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Thread: Making a Piston Stop from an Old Plug

  1. #1
    Yuuuuuupppppp... P72Ford's Avatar
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    Default Making a Piston Stop from an Old Plug

    Hey guys,

    I have heard of folks doing this in the past, and was wondering if anyone here had done it, or not? I learned tonight that the conventional 14mm thread piston stops available do not work with the GT40P projected reach plug holes.

    So I attempted to bust the porcelain out of an old plug, which did not work well. I ended up mangling the plug. Is there a trick to this? Everyone talks about doing it, but there are no specifics for how to bust the porcelain out.

    Should I cut it with a cutoff wheel? Drill?

    I am going to measure and degree (shooting for a specific ICL) the HO cam I have, and I also want a definitive TDC mark to install the timing tape on my balancer.

    Any tips on making the stop?
    **1987 Ford CV Tudor; Far from stock, stock from far
    304, GT40P, HO (straight up), 1.7s, Air Gap, 600 DP, MSD, E fans, FRPP Shorties, Flowmaster 10s, Dirty Dog 3400 NLU, Silverox VB, B&M pan, stacked plate cooler, aluminum shaft, 3L73, big brakes/ rear disks, police bars, urethane throughout, 18x9/10 Bullits (F:275 NT555s, R: 305 NT05R DRs). TW170s and AFM N41 in stock and on deck. Faceplated TKO to follow

  2. #2
    Mazda5: the Anti-Van! 1987cp's Avatar
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    Nathan, you have disappointed me.

    j/k :banana:



    Basically, get creative smashing up the porcelain any way you can. Once the ends were broken up the best I could manage, I recall clamping the shell in a vise and chiselling out the insulator, bit by bit, with a flat-bladed screwdriver (don't tell James May!). If you have a selection of small chisels or punches, you're probably better equipped for the job than I was. Once the porcelain is out, you're of course home free to run your 3/8-16 tap through there and get on with it.

    You may recall that I screwed up by making my first piston stop using the wrong style spark plug, so I immediately got to do it again. On the first one, I ended up drilling a couple of holes through the side of the plug to get a better go at the porcelain. That stuff was STUBBORN! For some reason, the second time around I don't recall having to drill the holes, so possibly I'd been a little more clever with my chiselling, or else I'd gotten lucky and that one's porcelain was just less stubborn.

    I think I broke it all out of the top just by pinching it in a vise ....

    My best tips are go slowly, work at it for short periods of time in between other tasks if you need to, and get creative about busting that junk out of there any way you can while still leaving enough of the shell intact.
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  3. #3
    I post a lot... GoodSamaritan's Avatar
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    Oh, and remember that stuff is seriously sharp. I sliced my finger pretty good both times I've done this.
    Owner of the only known 5 speed box wagon with a lift kit.
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    Axle codes
    Open/Lock/Ratio #
    -----------------------
    G / H / 2.26
    B / C / 2.47
    8 / M / 2.73
    7 / - / 3.07
    Y / Z / 3.08
    4 / D / 3.42
    F / R / 3.45
    5 / E / 3.27
    6 / W / 3.73
    2 / K / 3.55
    A / - / 3.63
    J / - / 3.85

  4. #4
    Mazda5: the Anti-Van! 1987cp's Avatar
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    Sharp? Really?

    Seriously, I didn't notice. Maybe I got lucky and didn't press hard on broken insulator the wrong way. Especially since I'm the same idiot who managed to cut the BACK of my FINGER on a SHAVER! (techless tip: don't flap your brush around in the vicinity of your loaded Old Type unless you enjoy bleeding on stuff)
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  5. #5
    Yuuuuuupppppp... P72Ford's Avatar
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    I'm going to make another go at this tonight. I was reading a thread on sbftech that said something about cutting the crimp ring... but I don't recall the plugs having a crimp ring.
    **1987 Ford CV Tudor; Far from stock, stock from far
    304, GT40P, HO (straight up), 1.7s, Air Gap, 600 DP, MSD, E fans, FRPP Shorties, Flowmaster 10s, Dirty Dog 3400 NLU, Silverox VB, B&M pan, stacked plate cooler, aluminum shaft, 3L73, big brakes/ rear disks, police bars, urethane throughout, 18x9/10 Bullits (F:275 NT555s, R: 305 NT05R DRs). TW170s and AFM N41 in stock and on deck. Faceplated TKO to follow

  6. #6
    Mazda5: the Anti-Van! 1987cp's Avatar
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    What's a crimp ring?
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  7. #7
    The sly one sly's Avatar
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    I would think it would be the little rolled over bit of metal on top of the nut section of the plug.

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  8. #8
    Graham: Your source for car repair and smartassery. 91waggin's Avatar
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    WTF is a piston stop supposed to do? I'm not sure I understand.
    Quote Originally Posted by gadget73 View Post
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  9. #9
    The sly one sly's Avatar
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    when finding top dead center... you stick something in the cylinder through the spark plug hole that will stay put and NOT move. This causes a bump point for the piston. When you turn the engine, it will stop. you mark that point in relation to a mark on the balancer. Turn the engine the other way and mark the stop point in ralation to the mark on the balancer. The midpoint between these to marks is top dead center.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 88 MGM, 93 Vic, 82 Mark VI,
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  10. #10
    I'm an air-conditioned gypsy gadget73's Avatar
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    obviously you rotate the engine by hand when doing this. Trying to use the starter with a piston stop is a great way to punch a hole in the piston.

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  11. #11
    fuck no, not today, thank you kindly 1990LTD's Avatar
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    Quote Originally Posted by 91waggin View Post
    WTF is a piston stop supposed to do? I'm not sure I understand.
    likewise
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  12. #12
    Mazda5: the Anti-Van! 1987cp's Avatar
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    Slymer's description is pretty much all there is to it, though I can attempt a longer-winded explanation. The core issue is the concept that due to production tolerances, etc., the timing marks that come etched on your balancer may or may not be accurate. This is a problem when setting the timing or installing a camshaft, since both procedures are done with respect to TDC. Checking true TDC with a piston stop allows you to physically verify the accuracy of your timing marks, and if they're wrong, to ignore them and create a new point of reference.

    TDC means the piston is at the absolute top of its travel. If you think about it, it spends the rest of the crankshaft rotation further from the top than it is at that point, so if you can physically stop it at some point before and after TDC, you know that the point of crankshaft rotation halfway in between those points is true TDC.

    To use a piston stop, you yank all your spark plugs so it's easy to turn the crank by hand, then turn the crank until it's about 10 or 20 degrees past the indicated 0 degree mark on your balancer. You install the piston stop in the #1 spark plug hole and extend it till it hits the piston, then rotate the crank slightly away from TDC and back towards it until it hits the stop and you can't move it any more. You use tape or a paint marker to record that position on the balancer, then rotate the engine 300 degrees or so till it hits the stop again. Mark that position and use a tape to measure midway between your two marks. The result is the crank position at which your piston is at the absolute top of its travel.

    You then ignore whatever marks are etched on your balancer and use your new TDC mark either to apply a timing tape or use it as your reference mark when using a fancy timing light that's eqiupped with an advance knob.
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  13. #13
    Yuuuuuupppppp... P72Ford's Avatar
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    Cutting the crimp ring is the trick.

    The crimp ring is the ring above the hex on the plug, which holds the porcelain into the metallic portion. All I had to do was cut the crimp ring off (with a die grinder), crush the visible porcelain piece in the vise a little, and the rest just fell out.

    I drilled the plug center to 5/16", tapped it, and added a long eye bolt and jam nut. I still need to make a vent hole; maybe tonight.

    I also radiused the end of the eye bolt. This is important, because the stop is less likely to damage the top of the piston at all (not that you should be slamming the piston into the stop anyway), creating a hot spot.

    I am going to take the engine apart tomorrow. Changing the rear main seal, oil pan, front cover, timing set, and adding the eccentric. While it is apart I am going to check the torque on the lower end bolts. I am also going to measure the cam, degree the cam, and check the pushrod length/ lifter preload.

    I am hoping the pushrod length checking goes well. I know it can be somewhat involved with pedestal mount rockers, and I am going to keep it as rigorous as possible. I am looking for as much valve lift as possible, while retaining a thin witness mark on the valve, and keeping it as centered as possible on the valve stem. I already have the Ford shim kit for setting lifter preload once the proper pushrod length is determined, and have converted one of the lifters to solid for measuring purposes.

    Alot of folks are under the impression that you just put the stock pushrods in and crank down the rockers, and thats it. Unfortunately, that is a gross assumptiom. The puishrods in this engine may be the correct length, and everything may check out. However, I want to ensure that is the case. If it is not, I am leaving power and efficiency on the table, which is not an option at this point.

    To be honest... at this point I am half tempted to order some good heads and rockers, head gaskets, and a cam... but I have other priorities, and thats $2000 I could spend, but would rather not. Plus the hassle of checking PTV clearance, etc... but it would be fun.
    **1987 Ford CV Tudor; Far from stock, stock from far
    304, GT40P, HO (straight up), 1.7s, Air Gap, 600 DP, MSD, E fans, FRPP Shorties, Flowmaster 10s, Dirty Dog 3400 NLU, Silverox VB, B&M pan, stacked plate cooler, aluminum shaft, 3L73, big brakes/ rear disks, police bars, urethane throughout, 18x9/10 Bullits (F:275 NT555s, R: 305 NT05R DRs). TW170s and AFM N41 in stock and on deck. Faceplated TKO to follow

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