Montesa World Racing 4RT engine got hot and blew out most of coolant. Refiled and noticed that the flow through radiator was non. Checked pump, OK. Checked seals, OK. 

No water in oil or compression leaks into coolant system. Bike has been running fine last 50 hours. After this happend the engine was low on cooland(due boil), but i also had to fill 150ml engine oil for some reason. Never used a drop before(can it be due it got hot?).

So i wonder why this happen, what to look for. This is a 2012 model Future World Racing 292cc Montesa with bigger radiator ++

Fan runs ok, so thermostat is ok. Else i wonder, can air block the coolant flow?

Edited January 18, 20179 yr by grim

You can get an airlock in the cooling system, but I would also suspect head gasket

I've filled up cooling system, started engine and checking for pressure/bubbels in radiator. But it seams dead, usually when blown gasket you will et smoke/bubbles in radiator? Oil is also fine, no water.

Keep an eye on the oil level.  There really isn't a lot in there and if it starts to go low you will start to go hot quick.  I found that when I change my oil if I don't make sure I pull the sump guard (bash plate) and make sure the cover is sealed well I loose a little oil and will start to run a little hot tell I top it off.

Best of luck.

Thanks  I've removed radiator, checked the Temperature sensor,  Measuring it in boiling water. Result war it went from 230 OHM and slowly down to 70 OHM as the temperature rises.

My first thought then was that its defective? From what i understand, the cooling fan goes on/off. So i figured the Temp sensor also should open or closed?

As we start the engine now, it gets hot fast. The fan don't start(fan is tested ok at 12v).

hi grim think you will find its you fan relay its a 12v rc2208 mitsuba 6681

If the temp sensor is going on/off and the fan works with a good 12v source then I would suspect the relay as well.  And a bad fan relay would cause boil over... 

There's a test procedure for the fan relay on page 6-9 of the manual.

The temperature sensor isn't an on/off switch, it's resistance changes continuously with the coolant temperature. It's not connected directly to the fan relay. The temperature reading goes to the ECU, and the ECU tells the fan relay when to turn on. The ECU also uses the coolant temperature reading for FI along with the other sensors. Manual page 6-5 says at room temperature, the temperature sensor resistance should be 2300 to 2600 ohms.

We found out that after an accident the radiator was pushed back a few mm. So it was in contact with radiator. Radiato then was leak, and after half an hour fluid was below leak and with out we noticed it got hot due lack of pressure. We didnt notice due fan removed fluid.

Now we fixed the radiator, and checked that al run smooth. We also checked temp when engine running.. and it's soo hot this one. Fan start at 105 degrees(5 above normal water boil), stops around 95/97 degrees.  Also we noticed that pressure on this system is 1 Bar. Not sure if that is normal tho, seams higer then normal Honda 4RT engines?

Anyway, this World Racing Future engine is amazing strong. We compared it to many bikes, also the new Montesa 300RR. This Future 2012 engine is stronger.. But.. always a but.. hehe. It has a knocking sound. I will make a record of the sound.. and maybie someon have an idea what it can be

check your mains if its run hot for very long you might have scalded the bearing if not addresed could throw a rod then you will have a grown up push bike 

Here is the sound from the machine.. There is a hard knocking sound i wonder what can be. Think it's camshaft, but worry it can be something else.

https://www.dropbox.com/s/pawjl9wonbkpa0b/Montesa%20ulyd.m4a?dl=0

I know it's hard to guess  But hoping somone else had same problem and will "remember" that knocking sound.

Could be a cam chain tensioner. Either way, quit running it and tear her down.

That sounds like cam chain tensioner to me as well. 

i hope its the camchain  tensioner share what you find out 

 

Edited March 22, 20179 yr by bbk

I hope  will get it checked out. Would be cool if that was the problem.

Ty for help so far