50cc scooter big bore kit.

Hi I have just installed a 80cc big bore kit in my Lexmoto 50cc scooter. After putting everything back to gether it seems fine but engine only turns a few times and the locks up. Has any one any ideas.
Many thanks

 

charge the battery? without more information im going to hazard a guess the little starter motor is not getting enough power to crank it over?

 

Hi the engine locks up when I crank it with the kick start after about 2 or 3 cranks. Then I have to take off the cam chain reset it to top dead centre and the same thing happens.

 

what parts came with the kit? did you get a new cam or cam chain.

and if a new cam was supplied with the kit was the pulley pre installed on to the cam or did you have to use the original pulley on the new cam

Only thing i can think of is the kit was supplied with a new cam and the pulley on it has a different amount of teeth on it to the original cam pulley.

 

Sounds like you haven't got the timing marks lined up correctly and the valves are contacting the piston.
You'll need to check you haven't bent one of the valves and if ok replace it all with the correct timing.
An easy way to check the valves is to take the head off and put the plug in and fill the inverted head with petrol and see if it leaks away.
Before trying it on the starter you should always try turning it over a few times by hand to make sure nothing touches.
If it's the GY6 engine the cam has the large timing mark/hole straight up at the top and the 2 smaller marks lined up with the top edge of the head surface the cover bolts on to.
Obviously the flywheel mark is on T or TDC.
Once together turn the flywheel with a socket using the centre nut. Turn the engine over completely at least once or twice and make sure you complete every 4 stroke cycle. Do not kick it or use the starter.
If it locks up loosen off the cam chain from the sprocket(leaving it lined up) and turn the flywheel 180 degrees till the T mark lines up again. Put chain on and line up the cam timing again and repeat turning the engine which should now be ok.
Double check cam and flywheel marks still line up after turning over a few times.

 

remove the flywheel fan so you can see the fly wheel. with your hand rotate fly wheel so the arrow on the fly wheel lines up with the F mark on the case, if there is no F mark there will be a little marker line or a thin marker spline on the case.

Now WITHOUT MOVING THE FLYWHEEL remove the timing chain cover and making sure the flywheel has not moved check that the cam spur gear is lined up correctly for the timing. you sometimes find that when installling a bore kit you knock the timing off a fraction . if this is the case have someone hold the flywheel at the F mark while you reset the cam timing chain to its correct area.

 

Just want to say thanks to everyone for all your advice. I will try your suggestions and let you know. It does seem like I have the timing wrong. I have even tried putting the old piston , barrel and head back on but it still locks up so I must be getting the timing wrong. I put the fly wheel on the T mark and then I check to make sure the piston is at top dead centre then I put the cam on lining the 2 small holes with the edge of the casing and the large hole facing away from the engine I then place the chain on tighten everything up checking that nothing has moved. Then I crack the engine slowly by hand.The piston moves freely everything seems ok then it locks up. So as you say the piston is now touching one of the valves. I will try your advice and see if I can get it right. Thanks.

 

Just to check when it locks up have a look at the cam and see if it's pressing one of the valves down.

 

Hi yes it does . I still cant fathom this out.

 

Assuming your timing marks are correct something is wrong as you appear to be 180 degrees out.
Your valves should be closed when the camshaft marks line up and indeed you should be able to put a feeler gauge in to both tappets.

http://www.49ccscoot.com/bbk.html

 

If after double checking the timing and you are sure it is correct and the valve clearances are correct I can only suggest you remove the head and check for a bent valve.
Is it still the original cam/head or did you get a new one in the kit?
Is the piston the correct way round? ( I'm assuming there are cutouts in the piston for valve clearance if not ignore that)