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Finding Top Dead Center (w/ Piston Stop) - HELP

Discussion in 'The Hokey Ass Message Board' started by Mattilac, Mar 19, 2008.

  1. Mattilac
    Joined: Oct 27, 2007
    Posts: 1,146

    Mattilac
    Member

    How can I make a piston stop in order to find TDC on my 292 y-block? The harmonic balancer on my 292 has slipped around over the years, therefore rendering the timing marks on it meaningless. I just need to make a piston stop to find top dead center so that I can recalibrate (& re-mark) the timing degrees on the damper in order to be able to time my engine accurately.

    Any ideas on how to find TDC accurately? Like I said, my original thought was to make a piston stop and get it that way...
     
  2. Gotgas
    Joined: Jul 22, 2004
    Posts: 6,230

    Gotgas
    Member
    from DFW USA

    Weld a short nail to the end of an old spark plug.

    Thread that into the spark plug hole on #1.

    Turn the crank (NOT with the starter) until the piston stops. Mark this on the balancer.

    Turn the crank the opposite direction until it stops again. Mark that on the balancer too.

    Halfway between the two is TDC.
     
  3. Brad54
    Joined: Apr 15, 2004
    Posts: 6,005

    Brad54
    Member
    from Atl Ga

    Buy a new balancer, too...if it's slipped over the years, it's going to continue slipping. Or, it could just give up the battle all together and come apart. Havoc will ensue, and the timing marks being out of place will be the least of it.

    -Brad
     
  4. RichFox
    Joined: Dec 3, 2006
    Posts: 8,391

    RichFox
    ALLIANCE MEMBER

    If the nail deal scares you, cut the crimp at the top of the sparkplug shell, and push out the porclelin part. then find something that fits the left over hole and radius the end. stick it in and weld that. Take it easy either way when you are bringing the piston up to the stop. remove all the spark plugs to make it eaisyer to feel.
     
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  5. Mattilac
    Joined: Oct 27, 2007
    Posts: 1,146

    Mattilac
    Member

    Yeah I was just about to say, what if the nail broke off and fell into the cylinder? Or even if it didn't snap off, it could bend, therefore providing inaccurate results.

    Thanks for the advice guys!
     
  6. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,198

    Bruce Lancaster
    Member

    Many spark plugs can be tapped for a long bolt if you drive out the porcelain then heatemup on the stove to remove hardening...thread through long bolt or allthhread with nut above plug, tighten down nut to hold bolt at suitable depth.
    For now, mark something else! Nothing you do on that balancer will stay put, and eventually it is going to come apart and BREAK THINGS!
     
  7. thunderbirdesq
    Joined: Feb 15, 2006
    Posts: 6,465

    thunderbirdesq
    Member

    First off, like others have already said, get a new balancer. No good can come of that and if it's slipped around that much, it's not doing it's job well either. As far as finding tdc, just pull the #1 plug, hold yer thumb over the hole and slowly turn the engine over by hand until you feel pressure, then insert a screwdriver in the hole until it touches the top of the piston and continue turning the engine over slowly until the screwdriver stops rising. Then just check to verify both valves are closed. viola, you're at, or at least pretty damn close to, TDC on the compression stroke!make sur
     
  8. Soviet
    Joined: Sep 4, 2005
    Posts: 716

    Soviet
    Member

    I gutted an old plug of the porcelain, and welded a valve stem in place, far enough down to provide a positive stop. Then coated the end with a bit of teflon tape, just in case. Using a long bar, with all the plugs but the stop in, rotate the engine over slowly by hand. It should give you the results you're looking for.
     
  9. 63ChevyII
    Joined: Dec 9, 2005
    Posts: 560

    63ChevyII
    Member

    can you post pics of a piston stop that has been made like this?

    I need to make one for my 292 L6 - want to make sure I'm doing it right. I also bought a new balancer for it because it slipped too.
     
  10. Nick79
    Joined: Apr 19, 2006
    Posts: 276

    Nick79
    Member
    from Austin, TX

    You can also pull off the valve cover and watch your valves. Another way to ensure you're on the right stroke and that will get you pretty close. Both will be closed at TDC on #1.

    Nick
     
  11. Mattilac
    Joined: Oct 27, 2007
    Posts: 1,146

    Mattilac
    Member

    Is there any way to make sure both valves are closed without pulling the valve covers off? It's kind of a pain in the ass in my situation, plus I'm a bit too lazy...
     
  12. DrJ
    Joined: Mar 3, 2001
    Posts: 9,431

    DrJ
    Member

    Break the insulator out of a spark plug. tap threads in the jacket and screw a 3-4" bolt into it with loctite on the threads.
    Cut the head off the bolt and round off the end with a grinder.
    Turn the engine over carefully BY HAND ONLY or you'll perforate a piston!
     
  13. Ole don
    Joined: Dec 16, 2005
    Posts: 2,914

    Ole don
    Member

    Y blocks are good for slipping the balancer. New ones are rare and expensive, Send the old one to Damper Dudes for rebuilding. Mine was about a hundred bucks including shipping, it should last as long as me.
     
  14. Mattilac
    Joined: Oct 27, 2007
    Posts: 1,146

    Mattilac
    Member

    Sorry, but how do you rebuild a harmonic balancer (a.k.a. damper)? Aren't they just a solid piece?

    Goes to show how much I know about this stuff...
     
  15. fiat128
    Joined: Jun 26, 2006
    Posts: 1,429

    fiat128
    Member
    from El Paso TX

    Not sure if this will work exactly on a Y block because I don't know much about them but I've done this to a Fiat to find TDC when I've lost it.

    I just take out the plug of the cylinder I want (#1 or whatever you time off of) and stick a 1/4" wooden dowel (a whole long one, not a short one that will fall in the hole) in the hole until it touchs the piston. Turn the crank by hand and watch the dowel. It will move up until the piston reaches TDC and then start to go back into the hole.

    You can hold it and feel the exact point at which the piston reverses direction.

    Hope that was helpful.
     
  16. Mr48chev
    Joined: Dec 28, 2007
    Posts: 21,166

    Mr48chev
    ALLIANCE MEMBER

    Almost all of the vibration dampers are two piece. the hub in the center and the ring on the outside with a rubber type material sandwiched in between.

    If you take a look at one it is pretty obvious when you see the soft material bonded between the hub an the ring. It is the reason that the ring sometimes slips on the hub and sometimes guys who don't quite know what they are doing will pull the ring off trying to pull the damper off the crank with a gear puller.

    What DrJ showed is what most guys would want to use but I think the bolt could be a bit shorter and work fine. The tool companies do sell them for the guys who don't want to make their own. But I can't see spending the money when 15 minutes of easy work is all it takes to make one.
     
  17. Don Dalton
    Joined: Mar 18, 2008
    Posts: 22

    Don Dalton
    Member
    from Austin,Tx

    Wouldn't a travel dial Indicator work?

    Don
     
  18. 63ChevyII
    Joined: Dec 9, 2005
    Posts: 560

    63ChevyII
    Member



    if I remember, I'll take a pic of mine when I pull it off. I wasn't sure if it separated or not, but the old damper had 3 or four marks on it - none of them lined up.

    EDIT: ohh here are some pics I took before:

    Here are some pics.
    [​IMG]
    [​IMG]

    Here are some pics of the multiple timing marks. When I had it together last time, I believed that #2 lined up with '0.'
    [​IMG]
    [​IMG]
     
  19. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,198

    Bruce Lancaster
    Member

    Here's the commercial version of what I made: http://www.jegs.com/i/Comp%20Cams/249/4795/10002/-1
    I added a nut above plug shell to lock the bolt at chosen depth. The plug rquires a few minutes in a stove burner flame before the tap would cut happily. Making one or phoning Jeg's will require about the same amount of effort...
     
  20. Fe26
    Joined: Dec 25, 2006
    Posts: 543

    Fe26
    Member

    Look at thunderbird esquires post (a few back), I've done it this way for years with no prob's, personally I wouldn't waste 15minutes making a tool for this job, I have too many already.
     
  21. Mattilac
    Joined: Oct 27, 2007
    Posts: 1,146

    Mattilac
    Member

    Sweet! I found TDC and tuned my engine properly. I made the piston stop by smashing out all the porcelain and stuff inside and breaking the little ground nub off. Then I just welded a nut on top which holds the bolt. I took a good sized-length bolt, cut off the head, and ground it down to a smooth dome. Then I just shoved it through the spark plug case and screwed it into the nut till it was tight.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  22. 63ChevyII
    Joined: Dec 9, 2005
    Posts: 560

    63ChevyII
    Member

    are you gonna replace the balancer still, or do you think it's ok?
     
  23. Asphalt Outlaw Hero
    Joined: Dec 9, 2006
    Posts: 963

    Asphalt Outlaw Hero
    Member
    from Dixie

    I have to do this all of the time on old motorcycles.
    Piston stop is the best.I've seen people do a soap bubble too.When the bubble gets the biggest,you are there.

    Here's what I do with motorcycles.
    1st you put a degree wheel on there.You can cut one of these out of card board.You can usually find one on the internet and print it.
    Find "aproximate" or theoretical TDC. Rotate the engine by hand about 45 degrees.Put in the piston stop.Rotate the engine back and take the reading. Say you get 37 degrees.
    Now rotate the engine the other way until it comes on the piston stop again.Say it reads 43 degrees.NOW you add the two figures and divide by two.43+ 37= 80 /2 = 40.
    Rotate the degree wheel on the crank to the figure of 40 and you are now spot on.
    Now you can rotate the motor back to ZERO and it will be at true zero degrees.
    I have to do this to time magnetos all of the time.
    Good luck.:D
     
  24. Mattilac
    Joined: Oct 27, 2007
    Posts: 1,146

    Mattilac
    Member

    Actually, I think its okay. It hadn't slipped very much at all, plus I think a lot of the problems I had with the timing and the marks was due to the timing chain/gears which seem to have mega slop.
     
  25. Porttownsend119
    Joined: Nov 19, 2012
    Posts: 35

    Porttownsend119
    Member

    I'm trying to deal with this right now and here's what I'm finding. On a 1955 Mercury Y-Block, the spark plug hole goes into the block parallel to the ground (level) thereby making it point right at the valves, not toward the top of the piston. I put a piece of wire into the hole and started turning the engine, but the only thing that happened was that the wire got pinched in a closing valve. The way it looks, I don't see how you could even use a piston stop in this engine.
     
  26. sunbeam
    Joined: Oct 22, 2010
    Posts: 2,793

    sunbeam
    Member

    Top dead center is top dead center the damper won't care.
     
  27. George/Maine
    Joined: Jan 6, 2011
    Posts: 952

    George/Maine
    Member

    If you take center bolt and washer off put keyway at 12 oclock.
     
  28. Jimbo17
    Joined: Aug 19, 2008
    Posts: 3,073

    Jimbo17
    Member

    I like to remove the head and then use a magnetic base with a dial indicator and a degree wheel.

    This way you can also profile the cam at the same time so that you know just what you have and also to find the center lines for the cam.

    Also remember to think about piston dwell at top dead center and see how many degrees of crankshaft rotation you have before anything starts moving again.

    On some motors years ago once I knew top dead center we would just set the ignition between 160 and 180 thousand down from top dead center,

    Hope that helps Jimbo
     
  29. aaggie
    Joined: Nov 21, 2009
    Posts: 2,454

    aaggie
    ALLIANCE MEMBER

    Many years ago when I raced motorcycles there was a tool that looked like a sparkplug base with a rod in the middle that was marked with lines .2MM apart. You screwed it into the sparkplug hole then rotated the engine until the piston contacted the rod and raised it to it's highest point. Now you unscrewed the tool to align the TDC mark. If the timing spec was .4MM BTDC you rotated the engine backwards until the rod dropped two lines then adjusted the points to open. It was simple, quick and cheaper than a dial indicator.

    Bultaco motorcycles, point ignitions and my youth are long gone but the theory is the same.
     

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