Possible 300cc conversion

The place to talk about your Tandem!
User avatar
ScottaKR
Premix Junkie
Posts: 1521
Joined: Fri Aug 10, 2007 2:52 pm
Location: Australia

Possible 300cc conversion

Post by ScottaKR »

OK, the Sheik and myself started talking about this off-topic in someone elses thread, so instead off completely hijacking his, I've copied most of the relavant parts of it into here.
ScottaKR wrote:The other I dea I've had for the tandem engine is doing a 300cc over-bore useing something like RG150 pistons. There's a lot more meat in the tandem barells so wouldn't be as weak after the bore out.

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.
Sheik Yerbouti wrote: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.
KR250 Tandem Twin (Naked) :mrgreen:
KR1 Red/White
KR1S Track Bike (has been put on hold for now)
ZXR750 H1 (Winter project)
StrokerBoy
Premix Junkie
Posts: 1087
Joined: Thu Jul 27, 2006 9:43 am
Location: Yorkshire
Contact:

Post by StrokerBoy »

It's already been done I think, by yet another one of you crazy Aussies ! =D>

Someone told me ages ago but I can't remember what he said. I'll have to dig through my old emails. Think 150cc strokers are still popular in places like Thailand and Malaysia ?
Kawasaki KR250 Tandem Twin (x4) & KS-II 80,
Yamaha RD350LC,
Suzuki GSX-R750RK & RB50 Gag.
User avatar
kwackman12
Oil Injector
Posts: 924
Joined: Wed Jul 04, 2007 10:06 pm
Location: Reading

Post by kwackman12 »

Just aquired a new set of "300cc" pistons for my Stan Stevens kr1 conversion (long story :cry: ) part numbers might be of use to you, they are Wiseco part no 7682p6094 & it reads on the box UK SUZ RGV250(60.94mm-2402CD

Clear: 0.0028(0.071mm)
KR1 race bike
ZXR 400 Race Bike
Aprilia RS250
Sheik Yerbouti
Heavy Smoker
Posts: 121
Joined: Mon Sep 29, 2008 1:43 pm
Location: South Oz

Post by Sheik Yerbouti »

Think 150cc strokers are still popular in places like Thailand and Malaysia
Yeah I believe that 150cc is the biggest bike they are allowed over there, hence the stark bollocking mad little nsr150.

Lets also remember kids, the stroke, how big a piston do we need here to get the 300cc? I cant remember what the stroke is on these things off the top of my head and don thave the manual here right now........

If strokerboy can find a bit more on what other people have used that could be a big help.
User avatar
ScottaKR
Premix Junkie
Posts: 1521
Joined: Fri Aug 10, 2007 2:52 pm
Location: Australia

Post by ScottaKR »

Standard stroke is 50.6mm, so technically it would be 295.6cc which is close enough for me (and stan stephens going by kwakmans post). 61.5mm would give you 299.3cc, but havn't found one where the rest of the specs even come close.

Kwakman: Thanks for the part numbers for those KR1 300cc conversion pistons, but unforunately the pin hieght is very different to that of the Tandem Twin engine. :(

StrokerBoy: Let us know what you find in your old emails, as it may be easier to copy what has already done rather than to re-invent the wheel so to speak.
KR250 Tandem Twin (Naked) :mrgreen:
KR1 Red/White
KR1S Track Bike (has been put on hold for now)
ZXR750 H1 (Winter project)
User avatar
ScottaKR
Premix Junkie
Posts: 1521
Joined: Fri Aug 10, 2007 2:52 pm
Location: Australia

Post by ScottaKR »

Seems they have RG150's in New Zealand, and standard, 0.25 and 0.5 O/S piston kits are readily available for them there.
Just do a quick search on www.trademe.co.nz and youll find a few guys selling them at reasonable prices.
I'm a long way off doing this conversion myself, but thought I'd post up what I found as a reference for others who may be thinking of giving it a go.

The other thing I don't know about these pistons is the ring peg location and whether or not they will snag in a port somewhere. I think this is probably the only thing that would stop them being used for this conversion.
KR250 Tandem Twin (Naked) :mrgreen:
KR1 Red/White
KR1S Track Bike (has been put on hold for now)
ZXR750 H1 (Winter project)
Sheik Yerbouti
Heavy Smoker
Posts: 121
Joined: Mon Sep 29, 2008 1:43 pm
Location: South Oz

Post by Sheik Yerbouti »

good find! Just need to have a look at one in a wreckers somewhere and see if the rings snag or not and we're in business.

Do you know of anyone in Aus who can do nicasil plating? Will I have to refinance my house to afford it?
User avatar
ScottaKR
Premix Junkie
Posts: 1521
Joined: Fri Aug 10, 2007 2:52 pm
Location: Australia

Post by ScottaKR »

Sheik Yerbouti wrote:good find! Just need to have a look at one in a wreckers somewhere and see if the rings snag or not and we're in business.

Do you know of anyone in Aus who can do nicasil plating? Will I have to refinance my house to afford it?
There's a few places in Aus that do nicasil, but I can't personally recommend any as I havn't had any barrells re-plated yet. I know Billy "The Kid" had some sent over to South Africa to be done a while back as they were apparently quite cheap.

www.electrosil.com.au is one that I've found while searching. Apparently they did plateing for the factory Kawasaki teams, so should be good quality. They can do over-bores and porting too apparently. Not sure on their priceing though.

Will be hard pressed to find a RG150 in a wreckers in Oz. :( NZ is the only likely place to find them (unless you speak Tawainese). May have to ask one of the sellers over there really nicely to do some measurements or at least take some photos from the side showing the ring peg locations in relation to the gudgeon pin.
KR250 Tandem Twin (Naked) :mrgreen:
KR1 Red/White
KR1S Track Bike (has been put on hold for now)
ZXR750 H1 (Winter project)
Sheik Yerbouti
Heavy Smoker
Posts: 121
Joined: Mon Sep 29, 2008 1:43 pm
Location: South Oz

Post by Sheik Yerbouti »

Yeah I wouldn't bother getting someone else to bore mine, I'll do it myself. If it comes to that I might be able to do yours too if you like.
Will be hard pressed to find a RG150 in a wreckers in Oz
Probably right, thats me not thinking before I type again ......

Who wants to take the plunge and buy one to check it for fit? :lol:
User avatar
ScottaKR
Premix Junkie
Posts: 1521
Joined: Fri Aug 10, 2007 2:52 pm
Location: Australia

Post by ScottaKR »

Sheik Yerbouti wrote:Yeah I wouldn't bother getting someone else to bore mine, I'll do it myself. If it comes to that I might be able to do yours too if you like.
Wish I had the equipement to do that stuff myself. :( What other machineing can you do yourself? Youd also need to O-ring the head as the head gasket wont clear, as well as re-working the combustion chamber and squish band.

Sheik Yerbouti wrote:Who wants to take the plunge and buy one to check it for fit? :lol:
Can't justify it atm, as I still have a sweet pair of barrells on mine.
That said, I do have my eye on another Tandem (non-running mess), so if I can get it cheap I may sell the current bike and build it as a 300.
KR250 Tandem Twin (Naked) :mrgreen:
KR1 Red/White
KR1S Track Bike (has been put on hold for now)
ZXR750 H1 (Winter project)
Sheik Yerbouti
Heavy Smoker
Posts: 121
Joined: Mon Sep 29, 2008 1:43 pm
Location: South Oz

Post by Sheik Yerbouti »

What other machineing can you do yourself
pretty much anything, I'm a toolmaker by trade and I've got the whole workshop at my disposal.
CNC mills, lathe, cylindrical and surface grinding and EDM.

Yeah this thing would be a last resort for me too. Just good to have a plan in case I seize the thing up, which I probably will........
User avatar
ScottaKR
Premix Junkie
Posts: 1521
Joined: Fri Aug 10, 2007 2:52 pm
Location: Australia

Post by ScottaKR »

Sheik Yerbouti wrote:
What other machineing can you do yourself
pretty much anything, I'm a toolmaker by trade and I've got the whole workshop at my disposal.
CNC mills, lathe, cylindrical and surface grinding and EDM
Now I'm really getting jealous here. I can only dream of haveing that kind of setup at my dispossal. =P~ =P~ If I do end up doing this conversion, I might end up sending a pair of barrells and head to you for machineing. [-o< :lol:
Sheik Yerbouti wrote:stupid here, but exactly what is EDM?
Sheik Yerbouti wrote:Yeah this thing would be a last resort for me too. Just good to have a plan in case I seize the thing up, which I probably will........
I actually thought of this conversion while looking for something to replace the standard KR piston as they arn't available anywhere, and the only possible option anyone has come up with is the KMX125 2mm o/s piston which isn't readily available over here it seems.
If I ever have to plate a set of barrells for a tandem I'll be trying out the 300cc theory for sure. :mrgreen:
KR250 Tandem Twin (Naked) :mrgreen:
KR1 Red/White
KR1S Track Bike (has been put on hold for now)
ZXR750 H1 (Winter project)
Sheik Yerbouti
Heavy Smoker
Posts: 121
Joined: Mon Sep 29, 2008 1:43 pm
Location: South Oz

Post by Sheik Yerbouti »

lol not stupid...... EDM = Electro Discharge Machining. Some people call it spark erosion. You make a copper or graphite electrode the shape and size you want to make and it uses high frequency sparks to "burn" that shape into the workpeice.

There might be a better explaination on wikipedia or something.

Anyhoo I've got three spare barrels here that all need plating and a couple need boring too, so I might play around with them a bit.

I like the idea of designing and making new pipes as well, but thats another adventure alltogether. I made one for an old DT125 I had a few years ago and it was a bitch of a job to fit.
All just dreams so far :roll: but why not?
Sheik Yerbouti
Heavy Smoker
Posts: 121
Joined: Mon Sep 29, 2008 1:43 pm
Location: South Oz

Post by Sheik Yerbouti »

Hey Scott, or anyone really.
have you got a KR1-s barrel lying around somewhere you can take measurements off? I've been noodling around drawing up a model of one of my spare KR250 barrels but I wouldnt mind revising/updating the porting if its much different. For the sake of the exercise twould be good to model up a KR1-s barrel that will fit a tandem.

would need transfer port heights i.e duration and width. Also details of the exhaust port and power valves.... Tall order I know, but if you've got a spare few minutes to measure one up it would be greatly appreciated. [-o<
User avatar
ScottaKR
Premix Junkie
Posts: 1521
Joined: Fri Aug 10, 2007 2:52 pm
Location: Australia

Post by ScottaKR »

The port timing is pretty different between the two. I've thought about porting a KR250 barrell to KR1-S specs but thought it could be something of a waste as the pipes may restrict it somewhat.
A few people have already made port maps of tuned KR1-S barrells. Our resident world record holder has been good enough to post up details of his tunning here.
http://myweb.tiscali.co.uk/teamsparrow/kr1stune2.htm

If you have a look through the engine section you may find some others as well.

Edit: found a post with a standard port map here.
viewtopic.php?t=2701
KR250 Tandem Twin (Naked) :mrgreen:
KR1 Red/White
KR1S Track Bike (has been put on hold for now)
ZXR750 H1 (Winter project)
Post Reply