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Discussion FZR250 - Cylinder 4 - big end bearing failure

Discussion in 'Yamaha 250cc In-Line 4's' started by simidau, Dec 11, 2009.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Boosting the pump output by making the rotor deeper is not that hard. Just need to find a good machinist/toolmaker/handy person to do it for you. Don't want to put an engine back together and have it crap itself again.
     
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  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    For comparison Honda CBR250 oil pressure is listed at 4.0-5.0kg/cm2 oil 60°C @ 6000 rpm
    Yet the Yamaha release valve is opening at similar numbers. Anyone know the release valve number for the Honda?
     
  3. gregt

    gregt Well-Known Member Premium Member

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    The bypass pressure is probably recommended by the filter manufacturer. Very easy to blow the O ring at the base of a filter if it blocks. Far better to have it bypassing than collapsing.

    The relief valve pressure is not bad at all. Most of the fours from the 80's were reckoned to have the relief valve open from about 7000 rpm upwards. But that's hearsay. Not hard to check with a gauge fitted.
    The only hard recommendation I ever saw was a TSB from Suzuki NZ on the early GSX750. Two 6mm spring washers under the relief valve spring. About 3mm height. It helped.

    Can i suggest looking at my thread -The sensible twin- As the point I put the pressure sender would work for a temp sender too.
     
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  4. manynathans

    manynathans Guest

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    I have an engine apart apart at the moment and did some measuring on the oil pressure relief valve to come up with some numbers.

    When the cotter pin is removed the spring assembly and top hat sticks out of the base of the relief valve housing by 1.7mm
    When the cotter pin is in place the spring assembly and top hat sit 5.1mm below the surface of the relief valve housing.

    This gives 6.8mm preload on the spring to allow for the factory standard relief pressure of 63-78psi
    I picked an M5 washer which seats perfectly inside the top hat and measured at 1.14mm thick
    This increases the spring preload to 7.94mm
    The spring is wound in a linear fashion.
    Some maths suggests that this 1.14mm washer being added has increased the relief valve pressure to between 73.6 and 91psi
    A 2mm thick washer would increase this to between 81.5 and 101psi which is maybe a bit high. It also wouldnt sit as nicely inside the top hat.

    All this providing the oil pump can flow enough to reach the higher pressure and overcome the relief valve of course.

    A new O Ring and cotter pin is a good idea too if disturbing the assembly.

    2 Pics below. First one showing the assembly as removed from bike, second one showing the location of the spacer. You could probably put it on the other side of the top hat too but it looks nicer this way.

    no shim.jpg shim.jpg
     
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  5. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    It is doubftul the increase will be linear as you will increase any internal leakage on the Oil pump gears (or rotors if that is what they are)
    There would be a good reason for the factory to run at the pressures they recommend.. I am not sure increasing the pressure is going to be any assistance..
     
  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I have never seen a 250 crank but I found this pic. What do you think and care to elaborate?
    I am hunting for a Fizzer now so this is on my horizon.

    s-l1600.jpg
     
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  7. gregt

    gregt Well-Known Member Premium Member

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    OK From the top.
    The main has the usual angled oil hole feeding the bigend. Countersink is off center with a sharp edge at around 6 -9 o'clock.
    I'd touch that one up.
    The top bigend has the countersink off center again and a sharp edge visible at 3 o'clock. Marginal at best.Needs sorting.
    The lower bigend again slightly off center and I'd touch it up as a matter of course.

    I cut a strip of thin alloy wide enough to cover the bearing and long enough to go halfway round the shaft.
    Drill an 8mm hole in the center. Wrap it around the bearing centering the hole over the oil hole.
    I use a worn 8mm ball grinding tip in a die grinder at a low speed to center the countersinks and remove sharp edges.
    The alloy strip protects from the inevitable slip.
     
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  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Pity no one has posted quality pics of the damaged big end.
     
  9. gregt

    gregt Well-Known Member Premium Member

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    I'll add to what I've said. The lower bigend is an example of something not often seen, the countersink has gone too deep.
    If you look closely, there are parallel sides to the hole left by the countersink bit.
    Those holes have sharpish edges which are only slightly relieved by the final factory linish.

    I'll repeat what has already been quoted. The 250 cranks are not finished as well as the bigger engines.
     
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Hi all,
    So while cranking over my R4 engine to get oil to the top end, one of these flew out and landed on the floor.
    PlugsInHead_Arrow.jpg
    So these plugs, (part number 90338-08174 and there are 12 of them), seal off the oil gallery that feeds each cam journal. They are held in place by small protrusions in the cam cover. The FZR250 has exactly the same configuration as my 400.

    If these were loose, damaged or had deteriorated to the point that they leak then bad things will happen. As I said way back in the beginning, "fitting another used engine" fixes nothing. In any case, no one has even posted images of the damaged big-end shells yet. Pfffft, why do we bother?
    Anyway, here is a pic of one of the plugs from my engine vs a new one.
    Plug.jpg

    The used item just falls into the hole, but you have to push the new one in. Does the old one leak at 16000 rpm? I bet it does, and there are 12 of them. Draw your own conclusions, or just go and buy another 35 year old engine and use that. What could possibly go wrong?
    Cheers
    Blair
     
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    Last edited: May 28, 2022
  11. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    This is from a dismantled 3LN1 engine
    They are soft and look "ok" but only the slightest pressure is needed to push them back in

    IMGP0014.JPG

    IMGP0015.JPG

    IMGP0016.JPG
     
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  12. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I've got one MIA also, how much each did thy cost?

    GOOD INFO!

    What could possibly go wrong - now that is an open ended question...
     
  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    They are about $1 each. Should be able to get them at your local Yamaha dealer.
    I'm just looking for leaks in the bucket. Anywhere where o-rings or rubber parts are used in the oil system is going to be a potential weak spot. Piston oilers are another.
     
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  14. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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  15. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    @GreyImport @ruckusman They are USD 0.97 at Impex but I know you guys have to pay the planet for shipping, but I don't. If you want a set I can put them with my current order from Impex, but you will have to pay the shipping to Aus AUD10.66, and could be a little bit more if I have to pay sales tax at my end.
     
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  17. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    When I get my workshop up and running Im going to attempt a couple of engine rebuilds ( FZR and ZXR ) ... as Im an engine rebuild virgin :D
    So when that time comes Ill be buying a ton of bits Im guessing
     
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  18. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    put me down for 12, ping me $$ payable and I'll transfer with excess for if you have to pay sales tax, it's still going to be a discount

    $7.20 each here just makes me nauseous with anger I'm afraid - they take it too far
     
  19. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I will have a lot of valuable information to share with you come the time - biggest issues were main journal and conrod bearings, and conrod bolts

    The bearing on the output shaft is a PITA, no OEM replacements available, there is one suitable alternative readily available - the sleeve which goes from the bearing to the sprocket has to be destroyed - it is on with a ridiculous amount of fit [interference]

    From 3 FZR engines I have inspected, main journals do not seem to exhibit visible wear [oil changes not having been neglected being a factor] - measurements need to go down to 5 microns for accuracy, big end journals and shells do exhibit signs of wear

    I need to turn my mind back to it and get the final details sorted, but there are alternatives from other OEM's for shells, the biggest hurdle IMO
     
  20. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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