rocker arms. Mucho potential for some lash in that lot somewhere so by all means check the valve clearances (cold) but don't go looking for a cam chain tensioner .
If you have bent a valve then you might see extra valve clearance on the bent one (it'll not be shutting fully). With a bent valve you might not notice any performance loss at high engine speeds, but may find starting harder or low speed running is rough. If you're not getting either of those then it's probably not a bent valve.
Such a long ride might've cooked the oil a bit if its old or been sitting for a while and now would be an ideal time to change the engine oil (take it for a ride first to get the oil good and hot so it brings all the crap out with it).
Wow no cam chain eh, gears sound like a much better idea when I think about it.
Bike starts fine, runs fine. I did find it a bit asthmatic when I went up some hills, speed went down to 45, which is scarey on the M1. Low speed it is fine but I will check the valves out any way and have a look at how the gear driven cams work.
The noise deffinatley comes from the top of the engine and I suppose with only the valves there it may be a bent one or not sitting properly.
Thanks for your advice Tappy
Scarily I think I woke up thinking about this a few days ago but have been away for a few days:
The other possibility may be a bent pushrod - so if one of the valve clearances is a mile wide, it could be that too.
xr125... BECAUSE ITS FUN
Ooh nasty - that happened to mi dad's GT550 years ago.
In that case - check the tappets etc for valve clearances and if one of them is a mile wide, find the problem. If all are fine, sounds like you might do well to pop the head and barrel off...
@ Bikerchef, did you diagnose exactly what the problem was? And was it easily fixable (and affordable!).
My CG125 has been 'rattling' for a good few months now (it started when I forgot to put oil in the engine for a few months or so and the bike ground to a halt whilst going up a hill). I'm thinking (and hoping) that the engine isn't discintergrated inside due to the lack of oil it had, but it has been working ok since, but only gets 50mph MAX on flat, and about 55 downhill (on big hills)!
The most annoying thing is that I need to do my practical test before september, and to get a Cat A licence my bike needs to do 62.1mph (which it can't!!).
Any help would be gratefully recieved! Cheers...
i litterelly had the same prob with my cg today , i was doing 60mph then it dropped to 40mph like instantly and nose dived. my bike runs fine , a little trouble with starting only 5 kicks but thats generally normal, mine make a rattling noise from the top end , a little less power output on acceleration not alot tho....im not honestly sure what gone on , maybe valve clearances or push rods arent closing the valves properly? anyone got any ideas of what the rattling could be? i need to run it to college 4 days a week
Well if you've neglected oil changes then there's a chance it's the little end, or a cracked piston or something.
Are you checking the valve clearances with the engine stone cold?
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