KR-1S.co.uk Forum

Skimming 20mm off the bottom of the barrell will remove the bolt up flange completely

Yeah I just had a look at a spare one i gots here and its totally out of the question...


What diameter are these RG150 pistons of which you speak? Are they common?
Wouldnt want to risk too much of an overbore on a barrel which is already as rare as hens teeth.

The RG150 pistons are 61mm diameter. Not sure how common they are, as I only found them in a piston catalogue while looking for other posible replacements for the standard slugs. I was thinking aboout doing the over-bore on a couple of really badly scored barells I have.
It's only been basic research so far, and the conversion would most likely also require head work and maybe skimming the top of the barell a bit.


PS. Sorry Tofty for hijacking your thread.

PS. Sorry Tofty for hijacking your thread

Yeah sorry Tofty.

The other thing to check out is the crankcase compression. I dont know if it'll make any difference with such a small increase in bore, but the greater volume of air being moved by the bigger piston raises the crankcase compression which can (correct me if I'm way off here, I know theres some racers on here who know way more about this than me) make the engine peaky.

61mm could be feasable though, as you said there's plenty of meat in these barrels. If the gudgeon pin is the same diameter and the same distance from the piston crown, then it should be a peice of the proverbial p*ss.

I don't know about the crankcase compression issue, but peaky is just fine with me.
Gudgeon pin diameter is the same and it's distance from the crown is about the same as far as I can tell.
Here's a link to the companies webpage which has a link to the catalogue.

http://www.mingyang-group.2u.com.tw/private/english.htm
Unfortunately, they don't seem to sell direct to the public, and I havn't found a supplier for them yet.

Think maybe we'd better start a new thread in the Tandem Twin section to continue this one.

Edit: OK, new thread started about this in the KR250 Chat section.

Just posted some info in the tandem twin section

TOFTY - liking the renders of the axle stand and the footpegs

but have you noticed the symetry of a KR head - for manufacturing a custom head it's going to be far simpler to make individual heads. (negating the KIPS cable mount)

The old YPVS mod - whether its beneficial to longevity - certainly probably better for piston to bore alignment and never warps heads.
Its a 10 minute job to hack saw a head up, cleaving off the themostat housing.

Then weld up the wall along each head where the thermostat was cast.
Lathe two tubes out that will become the new water outlet at the top rear most of each new head - weld into place. (source suit bends/hose to determine new outlets diameter)


If you have a meltdown on a particular cyclinder you now have only a single head to replace rather than throwing away a good cyclinder head on the twin set up. For those already with damaged combustions lying around this will make use of half pitted heads (use the good half).
Also becomes alot easier for someone to machine the correct squish clearances for each barrell.

Consider the radiator Y bracket to be made out of carbon fibre or plastic that would be more flexible than the pressed steel original. The purpose is allow individual expansion

Reuse part of the thermostat housing and have a backside made for it with 2 inlets from the INDIVIDUAL HEADS.

when you need a new head gasket tell them you only want to order half of one. (':-

http://www.vhm.nl/VHM/indexvhm.htm




The benefits of removable inserts is the ability to cheaply manufacture custom combustion chambers, squish clearances and compression ratios to tune for different fuels - probably not that worth while unless you are stripping down your top end every couple of months - whats the longevity of the o-rings?

KR-1R wrote: whats the longevity of the o-rings?

no prob to re-use them over and over (well, eventualy one has to change them, but not before having used them 10-20'th times)

Thanks to KR-1R excellent post here I was inspired to do this today. I'll post up some pics later but it is indeed a 10 min job. I am either going to use a RGV thermostat housing or the latest two way by-pass thermostat from the TSS.

Take care with it. I was told that the cylinder head holds the engine together.
This mod was apparently tried in the early '90s and the crankcases on modified bikes cracked!

When I designed my billet heads, though the heads were individual the design allowed a bridge to be fitted to replicate the bracing a one piece head provides.

Thanks for the tip that shouldn't be hard to replicate with a left and right hand thread to push the cylinders apart.

I was in contact with VHM in November who seemed quite happy to do a batch! for the KR at similar pricing to their existing kits.

The main problem with the KR head is the KIPS valves - sealing them if you want to run o-rings (combustion chamber inserts run close to where the KIPS bores are) - running the standard gasket isnt a problem

The other hinderance that DOESNT make it cheaper/easy A BOLT ON UPGRADE
is the thermostat/hose issue.

Im keen on a set of VHM, but for other people, pipes and carbs is money better first spent given that there is no measurable horse gain only bling

but for 40 euro a set, some VHM chamber inserts (maybe KTM 125/140 =56mm) might slip happily into a pair of standard KR heads after they are suitably milled out whether its a one head or two.