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Piston rings not sealing?


MicroMachinery

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Well.. I just did a compression test on the engine while hot.. 135/210/215/160.. Why..... WHY!???

 

The engine has a little over 1000 miles on it, and I broke it in as per http://www.mototuneusa.com/break_in_secrets.htm 's instruction. Followed the directions to the "T".

 

The engine is using alot of oil(a quart every 100-200 miles), but it's not billowing out smoke. I don't even know where it's burning it(there are no visual signs), and it definitely not leaking anywhere. I ran an L-18 that blew blue smoke out all the way down the road, and it used less oil than this thing. I don't get it. I did everything I was supposed to do, followed the directions, double checked everything. That the fuck did I do wrong!?

 

-Checked cylinders for taper out of round. Perfectly straight.

-Honed the cylinders 45 degree cross hatch. Cleaned and wiped down until no debris was found on cloth.

-Checked ring gap, installed rings into piston right side up, staggered piston ring gaps, checked oil control rings.. installed pistons into bores.

 

The engine runs smooth as butter, and makes good power. I just don't understand why it would run so nice and smooth if something were terribly wrong, as it appears to be. :blink:

 

Is it possible that the rings haven't fully seated? I am hoping that if they aren't, that they will seat up in the next few hundred miles. I just don't know.. I don't want to do something rash like remove the engine, tear down and start back at square one, just to find out that if I had just been more patient, things would have been fine.. Dammit, I don't know what I did wrong... did I do something wrong? I'm racking my brain here.

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I've heard of rings sticking after a rebuild for nearly 2K miles.

 

When I rebuilt my brothers Chevy V6, it smoked for a few hundred until we added seafoam to the oil. The shop that did the machine work suggested it since sticking rings aren't really uncommon in newly rebuilt engines.

 

My 73 Honda bike smoked after I put in new pistons and rings. Never did get it to stop before I sold it. My 210 emits smoke clouds that are the envy of WWII destroyers laugh.gif

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You're not using synthetic oil are you? Don't use synthetic until at least 500 miles, preferably even longer. Our autocross president learned that the hard way with an SR20 he built and put Mobil 1 in with only 200 miles on it, rings didn't seat. Had to tear it all back down.

 

Did you check the ring end gap before installing the pistons? You should have about .017 for the top ring, and .014 for the bottom ring or something thereabouts.

 

I didn't read the link, but they way I broke in my motors was to baby it for about 70 miles, then start beating the shit out of it. I literally take a long drive, with lots of up and down rpm (try winding country roads with elevation changes), try and keep it below 3500 for that first 70, then after that, screw it, go nuts. Drive it home, change the oil around 100-150 miles, then again at 300, then at 500 or better, switch to synthetic and resume normal 3000k changes.

 

There are a lot of different ways to break in an engine though. Did you redo the head? Is it possible you have a bent valve or a poorly seated valve?

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No synthetic. I used 30 weight for break in. How I broke it in was start it up, run it to operating temp, and take it for a 20 mile, 2k-4k run the rpms up and let the engine slow the truck back down. I have a windy uphill road right by my shop, so I went up that, then down, up, then down.. 5 miles in each direction. Got back and drained the oil out... let it drain overnight. The next day, I changed the oil and put 10w-40 in and took it for 500 miles of the same kind of driving.. minimal idling. Drained the oil. Changed filter, now I'm on the 1500 mile leg.. about 600 miles into it.

 

I don't recall exactly the ring gaps, but I wrote all that down, have the info logged, and compared it to the factory specs. They were all within spec, if not slightly looser. None were too tight, I made sure of that.

 

Head was redone, cleaned and a 3 angle valve job. I adjusted the valves the other day... a few were pretty loose.

 

I don't know.. I would think with as much oil as I'm going through, there would be a blue cloud following me.. not the case at all. The engine runs smoothly, and has lots of power. I live in a nice neighborhood with new paved roads, and there is ZERO evidence of the oil leaking anywhere. Currently, the crankcase is open to atmosphere, so I now it's not plugged or anything like that. I'm wondering if a bent valve is possible, or maybe one that's hanging up inside the valve guide somehow. I would have thought my machinist would have caught that, however.

 

 

It also seems unusual that my middle two cylinders have above 210psi.. could it be that cam is a tooth off? The two outside(1 and 4) are fairly close in compression as well.. seems a little odd...

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Quart evert 200 miles would see a cloud following you like Joe Spiffledick. Put cardboard under engine overnight and see where it leaks. The only other thing is it only leaks when out on the roar driving..... but it would be sprayed all over the under side of car. You have a remote oil filter or cooler???

 

Hainz may be right... hard chrome rings take longer to wear in.

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I just redid the valves 3 days ago. Some of them had loosened up, so much that you could hear them while the engine is running.

 

I have the filter in the factory location.

 

Like I said before, there is no PCV valve currently; the crankcase is open to the atmosphere, so there is no pressure to push oil up through the rings, and no vacuum to pull it into the intake.

 

Any ideas on why the 1 and 4 cylinders are really close in LOW compression, but the 2 middle ones are HIGH in compression? Could that have anything to do with cam/valve timing? I feel like I've seen this before in a situation where the cam was off a tooth, and the compression on 2 cylinders went up, and went down on the other 2...

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There won't be any pressure in the crank case. The valve cover has a vent hole and the PCV valve if it was connected draws air into the intake.

 

Is there oil wetness anywhere on the underside of the car?

 

A liter every 300 miles would make a huge cloud OR be all over the car and a puddle in the driveway..

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No puddles. No cloud. Only a little puff when I jazz the throttle.

 

I talked to a friend of mine who's built many, many engines over the years, and he just said to put more miles on it.

 

Specs when I built it:

 

Ring Gaps-

Top Ring: 1).021" 2).019" 3).020" 4).021"

2nd Ring: 1).012" 2).008" 3).011" 4).013"

Oil Control:1).039" 2).041" 3).042" 4).042"

 

Did a wet/dry compression test today, with the engine hot. 10cc of oil was added for wet readings.

 

Dry/Wet-

1)140/192

2)210/260

3)215/275

4)155/200

 

I do see that the readings went up almost exactly 50psi for both wet and dry, so that doesn't necessarily tell me that the rings are not seated. It just tells me that 10cc of oil will increase compression by 50psi :rolleyes:

 

The cylinders do hold their pressures, wet and dry. The compression reading doesn't dissipate after I'm done cranking, so I know that they are capable of sealing.

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Well, I can say with certainty that your top rings are all wide, your middle rings are narrow (#1 and #4 are in spec, #2 & #3 are both too tight which is asking for a broken ring there but explains the high compression) and the oil rings are all well past wide. In fact the oil rings are in oil-burning range.

 

The factory specs (in inches, rounded to feeler gauge sizes) are:

 

Top: .010-.016

Middle: .012-.020

Oil: .012-.035

 

All rings: .039 max limit in the most worn part of the engine (if not rebored). That's middle of cylinder.

 

I try to get all my rings on L20Bs at .015. If it were a race engine I'd run them at .020, with oil rings at .030.

 

They also should be measured in 3 places, the manual only says 2 but is somewhat vague as to where. I use 3/4" from top, 2" from bottom, and center of bore for compression rings and 2" from top, 1/2" from bottom, and center for oil rings. I also try to "normalize" the rings- I measure all rings in one cylinder, then measure one ring in all cylinders. That tells me which cylinders are what size and what rings are what size since they won't all be exact. Then put the widest rings in the smallest bores and the smallest rings in the widest bores to get the gap readings as close to consistent as possible. It's extra work, but hey I do that on V-12 engines that have 3 compression rings and 2 oil rings per cylinder... that's 60 rings to measure and even out. Takes hours.

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The specs I used say the same thing as yours, except the middle ring is .006"-.012".

 

What I was taught is that a little loose is allowable, but NEVER go to tight. The oil control is indeed a bit over, but I'm not terrified of that; I've seen a bigger gap yield good results.

 

Thanks for the response. I'll make a note about the 3 places to measure, and "normalizing" the rings. That's good advice, right there.

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I found this other chart in another post concerning Z22 specs.(http://community.ratsun.net/topic/22644-z22-torque-specifications/)

 

Pistons and rings

Z22 std – 86.985 to 87.035mm

Z20, 1984 – 84.965 to 85.015mm

1985 – 84.965 to 84.975mm

Z24, 1984 and 1988, std 88.965 to 89.015mm

Z24, 1985 through 1987, std 88.965 to 88.975mm

 

Piston ring end gaps:

Top - .25 to .4mm(.0098"-.016")

Second - .15 to .3mm(.006"-.012")

Oil ring - .3 to .9mm(.012"-.035")

 

Ring side clearance:

Top - .040 to .073mm

Second - .030 to .063mm

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Piston ring end gaps:

Top - .25 to .4mm(.0098"-.016")

Second - .15 to .3mm(.006"-.012")

Oil ring - .3 to .9mm(.012"-.035")

 

Since the oil control rings run the coolest I would run the least gap on them. Think of them as squeegees or windshield wipers that wipe excess oil off the cylinder walls.

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Well.. as much as I'm not thrilled about it, it's been done. I'll definitely keep that in mind for next time. You wouldn't think that .006" over would be the difference between burning a ton of oil and burning none, though, would you? That's seriously a hair's width, and there are two, which are staggered, and they are also pushed outward by the expander.

 

That does make sense, though.

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If you go through the Z24 engine build thread I'm still not done with, you'll note there is a big problem with piston rings from all manufacturers these days. Half the time you put them in and they're too wide. I filed down .030 over rings to fit my .020 over bore for that very reason.

 

I still go by the Datsun bible specs: .004 for each inch of bore on the top ring, .003 on the second ring. Multiply those two and you'll have the desired end gap.

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wow, those have to be the weirdest compression readings ive ever seen...

 

i guess ive gotten pretty lucky with the eninges ive built then... :mellow:

 

the only other thing i could think of is maybe the block soaked up some of the oil.. but with you saying its been a constant thing, that really wouldnt make sense.

 

reason i say that though, the last engine that i built for my luv, it had been hottanked, and all the machine work done... it was super clean and dry as a bone... that engine for the first week used a quart and a half... it didnt burn, or leak a drop... the block had to soaked up a good bit of oil.

 

the cast iron is porous to a small extent.. it makes a little sense... only thing else i could think of...

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