KR-1S.co.uk Forum

I'm a newby KR1 owner as of yesterday. Had lots of 2-Strokes over the years, but never a KR1.

The bike won't rev beyond about 6K, poors smoke out and is generally gutless. Checked through everything and found one of the KIPS valves is seized (and so stopping the whole system working). I am familiar with YPVS, but not KIPS. Is there a trick to unseizing a valve? Also, forgive my ignorance, but what do the 2 boxes on the sides of the cylinders do (apart from hold a small puddle of dirty looking 2-stroke oil)?

Amazingly, the KIPS motor still works fine depite trying to work against a seized system.

Thanks to the forum for the downloadable PDF manuals. I'd be stuck without them!

the boxes effectively alter the tuned length of the pipe as the valves open. basiclly a mix between the ypvs and h***a not very effective atac system. seems to work very well onthe kr though, when setup correctly. as for the seized valve. be very careful as the valves are a very lightweight fragile cast alloy and can be broken in your hand. they dont take a lot of force to break. i would douse liberally in a very good quality penetrating fluid and be patient. keep trying to free it and applying more fluid. hopefully you may have some success. if not then strip the top end, again carefully and look for signs of rubbing on the rogue valve. it may need reaming/machining very slightly as tolerances have allways been a bit of an issue (more journalistic myth tbh than truth but..) with our beloved kr1s'. before deciding the valve is the culprit though, be certain that it isnt something else ie warped head ect. check everything for flatness for elimination purposes and assemble the head/powervalves and barrels before putting the unit onto the cases. check the valves turn freely as you go along to find the tight spot. it could just be a case of been stood and seizing or carbong deposits/good causing it. whichever it is, good luck with it.

Thanks for the advice. I have already drowned it in penertrating fluid. I have poured it all around the top. It is the nearside (left) inner one. Outer one is fine and so are the other 2 on the RH cylinder. There is zero movement on the seized one, but the others are positively slack with end float and side to side play. Is that 'normal'?

After letting it marinate for a few days in penetrating fluid, just how much 'force' can I put on the seized valve?

And yes, the bike has been standing a long time. I really hope I don't have to strip the top end, as looking through the exhaust and at the head and piston crown, it all looks in remakably good shape (compared to some of the messes I have come across).

All advice appreciated. Craig

mgtkr1 wrote:the boxes effectively alter the tuned length of the pipe as the valves open.

I have absolutly no idea what "the boxes" are for, but I doubt that is the real answer.

'caus there is only on 1 KIPS a box. the other and the main exhaust port are not effected, so 3/4 of all exhaust gases are not effected and therfore I find it difficult to believe the length off the pipe is altered

this is just my brain working overtime, but sometimes my brain makes me say the stupidest things

Someone must know what these boxes do, or is this some sort wind up that all newcomers get at this forum?....

mgtkr1 is right. Check out the amazing explanation below. I have read it twice and I still don't understand how that little box can have such a profound affect.

Some 2-Stroke genius must have been thinking way off the radar to come up with this tuning trick.

http://www.dirtrider.net/justkdx/kips.html

Craig

If your valves are sticking it might be that the cables are to tight. A common and easy mistake, ( i have done it myself).
The boxes you refer to are there to allow smoother running at lower revs. The kips valves in the closed position allow exhaust gasses to vent into these resonant chambers (boxes). Indirectly they increase the volume of the expansion chamber (exhaust) allowing smoother running at lower revs.
Increase the revs to 8.5k and the valves will swing and shut off the resonant chambers, and direct full flow to the exhaust.

The 'box' just tricks the engine into thinking the pipe is longer than it actually is, giving more bottom end power than would have if it wasn't there. Idea isn't new and is still used today on some KTM's.
A neat trick is to make a 10mm spacer and put it between the cylinder and box, so you can see for yourself what it does.

TwoStroke Institute wrote: A neat trick is to make a 10mm spacer and put it between the cylinder and box, so you can see for yourself what it does.

So you would notice the difference? Hmm, could get some spacers made

cheers,
Charles

What exactly are we supposed to 'see'. Do the spacers create a gap so we can see lots of exhaust gases escaping? Or is it like having a waste gate on a turbo. Does it make an almighty noise when the KIPS valves open up? Tell us more. Craig

Cexley wrote:What exactly are we supposed to 'see'. Do the spacers create a gap so we can see lots of exhaust gases escaping? Or is it like having a waste gate on a turbo. Does it make an almighty noise when the KIPS valves open up? Tell us more. Craig

The idea of the spacer is to increase the volume of the chamber, not let gas escape. Think of it as a 10mm thick alloy gasket and youll get the picture.

They are basically Helmholtz resonators.

When the valve is open exhaust gases are forced into the "boxes" when the exhaust gas is flowing. As the return waves in the pipe build the exhaust system pressure, so the chamber pressure rises. As the system pressure falls this energy is released back into the exhaust, delaying the pressure fall off, thus effectively fooling the cylinder by creating the pressure pulse of a longer exhaust.

The volume of the box and the length that the gas has to travel has an effect on the effective length increase the cylinder sees.

Changing the orifice size through which the gases travel (i.e. F3 style KIPS valves) also changes the way they work. For a simplistic explanation of Hermann Helmholtz's work on acoustics see here:

http://en.wikipedia.org/wiki/Helmholtz_resonance

It does not by any means explain how to go about making the ones you have better suited to the pipes you have, you will need to go and read Blair's book for that.

Like anything they are a compromise to get more work out of the fuel being burned and they really will work at one frequency very well, but they do work at orders of frequency above and below the one chosen but not as well.

You will find them all over the intake manifold and induction pipes on modern cars.

They really will work better without the oil in them....

Charles wrote:

TwoStroke Institute wrote: A neat trick is to make a 10mm spacer and put it between the cylinder and box, so you can see for yourself what it does.

So you would notice the difference? Hmm, could get some spacers made

cheers,
Charles

If I recall correctly there is a divider inside the box to separate the right and left hand valves on each cylinder? (I know it is not a perfect seal, but it does not need to be).

In the spacer you will need to replicate this otherwise the waves from the right hand side will interfere with the left hand and you will not get the effect you expect.

The gas from the right hand valve is further from the 'box' on the left hand cylinder than the left hand valve and vice-versa so the volume each side of the pipe is working with is different.

Leave the separator out and you will effectively link the two valves as one and this will make the resonance effect much worse I think.

smithyrc30 wrote: If I recall correctly there is a divider inside the box to separate the right and left hand valves on each cylinder? (I know it is not a perfect seal, but it does not need to be).

No there isn't, ist just an empty box. On a RHS barrel only the exhaust gases from the RHS Kips valve enter the helmholtz resonator.