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Help Cam chain question

Discussion in 'Yamaha 250cc In-Line 4's' started by ajb0235, Jan 20, 2021.

  1. ajb0235

    ajb0235 Active Member

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    image.jpeg image.jpeg I'm checking everything, valve clearance ,valve timing because the bike has been stood for a long time, and I have no history, other than 33000 k from new 1989.
    My concern is the way the cam chain sits on the sprockets. It sits very high on the teeth, with plenty of daylight between the teeth and the chain.My concern is that the wrong chain has been fitted at some time. However it doesn't look as if the engine has been split, and everything checks out apart from 1 inlet valve where the clearance is below the 0.004 lower limitat 0.003".

    Is this cam chain/sprocket clearance normal?
     
  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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  3. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    Not sure what bike that is, but the cam chain on a ZXR will often sit up like that until the cam-chain tensioner is released/activated and you turn the engine over a few times (manually). If it's like that with the tensioner on, then I think you have a potential problem.
     
    • Agree Agree x 1
  4. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Yeah sitting up on the teeth is not good, it can jump a tooth like that. And yes the tensioner being out can do that. You likely need to pull and reset the tensioner. When it is out, make sure the crank and cams are on their timing marks. You can then try to rotate either cam a little to get the chain sitting right. Just make sure all the slack goes on the inlet side, you might have to pull the inlet cam to achieve this.

    make sure the cam caps are fully seated. I find it helps to set the exhaust cam in position and bolt it down first.
     
  5. jmw76

    jmw76 Well-Known Member

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    Hi Guys,

    I am late to the party I know, but is that the right chain for the application???? It isn't something silly like a silent chain being used where a roller chain should be used? That would certainly explain it sitting high.

    Peter.
     
  6. Bobbyr

    Bobbyr Member

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    My FZR 250 is the same, although I don't know if this is normal. Removing the tensioner did not cause the chain to sit lower in mesh with the teeth though. strange one
     
  7. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    FZR cam chains are the morse type and not roller type. ZXR's use a (tiny) roller chain.
     
  8. 2valve

    2valve Well-Known Member

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    I'm far from being a expert , but it's like the chain has stretched. I had the same problem with one of my old race pushbikes back in the day's. A new chain was fitted , and problem was resolved.

    It does look weird though sitting so high. To me it should be well seated into the sprocket , i'f my main drive chain was sitting that high on the sprocket , i wouldn't ride the bike.
     
  9. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Can we have a wider angle shot of both cams, the chain, and pictures of the timing marks please? With good lighting?

    If in doubt, remove tensioner, cams & reset the timing. Fit and bolt exhaust cam first and inlet second. All chain slack to go on inlet/tensioner side.

    If fitting a new chain (open ended with joining link) measure the whole length of the new chain, and compare to the old one when removed, along with flex in the plates when held sideways. Might surprise you how much they stretch.
     
  10. Bobbyr

    Bobbyr Member

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    exactly, when I noticed mine was like this the first thing I though was that someone has installed an incorrect chain for the cam sprockets. I've never seen anything like this before on any motorcycle or car cam chain.
     
  11. ajb0235

    ajb0235 Active Member

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    Have a look at pinned post"how to replace your FZR250 cam chain without splitting cases" by linkin, on this forum. Pictures of the cam chain sitting on the sprockets are very much like mine. If there is anyone out there who has their motor out at the moment have a look at the cam chain. I'm coming to the conclusion that they are all like this. Mine hasn't had a replacement chain.
     
  12. ajb0235

    ajb0235 Active Member

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    image.jpeg image.jpeg image.jpeg MHere's a few more pics.
    I've removed the inlet cam now to re-shim 3 valves. I require 2 X 175 shims and 1x 170 shim. Has anyone in the UK got these? I would swap for 3x180 shims that I have removed.
    Prices for new shims are crazy here. Has anyone tried lapping the shims down on 400 wet or dry paper to remove a small amount?
     
  13. Gen

    Gen Well-Known Member

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  14. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Lapping the shims is usually the last resort, but if you do make sure you grind down the side with the numbers on them so you do not get confused in the future.
     
  15. ajb0235

    ajb0235 Active Member

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    Yes, I lapped mine down using 600 wet orderly paper and WD40. I only had 3 shims to do, and only 2 or 3 thou to remove. Success!
     

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