250F Noise In Motor

Question for y’all, my boys YZ250F has a noise in the motor. First when I bought it it ran fine however over time (Last year) the compression dropped off and at the end of last year developed a noise. So first thing I did was look at and replaces the valve shims to the proper size. Compression is back but the noise is also. Now there’s a hole on the bottom of the case (right side) and we have oil and or antifreeze coming out of it slowly. Even when just sitting in the garage. So I don’t know whether the leak is associated with the noise or not. What’s the hole for? Any ideas on the knocking noise? Seems to run good, idle good and has good throttle response. TIA! Ryan
 
Sounds like the liquids are coming out the water pump weep hole. This alerts you that your water pump needs a rebuild.
It most likely will need ....new seals, bearing and maybe a shaft. The noise may be a worn out cam chain that needs to be replaced.

Paw Paw
 
Sounds like the liquids are coming out the water pump weep hole. This alerts you that your water pump needs a rebuild.
It most likely will need ....new seals, bearing and maybe a shaft. The noise may be a worn out cam chain that needs to be replaced.

Paw Paw
Can you elaborate? The chain seems tight? At least when I took the cams out and had to take the tensioner out in the process. I just can’t see the a loose chain making that much noise. Any ideas?
 

SRAD97750

Moderator
Staff member
Bottom end knock can occur when bearings get worn out. But typically cause it to run poorly or not idle.
What was the wrist pin to journal gap? Any detectable side to side play?

A loose cam chain will sound like marbles in the engine, or metallic slapping.
Typically will not cause any performance loss, but can be literally deafening.
What was the measurement of the cam chain for 10 links as per the manual? In spec at the time of overhaul?
When was the cam chain tensioner last replaced?

Coolant dripping slowly from the case weep hole indicates water pump seals, usually needing a water pump rebuild kit.
-BIG DAN:thumb:
 
Stretched out cam chain will be evident when lining up the punch marks on the cam gears. They should be perfect not just “close” The chain will always feel tight when tension is applied. The noise could also be a worn out slider. 4 stroke dirtbike motors are cacophonous anyway
 
Bottom end knock can occur when bearings get worn out. But typically cause it to run poorly or not idle.
What was the wrist pin to journal gap? Any detectable side to side play?

A loose cam chain will sound like marbles in the engine, or metallic slapping.
Typically will not cause any performance loss, but can be literally deafening.
What was the measurement of the cam chain for 10 links as per the manual? In spec at the time of overhaul?
When was the cam chain tensioner last replaced?

Coolant dripping slowly from the case weep hole indicates water pump seals, usually needing a water pump rebuild kit.
-BIG DAN:thumb:
How about oil coming out of the weep hole??
 
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