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Thread: Getting proper piston liner height when liners are flush

  1. #1
    Member bunni's Avatar
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    Getting proper piston liner height when liners are flush

    Second go around on engine rebuild because I'm crazy and decided to take this on almost 10 years ago This time around though, I've cleaned up the liner seats like I should have the first time. See photos, left is clean, right still has burned crud.
    IMG_1526.jpg


    My current situation is that all liners, no matter how I swap them, are all within 0.001" of the block deck. With most being basically flush with the deck. Measured with straight edge+drop indicator (see photos) and follow up with a flashlight to really show that there is no (or next to no) light penetration between the straightedge+liner or straightedge+block..
    IMG_1530.jpg IMG_1536.jpg IMG_1535.jpg

    The liner was freely placed, not clamped down, but there was zero wobble. Final measurements will happen with the liner lightly held in place with clamps. But the problem is getting the correct protrusion/nip from the liners. If they are flush without shims, the yellow shims (0.13-0.16 mm) boarder on not being thick enough. The superseding metal shims from Volvo are 0.15 mm. And the shims from DPI are 0.0055" (~0.14 mm).

    Whats the best way to move forward with this? Can I just use yellows (a "yes" answer to this makes me nervous unless there is some data behind it to back up that being on the low end/just under the measurement is still perfectly fine)? Are there known sets of thicker shims that are still compatible with the engine? Do I need to have 3-4 thou machined off the block? Did I completely botch the measurements somehow and need to redo it? Some other option I'm not considering?
    -Kris
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  2. #2
    Administrator Ron's Avatar
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    Quote Originally Posted by bunni View Post
    Did I completely botch the measurements somehow and need to redo it?
    Your gauge is not zeroed:
    NotZeroed.jpg

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    Member bunni's Avatar
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    Its not going to ever be 0 there unless its completely extended. That's the 10ths gauge as its a 1" travel plunger. The large gauge that's set at 0 is the thousands dial, and you'll notice in the two original photos, the 10ths dial is in the same position in both photos.
    -Kris
    #4222

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    Administrator Ron's Avatar
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    When you lay it on the block, it should be fully extended and read zero on both dials...

  5. #5
    Member bunni's Avatar
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    Quote Originally Posted by Ron View Post
    When you lay it on the block, it should be fully extended and read zero on both dials...
    I cannot adjust any of the dial arms, as they are calibrated and mechanically linked together. All that can be done is to rotate the outer rim to rotate the thousandths scale. So, I can only zero the thousandths, and only by rotating the dial face, the arms cannot be adjusted. If it were a digital gauge I could zero out the whole thing. But, like I said previously, between the two photos both dial arms (tenths and thousandths) are in the exact same position when in the final measurement point.

    In this setup, the plunger cannot be fully extended and flush with the straight edge. It would not be able to measure the piston liner protrusion from the block if the liner and straightedge are above the block since it would bottom out with the plunger being fully extended and therefore always read 0.

    Lets take a step back and presume I am measuring it correctly, and the liner and block deck are flush. What are my options in moving forward with that?
    Last edited by bunni; 06-13-2020 at 03:54 PM.
    -Kris
    #4222

  6. #6
    Administrator Ron's Avatar
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    That be the case, for that particular liner, you would need to go through several yellow shims to find one measuring at least 0.160mm (PITA), replace the liner (expensive), or shave the deck (~changes timing chain geometry).
    I would go with a 0.160mm+ shim. (This would put it within spec. ...and if they are all "short" like this one, you will get plenty of squish.)

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    While the gauge is nice, a straightedge and some feeler gauges can also work well. You can at least use it to verify what you are doing with the dial gauge is accurate. If you don't have the correct protrusion you need to either stack shims or get different shims to achieve the correct protrusion. I agree that the small dial does not have to be zeroed, you can do it all with the larger dial. The smaller dial is only to count full revolutions of the larger dial.
    David Teitelbaum

  8. #8
    Member bunni's Avatar
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    Quote Originally Posted by David T View Post
    While the gauge is nice, a straightedge and some feeler gauges can also work well. You can at least use it to verify what you are doing with the dial gauge is accurate.
    I used a straight edge and feeler gauges the first time around. I didn't get the most consistent measurements and eventually came to redo it because I was not comfortable with that inconsistency. When I recently re-measured with the straight edge and dial indicator before taking it apart again, I got consistent and repeatable measurements. From my notes, most of those were between 0.004-0.006", averaged around 0.005", with all but one already using yellow shims. 2 of the liners were incredibly off, with the three measurements being 0.010", 0.008", and 0.005" on one of them, and then 0.008", 0.007", and 0.004" on the other. That was the reason I took everything apart again to properly clean the liner seats and that has clearly had a positive impact.

    Note that, since I was using the yellow shims already and the above measurements are in-line with roughly the thickness of yellow shims, my engine appears to have started out with everything already flush. Unfortunately, whatever shims were used originally are long gone, and I did not measure the original protrusion at all. Its likely I could get away with yellows, but its also possible that some other shim had been used.

    Testing again with feeler gauges, I cannot get my thinnest feeler (0.0015") between straight edge and the liner top, or between the straight edge and the block, when the straight edge is laid across. My indicator gives me same measurements I got before. The liner I just tested with is actually a hair UNDER the block, and the measurements with the indicator (and flashlight test) reflect that.


    Quote Originally Posted by David T View Post
    If you don't have the correct protrusion you need to either stack shims...
    I've seen people say both "stack shims" and "do not stack shims" around here. Have you done a build with stacked shims or a link to a thread where someone else did? If so, hows it holding up? Did you use the metal ones? Paper? The plastic-ey ones? Use any sealant between them? I'm really just looking for what someone else did that has worked. I'd be surprised if I was the first person in this position.


    Quote Originally Posted by David T View Post
    ... or get different shims to achieve the correct protrusion.
    Do you have part numbers that are known to be compatible? I would assume there is no issue with using thicker shims as DPI appears to have once offered 0.0075" shims which would be exactly what I need here. But I have no clue where I'd find a compatible part for this.
    -Kris
    #4222

  9. #9
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    I have not actually built a PRV motor yet. I have done similar motors and have had to do things that are not recommended in the manual because of parts availability. For example in many motors you are supposed to try to match parts like they did at the factory. When you have a large box of pistons for example, you can pick and choose among a lot of parts. When you are rebuilding one motor you have to make the best of what you got on hand. Not optimum but doable. In the case of shims, if you don't have all of the sizes that were available "back in the day" it becomes a matter of using what you can get. My first choice would be to use metal shims with sealer and finish with a plastic one of the smallest dimension possible. Work with your machine shop and go with their advice, they have more experience than you do. Achieving the proper protrusion is VERY important to seal the head gaskets and prevent the liners from moving.
    David Teitelbaum

  10. #10
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    Quote Originally Posted by David T View Post
    I have not actually built a PRV motor yet. I have done similar motors and have had to do things that are not recommended in the manual because of parts availability. For example in many motors you are supposed to try to match parts like they did at the factory. When you have a large box of pistons for example, you can pick and choose among a lot of parts. When you are rebuilding one motor you have to make the best of what you got on hand. Not optimum but doable. In the case of shims, if you don't have all of the sizes that were available "back in the day" it becomes a matter of using what you can get. My first choice would be to use metal shims with sealer and finish with a plastic one of the smallest dimension possible. Work with your machine shop and go with their advice, they have more experience than you do. Achieving the proper protrusion is VERY important to seal the head gaskets and prevent the liners from moving.
    This is terrible.

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