NSR 125 R Cooling system problem

[david451]

Hi guys, i will try to explain the problem the best i can:

The bike was getting hot over time. Taking a look into cooling overflow tank i noticed that it was getting filled over the max level like if the bike were pushing it out there.

My first tough was thermostat not correctly opening, so i took it out. Result? the problem still there.

Then i tough that the radiator could be blocked?¿ so i bough an used one. No luck.

Finally, after months thinking what the problem could be i saw air with some coolant trying to get out by the thermostat joint.

I tough that maybe i didnt squeeze the "screw" (sorry dont know the exact word im not english) tigh enough. But no, it was correctly set up.

So it looks like some extra pressure was getting into the system. That would explain why the coolant was getting pushed to overflow tank.


So my question is: im not a mechanical expert, does my theory above makes any sense? and, if so, it would mean that some gasket are actually bad and are filling air into the system, pushing the coolant to the overflow tank?

and, if so, which gasket could be? the cylinder or could it be the one by the water pump? if it would be the cylinder one, shouldnt coolant be getting into the cylinder aswell as air is getting out?

thx for your time!

[Nobby the Bastard]

Yes.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[MCN]

What Nobby said.

And.

Fix the visible leaks.

With the engine cold.
Fill the cooling system to the marked level.
Run the engine until the thermostat opens. They begin to open around 80°C.
There should be no bubbles in the system. If there are bubbles in the system then it is hopefully just a cylinder head gasket that is leaking.
Usually a new gasket fixes that.
It could be worse andbthe cylinder head is cracked.
A replacement head would fix that.
Or it could be worserer.
The cylinder block could be cracked.
A replacement engine would fix that.

Low coolant and engine overheating causes those problems.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[david451]

Forgot to mention that.. about 2 years ago i replaced the piston for a bigger one.

Before replacing the piston a cylinder width measure is supposed to be done.

Since the cylinder had on its back about 50.000 km by then, i decided (by shopper advice, all be said) to buy the biggest one, without any measurement...

This leads me to another posibility, may a bigger and incorrect piston size be causing that extra unbearable pressure?

Anyway, i ordered a gasket set for the cylinder. I will check all the posibilties you told me and if everything is ok and the problem persist, an incorrect piston is the last explanation i can imagine of.

Thx for the replies.

[steve the grease]

So to replace the pistion the engine has been apart.

When it was put back together I guess the bolts were done up with a torque wrench. It is good practice to check the torque of the boilts after another 700km to make sure that they were tightened properly.
There is a big difference between an oiled bolt and a dry bolt this can affect how tight the bolt is when the torque wrench 'clicks'. Who knows how accurate the torque wrench was. All these factors can affect the tightness of the joint, and if it will leak pressure into the water after some time.

It's possible that the problems you have now are rooted in the work that was done to replace the piston earlier.

I'd be planning to replace the head gasket.

( I've done hundreds of car cylinder heads in the last 40 years)
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All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....

[david451]

[jeffyjeff]

Although a failed head gasket could certainly be the root of your problem, the issue might be as simple as a failing pressure cap. A weak pressure cap can fail to keep the cooling system pressurized, and vent coolant to the surge tank. I would start simple; test the pressure cap first before tearing into the engine. Make sure it is the right cap for your engine. The pressure value should be stated on the cap.
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History shows again and again how nature points out the folly of men - BOC

[Nobby the Bastard]

Where a.water based coolent system is involved, 4 stokes turn the oil to curd when the head gaskets fail. 2 strokes pressurise the coolent system.

Don't overcomplicate things.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[MCN]

[david451]

Hey guys, so i have got my hands dirty today and something is bugging me about the gasket. Look at the picture please:

The cylinder has a big hole bottom where its supposed to pass coolant? and the gasket is closed just in that place? does that make any sense? my model is NSR R 1997 and the gasket set is this one:

https://www.amazon.es/dp/B00IRWL20K/ref=cm_sw_r_apan_i_KT524CNTFJ41ETN9MS1W?_encoding=UTF8&psc=1

Which is tagged as valid Honda NSR 125 F / R 1986-2001.

The old gasket was wet with the exact form of the cylinder hole like if coolant were trying to go trough there.

[Nobby the Bastard]

Hold the gasket against the head and then the bwrrel and you will realise the reason I because of circulation of fluids.

It goes up one side, through the head above the gasket and then down the other.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[david451]

Mmm so that means the gasket is correct for the cylinder?

I still dont understand why there is a hole there when coolant is not supposed to go trough there?

Shoudnt it be easier to just had that hole closed? i mean, in the engine, there is also a hole in that place.

[Pete.]

Pretty sure that void just goes nowhere so there's no benefit to having coolant pass through the gasket.

Your first port of call should have been to test the pressure cap as Jeffyjeff suggested. Now that you have the top off though make sure that you clean the gasket off the top of the cases where that base gasket goes. Stuff rags into the casing to make sure none goes into the crank case and don't use emery or whatever you've cleaned the barrel bottom face up with. Definitely don't use it on the head gasket faces.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[david451]

[Pete.]

I could get that bolt out for you where are you?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[david451]

ahah wish you were here man, but i guess we are a FEW milles away.

Im here -> https://goo.gl/maps/oktG5KhYvNjPFiDw6 Spain.

If you anywhere near here ill gladly take your offer.

Many thx anyway!

[david451]

How hard would it be?

Its the nº9 bolt.

The inner radius of the hole is 8mm.

The broken bolt part is about 5-6 cm deep inside.

Shall i try?

[to v or not to v]

when i was a ham fisted teenager with a tzr 125 i broke a few bolts on the bike. they used to snap really easily.
i always managed to get the broken bolts out of the bike by taking a watch makers flat bladed screwdriver and gently hammering it into the shaft. the metal on the bolts was so soft that it didnt take long to be able to tap a slot deep enough into them to be able to unscrew it.
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current bike Yamaha Thunderace.
its old and fat, but its a damned good ride. the bikes not bad either.

[david451]

Well, after digging into the workshop manual i realized that its not needed to take the engine off to access the bolt, only the right case.

Now the work changed from "nearly imposible" to "doable" with the right tools.

Another thing is a piece dropped from the case and i cant find in the manual where it goes. Any clues?

[bikenut]

Oh dear dear dear...

You have a manual...

You know of CMSNL for the exploded views ?

Use CMSNL to see that "mushroom"...

Drilling that sheared off bolt out would be the last resort...

What year is the bike ?

Do you have a gas blow lamp to apply heat to the casing so it expands a bit ?

Do you have access to a mig welder ?
If yes, make a protective "washer" that fits over the bolt remains. Make sure it will turn and not foul anything. Mig the washer to the remains. Mig a pre prepared ( tapered end ) bolt to the bolt remains. You now have a means of unscrewing the bolt remains but consider heating the alloy case to make it expand a bit.

Thermal shock, heating and rapidly cooling the bolt/ casing can help.

What year is the bike ?

Was any "head skimming" done last time you had the engine apart ?

Was the coolant seen to circulate ?

Take your time...
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nuts about bikes

[david451]

[bikenut]

It is shown on the CMSNL exploded views, at least on the UK model bike.

No point in looking at the flywheel area view, just the area's you have been in....

It is there....just gave a good look....part 12 perhaps. Seek and e shall find.

What country are you in ?
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nuts about bikes

[bikenut]

So, your mechanics shop broke the bolt ?

Shit can happen but they broke it so they should fix it ?

Is there enough of the broken bolt sticking out enough to grip "

If so, heat casing and try to undo the bolt.
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nuts about bikes

[david451]

Im on Spain. So the mushrom is part of the flywheel? ill take a look when i have the time. I have to go now but ill go into it this afternoon for sure.

Many thx!

[bikenut]

The bolt is 6mm diameter with the casing having very thin walls....problem.

I would remove all fragile easily fried electronics and use the large washer/mig welder bolt method.

Will try posting a picture....
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nuts about bikes