KR-1S.co.uk Forum

I have had an idea in my head (rattles something awful!!) for a while now. To install aftermarket KX125 topends on a KR engine. So I'm going to call it the KX1R! I've been waiting to get a lathe before I could start. Just got one up and running so I've started test fitting things. For the crank I will be using one from an RZ350 (54mm stroke). Looks like it will need to be cut down in diameter to match the KR crank then use the KR center shaft, bearings and seals. Not sure if the outside seals fit yet but looks close. I'll know for sure when the seal kit arrives. I made some spacer rings to fit inside the KR cases to center the cylinders. The stud holes don't have to move far. I plan to plug weld the original holes, reinforce the cases with a little extra welding and drill/tap the new stud holes. The KX cylinders line up very closely. Won't take much grinding to get them aligned with the cases. I'll be test fitting/measuring all week. As I make some progress I'll update the post. Here is a pic of the cylinders on the cases.

Loks good so far. Keep us all informed.

excellent venture, look forward to hearing more in future =D>

Good work, keep it coming.
Now if you could graft on a pair of KX250 barrels (an idea of mine that has been rattling round my head, trouble is with me it'll stay just an idea)- full credit to you for actually doing it.

Mike

Looks promising, looking forward to seeing it progress! =D>

Charles

that for sure is a far better use off my former crankcases than just lying at my attic

looks very interesting.

pardon my ignorance from other threads but is this following on from one where you were talking about increasing the capacity of a KR lump?

Thanks for the encouragement! For now this will be a 250 (54 bore X 54 stroke) but athena makes a 58mm bore cylinder kit that would directly replace these giving 288cc. I have determined that the cylinders could be bored and steel (thinner, stronger) sleeves installed for a 64mm bore giving 350cc. That will be a fun one!! This week I'll be working on figuring what rods to run and what the deck will be to determine if spacer plates will be required. Also I'll determine what to do for a primary gear and iggy. Aside from relocating the studs and turning down the diameter of the RZ crank this project is bolting itself together. =D>

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NEAT ... SO JEALOUS
alot easier now the resonator chamber is front mounted

THE KX ENGINE IS UPRIGHT CONFIG - WHEREAS KR IS SLANTED WELL FORWARD so
MIGHT NEED TO SPIN THOSE HEADS 180°WOULDNT WANT AN AIR POCKET BOILING AWAY (in the upper head stay region)

you can clock/rotate/bolt down head in 72°angle increments - so water outlet would be 144° from front(standard) axis location - would be ok I think and could put adjacent barrel head outlet pipe close to other one
and you will likely grind those KX head mounts off later - not needed

Rough plan on barrel below...

Left is standard KX head fitment - right is KR (slant block)

WILL BE AN AWESOME KR - I feel some airline bookings coming for August 2011.

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It may sound stupid but why two kx125 cylinders, what more can you gain for what you carnt do with some porting on the standard KR cylinders.

Nice project though.

better porting design (guessing btw), better config ie 54x54 is better than 56x50. the h***a rs250 has been the 54x54 for a number of yrs and i think newer tz's are aswell. most of the mx bikes prob are aswell which tells a story. its obvious that kx cylinders (newer) will be better than kr cylinders for a variety of reasons. the firsat is the lack of good kr barrels and the low numbers of tz pistons required if you want to tune kr barells for max port area. the kx jugs will not have such issues

mgtkr1 is correct. The 125 single (and 250 twins) evolved into the 54x54 configuration. If you look at the KX cylinders from the same years as the KR you will notice they are the same. So I concluded that if the KR was still in production it would have followed suit. Once the crank and cases are modified to fit the cylinders you will have a motor that has about 75hp to start with. That's more than a modded KR. I should be able to get 90hp with out too much work on the KX cylinders. These mods will work for a KR run on the street as well. Also the door is open to larger displacements. Up to 350cc is easily obtainable, more if you get a little "creative". The heads were just placed for the photo. I was planning to rotate them back and remove the mounting lugs. Just requires the redrilling of the locating dowels. This build is super easy compared to my other project. A Kaw S1 with KX 85 cylinders, cranks and a six speed trans.

Jim - excellent project but I don't envy you the work involved.
Crank at 54mm will be interesting especially if it is pressed. There is very little meat on a stock crank and extending the stroke 3.4mm - moving the pin 1.7mm doesn't sound a lot but that is going from an integral pin.

If the RZ Crank gets a bit thin have a look at some of the Jap cranks - VJ23 is still available.

Jan Bros mentioned 2011 - plan to be back at Bonneville then so hopefully catch up.

All the best

MJ

Hello mj, how are you doing? If you look in the engine section under "cranks" it was determined that the crank would work. There will be 6.5mm space between the OD and pin. Same as a Banshee stroker crank. If those work so will this one. Also the stock KR flywheel fits the RZ taper so stock iggy can be run. I'll post the crank stuff in more detail when I have the primary gear and rods figured out. I'll have this and more ready for Bonneville if you want to give 'em a spin!

mj43 wrote:Jan Bros mentioned 2011

you lost me there