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Help FZR250 cam timing question

Discussion in 'Yamaha 250cc In-Line 4's' started by beano, Oct 25, 2017.

  1. beano

    beano Well-Known Member Premium Member

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    i was doing the valve clearances on the donor bike i got, to see if i could get it going and noticed that no matter how hard i tried, once i got cylinder 1 to tdc i could not get the dots on the end of the cams to line up properly, no matter what way i did them they were always half a tooth out one way or the other once the tensioner went in.

    0C9A96B6-DB36-4974-8D73-EDFFAADA1E0F_zpsntu3tl0q.jpg

    C2E1B36D-B648-498C-A96A-58880675ECD3_zpsu67ugqoy.jpg

    AD857EF2-E697-4C57-9FE6-A09BF83D3B6D_zpsbb9t3taa.jpg

    just wondering what does this point to?? stretched cam chain??

    thanks in advance for the advice.
     
  2. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Get the cam chain tight as you can on the exhaust side, bolt down the exhaust cam in the correct place, then use a zip tie or two through the sprocket on the exhaust cam to ensure the chain doesn't slip over a tooth.

    Start installing the intake cam and caps and do the same. When you install the tensioner, take the end bolt out and use a socket extension to extend the ratcheting mechanism to take up as much of the slack as possible. Reinstall the tensioner springs and bolt.

    What I then do is very slowly rock the crankshaft back and forth until the teeth stop ratcheting. This helps take up the rest of the slack in the chain and helps to stop the chain slipping a tooth on either sprocket.

    Carefully rotate the crankshaft by hand until you come back around to your timing marks. Check how much slop is in the chain between the camshafts - it should be very tight. If there is slop, the chain needs to be replaced (taking a link out is NOT a solution). Note that the tensioner may not fully extend even if the chain is worn beyond the service limit.

    If you are lucky, everything will line up and you'll be good to go.

    If the intake cam is out, you can back off the tensioner body bolts, lift the chain, and rotate the cam as required, then torque down the tensioner again.

    If the exhaust cam is out, everything out and start again.
     
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  3. beano

    beano Well-Known Member Premium Member

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    thanks, ill give that a go now, just one more thing ive noticed, as you can see in the second last pic, someone has put a mark just to the left of the dot, and its this mark that aligns with tdc.

    just wondering before i head out if this would point to anything?? i suppose the only way to find out for sure would be to check it as per your instructions above, but it looks fishy to me anyway.
     
  4. Joker

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

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    Linkin's right, the issue here is that you need to ensure ALL of the slack is on the intake side to be taken up by the CCT. This is why the exhaust cam should go in first. The dot someone has put there - ignore it. I reckon you're not eliminating that slack and that's why you're having so much trouble.

    A trick I do sometimes is to leave the cam chain guard off (the part that goes in between the cams). You'll notice the chain is slack in that area, so as soon as you put tension on the CCT it will take up that slack. I do it before putting in the CCT by holding the chain onto the sprokets with one hand (ie preventing the chain from skipping up on the teeth) and pushing through the CCT hole with my finger. This sometimes rotates the cams a little, but if the tension is taken up in the chain you will get a true picture of the alignment. If all is good install the CCT and rotate the crank a few times. I reckon rocking it back and forth like what Linkin said is another way to achieve the same thing, I couldn't get that method to work so I came up with my own (after I invented a new dictionary of profanities).

    Anything within about 0.5mm either side of the cam cap dot in terms of alignment is pretty much accurate. The other issue you might be having is a severely stretched cam chain, that would mess the alignment up as well.
     
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  5. Joker

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

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    IMG_2986.JPG

    This was correctly timed on a previous engine, see what I mean by slightly out. This was a slightly stretched cam chain.
     

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