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Thread: kr help

  1. #1
    Join Date
    1st May 2019 - 20:57
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    kr250
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    alexandra
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    13

    kr help

    Hi run a kr250 in pre 89 and having a few crank problems . kr is a rotary and reed valve inline twin,vertically split crankcases, with two cranks driving onto the primary gear .My main issue is it has die cast ally inserts for the main bearings that are cast into the crankcases and are working loose and sometimes cracking,mainly on the flywheel side of the engine and the main shaft is wearing inside the bearing. Wanting to know if any of your bucket engines have same type of insert and issue .The fault maybe in the kr design as it has very heavy cranks 2724grams each with thick webs and long crank pins then out side the crankcase the front has altenator 1290grams the rear a flywheel 1482grams the rear flywheel is smaller diameter the alt has most of the weight on the outside ring, both run in oil from the gearbox casing. The drive side has a gear hub with a three lobe cam and matching internal splined cam held together in tension with a stack of cupped washers like a mini version of what the old pom bikes had.The cams are not symetrical and can rock up to 15 or more degrees but the shim stack has little compression height so it cannot rotate,each drive onto a primary made of two gears on a rubber cush hub .There is no control of side float of the cranks apart from the main bearing spacing and the drive gear floats on the main shaft spline and has a outrigger bearing in the primary case .I think the last of them (only three year model life) did have a thread on the shaft and a nut to hold it .Have added some pics thanks
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  2. #2
    Join Date
    24th April 2016 - 19:07
    Bike
    2001 zx9
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    bop
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    244
    Hmmm , kawasaki usually make decent engines imo but i'm not so sure about those alloy inserts for the main bearings...as soon as there is a whisker of movement of the bearing on the crank or of the bearing in the case then trouble is heading to your wallet. i can't think of why those ally inserts would be fitted (if anyone knows or has a theory...) I don't think the weight of the cranks is an issue so long as they are nicely trued.
    To fix it i would carefully prepare (re depth and chamfer angle) the main journals and get them hard chromed and ground to give around 0.01mm inteference on the drive side and size-for-size on the ignition side (measure the bearings because they can vary .01 or even more. (i've done this on race engines before and never had any trouble so far)
    for the cases my first thought would be to fit a 4340 steel inserts to give some durability but it'd be good to know why they were made like that first...
    Its a good help you've given a detailed description of the layout and plenty of photos but i'll see if we can find some more info on those engines. What year/model is it?

  3. #3
    Join Date
    20th January 2010 - 14:41
    Bike
    husaberg
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    The Wild Wild West
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    Cmntact these dudes in England
    http://bdkraceeng.co.uk


    Sorry just seen it was the tandem Your on your own there...........
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  4. #4
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    13th June 2010 - 17:47
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    It should be possible to scotch key the inserts to prevent them rotating. Shaft wear can be reclaimed by hard chroming.

    I'd recommend tracking down Ned Kelly in Timaru as he has done quite a bit with these engines.
    I don't have a contact - but try via Grant Ramage at the Timaru Yamaha shop.

  5. #5
    Join Date
    1st May 2019 - 20:57
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    kr250
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    alexandra
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    13

    kr help

    As these bikes were only sold in low numbers in Japan , South Africa, Aussie and NZ there are no new parts and little nos come up for sale so I had a friend grind and hard chrome two sets of cranks and fitted with longer Yamaha rods to suit pistons with different pin height but would like to try and solve the problem as they will do the same. I have four complete bikes and three extra engines all in poor condition some with drilled bungs ,so old race bikes. I have stripped all the engines and only one set of cases has .04mm interferace on the mains most are 0 and few oversize or cracked . I have turned up steel inserts .1mm oversize to shrink in and hopefully lock in the ally ones .Mains are 62x25x17 mm so have gone down to 52x25x15 ,what is the most common size in the bucket engines. I will also bore out a set of ally inserts and make new bronze ones to take std bearings ,have been told bronze is better than steel as it expands at the same rate as the ally cases

  6. #6
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    13th June 2010 - 17:47
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    Again - talk to Ned Kelly. The old B knows a lot about these engines.

    Never heard of pegging the inserts or bearings ? Old trick with mains on Brit engines.
    Look at the layshaft bearing in the pic to see how it's done. There's a half-round recess ground in the outer race of the bearing.
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  7. #7
    Join Date
    2nd July 2013 - 11:52
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    GPR150
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    palmertson north
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    2,389
    show us a picture of your race bike
    i'm over buckets

  8. #8
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    20th January 2010 - 14:41
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    husaberg
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    https://www.klemmvintage.com/mxblueprint.htm

    As rumph said there were special sleeves they used to put in JAP and G50's and Manzx etc and they were contersunl screw located from memory
    like this
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    its covered in old books like Tunning for speed.
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  9. #9
    Join Date
    24th April 2016 - 19:07
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    2001 zx9
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    bop
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    244
    It sounds like you've got this under control ok - as always the details are so important...Fair call on the presumably ally-bronze sleeves but you don't want the bearing bores to grow away from the bearings, esp on an engine thats predisposed to trouble there so i would still favour the steel sleeves shrunk in with loctite 680 perhaps up to .1 interference but certainly no more . If you need to peg the bearings you can drill in to the outer race with a 2.5mm carbide drill bit then make a peg out of the shank of a normal drill bit - green loctite again for the peg. at full revs each crank will have a force of around half a ton circling backwards about 180 times a second trying to shake the shite out of your work so any weakness will show up - usually in the first practice after you've driven for hours to your favourite track ... good luck with it, let us know how it turns out

  10. #10
    Join Date
    1st May 2019 - 20:57
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    kr250
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    alexandra
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    13

    kr help

    Thanks for the replies and will try a few methods of repair but was hoping to find why this is happening rather than just make it stronger all my engines in the past the cases have split the other way and never seen this before may just be the vertical split is not as good ,as I now intend to increase hp and rpm witch may make it fail earlier. The engine was built form the best of my secondhand parts and the bottom end has run about 1500 race k's at a max of 9500 rpm but looks as if it was failing a lot sooner

  11. #11
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    1st May 2019 - 20:57
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    kr250
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    alexandra
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    13

    kr help

    Quote Originally Posted by mr bucketracer View Post
    show us a picture of your race bike
    Bit untidy but have no good pic's ,will have to change to red the John Deere green doesn't like the tarseal .Intend to build a single cyl version to do development on an run in bucket class
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  12. #12
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    20th January 2010 - 14:41
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    husaberg
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    Quote Originally Posted by eddie View Post
    Bit untidy but have no good pic's ,will have to change to red the John Deere green doesn't like the tarseal .Intend to build a single cyl version to do development on an run in bucket class
    there is a ready made single version
    https://motorcyclespecifications.com...ar125-1984-85/

    is that a early GSXR400 front end
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  13. #13
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    20th January 2010 - 14:41
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    husaberg
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    Okay i had a poke arround
    I are beging to understand what the OP was saying
    it has a belleville washers spring set up on the crankshaft shock absorbers.
    i would start there and make sure the washers are within spec the stack was correct.
    Any time the japanese give so many pages they are expecting trouble
    also the revision says there was trouble.
    http://www.kr250.org/manual/KR_manual_chapter_17.pdf
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    sites like these disapear every day on the net if you have one save it.
    Also ask around at some of the olde kawasaki dealers there waill be supplements that will soon be biffed detailing the mods and fixes and service manuals.
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  14. #14
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    20th January 2010 - 14:41
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    husaberg
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    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  15. #15
    Join Date
    1st May 2019 - 20:57
    Bike
    kr250
    Location
    alexandra
    Posts
    13

    kr help

    Was setup to manual specs when built up and haven't rechecked yet with this strip down and as they are set to a height and with old washers you can't be sure they still have correct tension. With using the same bike with one crank and barrel removed any mods I do and work I can move onto the twin ,very tempted to lock those primary drives and thread the crank end to fix them on tight

    Forks and yokes are rg400 ,wheels and brakes gsx750f

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