Coolant leak

[CombatYoga]

I recently put an S3 head on my bike when I did a new top end.

Our race last weekend was a mud race - lots of slippery, slower riding.

My bike was steaming up pretty good in a few spots; I checked it at one point and I swear the coolant leak is bubbling out around the spark plug.
That seems bad, but I ran the whole 4 hour race (tag team) and topped off coolant a couple of times.

The O-rings under the head are notorious for getting them to stay in the groove. I used some grease and I think I got them to stay. Could this be the cause? Or is it something more sinister like a cracked head?

It seems to get worse if the temps go up (i.e. slow riding or stopped/idling), and may actually even subside completely if I'm moving at a good pace and keeping air going through the radiators.

I am going to pull the head off later this week and have a look, but wanted some advice on what I might be getting into.

Thanks in advance for any hints/tips/suggestions!

[Zman]

O-rings are supposed to be lubed to do their job. Silicone grease is a good option for lubricating and preserving rubber parts like O-rings. Silicone grease doesn't soften or swell rubber hydrocarbon based oils and greases. Silicone also does a good job of preventing corrosion.

Maybe do a very close inspection and look for burrs or surface imperfections in the O-ring sealing area that could be allowing a leak.

[pscook]

Look at the "Tee" fitting right next to the spark plug. I had a gasket go bad (okay, I installed a torn gasket and hoped for the best...) and it looked like a cracked head. it might also be a hose clamp on the tee fitting or somewhere along that hose line. "Occam's razor" may prove true in this instance, so check the easy stuff first.

Also look at the bolts holding the tee fitting to the head. They penetrate the water jacket, so a loose or poorly seated bolt can provide a leak opportunity.

1. Hose clamps at tee fitting
2. Gasket at tee fitting
3. Bolts at tee fitting
4. Hose clamps at radiator (coolant might be running down the hose, least likely)

[CombatYoga]

Fantastic advice guys - many thanks! Hope to tear into it over the next few days...

[gasgasman]

When you reinstall the head, screw the spark plug in. The holds the dome and head in place.

[pscook]

Sorry, I didn't take the S3 head into account. I don't know how they are configured, but be prepared to pull it apart if the sparkplug really does hold it together during assembly and my list checks out.

[Jakobi]

Did you install the o-ring into the head insert? There is one that seals the insert and outer head around the o-ring.

Other options are water inlet tee and coolant lines there too (particularly if still using the snap lock clamps).

[memphis2857]

Spark plug doesn't hold anything together? It screws into the insert and doesn't touch the outer housing of the head. My money is on the o-ring around the plug hole.


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[Jakobi]

As above. Spark plug threads into the insert. Its the cutaway in the insert that the bolts run through that lock it into position.

O-ring for inner to outer is 31mm I.D. x 2.5mm Viton.

[CombatYoga]

Jakobi - I want to make sure I understand what you are saying, because this might be the culprit.

There are 2 o-rings under the original head; I replaced those with new o-rings when I installed the S3 head.

It almost sounds like you are saying there is a third o-ring that is new to the S3 head and installs between the new S3 head and the dome insert. Am I understanding you correctly? I did not install that o-ring.