KR-1S.co.uk Forum

Just to ask you Gurus on here
Right if i have a 1.80 thick 0 ring do you need to cut a groove 1.20 deep to get an effective seal ?
Also true or false do you need to compress an o ring 45% to seal properly ?

I have 2mm thick rings, and use a groove 1.50-1.60.

remember to use viton rings

May have a prob then
The combustion 0 rings looked like they were "sitting in" the groove a bit deep compared to the water jacket outer 0 ring.

Local RGV tuner who uses 1.80mm 0 rings cuts a groove for 1.20mm to leave 0.60 sticking out.

Mine are a bit all over the place
1st dome 1.52-1.55mm depth
2nd dome 1.58-1.67mm depth

That leaves 0.25 and 0.13mm sticking out which is a long way off 0.60mm

Outer water jacket 0 ring groove depth is 1.24-1.32mm which leaves 0.48mm sticking out which seems o.k. ?

Thing is it's the combustion 0 ring that is the important one which has to handle the pressure,so how do i get around this

Maybe you could run a 2mm o ring for the combustion, although you may have to widen the goove a tad.
Or you could shave 0.4mm off the head surface, and then re-cut the groove for the water jacket o ring to the correct depth.

Hi HC,

Give Clive at BDK a shout, they offer a O Ring service (Machining the heads and providing the O rings) he may be able to help you out. Or at least give you some advice.

Cheers,
Bernie

best is to make the groove a bit wider than the ring. The wider the groove, the more clearance you can give, because than the ring will be "oval-ed" in the groove. if the ring is a tight fit in the groove, you don't need much clearance because there isn't much room the ring can be pressed in.
A ring can not be pressed together a lot. If there is too little room for the ring to be pressed in, some of the ring will be pressed outside the groove and between the head and cylindres. it will still seal normaly , but the ring will be damaged and not suitable for re-use.

so if it's a tight fit, just install as it is, run it one time so the engine is properly heated, and take the head of again and check for signs of leaks and ring damage

I think a 2mm o ring looks like the best option and that will be a better seal for the combustion

Does anyone know a supplier fot the Viton rings in the UK ?

headcoats wrote:Thing is it's the combustion 0 ring that is the important one which has to handle the pressure,so how do i get around this

As I understood it, the gas pressure is sealed by the head to barrel, not by the O ring itself. The O ring even if made from Viton will stand only around 260C, the gas temperature is way higher than this, so if there is any sort of gas to O ring contact it will burn/damage the ring.

The O rings are there to seal water from the cylinders and are required by the cylinder because of the temperature gradient (water at around 100C cylinder walls at around 300C) which can cause water leakage back across the joint. The water pressure is always there, the gas pressure is very transient.

Be very careful with Viton if it is burnt, it is a Flouro-carbon material and releases Hydro Flouric acid when burnt. If you get this on your skin, even in very small quantities it will pass right through and start dissolving your bones. It loves calcium....

Oh boy and i thought switching to 0 ring heads would be bye bye to head gasket issues

headcoats wrote:Oh boy and i thought switching to 0 ring heads would be bye bye to head gasket issues

it does, when fitted properly

Found this site and they have quite a variation in sizes,so may just have the right one for me

http://simplybearings.co.uk/shop/Seals- ... index.html

normaly a compression of 0.1 or 0.2mm is adequate to seal an oring for general purposes, not sure if it would be the same on cyclinder heads. 0.6 sounds exsessive but should still work ok

There are some oring size calculators online like some where at
www.dichtomatik.com but they don't deal with small orders so you would have to purchase from your local bearing supplier

normal nitrile oring should last ok but viton ones are more durable and withstand the ethenol in modern fuels

I measured an 08 RM250 head last night with used orings in it

the orings protruded 0.35 above groove so maybe 0.4 with new ones.
the inner oring was viton and the outer looked to be normal nitrile. the grooves in the top of the barrel are faily square in section allowing plenty of room for defformation

it used 2mm diameter orings, I think KTM use slightly thicker around 2.5 so you could have yours accurately machined and use a slightly thicker one.

For the head I O ringed I used 2.364" x 0.07" Viton orings

They cost a small fortune

For the Lomas exhaust I used a different company - much cheaper.

70 o rings didn't cost a great deal.

Packet with exhaust viton o rings is marked Polymax tel 01420 474123