140cc bad rattle in the head ??

[arkark]

hi ,,was riding for 2 hrs and the head of the bike made a loud sqeel and then started 2 rattle bad ,, one sec it was running good then the sqeel ,,then it was missing ans back firering i stoped the motor straight a way ,,,and let it get cold and restarted it and the rattle was 70% gone ,,, 30 % still there ,, i was thinking it may be the valves or the cam chain ,,, its a new motor with just 2,000 km on it and i have not ever reset the valves ,, do you,s think it be the valaes >???? any ideas at all plz ????

 

[Cactus Jack]

Definitely detonation ........ don't keep riding it or you'll pay dearly ......

IF you haven't adjusted the valves ...... then do it and see if the pinging stops ..... a glowing exhaust valve can be the cause ...... If the valve is being held off the seat from lack of rocker clearance , it can't get rid of built up heat ...... exhaust valves basically live in searing flame for most of their life .......

You might also have gotten a bad batch of fuel cut with too much ethanol which makes the mixture get leaner and the engine run hotter ......

I'll post up some links to threads for people to read ......

 

[arkark]

hi and thx ,, it was more of a bad rattle then pining ,,, and had 2 bikes runing the same fuel ,, and other bike ran 100% ok ,,, when it started first,, i been riding for 2 hrs and the motor was hot then it just started rattleing ,, coughing and spluttering and would not rev up ,, when i got it home ,i started it up cold and the rattle was 70% gone ,,but as the motor started 2 warm up the rattle get,s louder ?? that loud of a rattle ,, you would think parts were bousing aroud in the head/cam ,, and it starts easy ,, still ??? b4 it started i was just going along at 20 kmh , bike runing 100% ok ,,then next i heard a noise like a fan belt slipping creching then i notice the bad rattle and and bike started running bad ... the notice is a little like coins rattling !

 

[Cactus Jack]

Are you sure you know what detonation (aka pinging) sounds like .....

Engine starts rattling when hot. - Planet Minis

An excerpt from a link on detonation ..... it sounds different in different types of engines .....

Browser Warning

[So what does detonation sound like? It’s hard to describe but firstly, it’s a new sound – not one that’s there at light load high revs, or on the over-run. Secondly, the sound that is heard is caused by the ringing of the block as the hammer-blow of improper combustion strikes the piston – that gives you a clue to how it will sound. It’s usually a higher-pitched ‘ting’ sound, a little like coins rattling in a coin tray. It can occur in very fast succession (ting-ting-ting-ting) or can be a transient noise that occurs, for example, ting!, only on sudden throttle applications. The big danger is when (1) it occurs at high loads and (2), it is continuous ie the knock sensor doesn’t pull back timing (or drop boost, or close the throttle, etc) enough to stop it.

Whenever detonation is heard, the driver must immediately back-off – don’t let it keep occurring!]

 

[sick150]

have the same problem with my 150

 

[arkark]

hi all, and thx 4 all the help Cactus jack ,, i set my valves to .003 in and .005 out and the bike is running 100% better ,, still a little tiny rattle in the head ,,, when cold and go,s a way as it gets hot,, i think i was the tinyest little bit out when seting them ,, first time at it ,,had trouble getting the feeler gauge in at first ,,,loosend it off then ,put in the .003 then did it back up with the .003 gauge still in ,,the gauge could just go in and out after i tighten it,,

 

[motoXXX]

it shouldnt be a loose fit but it shouldnt be a tight fit so if i can go in and out nicely with brabbing or just sliding out your good to go

 

[arkark]

ok thx man ,, it should be ok then it,s going good ATM ,, i,ll test ride at home 4 the next week ,, see how it go,s get it hot hot ,, then have a look at the valves one more time when it,s cold ,,b4 going bush 4 a hard ride how much rattle in a china motor is 2 much ???? lol

 

[numroe]

Interesting. So what were your valve clearances before you reset them?

My fun guess is your valves were way tight, and at some stage when they got hot they weren't sealing and that sound squeal you heard was the valve singing as the air pushed passed it. Then the rattle might have been the hot valve touching the piston. Just a theory. If right or close, then your valve(s) are most probably damaged and you'll run into problems in the near future.

Last month I adjusted the valves on my daughters 70cc ducar from tight (less than 002) to around 005, and now her low reving little torque monster runs unreal.

A friend has a Yam TTR125L-04, and I found his inlet valve was at 005, so I put it at 003 and told him it'll probably do nothing. I just wanted to adjust it, to justify me taking his fuel tank off to get in there. He rode the bike the next day (we did the work at night when drinking beers) and told me "it feels great". I thought his reply was placebo BS, so I rode the bike myself, and he wasn't joking.

But your story is not a happy one. Something evil seems to have been going on.

btw: how did you measure 2000km? Your bike road registered?

 

[Cactus Jack]

have the same problem with my 150

IF it's a YX 150 then they are more rattly up top than other engines .... just make sure you keep your valves and timing chain adjusted and recheck them regularly ... as numroe says .... a non seating exhaust valve will get hot and can seize when the oil fries in the guide .... high pressure burning gas squeezing past the seats reacts with oxygen in the pipe and can oxy cut them .... the precise cause of burnt exhaust valves ....... stainless steel valves are used because staino resists being oxidised .....

And what numroe says about reducing his mates valve clearances making the bike run better is fact since less clearance increases cam duration and lift ......

Honda XR75's only run .002" inlet and exhaust but if you run that clearance in a china engine you'd probably have problems ..

 

[arkark]

hi and yeah ,, i think the valves, may of got damaged ,, valves were set at .002 in and .003 out b4 i reset them to .003 in .005 out,, but bike is running well atm and has a little rattel still ,, but i,ll keep good oil in it all the time and keep seting valaes when needed ,, ride it hard untill it,s dead ,, then get a 150cc yx

 

[arkark]

??? how does one adjust a cam chain ,in a 140cc and 150cc ?