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Discussion FZR250 Split crankcases

Discussion in 'Yamaha 250cc In-Line 4's' started by ruckusman, Nov 7, 2016.

  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Anyone out there who split the engine crankcases can tell me for certain that the cylinder head and barrels need to come off to access two or more bolts below the barrels?

    I'm looking at this breakdown on the zealous site, which does show at leas one bolt below the cylinders...part 14

    Looks like this means I will need head and cylinder base gaskets after all

    [​IMG]
     
  2. Joker

    Joker See "about me" for contact details. Contributing Member

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    I think your image didn't work mate. I have the bores and top ends off both my engines at the moment so i can take a few photos for you if you want (have to be this weekend as I'm travelling). Maybe @Linkin @Grasshopper or the big cheese @GreyImport might know offhand...

    Btw the base gasket isn't grooved... I'm inclined to reuse the good one I have with copper gasket cement. Think I might replace the head gasket though.
     
  3. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Part 14 shown with two going down into the upper case

    13.jpg
     
  4. Joker

    Joker See "about me" for contact details. Contributing Member

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    I'm going off memory but they seem to be outside the mating face of the bore... I don't think leaving the bore on will prevent you from undoing them? At worst maybe the head may need to come off perhaps?
     
  5. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Number 14 look's like the bolt under the starter motor ?
     
  6. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    There's three 14's in the diagram, there's two on the upper one, one is beneath the starter motor, the other is inside the crankcase beside the camchain tunnel
     
  7. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Ok, yeah i can see it now.
    So you've answered your own question then, cylinder need's to be removed
     
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  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Yep I think I have, I was hoping against hope that it would be otherwise...perhaps that the bolt didn't need to be removed if it didn't go through the case halves and join them
     
  9. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Yes 100% head and barrels must come off to access bolts numbered 1 thru 4 from memory.
     
  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    OK so my next question for those more knowledgeable, has anyone compared OEM to aliexpress head and cylinder base gaskets?

    I seem to recall seeing someone post that the base gasket had asbestos so I will be avoiding those at all cost
     
  11. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Yeah just go with genuine ones. They are cheap in the grand scheme of things. I got my last set from jp-parts.com

    The aliexpress ones were no good. Base gasket is asbestos and leaked. Head gasket was a very tight fit.
     
  12. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    How much did the gaskets set you back landed?
    With my engine development plans I'm going to need more than a few head gaskets which is likely to get quite expensive
     
  13. Joker

    Joker See "about me" for contact details. Contributing Member

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    Why not reuse the base gasket?
     
  14. risky

    risky risky

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    genuine i picked up top and bottom for 105 on fleabay but ali express was like 40 but not a patch on quality.
     
  15. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    both good points gents, I'm borrowing some space to do the dis-assembly & re-assembly so need to have everything ready to go

    I will try and re-use the base gasket if possible.

    My plan was to get the bike back running as simply as possible with the carbs reconditioned so I have a comparison to check against...

    But I may just go the whole hog and do the 54mm overbore and check all bearings, replace cam chain and check the head/valves in one hit and see where I end up
    Then begins any head development work
     
  16. concrete

    concrete Active Member

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    Hi, I've just rebuilt my 3ln6 and used genuine gaskets which were very well priced, however here in the uk i was unable to get a genuine base gasket as the system says they're no longer available. i chose to reuse the original but with hindsight a pattern part would have been less hassle because the original part is a single layer steel item with a plasticised coating. obviously the coating is a one use only affair which meant completely cleaning all the remaining coating off and applying rtv sealant to both sides of the gasket at the point of rebuild. Since i didn't want to risk accidentally removing sealant while refitting the barrels, this had to be applied whilst the barrels were on but not fully down. In short a pain in the arse!!
     
  17. beano

    beano Well-Known Member Premium Member

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  18. gregt

    gregt Well-Known Member Premium Member

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    Don't use rtv. To reuse the shim base gaskets - and i've reused many over the years on most size yamahas - clean off all the original coating using a pot scourer, gently...I do it in the sink in warm soapy water.
    Once clean and dry, repaint with your choice of paint. There are a couple of aerosols available specifically for this but I simply use a good quality engine enamel.
    It is possible to do the same on head gaskets too - but it's not generally as reliable as doing it on a base gasket.
     
  19. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    thanks guys

    I ordered OEM head gaskets as they're readily available @ $32, base gaskets however no longer exist by all accounts as you've discovered.

    Someone else posted recently that the paper base gaskets available on jauce and aliexpress aren't up to the task and leak.

    I may attempt repainting the OEM base gasket, however I am likely going to use Hylomar blue
     
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  20. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    For what it's worth I was able to get a new base gasket from jp-parts... but that was nearly a year ago by now
     

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