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246 chain malady

Discussion in '206/246' started by Gary48, Sep 13, 2005.

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  1. Gary48

    Gary48 Guest

    Dec 30, 2003
    940
    #1 Gary48, Sep 13, 2005
    I am having chain noise problems on my 246 after an overhaul. We adjusted the chains according to the workshop manual to no avail. At overhaul we did not install new chains as they were replaced 10,000 miles before the overhaul. Perhaps the chain tentioners have exceded their limits with stretched chains. We had success ajusting the chains once, but not the second time. Any hints much appreciated.
    Has any one replaced the chains with the motor in the car? Does there exist replacements that are superior to o.e.m.?

    Gary
     
  2. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,089
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    #2 Rifledriver, Sep 13, 2005
    Pay VERY close attention to the condition of the jackshaft bearings. Many have thought as you do but the real culprit was a failure of the jackshaft bearings. That is not to say it may not be chains, those get changed like underware but the bearings are a serious weak link as well.

    The entire cam drive in that motor was problematic.
     
  3. Gary48

    Gary48 Guest

    Dec 30, 2003
    940
    #3 Gary48, Sep 13, 2005
    Rifledriver. something in the back of my head suggested to me to double check this area as the idler jackshaft bearings appear to be a little under-engineered in the size department, so I used the best bearings that I knew and which were available. I replaced the old, very loose bearings with SKF. I wonder if there is anything out there that might be better?
     
  4. lm2504me

    lm2504me Formula 3
    Silver Subscribed

    Aug 26, 2004
    1,122
    Nipomo, CA
    Full Name:
    Richard
    #4 lm2504me, Sep 13, 2005
    Gary,
    I know what the workshop manual says, but I will always verify the tension of the chains between the intake and exhaust sprockets. This is done with the valve covers off. I may be going overboard, but I don't want to do a valve job.

    For the 206 Dinos, I would adjust the tensioner for a tension on the chain which you check by applying 44 pounds of force between the sprockets in the upwards direction and measure 9/32 of an inch deflection. I have made the normal adjustment per the 246 workshop manual and have found the tensioner rod will sometimes jam and not apply the full tension to the chain.

    Have you checked the tension of the chain by hand or scale?


    Richard
     
  5. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    #5 jselevan, Sep 13, 2005
    Gary - you mention an overhaul. Was the Dino engine completely torn down? If so, I assume that you replaced the rubber runners that sit in the head opposite the tensioner mechanism. If not, the rubber may have been worn, and now the chain is hitting the metal seat.

    This would occur if the chain were a bit too loose. Sounds like you tensioned them properly. Did you modify your tensioner "chucks" with the 6 mm (10 mm head) bolt drilled through the cap of the tensioner chuck? This acts as a stop, preventing the tensioner piston from creeping back into the chuck. If not, this might account for a now-loose chain.

    Finally, yes, you can remove the chains with the engine in the car, should you find this necessary. First, recall, or carefully inspect your chains to see if there is a master link. This makes life very easy. Simply remove the master link, twist a length of copper wire to one end of the chain, and tease the chain around the lower gear, pulling the wire along with it. The wire will now be used to guide the new chain around the gear and into position. The copper wire also keeps you from dropping the chain into the front case.

    If you do not have a master link, you can stuff the front case with rags and cut the old chain. Use a hacksaw or torch, being careful of all the flying metal that it does not fall into the engine somewhere. Now install a new chain with a master link.

    By the way, the chains were previously available from Reynolds (with master link). These were used on motorcycles during the 1960s and 1070s.

    Jim S.
     
  6. Gary48

    Gary48 Guest

    Dec 30, 2003
    940
    #6 Gary48, Sep 13, 2005
    Jim and Richard, thank you for your very good tips and hints. It seems that the the collets that secure the tension provided by the spring, has slipped on us twice, which has us confused a bit because we have tightened them well. The securing 6mm screw is a new one for me and certainly an added fail safe. This is something we will implement before digging into the engine. When assembling the new engine the chains were very snug and every thing appeared in order, but after about 100-200 miles the noise came back. So after your very good advice it seems that we cannot keep them secure. The rubber chain slides that were mentioned were in very good condition with only one showing very slight wear. It seems clearer now what I must try. Sometimes when loosening collets, simply loosening the nut will not do it, so you must give it a jar by striking it with a brass drift and hammer to get full release and then go ahead with the re-adjustment. We did not do this the last time. Kudo's to you guy's for getting our heads engaged and my thoughts are that a combo of these ideas will serve us well, at least worth the try before chain replacement.

    Best regards

    Gary
     
  7. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    #7 jselevan, Sep 14, 2005
    Gary - yes, you must "convince" the tensioner to spring out and press against the chain. I have accomplished this by rotating the crank backwards a few degrees while the collet is loose. This will force the shaft deeper into the collet, and then when rotating in the correct direction it will snap back with force as it should.

    If you need more detail on the modification to prevent the shaft from slipping in the collet, let me know. I can take a picture. It is quite easy once you remove the mechanism. Drill and tap the middle of the cap to accept a 6 mm (maybe 8 mm - the same size as the cam cap and cam cover studs - whatever those are) screw. Secure with a copper washer to prevent oil seepage, and use a locking nut. Loosen this new screw all the way out. Adjust the chain tension. Then advance the new screw until it touches the bottom of the shaft, and then give it a 1/16 turn for preload. Then secure the lock nut, and that's all she wrote. The shaft will not slip again.

    Jim S.
     
  8. Gary48

    Gary48 Guest

    Dec 30, 2003
    940
    #8 Gary48, Sep 15, 2005
    Jim good ideas! After all this I have a confession. I have realized that during my zealous pursuit of friction reduction, during assembly I had applied by spray a coating of teflon on these very plungers as I did on bearings ect. so the contact area of the collets was coated with teflon and probably the very base of my problem. I still will implement your idea of the stops as this will prevent future slippage, so, I am humbled again and continue to learn all the idiosincracies of this little beast. Thanks again.

    Gary
     
  9. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    #9 jselevan, Sep 15, 2005
    Last edited by a moderator: Sep 7, 2017
  10. Gary48

    Gary48 Guest

    Dec 30, 2003
    940
    #10 Gary48, Sep 15, 2005
    Jim, I see the modification perfectly and I understand. I think that this is a major advancement in creating or perfecting a slightly imperfect mechanical system and building in dependability. Thanks for the pics. I do know that when the chains started to loosen, performance also deteriorated as the cam timing also changed. I hope others benefit from these hints.
     

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