Coolant leak

CombatYoga

CombatYoga

Gold Level Site Supporter
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!
 
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.
 
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)
 
When you reinstall the head, screw the spark plug in. The holds the dome and head in place.
 
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.
 
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).
 
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.


Sent from my iPhone using Tapatalk
 
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.
 
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.
 
Affirmative.

The inserts have recess cut into them to accomodate an o-ring (around the spark plug threads) which then seals against the outer head. They do flatten out with time. They can also fall out if you're not aware/watching but should show up as a leak pretty quickly.

kit-culasse-s3-stars-head-ktm.jpg
 
If you bought a brand new S3 head it should have came with 2 of the O-rings in question. One for immediate use and a second one as a spare.


Sent from my iPad using Tapatalk
 
I will bet money that this is the cause of the leak that I am seeing!

Hopefully tear into it over the weekend - will report back - awesome guys - thanks a ton.
 
im kinda guessing here but with the different coolant routing near/about the sparkplug, could it be leaking at the spark plug especially if you recrushed a used plug gasket.
 
Jakobi nailed it! o-ring fitment issue

I pulled the head off today and confirmed that there is no o-ring around the spark plug hole on the insert. This is definitely the cause of the coolant leak I'm seeing.

I looked in the box that my S3 head came in and found a bag with 3 identical o-rings.

It looks like the o-ring should fit down in the groove that encircles the spark plug hole. These o-rings do not fit in that groove - not even close.
The picture below shows where it sits. Is that correct or is the o-ring supposed to sit in that groove? If so, they've sent me the wrong o-rings.

The other picture is a shot of the underside of the head. It shows where the o-ring will sit if I leave it as is. You can see that it is off-center; it would have to be due to where the bolt that holds that water T-fitting is - I think this o-ring would actually deform when I tightened the head down.

I feel certain that a proper o-ring should sit down in that groove. Hoping someone can weigh in with a definitive answer.
 

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Correct, that o-ring is too big and sits outside the groove which is where the o-ring should sit. As per previous post...

31mm I.D. x 2.5mm Viton.

Check that against the measurements for the groove and the o-ring you have.
 
The plot thickens...

Matto Cycle checked another S3 box and found the same o-rings within - they don't fit the insert grooves! They are going to let them know obviously. The S3 factory burned down not too long ago, so maybe they get a break.

Jakobi - I think you need to check the dimensions on that o-ring. Matto is telling me 22mm I.D. x 2.5mm Viton.

I'm going to source a proper o-ring from a KTM dealer here in town. Didn't have much luck at O'Reilly's Auto Parts.
 
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