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Hello all. I'm in the middle of trying to overhaul my engine. I wanted to freshen it up now, before I delve into body work. The block is cracked so I trying to freshen it up and reduce the haze of blue smoke that comes out of it whenever it runs. Prior to the teardown, my compression was 95-85 psig on all cylinders, but it smoked (blue) no matter engine temperature. I only put maybe 20 or 30 miles on it, so I can't tell you if it was burning significant oil.

I have two questions.

1. I measure the cylinders for taper, and as far as I can tell, all of my cylinders are 3.440" (+/- 0.002") in the middle and bottom of the cylinder. Top of the cylinder, just below the carbon ring, seems to be 3.450", +/- 0.002". It is my first time trying to take these measurements, but I took all of them twice, and it seemed pretty consistent, so I think I am doing it close to right. What is the specification for cylinder taper? I cannot find it for this engine. I am not terribly confident in my measurements because it is the first time I've ever done it. The cylinders were clean and dry, but I haven't run a ridge reamer through it yet. My upper measurements were just under the carbon ridge.

2. Two of my pistons are slightly damaged. Should I replace them? See pictures below. Also, anyone have a source for NOS pistons? (No, flackmaster doesn't have any!). One is marked D and one C, so one is 0.0015" over and the other is 0.001" over stock size. The other four pistons are flat.

Thanks!

(Many more pictures in my project blog)

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I'm not surprised you found no specification for allowable taper, you might find that recommendation in a Motors Manual but car manufacturers would frown on fitting new pistons and/or rings in worn bores. Years back when money for engine work was quite limited, we often did what we called "semi" rebuilds on engines with a good crankshaft and taper of perhaps 0.007" or less and we expected to get maybe 10,000 or 15,000 miles of reasonable service life from our efforts. We cut the ridge of course, honed the cylinder walls, and either knurled the piston skirts to expand them a bit or fitted piston expanders. Ring grooves were usually well-worn so they were often recut for new standard rings with spacers. We usually fit oversize wrist pins, new rod bearings, new timing chain and sometimes new gears, and often did a valve grind.

This surely isn't the best way to go, but if it's all the budget allows you can get some further mileage from your engine, though certainly not to true rebuilt standards and it begs the question was the money well spent as opposed to saving enough to do the job properly. If you need to replace one or more pistons, replacement pistons should be the same weight as the OEM but best to check on a scale to be sure they are within +/- perhaps 7 grams or less of the old pistons. Kanter, Max and Egge all have replacement pistons though I don't see from your pictures just what damage yours have.

I don't know what engine you're speaking of, perhaps a 115C? For that engine I don't think compression of 85-95 psi is all that low so I'm not sure that's the cause of your smoking condition. If the engine has only been driven 10 or 20 miles since it's been back in service, perhaps tearing it down was premature? In particular, were the oil control rings unbroken, free in the grooves, and the oil drain holes in the piston groove open and clean?

Owen, I want to make sure I understand you correctly- you think I should just replace the broken valve springs, clean out the carbon, and put it back together with the original rings? The goal of the semi-rebuild was to stop the smoke, and get the engine as good as possible without throwing good money after bad.

I am working on a 1082 115c. I started restoring it about three years ago, but then the tour I was doing in the navy precluded me from working on it, so it has been sitting for three years. I'm now on a new tour, stationed in upstate NY.

The block is cracked on the driver's between 5 and 6 cylinders, and it is a cold water leak, so I don't want to waste any money on machine work. I thought this would be a good way to learn, and if the engine gives up the ghost in a few years, I can get an uncracked block and perform a full rebuild.

The piston damage I was concerned about was the pits in the tops of the pistons shown, and #2 has a piece missing from the crown

More pictures of the tear down are on my project blog:

packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=6550&start=160

A couple of pits are what you are losing sleep over?? !! As long as the chip at the perimeter of #2 is not down too close to the ring groove, run'em. May cut back on the nitrous or the blower pressure, but all in all, I'd sleep like a baby...

I say clean the grooves real well and slide in some new rings, lap the valves, quick clean-up hone on the bores, make sure the timing chain is decent, the distributor bushings not too worn, clean the oil galleys, fresh set of bearings, etc and look for local car events.

DAF

Remove the rings and keep them in the order and position that they were installed. Look for any conspicuous wear or damage to the rings.
Smoking can be due to rings installed upside down and yes, compression rings installed upside down can cause smoking.

The .010" "taper" (actualy what u describe is bellmouthing wear not taper) is not desireable but not severe either. This becomes a personal judgement call based on future expected service demand from the engine.

At this point i would inspect the rest of the engine to determine condition of bearings, crank etc. Somethingg called plastigauge can be used to measure bearing cleaarence.

For light to moderate service demand i would probably not worry about the bellmouth of the cylinder. Check with a REPUTABLE piston ring manufaturere about how much taper or bellmouthing is allowable for rings. I think u will find that up to .017 taper or bellmouthing is max allowed.
The pistons look ok. I'd run them based on the pics. Unless there is other problems not evident in the pics. I've sure ran worse.

The MAJOR issue of any engine overhaul is INSPECTION and analysis of the existing parts.

Let me put it this way:
Short of any conspicuous bore damage for nearly any gasoline engine it is cylinder bore and pistons that one can be rather sloppy with and still produce a good overhaul. It is THE BEARING FIT AND AND CONDITION of BEARINGS and crank that are critical. Valve seating and stem to guide wear can be critical too.

In this particular case it is a prewar engine anyway???? Which makes it little more than a 40K mile or 60K mile at the max service life engine when it was brand new from the factory.

BTW. Cylinder bores need to be measured TWO different ways: Perpindicular to crankshaft (where most wear will be) and measured parallel to crankshaft (least wear). Two different measures to determine if how much out of round the cylinder is.

U mentioned a cracked block. WHERE is the block cracked??? internal to allow coolant into the crankcase or external allowing coolant to the drip to the ground???? MAKES A DIFFERENCE!!!

Owen, I want to make sure I understand you correctly- you think I should just ....... put it back together with the original rings?

No. As long as the lower end is good, install new rings as long as you have it apart. I was just wondering why it smokes, your compression numbers aren't all that bad and was wondering if there wasn't another contributing reason.

1. It is a FLAT HEAD engine. Which means OIL smoking is due to rings.
2. Rings: smoking because of worn or broken rings OR POSSIBLE RINGS INSTALLED UPSIDE DOWN. No, not just the oil ring upside down but compression rings upside down will yield GOOD compression but HEAVY oil smoke.
3. INSPECT the rings!!!
4. Possible the TOP ring is chrome. Do not use chrome rings. Use CI rings.

1. Remove the rings from the piston one by one. KEEP THE RING(s) in its identicle orientation as it came from the piston. up is up, down is down, top ring is top ring etc etc.
2. LOOK at the ring. is it upside down??? or right side up????
3. Look at service manual for specs. Measure thickness and width.
4. put ring in cylinder bore and measure end gap.
5. See the specs in the service manual for measurements!

Hi Ken:

Worn rings and valve guides can cause the smoking. Even with flathead motors.

External cracks on monoblock Packards are not rare. The principal issue is whether the leak is the result of a rusted block rather than damage. Sometimes weak castings cause that kind of persistent leak.

The usual diagnosis for rings is if it smokes under load it's rings. Your case sounds severe so take the valves out and check the guide clearances. You can buy ball gauges for a micrometer from McMaster-Carr.

As well, sometime rings stick and cause smoking even with good compression.

Hope this helps.