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Dino Saga 051127

Discussion in 'Corbani's Corner' started by John Corbani, Nov 27, 2005.

  1. John Corbani

    John Corbani Formula 3
    Honorary Owner

    May 5, 2005
    1,153
    Santa Barbara, CA
    Full Name:
    John Corbani
    #1 John Corbani, Nov 27, 2005
    Last edited by a moderator: Sep 7, 2017
    Dino Saga 051127

    These threads have concentrated on the past. Now to the present.

    About a month ago I decided that there was so much wrong with last year’s engine rebuild that I had to start from scratch. Low compression, smoke, leaking and burning oil to the tune of a quart every 150 miles. Every time I found another cause of a problem, abominable workmanship was a key factor. The mechanic was out of business, just divorced and unfindable. The shop itself had been bulldozed and was now a parking lot. Oh Joy! Funny thing was that car ran like it’s old self. Strong again. But I had no faith that it would last any given day.

    The machine shop that had done valves, guides, pistons and bearings said that they would take on the task of tear down and rebuild if they could have some help. I went to talk to my old mechanic from the 80’s, Jack Bianchi. Jack is an F 250 owner and has worked on exotics since the 50’s. He pulled my engine shortly after I bought it. Broken head stud. His rebuild lasted 18 years and 130,000 miles. He dropped exotic mechanical work and concentrated on bread and butter insurance body work during the 90’s. He is getting older now (as am I) and has turned the body work over to a younger crew. He has has returned to playing with exotics. He agreed to pull the engine, kibitz on the rebuild and put everything back in the car.

    As the pieces came apart we found more grief. Many nuts were loose,conical spring washers had been replaced with flat steel washers, parts were bent or broken, hardware in pan, silicone sealant bits and strings everywhere. Some assemblies had never been completely apart, o-rings never replaced, seals bent or torn, bolt locks broken or missing entirely. The only major parts found bad (so far) are the cam chain rubbing pads and the pistons themselves. One rubbing pad was broken. The other worn. The pistons showed marks where the exhaust valves had just touched the sides of the piston reliefs. All gaskets and seals needed replacing.

    Pistons were custom made and the company said they could fix easily. Be back next week. Valves, guides, main bearings appear fine. Called GT Car Parts in Phoenix and they had everything else in stock. I ordered last Friday evening, they shipped Monday, parts got here Wednesday afternoon. Good guys. Fair price. Happy Thanksgiving present. Next week we start putting things back together.

    Tried to figure the broken chain guide. Old mechanic had said that he had trouble with new chains, too short. He said that he just barely got sprockets on cams. Pics show chain tensioners clamp nuts. They had never had the lock screws retracted. No wonder he had problems. The lock screws and nuts do not show on the drawings and are not mentioned in the tension setting instructions. I did the heads myself about 10 years ago and learned the drill. Lock screws were where I had left them after last check with 33 year old chains.

    Do not know if the lock screws are factory or were done later. I have seen another Dino with the screws so probably an early mod. When you set chain tension, you loosen large clamp nuts allowing spring tension to tighten chain. Turn engine over two revs and tighten tensioner clamps. Tension is set.

    BEFORE you can even install chains, the tensioner lock screws and their locking nuts have to be completely retracted, Tensioner spring completely compressed and clamp nuts tightened to hold everything together. Spring is very powerful and can get loose. Idler sprocket guide rod can go clean across shop and through 1/4" plate glass window when that happens. Found out the hard way!

    Once tension is set as above, the clamp nuts are tightened, the lock screws are turned in until they touch the guide rod and the lock nuts are tightened. THEN you are done and the chains can not come loose if the guide rod starts to slip in its collet.

    Pics show some of what we found. Will keep you up to date on the re-rebuild.

    Patience,

    John
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  3. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,858
    John - the tensioner lock screw was a late modification out of the factory. Most experienced mechanics read of the modification and performed it on early Dinos as they came to need engine work. I modified 5 Dinos along the way, but recently found this modification on a 1973 GTS that had not seen its engine removed or worked on in the past. Further inquiry confirmed that this modification was a factory update during late 1973 through end of the series.

    And yes, you mention a very important point. The tension is properly set by the spring alone. Some have been known to use the set-screw to add a little extra tension before tightening the collet. This is a no-no and can lead to chain or bearing failure.

    Jim S.
     
  4. Gary48

    Gary48 Guest

    Dec 30, 2003
    940
    John, I too have done the screw modification because the locking collets just don't do the job of holding the spring shaft ( as the factory had obviously found out). I had found that on one side the spring also did not do its job of tightening with new chains and two turns of the crankshaft, so I used the jacking screws to tighten to the same values of the good side. Sometimes you just have to follow your gut and go with what works. At any rate it runs great and as good as its ever run. Good luck on your second rebuild.
     
  5. lm2504me

    lm2504me Formula Junior
    Silver Subscribed

    Aug 26, 2004
    736
    Nipomo, CA
    Full Name:
    Richard
    Gary,
    I too found one side to be too loose after turning the motor by hand with the tension collet loosened. I compared the both sides and one was too loose. I tightened it to the same tension as the Dino 206 using the jacking screws. Skipping a tooth is something I don't want to go through. Another local Dino 246 owner skipped a tooth on his front bank from lack of tension on the chains by the previous owner. Whenever I check the valve clearances, I always check the tension on the chains to ensure they are not too loose.

    Richard
     

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