bubbles out of the radiator overflow

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trix
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bubbles out of the radiator overflow

#1 Post by trix » Sun Feb 18, 2018 6:14 pm

Hi guys. I thought my head gaskets were leaking; creamy emulsion collecting in tailpipes and bubbles coming out the radiator over flow. You can see it in this video



I had used aftermarket head gaskets so I bought Yamaha Head gaskets and lapped the heads until they were definitely flat and installed them, tightening to 22Nm. I warmed it up to about 60deg C then re-torqued all the head nuts. let it cool down and re-torqued again. All looked good. Ran the engine again and let it run a bit longer to about 80degC. Air bubbles coming out of radiator overflow again but no emulsion visible on tailpipes. Perhaps its normal for bubbles to come out as it expels any air in the system? Does anyone else have a clear overflow pipe? Did you observe bubbles coming through when it gets up to operating temp when you have recently drained/refilled the coolant system?

I have black tubes on my other bikes so have never noticed.

Hope you can help! If the gaskets are still leaking I'll go nuts.

silverstrom
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Re: bubbles out of the radiator overflow

#2 Post by silverstrom » Sun Feb 18, 2018 11:00 pm

The exhaust looks good. Hold a clean white rag over the exhaust. If there is any coolant you'll see it. You'll smell it too.

The system will bleed itself. Unless the air in the line continues or the bottle blows coolant everywhere I don't think you have a problem. It was bubbles and the mess coming out of the pipes before that suggested a head gasket problem.

When you pulled the heads did you see any evidence of coolant washing the cylinder walls?

Ron57
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Re: bubbles out of the radiator overflow

#3 Post by Ron57 » Mon Feb 19, 2018 3:33 am

Hi trix, did you check the height of the studs out of the barrels, when you rebore the
barrels studs are removed if they are not cleaned out properly studs will sit higher than original.
have the heads been machined down, look at the acorn nuts and see if the studs had topped out
inside, happened to me, if so double up on the copper washers.
Cheers Ron.

trix
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Re: bubbles out of the radiator overflow

#4 Post by trix » Mon Feb 19, 2018 7:11 am

Hi Guys
Thanks for this; when I took it apart I couldn't see any sign of coolant washing the cylinder walls, however I had only warmed it up a few times, I haven't actually ridden it yet since the rebuild. I couldn't see any signs on the gasket or mating faces where it had been leaking either.

The studs are fine. I'm certain that there's no contact between the studs and the inside of the acorns as I checked the lengths of these when assembling the last time.

I held a clean cloth over the tailpipe and found nothing significant, generally clean.

I'll run it up a few more times and take it for a ride and see how it goes.

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Speed Freak
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Re: bubbles out of the radiator overflow

#5 Post by Speed Freak » Wed Feb 21, 2018 2:01 pm

Is the overflow hose ending below the water line in the expansion tank?

If not the system will spit out water during warm up and suck air back in while cooling down.
Next warm up a coolant/air bubble mixture will come out of the radiator again until there is enough air in the radiator to compensate the thermal expansion of the coolant and the radiator cap doesn`t open again...

Correct filling of the coolant circuit:
1) Fill up the expansion tank to the correct level (between min. and max.)
2) Fill up the coolant system
3) Start the engine with open radiator cap
4) Shake your bike a bit left/right, pull the throttle to get a bit higher rpm`s (slightly above idle...)
5) The water level in the radiator will drop with every air bubble which is coming up form pockets and corners in the cooling system => fill it up until the water level is at the height of the overflow spigot
6) Repeat 4/5 until the warer level stays the same and you can`t put more water into the system
7) Put the cap onto the radiator
8) Let it warm up to full operating temperature
9) Let it cool down completely
10) Check the water level in the expansion tank, add water if necessary. The level should be slightly above "min" in cold condition.
11) Duing the next ~2 heat up cycles some air bubbles might come out of the system but then the hose should be completely filled with coolant.

If there is air in the hose when the bike is not operated for a day then check for air leaks (and add a clamp/cable tie to the radiator outlet spigot)
My bikes:
RD500 YPVS 1GE
RD350 YPVS 31K 1985
Honda CBR 1000 RR SC57
Yamaha R1 RN04

begbie
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Re: bubbles out of the radiator overflow

#6 Post by begbie » Wed Feb 21, 2018 2:38 pm

Just kicking the engine over combustion pressure's are well above 100 psi this is before the pipes start working and increasing psi futher, the engine could well push gas out and not let coolent in once stopped, I had the same thing happen on an RG500.

silverstrom
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Re: bubbles out of the radiator overflow

#7 Post by silverstrom » Sun Mar 04, 2018 4:37 pm

begbie wrote:Just kicking the engine over combustion pressure's are well above 100 psi this is before the pipes start working and increasing psi futher
Compression is measured with the exhaust port closed, when the piston has raised above the exhaust port. The pipes have nothing to do with the compression number. If you measured compression with the exhaust port open it would be very little because pressure is pushed out the exhaust port.

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Jeff B
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Re: bubbles out of the radiator overflow

#8 Post by Jeff B » Tue Mar 06, 2018 3:26 pm

begbie wrote:Just kicking the engine over combustion pressure's are well above 100 psi this is before the pipes start working and increasing psi futher, the engine could well push gas out and not let coolent in once stopped, I had the same thing happen on an RG500.
I've had a mild head gasket leak like you are describing. I think its the combustion pressure that pushes the gasses past the headgasket. Coolant doesn't have enough pressure to enter the cylinder.

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