Project Kawasaki boss --> 250cc

Discussion in 'General Discussion / News / Information' started by katana, Jan 18, 2009.

  1. Hi all.

    We are just about to do a prototype for converting the Kawasaki Boss to 250cc.

    Anyone done this before ?
    Anyone forsee any problems ?

    The plan is to sleeve the existing motor and insert a larger piston thus increasing the bore while keeping the stroke the same and probably a small increase in compression.

    The head will also recieve larger valves.

    The aim is to increase the power to weight ratio and to allow the fitting of a taller gearing to make crusing easier with less gear changes.

    The projected cost is aprox 8500 baht including labour.

    I will take some pics when it goes in and update the specs and types of materials used in the convertion.

  2. Hey young fella I was thinking of doing the same with Phantom so last week I made enquires at the Phantom shop (cnx) the owner informed me he tried it on a phantom motor once and blew the bastard up, maybe worthwhile to have a talk with him. Usually he is not so friendly but that day he was and didn't try to offer alternatives to make a buck. Good Luck
    P.S. Maybe a good phantom is for sale at 58,000 baht ....Cheers
  3. You want to increase a 175cc motor to 250cc just by stroking it?!
    My advice: don't mess with things you don't understand. You can't paint stripes on a cat and expect it to be a tiger. Buy a Phantom or get a 250cc engine and try fitting it into the Boss frame, that may be easier. Then go easy on the throttle.
  4. Sorry, I got it wrong, you want to bore it. Have you figured out how big the bore would have to be to increase the cc by almost 50%? You bore that big, the cooling fins are gonna fall off...
  5. Agree with Kz, don't know how you're gonna get that kind of increase without fitting new engine!

    The maximum generally accepted increase in engine capacity from boring is 10%, any more and you'll jeopardise the whole thing when you open up the throttle.
  6. Arh, my old 125 Honda Wing had a 175 kit in it. Added an oil cooler & it ran like clockwork for tens of thousands of kms.
    Once my Wing 125 was rebored to 175 at least half a dozen other guys did theirs. Once of them is still running after 15+ years. Jan just did a trip through Laos with his 20+ yr old Honda Wing "125." The bike's got over 100,000 kms on it & still runs like clockwork. He still rides all over Thailand & down to Malaysia, & now Laos.

    Ok I know this a Kawasaki Boss, but give it a go, do it carefully, fit an oil cooler if possible & take care riding it.

    Time for a comment from the Snail.....
  7. I guess the first thing you should take into consideration is the standard bore and stroke. I cant find the figures for a Boss but the engine and indeed the whole bike look very similar to a Kawasaki Eliminator 125 which has a bore and stroke of 55.0 x 52.4 mm. If the Boss uses an overbored Eliminator engine I think you can forget about boring it out any more. I remember the old Yamaha DT125MX and DT175MX used the same stroke engine, 56 x 50 and 66 x 50 according to my old 2 stroke tuning book. Indeed you could even swap top ends on them, handy what with the 125cc limit on provisional riders in the UK. So in theory the Boss engine could possibly go up to around 250cc if it's not already too much of a short stroke motor and there's enough barrel left for the sleeve to fit into.
  8. Hi

    The guy advising on the actual engine mods regularly does 125cc honda to aprox 200cc conversions for use in enduro "scooters". Which is why I asked about the boss.

    In the end if it blows up replacing the engine is cheap and easy which is why I am doing a prototype first.

  9. According to the owners manual the boss is 174cc 65X52.4 comp ratio 9.0 to 1.

  10. Same stroke, different bore. Seems like the 175cc engine is already maxxed out.
    If there are several engine sizes the same make like a 110cc/125cc/175cc or a 250cc/350cc it's sometimes possible to fit the bigger kit, or an after market cylinder and piston kit. But boring out is another story, ususally there's not that much "meat" to go bigger than 10%. Taking the cylinder and piston from the 175cc Boss and plant them in a 125cc Eliminator engine may well work, but boring out the 175cc cylinder to get a 40% increase in cc will weaken it and make it crack under pressure.
  11. The boss is indeed the update of the 'eliminator'.... (Who comes up with these titles?.... The boss being not much in much of a position to demand anything very much unless it's done at moderate speed)......

    Its actually made under license in India by Bajaj and assembled here in TL. In India it's a 200cc engine but otherwise pretty much the same as TL.... In South India certainly it's a serious rival to the bullet 350 (Enfield) commercially.... Which may explain why its required to be a bit of a chugger. To be fair it does seem very reliable.

    Mine just completed a tour of 7000 km plus around TL with nowt by the way of hiccups except a flat tyre, a replacement of chain/ sprockets and a near miss with a pickup driven by a blind idiot..... It will be heading to Nakhon Si Tammarat and Songkhla shortly.... Won't be quick. Its done just over 20,000kim in the last ten months with no problems at all.

    How much oomph do you think the rebore will give you? Will you be sacrificing the very conevenient, placid reliability of the Boss as it stands the way it was manufactured?....... Its hardly going to make an awful lot of odds in terms of performance surely?..... Its hardly built for speed. Depends where you go, but you may find yourself sacrificing the good side of that bike for very little real gain....... Only a thought.

    That everlasting Honda Wing sounds amazing.
  12. Interesting, Dan - didn't know that Kawasaki has a factory in India. Or is it assembled as a "Bajaj" and rebadged? That would explain that I saw the same bike in Malaysia with a malaysian badge on it.
    I agree with you here: "you may find yourself sacrificing the good side of that bike for very little real gain......." - I'd say save the money and the hassle of an operation where the patient may die, sell the Kwak and simply buy a used Honda Phantom. I've had both bikes and the Honda is definitely the better bike. It has a long stroke and way more torque, so cruising at 100km/h is really relaxed on that bike; top speed is around 135km/h. The Kawaski engine is actually a high-revving street bike engine.
  13. Yes..... You see them everywhere around Bangalore. I had some interesting chats around Karnataka and Tamil Nadu with those on the 'Avenger' (good grief.... Keep a straight face if you can when you say that out loud!) in April. No time to test one out since I was busy working, but it is exactly the same as the boss with a slightly bigger engine.....

    There was a debate on the merits of phantom v. Boss when Colin was looking to buy his new bike for his mammoth northern touring project.

    On balance the phantom wins largely because of the universal backup of Honda.

    I very much like the boss because it seems lighter and a little less bloated in terms of tank etc for a small engine bike. I kind of prefer it, but in the end they are very much the same beast, although as you say the phantom probably wins at the very top end. Boss is very happy at a 100, but starts squealing past 110 and barely reaches 120. Phantom has a bit more reach with gear etc I think. Honestly, the main reason I got a new boss rather than a new phantom was the paintwork. No offence to Phantom owners, but the sort of flame proto-Harley-chopper paintwork made me want to vomit, so I bought a kawa from the same shop. The old phantoms are not vomit-making at all. They are pretty business like. As I say, no offence to the American style syling fraternity, each to his own.... Just not my cup of tea.

    I wonder if there are motorcycle boards in India from which one could find out where to buy an avenger engine and plonk it into the boss..... Frame and that is the same.
  14. Cool... I will be heading down via Nakkhon Pathom-Ratchaburi- Phetcheburi.... Will be around there and Cha'am for a few days.... Then on to Surat, Nakhon Si Thammarrat and Songkhla.

    If you are headed that way, you can do the side trips off into Kaeng Kratchan...... Mae Hong Song it ain't, but its still pretty good. Defeinately worth some methodical road reports I would have thought..... GT rider being the rescource that it is.

    When you know your movements let me know........ Cold beer and that.
  15. Here is the web page for the 'Bajaj Avenger'.

    The main slogan is...... Wait for it....

    "Feel Like God"

    So there you go...... God rides a 200cc four stroke. Not a lot of people know that.

    As you will see from the pics.... Its the same as a Boss. Not quite sure how the slightly reduced engine capacity of the Boss affects the feeling of actually being God....

    The advertising is misleading since when negotiating the backroads of Kerala God is well known to riide a 350cc Enfield Bullet with diesel conversion.

    India is great for bikes in the 100cc to 350cc range. The competition is intense and they have to be tough workhorses, Indian roads being a little bouncy on occasion. The Avenger is an eliminater with a Pulsar engine which is actually 178.6cc acording to the specs.
  16. [quote quote="katana....converting the Kawasaki Boss to 250cc.
    Anyone done this before ?
    Anyone forsee any problems ?

    thought to ask the same,
    or maybe a little bigger than
    250...500, ..i know is a crazy plan
    but if someone know engines
    about that size, i am interested.

    it will need welding the frame,
    many things, so for that same
    money could get another,...SURE.

    ... this kawa boss
    is not so dear for me but just want to know
    what could be done :twisted: :twisted: :twisted:

    bigger bike is 750 cbx.

    some updated info about
    used bikeparts around pattaya/bkk

    thanks regards, and cheers,

  17. "So there you go...... God rides a 200cc four stroke. Not a lot of people know that."

    And I thought he rode a donkey... Or maybe you came to the wrong cocnlusion - what they're actually saying is that when you ride this 200cc indian made motorized contraption you feel like riding a donkey!
  18. Ah KZ...... But you realise that in India the religious pantheon is large. Brahma, Vishnu and Shiva have countless manifestations and use many vehicles. Shiva has Nandi the bull as a nip-around for instance.....

    Ganesh...... the justifiably popular 'wally' God with the head of an elephant, may well ride the Bajaj Avenger (!)...... with the Pulsar engine...... But Vishnu in his purest incarnation would only ever do his thing on a Bullet.....

    I'll have a quick check of the Mahabarata...... But I m pretty certain that's the way most orthodox Hindu theologians interpret it.....

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