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Dino cam chain tensioning

Discussion in 'Technical Q&A' started by mikeyr, Jun 17, 2004.

  1. mikeyr

    mikeyr Formula 3

    Jun 17, 2004
    2,155
    Santa Barbara, CA.
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    Mike Rambour
    Forgive the intrusion, its not a Ferrari but it is a Dino motor.

    I recently purchased a FIAT Dino Spider and as I go through the motor getting it ready, I found that my cam chain is loose on the passenger side of the motor. I have found that my motor is butchered with a mixture of later and early heads. On the one early style head, there is a lock nut on the front of the head that you loosen and then can tighten or loosen the chain tension. I have one of these heads on my motor.

    The other head uses what I believe is the 246 style of chain tensioning, that is some type of spring adjustment. How does one adjust the chain tension on a 246 ?

    By the way on a 206 Dino the chain tension is 7mm deflection with 20kg pull, is that the same on the 246 ? or do the springs take care of it ? I have the manual for the 2Litre but not the 2.4Litre.

    The motor did run when I purchased the car a month ago, it ran very poorly with welded centrifugal advance weights in the distributor (timing was forced somewhere around 30BTDC so it would not idle but ran nicely at high RPMs) and approx. 15 year old gas in the carbs but it ran so I dont think the mixture of heads will be be a factor once I adjust the tension and put it back together. I am fantasizing getting the car on the road this weekend as I have all the other parts finally.
     
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  3. vincent355

    vincent355 F1 Veteran
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    Apr 8, 2003
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    Awesome!

    I remember reading in Forza that these were the same motors. So you're measurements for tension should be the same. I've just moved so I can't find the issue (disclaimer). But there was a side by side comparison of these two cars and they had the same powerplant.

    Post a pic please.
     
  4. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Steve Magnusson
    The 246 chain tensioner design seems to be similar to the 308 belt tensioner design in that a large coil spring (working in conjunction with the chain path geometry) is used to initially set the chain tension, but then the whole assembly seems to be physically locked into a fixed position (or held within some restricted range) by some sort of threaded fastener mechanism with a lock nut. The wild thing is that the mechanism for "retensioning" the 246 chains is designed to be accessible from the outside of the engine so they give instructions in the OM for when things get a little noisy. Below are the SPC illustration from the FerrariUK site and what's shown in the 246GT OM.
     
  5. mikeyr

    mikeyr Formula 3

    Jun 17, 2004
    2,155
    Santa Barbara, CA.
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    Mike Rambour
    Thank You, THANK YOU... I will try that this evening, I assumed it would be easy just not that easy. Well I have to move a few things first, like the thermostat housing so it wont be totally easy. I rebuilt the distributor last night and it might even fire tonight.

    So the only question left is, after following the steps for tensioning, do you check it with a guage and ruler like the older style or just assume it is ok because the springs tensioned it ?

    As far as pics go, I assumed no one would want a pic of non-Ferrari Dino but I will post one this afternoon. It is the same motor as the "true" Dino but in front of the car and maybe de-tuned slightly, some say it is, some say it is not.

    Mike
     
  6. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Steve Magnusson
    You're welcome Mike -- glad to help out a relative ;). You should try asking at the www.owners.ferrari.com site if you could be allowed registration so that you could get the 206/246 car manuals and access to the 206/246 SPC stuff at the FerrariUK parts site.

    My guess would be that F probably didn't give a specific lateral deflection vs lateral force spec and just relied on the spring to do the deed -- but I'd be very surprised if it wasn't in the same ballpark as the one you quote (if the chain size and sprocket path/geometry is similar) -- but I'm only guessing and the 246-ers/professionals should speak up. If you've got the access to make a lateral deflection vs lateral force measurement it sure wouldn't hurt IMO to note what it is after making the adjustment for future comparison.
     
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  8. mikeyr

    mikeyr Formula 3

    Jun 17, 2004
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    Mike Rambour
    #6 mikeyr, Jun 17, 2004
    Last edited by a moderator: Sep 7, 2017
    I did consider joining the owners site you mentioned but they want a VIN number and mine would not match up with a Ferrari VIN, still I will try.

    Here is a picture of my FIAT Dino, assuming I did this right.
    Image Unavailable, Please Login
     
  9. racerboy9

    racerboy9 Formula 3
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    Nov 3, 2003
    2,070
    Get that timing chain tension right before you fire it up or you may have problems. The later 246 tensioners had a positive stop in the form of a bolt that threads into the external part of the tensioner (sleeve nut in the picture) and is secured with a nut. Earlier versions without the nut can be modified by drilling and tapping a hole in the sleeve nut and installing the bolt and lock nut. The earlier version tended to back off (lose tension) and so the bolt and nut were added as a positive stop to prevent this happening. The hand book say to loosen the sleeve nut a couple of turns and then turn the engine over by hand 2 or 3 times and then retighten the sleeve nut. I always tap on the sleeve nut LIGHTLY with a tiny hammer before I turn the motor over. Once the sleeve nut is tight screw in the stop bolt till it hits the tensioner end and then tighten the lock nut. Personally I would get a manual and check the cam timing and valve clearance before I did the tensioners. Don't get in a rush to get it running. Set the head up right, check the timing, balance the carbs and then have fun.
     
  10. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,858
    MikeyR - Racerboy9 has it right. Perhaps I can add a little description.

    1) Tension is pre-calibrated with the spring. It sets the proper tension. No measurement of the chain is required.

    2) Loosen the nut on the end of the tensioner mechanism. This opens a "jaw" that clamps the spring piston. The spring piston compresses the spring and forces the tensioner gear onto the chain with proper tension. With the jaw opened, the spring piston and gear will slide freely up and down the tensioner housing. I usually move the engine with a large socket on the pulley bolt. I rotate the crankshaft back and forth a few degrees to free up the spring piston, as Racerboy9 does with a tap of a hammer. It should slide freely, but may seize in the bore. Tapping or rotating the engine will free it to "spring" back at the chain. After rotating or tapping, I then turn the crankshaft several times in the normal direction of rotation (don't go opposite as this will cause the chain to push the tensioner too far back up its bore). I then tighten the end nut good and snug.

    3) The next time you have the engine out, or have the desire to get dirty, you can remove the tensioner mechanism from the block. A recommended modification (which I have done on 4 Dinos) is to drill and tap an 8 mm screw through the nut on the end of the tensioner mechanism. After adjusting the chain tension and snugg’ing up the 15 mm nut on the end of the tensioner mechanism, one then turns the 8mm screw down until it bottoms on the spring piston. A turn of a lock nut on the 8mm screw to "lock" it and you are done.

    The jaws cannot get sufficient purchase on the spring piston, and the piston has a tendency to creep back up with consequent loosening of chain tension. That is why the modification is performed.

    Have fun.

    Jim S.
     
  11. mikeyr

    mikeyr Formula 3

    Jun 17, 2004
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    Mike Rambour
    Cool, it seems to have worked, the chain is still looser than the other side which was set the "old" way by using a tension gauge and screwing in the adjuster. On the other side, the new style with the spring loaded tensioner I followed the instructions provided here and it tightened the chain up quite a bit so it must have worked.

    Once again Thank You.

    I do have the correct manuals for the 206 car but that style of chain tension is from the 246 and i dont have those manuals. I am wondering if I have a 246 head on a 206 motor or just someones modifications but I will worry about that when I rebuild the motor this winter.

    I had already checked the valve clearances and more importantly the valve timing since the car has been so butchered in its previous life that I am checking everything prior to running it again. I got the valve covers on and I am fairly certain all is well. I also got the distributor back together with new weights and springs and have it static timed. I did however find that the fuel pump was wired "wrong", when trying to set the static timing I pulled the fuel pump fuse and the pump kept running...oops. I eventually pulled every single fuse in the car and the pump kept running so I was working on that instead of trying to make it run, it was wired straight to the ig. switch bypassing the fuses. Fixed that and now I am going to check some other electrical stuff, I dont like Dinos to pretend they are candles. Tomorrow I will fire up the motor not the car and then will rebuild the carbs after I get it running a little. I belong to the "break one thing at a time" club and didnt want to dismantle the carbs until I had the ignition back together.

    This weekend if you are in S. Calif. and see or hear a beautiful Dino, wave and say hi...its not a "true" Dino but it is MY Dino.
     
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  13. Adds406

    Adds406 Rookie

    May 17, 2011
    26
    Hi sorry to trouble you, have removed the cam covers on a 246 Dino and marked the cam positions before I started, I was trying to replace the paper gasket under the spring loaded tensioner. I've hit a snag I can't get the tensioner back into the head. Despite blood , sweat tears and pleading with it.
    Anyone have any hints...
     
  14. swift53

    swift53 F1 Rookie
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    Nov 17, 2007
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    Alberto
    A very large flat screwdriver ought to push back the tensioner in place, if anything like an Alfa Romeo.

    Have not assembled my Dino yet, so only guessing as the two systems appear to be quite similar.

    Of course, in this crazy society, I assume zero responsibility.

    Regards, Alberto
     
  15. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    27,086
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    Brian Crall
    Tensioner needs to be completely collapsed then locked prior to installation.
     

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