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Thread: Tr3 / 4 piston clearances

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    Tr3 / 4 piston clearances

    Hello All,

    Ok so I am in the process of reassembling my tr3 engine with almost all new parts! With only 54K on the car I was astounded at the amount of wear i found! I have purchased the 87mm liner piston and ring set from one of the three big parts houses. Upon sitting down to check my ring gaps i found that at about 1 inch into the bore nearly all top rings measure a .018 gap and the middle rings measure .014 to .016. My Question, are those gaps acceptable? Secondly I have yet to figure out a way to get an accurate piston to liner clearance. how is this accomplished, i have tried with a feeler gauge set and the clearances appear to be through the roof when measuring from the top of the piston! please any help on the subjects would b greatly appreciated being as i would like for this engine to have a little compression and not piston slap like crazy!

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    Re: Tr3 / 4 piston clearances

    The ring clearances are about average for standard rings. In some applications you can buy rings that are too large and file them to a specific gap clearance...but yours are perfectly fine for street applications.

    Measure the piston bore clearance at the skirt, not at the crown. The crown gets the hottest, and therefore expands. The clearance at the skirt is what you are interested in. I usually meaure with a bore mic...but that's usually limited to a machine shop. Feeler gages will work if you are in a pinch.

    Oh...forgot to mention. I assume you are using new bores. If so, measure the ring gap at any convenient point inside the bore. But, if you are using used bores, then take the measurement with the ring near the bottom of the bore. This area sees the least wear, so will give you the tightest gap clearance, which is what you are interested in (to make sure you are not going to get a bind or have so much clearance you'll get piston slap. Same applies to measuring the piston clearance. You want right on, but too loose is far better than too tight.
    John

    1955 TR2

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    Re: Tr3 / 4 piston clearances

    No, those values are way high. The spec is .003" to .010" (and even .010" is more appropriate for a race engine). Are you sure you are getting the rings exactly square to the bore? Also with new liners, you should be getting the same gap at any position within the cylinder; new liners should have no taper even though there is a wear allowance of .002" taper (IIRC).

    The best way to measure piston to cylinder clearance is by measuring piston diameter with a micrometer and bore diameter with a bore gauge. But you should be able to get reasonably close by inserting the pistons without rings, and pushing a feeler gauge between the piston skirt and wall. Note that the "head" of the piston (where the rings are) is deliberately smaller; the clearance is measured down on the skirt at right angles to the wrist pin.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Tr3 / 4 piston clearances

    In my manual, Why is there such a large difference between the .003 - .010 gap for the tr2 and 3, and the .010 - .015. for the tr4, i know about the .003 for every inch rule, and that puts the gap at around .011. I have read reports of people seizing rings at as low as .010 although there were most likely other factors at play! Also remeasured the piston to liner clearance and it is good. Thank you!

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    Re: Tr3 / 4 piston clearances

    This is a ring gap formula from Total Seal Rings, but I've seen the same exact formula from other ring provider for decades, this is good guideline to go by, and has served me well for three decades, and many engine rebuilds. Hope this helps. No harm meant, but .003" ring gap would cause a big problem.

    TSringgaps.jpg
    Acme Speed Shop - Hap Waldrop (864) 370-3000 www.acmespeedshop.com
    MG-Triumph Performance Engines, heads, SU carbs, engine rebuild kits, and more

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    Re: Tr3 / 4 piston clearances

    ok according to the table my gaps are acceptably near the prescribed dimension. now being as i have never installed this type of ring i am wondering about the orientation. the top ring is squared face and looks universal whether put in one way or the other. the second ring has a hook type wedge. and if im not mistaken that faces down. the bottom oil control ring has a beveled or "tapered edge. what direction does that face? also i received No instructions from the manufacturer...
    Thank You

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    Re: Tr3 / 4 piston clearances

    It's my experience that manufacturers provide the rings at the way high side to prevent a bind in the smallest possible cylinder. If you want the gaps tight, you normally have to specify "oversize" and file them to size yourself. Probably a good choice on their part, as most shade tree mechanics never take the time to check the end gaps...

    I am not sure about the tapered oil ring. If you have a picture, I'd like to see what it looks like.

    For the other compression rings, the rules kinda go like this...

    If there is a mark (letter or dot) it goes up.
    If there is a bevel on an edge on the inside of the ring, it goes up.
    If there is a bevel on the outter face of the ring, the sharpest edge of the bevel goes down.

    Beyond that, best to google or call the manufacturer to be sure.
    Last edited by CJD; 07-23-2013 at 11:17 PM.

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    Re: Tr3 / 4 piston clearances

    To add to this, here are charts that will aid you with piston rings, some manufacturers do a better job than others of giving you the proper information to work with. Hope this helps


    RingInstallation1.jpgPISTON_RING_END_GAP_LOCATION.jpg
    Last edited by Hap Waldrop; 07-29-2013 at 10:33 AM.
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