FP4NC Flip Emergency IC engine repairs
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  1. #1
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    Default FP4NC Flip Emergency IC engine repairs

    Some light entertainment here....
    Big scramble this week.
    Have an Alfa Romeo 6-C 2500 engine that is nearing completion that needed some TLC.
    This is an engine that Alfa made is some numbers from 1938 through 1952.
    Twin cam iron block with an aluminum head....
    Anyhow this project was just back from running on the dyno...in effect finished.

    On the post Dyno work the spark plugs were removed to install a fresh set....
    Trouble is that the head originally built with 18mm spark plugs, has had inserts fitted to allow use of 14mm plugs.
    Of course a number of the inserts decided to come out with the plugs, and in so doing buggered the 18mm threads.

    Normally this would be a small matter. Remove the head and set it up on the mill and install thread inserts to repair the damaged threads....
    Further it was deemed important to return the head back to using the 18mm plugs as originally built.
    Problem is that getting a new head gasket in short order (promised delivery schedule) was not in the cards........

    Now for those familiar with spark plug repairs, there is a relatively simple fix to over tap for an STI insert. Kit consists of a special stepped tap.
    Having the 18mm thread at the end for a short portion, and then a tapered reamer portion leading to the 18mm "STI" tap ....
    Theory is that the small thread starts in the original thread (what is left) and as you thread it in the tapered reamer portion opens the hole up to accept the oversize
    STI tap....This more or less gets the threads started true to the original plug thread, and gets a good hole for the oversized tap portion....

    Well here this setup does not work! The head is made with what i call a "fire slot" ...the spark plug actually fits into a bore that has a floor that is machined with a small slot
    that enters the actual cylinder chamber....This arrangement was used by Alfa in lots of their engines...Seems to give better control of the burn with poor fuels.
    Anyhow the net effect is that there is no through hole into the chamber so no trick aligning tap.

    Solution seemed to be that there needed to be an accurate way to drill and tap the insert hole/threads....All requirements pointed to using a machine.....


    We own two Deckel FP4NC's. An early "camel back" that i run almost every day...fitted with the "Tool Makers Table" (2038)
    And a later "Flip" having the rigid table.....

    It was decided that due to height needs the "Flip" was the best option. Having the rigid table mounted roughly 3.5" lower than the 2038 would provide just enough vertical height to
    enable my repair [plan.



    So here is the basic setup:
    Fully assembled engine, stand up on bell housing mounting flange of the block.
    Use horizontal spindle to bore damaged plug hole and align tap for threading for thread insert....
    Fully assembled engine, need to contain any chips from entering the engine.

    Alignment to the plug hole was accomplished by tramming the ground shank of an 18mm tap run into the original plug hole.
    This allowed indicating in 2 planes using the top and side of the tap shank.....Adjusting the engine to be flat in the horizontal plane was accomplished using feeler stock under the
    bell housing mounting flange and screw jack.

    Finding the center of the original plug hole was done using a modified spark plug.....Removing the insulator form a normal spark plug leaves a concentric ID bore that once the plug is screwed into the head
    provides an indicating surface to align the center of the machine spindle....





    As to the issue of chips....my solution was to make an adapter pipe that fit to the engine's exhaust flange.....
    to that pipe i connected a hose from the exhaust side of out shop vacuum.....
    The engine was rotated until the exhaust valve was open on the cylinder being repaired.....
    The vacuum turned on and air forced out during the machining operation......



    In all three spark plugs (of 6) were repaired.....In all a good job.
    In order to get to the final plug (#6) the engine was lifted and placed up on 2,4,6 blocks to give the needed height. Of course realignment was required after the lift......




    Side note here:
    In order to do this job, i needed to remove and clean the "X" axis scale. Machine had been down with a fault on the scale, and this job pushed that repair to the front....

    Cheers Ross

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    Ross,

    Always nice to see the interesting and creative work that you do. It makes me feel nervous to see what must be a few hundred pounds of engine apparently sitting half over the edge of the table tippytoe on 123 blocks. Is there a safety line going up to something solid overhead? Or have you done this so many times that you are confident it will stay put? Just wondering if you have some system for this or a trick up your sleeve that we could imitate.

    Cheers,
    Bruce

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    Bruce:
    The engine was hoisted to the table using a hydraulic shop crane. If you look closely you might see the slings still in place on the end of the engine, but the crane is disconnected once the engine is in place..
    No sky hooks or other safety as i need to be able to move the table to find center and check tram...

    You are correct in that the engine is sitting half way on the diameter of the rear bell housing flange ...needed the distance in order to get tooling in place between the machine and the engine....
    Forward portion is the block (cast iron) while the overhanging portion is the sump (aluminum) and of questionable value in making things more stable.

    Once set on the table , i did test the engine to see if it wanted to tip forward or back when the tension was slackened...This engine was pretty neutral.
    Heavy iron like this if setting on a relatively flat surface tends to stay there...unless shoved or nudged to upset its balance....
    The flange was also clamped using hold downs to keep everything in place. In all it seemed pretty stable...better than some i have done.
    Cheers Ross

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    Ross

    what steps followed application of boring head?

    is spark plug type long or short insulator?

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    J:
    After boring to the STI (Heli-Coil) tap drill size , i cut a small chamfer at the start of the bore using a standard 82* countersink.
    Did this to aide is starting the tap.

    Starting the tap needed a bit of help. The repair kit as stated earlier comes with a special tool that guides the oversize tap. To run this job without being able to use the the special tap i was left with the finishing
    tap from the kit. *(bottom) which was good to get to the bottom of the spark pulg bore, but a bit grumpy at starting...

    Changed to a tool holder that had a 60* center point on a relatively short 1/2" tool>(drill rod , turned to 60* on the end and flame hardened/quenched at the point end)

    Center was used to support the 18mm STI tap , followed into the hole using the sensitive quill of the spindle. Tap run in using an end wrench on the flats (no room for a proper tap stock)

    After threading , a corrected for length (shortened an over length thread insert) , the thread insert is installed using the install sleeve and mandrel....then the final was to use a pin punch
    to break off the thread insert install tang......

    All pretty simple, but long on initial setup.....

    Spark plug is an 18mm, 3/4" reach, non projected tip style plug.....
    Cheers Ross

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    Quote Originally Posted by AlfaGTA View Post
    J:
    After boring to the STI (Heli-Coil) tap drill size , i cut a small chamfer at the start of the bore using a standard 82* countersink.
    Did this to aide is starting the tap.

    Starting the tap needed a bit of help. The repair kit as stated earlier comes with a special tool that guides the oversize tap. To run this job without being able to use the the special tap i was left with the finishing
    tap from the kit. *(bottom) which was good to get to the bottom of the spark pulg bore, but a bit grumpy at starting...

    Changed to a tool holder that had a 60* center point on a relatively short 1/2" tool>(drill rod , turned to 60* on the end and flame hardened/quenched at the point end)

    Center was used to support the 18mm STI tap , followed into the hole using the sensitive quill of the spindle. Tap run in using an end wrench on the flats (no room for a proper tap stock)

    After threading , a corrected for length (shortened an over length thread insert) , the thread insert is installed using the install sleeve and mandrel....then the final was to use a pin punch
    to break off the thread insert install tang......

    All pretty simple, but long on initial setup.....

    Spark plug is an 18mm, 3/4" reach, non projected tip style plug.....
    Cheers Ross
    Why did you not just mill the threads? Seems it would be a lot easier than screwing around with that tap.

  10. #7
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    I did not thread mill the threads for several reasons....
    First and primary is i did not have the head room.....Length of the engine on the table was almost at the full "Z" travel....no room to contour the bore for
    thread milling.....Doesn't seem like much, but i was at the limit. That is why i went with the machine that i needed to repair the "X" scale to begin with,
    as having the rigid table gave me just enough height.....

    The second issue at thread milling is in gauging the thread.....Not a rigid insert, so size is a bit variable, and becomes a problem if you install the insert in a thread that is undersize...then the plug won't
    go in the hole...Becomes a problem to rework as the insert is fitted and can be difficult to remove...Possibility of damage.
    Could i suppose use wires to mic the tap, then make a thread gauge to check the thread milling...but by then the tap would have already done the repair.

    As to the tap...pretty straight forward and pretty fast. Got good quality threads And i already owned the appropriate tap.

    Cheers Ross

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