cam chain tensioner questions

  • hi all,


    i've opened the front of my engine up to inspect my cam chain tensioner.
    there are some things i would like to know more about.


    1: i found no groves in the lower tensioner, i expect this to be still ok? correct?


    2: the tensioner unit has a part that has a slot along its length( turned), this item also has a foot, that has a crowned edge. This is used to keep the tensioner from jumping back in to position after a certain point (picture of this item below). this foot is NO ridged to the "tube" part... is this correct, or should it be solid??


    3: after installing the tensioner again, i noticed the chain to be slackened, using a big flathead screwdriver i gently pushed the tensioner up, so it jumped to a position that did tension the chain (chain seems to be TIGHT now) is this allowed or should the oil pressure do this and should i not fiddle with it? I also noticed this "new" position to be much "higher" than the old position (see comparison pictures below)


    4: how much effect has the oil pump on this item, if the pump is worn or not up to scratch, could this result in a malfunctioning tensioner?


    hope you can help me out!


    picture old position of the tensioner:
    [Blockierte Grafik: http://lh5.ggpht.com/_4DMzYTZxbYA/S83eRyd0qQI/AAAAAAAABko/6ZDllntD54I/s720/DSCN6511.JPG]


    picture of new position:
    [Blockierte Grafik: http://lh5.ggpht.com/_4DMzYTZxbYA/S83rpc4m6mI/AAAAAAAABnI/I6w2C55XJfE/s720/DSCN6522.JPG]


    to prevent a "optical illusion discussion" it is higher, i would guess a full click.


    here some pics of the guide rail
    [Blockierte Grafik: http://lh6.ggpht.com/_4DMzYTZxbYA/S83kjrHex8I/AAAAAAAABmY/RXJWuvcUoWY/s720/DSCN6519.JPG]
    No groves or anything.


    Some nice pictures of the tensioner disassembled:
    [Blockierte Grafik: http://lh6.ggpht.com/_4DMzYTZxbYA/S83kLLL0MfI/AAAAAAAABmE/wvc2PPTdvTQ/s720/DSCN6516.JPG]


    here a picture of the "lose bit", in the lower left corner:
    [Blockierte Grafik: http://lh4.ggpht.com/_4DMzYTZxbYA/S83kawzPzsI/AAAAAAAABmQ/DSBlYBasoo4/s720/DSCN6518.JPG]

  • Hi tmoons,


    1. If the chain guide has no visible wear I would reinstall it.


    2. This is all part of the tensioner's ratcheting mechanism: As the chain wears and slackens, the spring inside the tensioner assembly pushes the tensioner guide upward to take up the additional slack. Due to the axial movement the spiral-slotted cylinder part with the crowned part at the bottom will be forced to rotate a tiny little bit. If the slack and the axial movement of the tensioner guide is big enough, the crowned part of the cylinder will slip to the next notch of its counterpart on the bottom of the tensioner housing, minimizing any mechanical play. So if you're saying that there is no crowned pattern at the bottom of the cylindrical part of the tensioner housing to match the crown of the spiral-slotted piece, this doesn't sound right to me - or at least it doesn't match the tensioner design on my 87' K100RS.


    3. I would not apply any excessive force, i.e., using a lever or other tool to increase the chain tensioning force. The tensioner has a ratcheting mechanism. Any excessive tensioning may result in higher loads on the camshaft and crankshaft bearings. The spring inside the tensioner should generate sufficient force to achieve the correct tensioning.


    4. I don't believe that the oil pump and oil pressure has any significant effect on the tensioning force. The oil supply orifice is extremely small and the oil leakage due to the tensioner clearances is soo large that there shouldn't be any significant pressure build-up underneath the tensioner piston. I would claim that the oil is for lubrication only.


    Tom


  • Tom,


    on number 2. the crown is there, but there is play, the crown bit wiggles in respect to the tube bit.
    it is not solid.

  • Zitat von "TomPIT"

    Hi tmoons,


    1. If the chain guide has no visible wear I would reinstall it.


    true, but you should try and find out if and how much the chain has lenghtend and how much die sprockets are worn...they are usually due for changing at about 150tkm


    Zitat von "TomPIT"

    2. This is all part of the tensioner's ratcheting mechanism: As the chain wears and slackens, the spring inside the tensioner assembly pushes the tensioner guide upward to take up the additional slack. Due to the axial movement the spiral-slotted cylinder part with the crowned part at the bottom will be forced to rotate a tiny little bit. If the slack and the axial movement of the tensioner guide is big enough, the crowned part of the cylinder will slip to the next notch of its counterpart on the bottom of the tensioner housing, minimizing any mechanical play. So if you're saying that there is no crowned pattern at the bottom of the cylindrical part of the tensioner housing to match the crown of the spiral-slotted piece, this doesn't sound right to me - or at least it doesn't match the tensioner design on my 87' K100RS.


    true, there ist a ratcheting mechanism to avoid the tensioner falling down to the lowest position when the engine stops.


    Zitat von "TomPIT"

    3. I would not apply any excessive force, i.e., using a lever or other tool to increase the chain tensioning force. The tensioner has a ratcheting mechanism. Any excessive tensioning may result in higher loads on the camshaft and crankshaft bearings. The spring inside the tensioner should generate sufficient force to achieve the correct tensioning.


    almost true: see 4.


    Zitat von "TomPIT"

    4. I don't believe that the oil pump and oil pressure has any significant effect on the tensioning force. The oil supply orifice is extremely small and the oil leakage due to the tensioner clearances is soo large that there shouldn't be any significant pressure build-up underneath the tensioner piston. I would claim that the oil is for lubrication only.



    The main force for the tensioner comes from the oil pressure, that is why a slack chain makes rattling noise, after starting the engine and before the tensioner has been fully activated by oil pressure. That also is the reason for the ratchet mechanism, the tensioner should not fall to zero position, without oil pressure. So a bad oil pressure can have an effect on the tensioner, but I guess, the effect on the rest of the engine will be worse. If the tensioner doesn't tension as it should, you will hear a rattle from the timing chain.


    :mrgreen:

  • I wIll try to explain how this is supposed to work: Oil pressure pushes the tensioner up und the lower part is pushed down. The lower part with the ratchet turnes at the same time because it is guided by that curved groove. If oil pressure goes down again (eingine stopped) the ratchet avoides this whole assembly to fall down again, as so the tensioner is kept up into a "high" position. The assembly will automatially adjust towards longer, and stay longer by these means, as the chain is getting longer and slacker by the time.
    I hope, i could express myself clear enough for you to give a hint, how this setup is supposed to work. :mrgreen:

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