Knocking noise in 125cc bike engine!?

Question

I have a Yamaha TDR 125cc and there is a knocking noise coming from the engine!!! you can only hear it when its ticking over but when you rev it up the noise faids.

from what i know about engines its either the big end bearing or the previous owner put in the piston the wrong way around!!! or could be the gudgen pin.

Also i bought the bike not so long ago and the previous owner had CAR gear box oil in the sump!!!! when normal 10-40 oil should have been in it!!!!

Answer 1

lol...only way to find out what it is is to remove the head and barrel...it only takes 20 mins....when its removed grab the con rod and lift up/down...there should be no movement,if there is thenit needs a new big end...if it was the little end then it would be more of a tap then a knock...check for a lipin the top of the barrel which means a re-bore....if you spin the crank listen for a rumble meaning main bearings....

prices..

big end £40 pus fitting

mains £14 each[thers 2]

rebore plus piston £60

hope this help...done lots of them..

SORRY JAY BELOW...

but the TDR is a 2 stroke...no valves

Answer 2

I assume, TDR Pre 1993 model, TZR 125 engine most likely big end bearing failure. But without hearing it you will have to investigate.

Or just grab a tzr engine off ebay for £30-£50

Answer 3

You have not mentioned how many miles on the odometer. Could be the possible reasons

1 - may not be the engine at all. Check for loose parts. For some parts the natural frequency matches the vibrations at idling speed and when loose, they vibrate leading us to believe the noise is coming from the engine.

2 - It could be the gudgeon pin or that the piston rings are worn out - have you experienced a slight loss in power when you accelerate?

3 - The piston / crank bearings are worn out - that would explain the car gear oil in the sump - to dampen the vibrations from worn out bearings. Since he was selling anyway, he decided to take the easy out.

If it is from the engine, you have no choice but to dismantle and check for specific location.

Answer 4

Ok. 2  possiblilities here.

#1. Your valves need to be adjusted.

#2. Piston

You need to get it checked out at a dealership or repair shop.