Getting proper piston liner height when liners are flush

[bunni]

Second go around on engine rebuild because I'm crazy and decided to take this on almost 10 years ago :hysterical: 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.
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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..
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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?

[Ron]

Did I completely botch the measurements somehow and need to redo it?
Your gauge is not zeroed:
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[bunni]

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.

[Ron]

When you lay it on the block, it should be fully extended and read zero on both dials...

[bunni]

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?

[Ron]

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.)

[David T]

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.

[bunni]

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.



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.



... 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.

[David T]

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.

[Delorean Industries]

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.

[Delorean Industries]

Kris, from the above measuring pictures and dimensions you have given once the block deck surface has a high micron finish applied for true up and gasket sealing you will be within spec. I would advise having this finishing process done prior to your shim measurements as .003-5 will be removed during this. We have switched over to a one size fits all shim process as posted elsewhere on this site and achieve protrusion based on what is required in the block spec true up process and touching the face of the liners.

[David T]

This is terrible.

I have done "top jobs", cylinder heads, on several Deloreans but never the whole motor. I think it shows the durability and longevity of the basic PRV. On many other old cars it is common to have to completely rebuild the motor, not so on Deloreans. On one Delorean I found and restored, it had been sitting for many years. The motor, at first, would not even turn over. After some lubrication and careful movement, I got it loose and it had great compression and oil pressure. My point is, the PRV is a pretty good little motor and most of the time does not require a full rebuild. That said, if you really cook the motor and overheat it badly, it should not be a surprise when it requires a full rebuild. Luckily most (but not all) can be fixed by only doing the heads. It also seems that once you rebuild a PRV, the chances of it leaking coolant seem to be very high unless you really know what you are doing. I see this not from my own experience, but from the posts on this forum over many years. IMHO the motor is the most durable part of the car (if you don't overheat it!).

[Ron]

Assumptions aside :smile:, is the negative nip at cylinder 2 or 5?

[bunni]

... once the block deck surface has a high micron finish applied for true up and gasket sealing you will be within spec. I would advise having this finishing process done prior to your shim measurements as .003-5 will be removed during this. We have switched over to a one size fits all shim process as posted elsewhere on this site and achieve protrusion based on what is required in the block spec true up process and touching the face of the liners.

Thanks for the info. After a few conversations with people locally, a touchup sounded like the ideal path. But with the engine being somewhat uncommon I wanted to see if there were other options or to confirm that surface touchup of the block was viable. The deck has not been touched at all since it was originally opened so this would be the first time anything has been taken off (to my knowledge).

I assume that the deck surface prep is something you've done successfully a number of times without issues? Also presuming I follow up with the valve clearance process (again) as well.




... On many other old cars it is common to have to completely rebuild the motor, not so on Deloreans. ... My point is, the PRV is a pretty good little motor and most of the time does not require a full rebuild. ... It also seems that once you rebuild a PRV, the chances of it leaking coolant seem to be very high unless you really know what you are doing. ...

My rebuild was a combination of "I did it wrong" (liners ended up moving), "while I'm in there," and "the experience." Not necessary, but here I am, and I want to make sure I do it right the first time. You highlight a very important point, "leaking coolant." Which is why I'm asking for things that are known working with this specific engine and not a shoot from the hip.

If it were purely a shim, then I'd have no issues stacking them. But they are also a gasket separating oil from coolant, which adds a lot more complexity to the equation. This is why I'm back to square one and want to make sure I do it right. I appreciate your knowledge, but offering an unproven suggestion for something that is the interior-most part of the engine, and one that you deem critical too, is potential waste of a lot of time for people. I know I'd hate to get done only to find that I've now got cross contamination that could now either be a head gasket or a complete rebuild. Having the confidence that the shims are done in a way that is known working makes any future troubleshooting that much easier.




Assumptions aside :smile:, is the negative nip at cylinder 2 or 5?

Cyl. 1 has a bit of a skew, one side is a hair under, the other is a hair above. Cyl. 2 is ~0.0005" under on one side, with just a hair under on the other side. Cyl. 5 is basically flush. Same with the rest of them.

I'm curious why 2 and 5 would be special here. I've not come across anything around here that would be a reason these would be negative.

[Ron]

Cyl. 1 has a bit of a skew, one side is a hair under, the other is a hair above. Cyl. 2 is ~0.0005" under on one side, with just a hair under on the other side. Cyl. 5 is basically flush. Same with the rest of them.

I'm curious why 2 and 5 would be special here. I've not come across anything around here that would be a reason these would be negative.


This is confusing because in post 8 you said, "The liner I just tested with is actually a hair UNDER the block, and the measurements with the indicator (and flashlight test) reflect that." Anyway, using the measurements above, you have neither -- All of these liners should be considered to be above the deck or level since you use the highest measurement.
If the nip was negative at the center bore of a bank (2 or 5), you would have to chase down a liner having a nip falling between those on the two ends, to maintain stepping. Otherwise, you could have used use any liner that has a nip <= to the adjacent one (center). (Although some of the manuals ignore step as long as the difference between adjacent cylinders is no more than 0.04mm, I would suggest rotating the high side of #1 toward #2 and the high side of #2 toward#3...)

Back to the shims- If you are still nervous about the shims, call Mike at DMCMW. They do this all the time and I'm sure he will also suggest that you use the yellow shims since the nips are so close. If that don't do it for you Josh had the best solution, imo.

Hope this helps...

P.S. FWIW, I thought you had an adjustable stem (clipped off in your pics...). Sorry for the assumption/confusion!

[bunni]

This is confusing because in post 8 you said ... you have neither -- All of these liners should be considered to be above the deck or level since you use the highest measurement. ...

I apologize for the confusion. I was referring to Cyl. 2 in that post which would be considered negative nip in that situation since the highest measurement is still (every so slightly) negative, correct? In the photos I was measuring liner 1, which was the one slightly above on one side and slightly below on the other, which would mean that during the shimming process, it would be still a positive nip, correct?



Back to the shims- If you are still nervous about the shims, call Mike at DMCMW. ...
Not a bad idea, didn't cross my mind to give any DMC shops a call since I don't usually call a mechanic and ask to troubleshoot on the phone. The only times I try to ask questions of DMC shops is either at tech events, on the forums here (if they respond), or if I'm about to actually send money their way and am asking about a product or a process for it. Though I've surely contacted someone and then later felt like an ass about it. Is calling up shops for things like this considered to be okay in the DeLorean circles?

[Delorean Industries]

Kinda like going to a house of worship. You are expected to tithe as a franchise will only deal with you while one hand is in your pocket. On the other hand, we are always more than happy to tell you the only proper way to do something right for free. But instantly wash our hands of any situation where said advice isn't implemented or continual polling of the internets at large ensues. Six of one-half dozen of the other I guess!

[Ron]

I apologize for the confusion. I was referring to Cyl. 2 in that post which would be considered negative nip in that situation since the highest measurement is still (every so slightly) negative, correct? In the photos I was measuring liner 1, which was the one slightly above on one side and slightly below on the other, which would mean that during the shimming process, it would be still a positive nip, correct?NP!

Technically #2 has negative nip. But since the specs round at three decimal places, 0.0005" => 0.001, and a hair under is rounded to 0.000". I'd consider it flush and not worry about it because both of the adjacent cylinder's nip are flush = 0.000". I.E., the specs allow 0.0016" step so they will not interfere with the gasket material around #2 from getting the maximum compression when it is torqued down. (Fwiw, I prefer the torque once gaskets and strongly suggest you use them in any case.)


Not a bad idea, didn't cross my mind to give any DMC shops a call since I don't usually call a mechanic and ask to troubleshoot on the phone. The only times I try to ask questions of DMC shops is either at tech events, on the forums here (if they respond), or if I'm about to actually send money their way and am asking about a product or a process for it. Though I've surely contacted someone and then later felt like an ass about it. Is calling up shops for things like this considered to be okay in the DeLorean circles?Hehe...I basically agree with Josh on that one.

Tithe where you are fed.:deviltail: