mz 125 sm pushing coolant out the overflow

[misios1410]

so i am having a bit of a problem with my mz as it started to spit coolant out the overflow pipe for some odd reason ? i changed the cap but no luck got rid of thermostat as it was not opening all the way but still no luck ? any suggestions ? should i get ready to buy new headgasket ? i cant do the cooling system pressure test as cant get the adapter to fit my radiator unfounetley

[stephendacosta]

Check the water pump first. haven't heard of a head gasket causing overheating in these 125's. Keep me posted; I have one doing it also. Just haven't had time to open it up.

[DAVID THOMPSON]

may have lost teeth on the gear that drives the pump
easy to take a look at
lay bike on left side after removing battery and fuel tank
then remove the oil filter and right side of engine
becarefil and get no dirt in the engine
when inspection complete put it back together
with out having to drain the oil
while in there look at the timing chain and make sure the tinsioner is working and no chain grinding at the case

if there are problems then suck out the oil and set it upright

dave

i even hang them upside down to weld the sidestand back on

[misios1410]

i am sure that loosing a tooth form the waterpump gear will not couse this kind of problem ? it looks to me as it is either spinning too fast ? impssible as its driven form crank shaft by gears , overheating it will overheat when most of the fluid is pushed out or the headgasket needs replacing which is possible as whhen you open the coolant cap and hold the revs up the fluid rises up and also you can see bubbles in it sometimes i also have another thought possibly the cooling gallery (cooling jackets) in the head and cylinder being blocked ? well i bought new headgasket anyway so will let you know what happens when i change it

[DAVID THOMPSON]

lost teeth equals pump not running ...water setting still in the head makes steam and that blows up all kinds
of stuff water out the overflow is first warning second is blown head
gasket

[misios1410]

i took the engine apart to change the head gasket found that the black paint from the headgasket has fallen away into like a chunks it is still on the desk as i am working will be back in on saturday i hope now.. i've got another sm engine which i was planing to change whole of the top end to my bottom end however i found out that my valve shims have no actual shim in them they are solid (dont have like a circular plate in the middle) also my cams are considerably larger than the other sm cams ?

also how do you people do the timing ? do you use 5mm allen key into the crank case and 2 tight fit drill bits into the cams so that they rest on the head edge ?

i am thinking of installing an electric water pump as and addition to the normal pump i have any comments on that ? basiclly one of my rads is usully cold i will give them a flush in the garden with a hose on saturday but i think that electric pump is not a bad idea ? on off a mercedes for example ? or any other car

[DAVID THOMPSON]

if you do the extra electric pump ..cram a bigger battery in it or get good at bump starts
most bikes need a bigger electrical system even befor adding any extras that use electricity

[stephendacosta]

I have recently gotten an electric jacket liner and electric gloves. My 125sm is able to handle the extra load with no battery problems. Check to see which pump has the lowest electrical draw.

[misios1410]

well if i add a electric water pump into the system it should be fine

any comments on the cams then ? i am curious why they are bigger and valves have no shims to adjsut them ? i need to adjust them as they are a bit lud but since i have ot got shims in them i am wordering what to do now ?

[roloscotusa]

I have an MZ 125 SM exhibiting the same problem; spitting out water from the overflow radiator pipe. It happens when I am riding and the bike comes to a stop and then it spits water out. I have replaced the radiator cap, the thermostat, compression checked the engine and the cooling system. All looks normal!!!!!

I have spare water pump that can be replaced but I am not sure that it will fix the problem

This seems to be a common problem with MZ 125s. Has anyone found the root cause of the problem?

[DAVID THOMPSON]

i remember having this happen on a car years ago

i think we determined the impeller was slipping on the shaft in the water pump