Freshly rebuilt L28/N42 puffing smoke

[Boog]

Hi guys,

 

I just recently finished rebuilting my L28 in my 280z. It is NA, F54 block, N42 head. I had a machine shop check and hone the cylinders, as well as tank the block. Head was "gone over" as they said, but I put new valve seals in it within the last year or so prior to this. Fresh plugs, fresh rotor and wires, 80 miles on the rebuild so far. New oil pump, water pump, bearings, pistons, and rings. I did all the assembly myself. The motor has great oil pressure, also great operating temperature. 

My main problem is it has been puffing oil smoke.This blue smoke occurs when I am on mid throttle, just starting out from a stop light, or maybe some on heavy throttle or engine braking. I can easily make it puff a plume if I give it a light rev up to 3 or 4 thousand, after it has been warmed up of course. There is no oil smoke on startup, which makes me think that the valve guides are fine still. It also stays the same or maybe gets worse with warming up. I am worried that I did not break my engine in properly. I had some trouble getting it started at first with megasquirt, and I ran it with incorrect timing (around 10 degrees) for the first 10-15 miles before I realized the problem and fixed it. It also may have ran rich. 

 

My main concern is that my rings did not seat properly. I cannot think of any other problem, as it does not match the symptoms of valve seals. My valve cover and my crank case are both vented to atmosphere with filters, as I could not retain my crank case vent to the intake with my headers. Am I right in assuming that these are not contributing to oil smoke? 

 

I am planning on doing both a compression test and a wet compression test as soon as I can borrow a tester from a friend. Until then, does anyone have an idea on what is causing the problem, or what I can do to fix it? I had the car running before the rebuild with the vented valve cover and crank case, and they did not cause the exhaust to smoke like this. I am worried my rings did not seat properly, Thanks in advance for your input. 

[Conedodger]

I use this method to set the rings on newly built motors, find a place with a straight section of flat road. It should be somewhere that you aren't going to piss people off. steadily, in second gear accelerate forward to 5K rpm. When you reach 5K, let off the gas and coast back down to idle. Do this 10 times or so and you should have the rings set.

 

80 miles isn't a whole lot of miles if you haven't consciously set the rings. Do the compression and leak down if this doesn't work.

 

Good luck. Let us know how it turns out.

[BJSZED]

You said the head was gone over. If the valves were removed, were the same seals re-used? If so, they are likely damaged , just a thought?

Vacuum is highest under deceleration, sucks the oil past the seals.

[Boog]

Thanks for the ideas. I'll head out today and do the second gear pulls. The majority of my driving so far has been spirited, not beating on the car but not just putting around town. The reason I have been thinking it isn't valve seals is because the worst of the smoke is just starting off driving from a stop. However, I took my head to a NAPA machine shop for the work and I HIGHLY doubt they replaced the seals. Then again, I highly doubt they even pulled off the valves.

[zforce]

When starting off from a stop is when bad valve guide seals leak the most. With the proper tools replacing the seals is about a 3.5 hour job. Mine lasted about 15 years on a Top-End Performance built head. If you change them out and it's still smoking the valve guides themselves might be the problem. Kd tools no longer makes the valve spring compressor but you might be able to find one on e-bay. When I built my engine I don't recall any smoking due to rings not seating, my experience was the motor ran a little hot for about 300 miles but no smoking.

[Pillar]

It takes more than 80 miles to properly break in an engine, so you may be burning a bit of oil because the rings have not had enough time to wear in to the cylinder walls.  What Conedodger said is the way you want to seat your rings at the beginning of a break in.  Coasting back down from the 5k range while in gear causes the cylinders to build a lot of vacuum, which then "sucks" the piston rings out to the cylinder wall.  Doing this repeatedly will help to wear them in better and faster than just cruising around town for the duration of the break in period and should help the rings seal better.

 

I see that you said the machine shop "checked and honed" the cylinders.  Did you just replace rings, or did they bore the block for new pistons?  Trying to get new rings to seat against a worn bore (even one that is still within spec) can be tough.  If the cylinder is out of round even slightly, or it is at the outer limits of the bore spec for stock pistons, then you increase the chance of blowby considerably.  

[seattlejester]

Glad you got it back up and running. How did you assemble the pistons? Even if you dipped them I'm thinking it shouldn't be burning oil for this long. If you used some lubricant mix though it could be smokey until it clears.

 

The valve seal comment is indeed concerning, what does go over mean? Did they just look at it and say it's ok?

 

What oil are you running?

 

Have a picture of your vacuum running? If your venting to atmo, do you not have any PCV?

 

What about the turbo? Rebuilt? 

 

A friend had a similar situation, turns out it was the atmospheric venting for him. Running a catch can routed to the pre-turbo intake caught a lot of oil that was burning up in the intake and causing him to smoke. 

 

Really it is a matter of forensic disassembly. Pull off the turbo intake and take a look. Do you see any oil? Take off the compressor housing. Do you see any oil? Look in the intake tract. Do you see any oil? Each stage should tell you something as you go.

Edited April 3, 2017 by seattlejester

[Chickenman]

 

 

My valve cover and my crank case are both vented to atmosphere with filters, as I could not retain my crank case vent to the intake with my headers. Am I right in assuming that these are not contributing to oil smoke? 

 

Not running a PCV system certainly doesn't help matters. Headers shouldn't make any difference. You can still run the PCV system. I have headers on my 1976 280Z and run the factory PCV system.

 

I did however replace the section that runs close to the headers with high temperature silicon vent hose. I cut the factory hose off just after the section where it necked down from the block breather tube and joined the two pieces of hose together with a brass coupler.  

 

The factory 280Z PCV hose appears to be made out of rubber, with some sort of heat reflective coating sprayed on. The Hi-Temp silicone hose works better and is cheaper. I use it on my Audi 1.8 Turbo engine as well. A couple of the factory vent hoses run near the Turbo. They are rubber and are always cracking. The Hi-Temp silicone hose solves that issue nicely.

 

As mentioned. 80 miles is nothing in regards to ring seat.  A rebuilt engine is still seating rings up to 1,000 miles of street use. 

Edited April 4, 2017 by Chickenman

[Chickenman]

Call the machine shop and ask them if they replaced the valve seals. Not replacing them could certainly be an issue.  Is this a Normally aspirated engine or a Turbo. Comment about headers made me think it was NA, but then SeattleJester was mentioning a Turbo???

[Boog]

I no longer am running a turbo, I was before but my oil pump failed and killed everything in the engine oil related. I am back to NA until I can get the engine running happily and solid, then I'll consider slapping the turbo back on. The machine shop said that the cylinders just needed a light hone, so I went with standard size new pistons and rings. The reason I got new pistons is because the old ones were donezo after running with no oil, and the donor block had flat tops. My head is slightly higher compression, so I decided to just stick dished ones in it on the off chance I go turbo again soon. Today I was able to drive the car about 10 miles of city driving, with a few small pulls. The oil smoke has definitely gone down, but is definitely not gone. I am definitely considering just doing the valve seals, for peace of mind. All things considered, they would be about 80 bucks and a few hours time to knock out. I'll do the compression test first though. 

[BJSZED]

You can get the felpro seals at rockauto.com much cheaper

[seattlejester]

Oops, I just assumed based on the last time I saw the car. Bummer to hear about the oil pump.

 

Without the turbo in play that kind of eliminates all the intake bound stuff and points more towards the engine.

 

I think a wet and dry compression test will tell us quite a bit. Either the valve seals are not making a good seal. The oil rings are not doing a good job of pulling the oil down. Or the lack of the PCV is messing with the situation. 

[grillhands]

Dont be nice breaking in the engine. While the hone is still fresh you gotta drive it hard to set the rings. First 50 miles I do alot of engine braking. After that I change the oil and beat the crap out of it. My 1.8t was broken in like that. Once i hit 50 miles the engine saw full boost on a t3/t4 50 trim pushing 28lbs. She never puffed smoke for the 2 years I daily drove it.

Edited April 4, 2017 by grillhands

[Boog]

Hey guys, small update. I really took care to watch the exhaust while doing a short drive on it today. I really beat the heck out of it, and made sure to do a ton of engine braking. The smoke occurs on acceleration, deceleration, and transitioning between the two the most. When idling, it really doesn't smoke at all. It also didn't smoke at all when I started it, or when it was warming up for 5 minutes idling. Isn't this different from valve seal symptoms? I thought those leaked down into the cylinder and smoked a ton on startup. Compression test is planned for this weekend.

[Boog]

I also just had a break through that I hope comes to fruition. My crank case vent is basically the oem hose turned down with a filter, wedged near the motor mount. Based on my symptoms I have told you guys, plus what I assume is my leaking main seal and my leaking capped turbo return bung, I think that my hose might be kinked and that there is no crank case venting. All that pressure is causing the the seal to leak in the rear (apparently this is common on mustang 5.0's). I am going to go check it right now and I'll report back. I am also going to hook back up the valve cover vent to the intake. 

 

EDIT: My vent hose was not kinked. I tried re positioning it, but no fix. I also paid close attention to when the engine started smoking. I started the car up, and there was no smoke. I gave it a very light rev, no smoke. I was starting to think it was fixed until the tail pipe started wisping smoke around the 2-3 minute mark. It then got worse and worse as the engine warmed up. After it was decently warm, I gave it a rev up to about 4k, and smoke blew out. I also noticed the wall behind the tail pipe had a black soot circle on it. 2 feet away, and it left a black circle probably 8 inches around. Is it possible I have oil in my exhaust that is burning off?

Edited April 5, 2017 by Boog

[Boog]

So really big update. I tried three things to fix the problem. Firstly I tightened my manifold bolts. Then I went to napa, bought a pcv valve and hooked back up my crank case vent. I also stuck a hose from the valve cover to the throttle body. The smoking stopped completely, I went and drove it around and it was great. However, the idle got all weird. It stumbles between 1500 and 1000 rpm and drives worse. I took the valve cover hose off and capped the throttle body, which made the idle much smoother and it ran way better again. However, with the valve cover hose disconnected and venting to atmosphere, the smoke from the exhaust came back. I love that the smoke is gone, but I can't drive it with that hose connected. Which port on the throttle body should it be connected to? Does this point to valve seals? It doesn't smoke until warm, but it also doesn't smoke when there is vacuum to the valve cover. Help!

[NewZed]

Seems like your oil scrapers maybe aren't scraping.  The bottom set of rings.  Everyone focuses on the sealing rings but the oil rings are important too.

 

You haven't given any details on the type of rings, the matching hone, or who did the work and their experience with Datsun motors.  Just a machine shop that did a hone.  Do you have anything more to work with?  NAPA is just another parts store these days.  Who really knows who's in the machine shop or if it's even not just farmed out.

[Boog]

I bought ITM pistons with the rings they came with. I used NAPA's machine shop, which is a separate location from their normal chain stores. I assembled everything myself, with proper oiling, lubing, torquing, and ring alignment. I can guarantee you that the gaps are within spec and lined up properly.

[NewZed]

The hone, or final surface quality, needs to be specified to match the material of the rings.  I don't think it's a killer as far as getting the rings broken in eventually but it can take longer.  If you don't know what you started with or what the machinist did you might get to a point where you just start using it hard to get the rings to wear to the bores.

 

The amount of detail you're giving suggests that you left it up yo the machinist to decide.  So unless you know what he based his decisions on, you don't have a lot to work with. 

 

If you have loose rings you can get oil burning to cause smoke and blowby that will affect your air quality when the PCV system's connected.  You don't have any measurements either, so it could be that you really could have used a boring.  I'm no expert, I just don't see any detail or numbers to work with.  You depended on the shop to get it right and it sounds like they might have missed the mark.  Did you get any paperwork, even a receipt for the machine work?  Might tell something.

[seattlejester]

Definitely need some picture or numbers to work with.

 

The sooty ring kind of suggests maybe you are just running very rich? If your near the rich mark then it wouldn't be unexpected for you to stumble when you put oil through the intake.

 

What is your AFR sitting at?

 

Leaky valve seals would kind of deposit a bit of oil as the oil drains a bit back into the pan so you would expect some smoking on startup. Then as the oil is flung around you would expect it to leak past the seals. Putting vacuum on the system using the PCV would kind of condense the mixture and have it burn through the engine which wouldn't be very visible.

 

If the smoke which is your concern went away when you vented it to the intake then throw a catch can inline. Oil vapors will hamper the air fuel mixture which might explain why the car stumbles.

 

Honestly I think the rear cap seal is more so the culprit over the rear main seal most of the time. Hammering in those metal strips making sure you don't slice the rubber seal is quite the task.