I6 250 '76 Upgrades - ready to roll

Discussion in 'Technical' started by bobdobbs, Apr 26, 2016.

  1. bobdobbs

    bobdobbs Member

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    Tax return is here and I'm ready to put in an order. I have my head removed and I'm going to swap the timing set while I'm in there.

    machine shop
    -valve job
    -shaved head (.025" to compensate for the thicker gasket (original gasket is .025 compressed thickness and aftermarkets are .050 or so)
    -2v conversion

    shopping list
    -pre-72 timing set
    -oil pan gasket
    -timing chain gasket, chain snubber, and oil seal
    -head bolt washers (per falcon performance manual)
    -head gasket (felpro?)
    -valve cover gasket
    -carb & linkage (haven't decided yet)

    Procedure:
    -Remove radiator
    -Remove pulleys and pan
    -Remove harmonic balancer (buy or rent tool for this)
    -Swap timing set
    -Put it all together

    For those of you that have done either of these jobs, is there anything special I need to look out for? The manuals I have are pretty vague. For instance, does the oil pan come out without much fuss?

    Also, anything else I should do while I'm in this deep?

    Is there really any value in installing the 3/4 exhaust port splitter? I will be using headers from C.I.

    Thanks
    Cody
     
  2. 71gold

    71gold Frank Cooper Supporting Member

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    how many miles on the engine?
     
  3. rthomas771

    rthomas771 Member

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    I'd shave the head .050-.075 for more compression (per falcon performance manual) or you will be in the same low compression boat that you're in now.
    Got to drop idler arm from frame rail to remove oil pan...might have to jack engine up an inch on driver's side also. Install chain snubber before installing oil pan or you want get it back on. Re-curve the distributor to advance faster with weaker advance spring. You you got many miles on the engine...the rings will be the weakest link with fresh head and valves that seal.
     
  4. bobdobbs

    bobdobbs Member

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    Hi Jeff. I'm still doing research (math) about how much to shave the head. My falcon performance manual (great book!) refers to some online calculators, but those links are dead. Know any good ones?

    The CI site lists the stock rocker assembly as good to use with up to .125" shaved. Assuming this doesn't account for the thicker aftermarket gasket, I can probably shave 150 thou off the head without messing with new pushrods or rockers.
    http://classicinlines.com/rockeroptions.asp

    I'm just not sure I'm going to get much bang for the buck out of added shaving, higher compression, at this point. I could see spending the money and time on phase 2, but not now. Unless you have a set of roller rockers you are giving away ;-)

    Frank, the odo says 60,000 miles, but I can't trust that. It was someone's project car, then owned by an acquaintance for a while, then sold to me. It does have good compression and no smoke, so I believe the rings are in decent shape, and I'm (probably) not going to hotrod it enough that they'll be an issue.
     
  5. 71gold

    71gold Frank Cooper Supporting Member

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    it would have been nice to have had compression #s before tear down, just to compare.
     
  6. bobdobbs

    bobdobbs Member

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    Well I got the pan dropped but not out. It comes close to coming out with the stabilizer bar removed, but not quite. I'm going to pull the two bolts holding idler arm to the frame and I think it will clear. Had to pull the starter back to get to a few of the pan bolts.


    [​IMG]
     
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  7. bobdobbs

    bobdobbs Member

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    I've about decided to 85 or 90 thou off the head. 25 thou to make up for the aftermarket gasket and another 60 for added compression. If I add .060 washers to the head bolts and rocker shaft shims to keep the geometry correct, it should be fine. Falcon Performance Manual covers this pretty well.
     
  8. falkon

    falkon Member

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    Not sure if they make one but a double roller timing chain, I put one in my 200 from classic inlines but I don't see one for the 250, I can't remember who made the 200 one. If your shaving the head that much plus the new style thicker head gasket you may need a custom length pushrod to, I used mantonpushrods, very quick delivery and excellent quality
     
  9. rthomas771

    rthomas771 Member

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    You could also add shims under the rocker arm pedals or use early 60's adjustable rocker arm.

    100_2384.jpg
     
  10. groberts101

    groberts101 Member

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    Have to be careful taking everything as the gospel or factoring in some loss of interpretation. If you look at the chambers on the I6 head it will become obvious that due to the dual quench pads(larger and smaller flat pads) located on both sides of the chamber.. that simply removing .025 thou more while milling them will not equate to the same volume as that additional .025 of thickness being added to the gasket thickness. The gasket is also bigger than the bore so you lose a tiny bit of additional volume there as well. Best way to know for sure what you have is to cc the heads. Very easy to do with small piece of plexiglass and cheap syringe.

    Or at least cut some of the expectation for reduced compression volume down to a much more realistic goal of around 1.2 cc's per .010" milled or reduced deck height. Simple physics shows that the smaller CID motors and bore sizes just don't respond to milling and deck height reductions like the bigger motors do. Typical V8 engines having 4" bores are around 1 cc volume reduction per .0065" milled. Larger bores with open chambers can be well more than that. Even more compression can be gained via deck height reductions/pin height increases and smaller piston dish volumes than by head milling alone.

    Also be aware that the previously mentioned .125" figure was not derived from just the cylinder head milling alone. It is typically achieved through combinations of head milling AND deck height reduction/pin height increase. The CI site specifically mentions..

    "when the cylinder head and/or block have been milled more than .125" to increase or maintain the C/R."

    "FYI: All small six cylinder heads can be safely milled .090". If you need to go more than that you should do some sonic testing to determine the thickness of the cylinder head deck. You should maintain at least .100" thickness to have a good, true, solid mating surface. If you have to go more than that to achieve your desired C/R, you really should consider decking the block, using different pistons (flat-top), a taller pin height, or off-set grinding the crank."

    Just keep in mind that taking shortcuts by leveraging all the cc reductions in the cylinder head alone can potentially lead to gasket sealing issues as the heads deck gets thinner(not an overly thick casting to begin with and it's also quite long) and especially a concern if this motor ever gets hotter than normal(more compression, rpm, and power automatically = more heat production). The margin for durability could become paper thin. I've built up and blueprinted well more than a few motors, including these little guys years ago, and not trying to burst bubbles here.. just trying to help.
     
  11. OLD GOOSE

    OLD GOOSE Member

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    i'd save my money and put in a v8 I rebuilt a 250 six just like you are going to do it was still a slug
     
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  12. bobdobbs

    bobdobbs Member

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    Very good points groberts101, and I've been around long enough to value your experience over guesswork and theory. I'm going to cc the chambers and see if I can find a good formula to find a sweet spot for how much to mill. All the links for formulas from the falcon manual are dead. Do you know any good ones?

    p.s. I may pull the motor and do a low-end rebuild & mill at a later time, but this is the 12th year I've owned this beast. If it sits over another winter, the wife is gonna light it on fire and make me watch it burn.

    p.p.s Has there ever been an I6 thread where someone doesn't say, "F this, put in a v8."
     
  13. OLD GOOSE

    OLD GOOSE Member

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    no never you can buy a running 302 for 5-7 hundred bucks the payoff is way better than a six
     
  14. groberts101

    groberts101 Member

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    Thanks Bob. Nice to be appreciated and understood as just trying to be helpful vs the know-it-all that some may assume I'm trying to be.

    Too bad you don't have experience?.. with a grinder and carbide bits/tootsie roll sanding cartridges. You can really help these longer stroked motors make far more low rpm power than some may ever realize. As big a following as a V8?.. or as many supporting parts and maximum bang for the buck.. no. But they can still surprise many an unsuspecting and slower reacting driver of much more powerful cars.

    Typical hotrodding rules and tricks still apply to all shapes and sizes of ICE's and some get too caught up on doing it just like everyone else does it. Which is just plain boring if you actually enjoy being unique.

    More Induction, Exhaust, Compression, Cam, Spark = more fun without having to break the bank while doing it. Just do what you can right now(don't forget the positive style valvestem seals!).. and finish up the bottom end later on.

    PS. Wallace racing calculators has really good tools for engine calculations and design. I use it often and it's pretty damned close because that guy's an ace in mathematics.
     
  15. 71gold

    71gold Frank Cooper Supporting Member

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    "I'm (probably) not going to hotrod it."

    yep...at the end of the day...it's still a six...I've been there done that...:yup:
     

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