The synthetic oil didn't cause your problem. I think you're going to find a larger issue that a re-hone isn't going to fix.

Otherwise, it is standard practice to run a home through the cylinders when replacing rings. If anything, it cleans the cylinders.

Maybe there will be some other things, that causes oil consumption, but if cylinders were honed only few thousand km ago and there is no damage to cylinder walls, is it really necessary to hone again if replacing rings? Or new rings can seat only on freshly honed cylinders?

If you find the problem is not the rings then you won't need to replace them and in that case you won't need to hone.

Who did the machining work, and how did they do it?
What's the piston-to-cylinder clearance? Cylinders checked for out-of-round or taper?
What did the machinist say about piston ring selection and break-in?
How are compression and leak-down?
What do the sparkplugs look like?
Is there evidence of one cylinder being responsible or are things reasonably even across all cylinders?

I presume you've checked the silly stuff. Crankcase venting, valve stem seal installation, etc.

I have an oil-burner engine myself, but given that the vehicle it's in isn't worth what it would cost to professionally repair, and the amount of oil consumption is remaining stable (about 1 litre per 1200 - 1500 km) and it runs well otherwise, I have just consigned myself to frequently checking and topping up the oil until something big goes wrong with it.

No, engines are often re-ringed without being rehoned.

Unless there is damage to the cylinder walls visible on a borescope or other obvious issues I would start with an exhaust gas analysis to confirm that oil is being burnt and not lost elsewhere, then troubleshoot accordingly.

Over 2 quarts per 1000 miles? There should be smoke visible in the exhaust during an accelerate/coast/over-run cycle.

I'm guessing "old" is not old enough to have replaceable liners.

How was the block , especially the cylinder bores, cleaned for assembly?
Honing grit can tear up rings permanently. Sometimes the rings and cylinders die together.

Some heavy throttle in short bursts is needed to force the rings against the cylinders for a good break-in.
https://www.us.mahle.com/media/usa/motorsports/mms...

Depending on the results of thorough compression and leak-down tests, performing te following steps of the break-in from the above MAHLE link is worth a try.

Engine block was given to machine shop with new pistons, so they said that cylinders were bored to exactly match new pistons size, and all engine was cleaned by them before and after boring and honing. I didn't ask them about clearances, because they anyway done boring to match new pistons and also I don't have tools to measure cylinders. I checked spark plugs after about 1500 km, one of four was more black than others, but there wasn't much oil on plugs, and as I saw through spark plug holes, all pistons were black. It's very strange, but I didn't saw blue smoke at all when driving, only white fumes, but tailpipe is all black inside, so it means that oil is being burned, not leaking (engine is dry, if it was leaking so much oil, it would be all wet). I also done compression pressure test, all cylinders were about at 145-160 psi

You'll just have to tear down and inspect. It's possible a ring was broken during install. If you're lucky this doesn't damage the cylinder so you can slap new rings on that piston and send it.

"all engine was cleaned by them before and after boring and honing."

Who assembled the engine ?

Tmoose - I assembled this engine, machine shop only bored, honed and cleaned cylinder block, polished crank, also they replaced valve guides and resurfaced cylinder head

Sounds like the rings didn't bed. Follow the steps at the bottom of Tmoose's post. I have ALWAYS done that with a rebuilt engine as soon as it is warmed up for the first time.

Were the ring gaps checked?
Are you certain the compression rings were installed the correct way up?
Check with the supplier of the rings. Some modern low tension rings can be difficult to bed.
Ask the machine shop about their honing procedure - grit sizes, honing steps etc. Presumably they are performing an appropriate "plateau hone". Make sure this aligns with the ring-suppliers recommendation for honing.

je suis charlie

Lack of smoke and good compression make me more suspicious the problem is not the long-block. Unless you're seeing an oily sludge in plugs or exhaust, excess carbon could simply be a rich fuel mixture. Oil disappearance doesnt necessarily mean its being burned or leaking externally, it can leak internally into the cooling system, transmission, or elsewhere.

That said, any shop that wants the pistons onhand to bore the block begs the question - Why, are they not boring to spec?

Automotive machine shops don't have the luxury of climate controlled measurement rooms. There is too much variability in their measurements to maintain the 0.0005" accuracy necessary to fit pistons to spec. It's easier to have the piston and the block in the same room and measured with the same tool. It eliminates one source of error.

Also, most OEMs use a "select fit" process with multiple piston sizes to select the best fit for the bore.

I bought this engine knowing it was an oil burner. No smoke, was getting hard to start due to valve recession, burned a similar amount of oil.

From the description, the engine is consuming oil on all cylinders. Synthetic oils typically produce less visible smoke. Good synthetic oils have high solvency and create less "coking". The black carbon in cylinder and tailpipe is more likely rich mixture.

je suis charlie

Thank You all for answers, I will try to tear down this engine again in spring and inspect where is the problem. And if I'm lucky, maybe new rings will solve my problem. Also I heard few cases, that on these engines valve stem seals can fly off from valve guide boss, if it's my case, then it will be pretty easy to just replace stem seals. I just don't want to remove all engine again and pay for honing and other work, because this car is too old and too cheap to spend so much money and time again.

P.S. sorry for my English

"I assembled this engine, machine shop only bored, honed and cleaned cylinder block, polished crank,......"

Unless the parts were wrapped in plastic and had labels explicitly saying "clean enough for assembly" I would doubt they were CEFA.
Actually I prefer to do my own cleaning prior to assembly.

Cylinder bores in particular need to be very clean. Most solvents are insufficient.
A thorough scrub brush and hot soapy water has long been popular.
A final test is a white rag damp with clean engine oils MUST stay white after being rubbed in the cylinders.

Older Alfa cranks had complicated drilled oil passages, with intersections and some holes plugged with soft plugs pounded into place.
https://www.alfabb.com/attachments/p1110064-medium...
Trying to flush all the grit out of a ground crank is futile. The plugs must be removed. Tapping the holes in the hardened crankshaft for threaded plugs to be installed after proper cleaning is challenging. Over 2 score years ago a friend had is Alfa 2 liter engine rebuilt. The assembler did not clean the freshly ground crank properly. When the oil pressure went to hell after a way less than 1000 miles it was a very sad day.

https://www.mahle-aftermarket.com/media/homepage/f...

("Most solvents are insufficient.") A bit of oil on a rag sort of helps that and gosh in the old days they would dump Bon Ami down the carburetor to help break in rings so? If not clean, then ring break in should be good to completely wasted ring packs. How do they look? End gaps?

Do not tear the engine down again until you have followed the break in procedure. Choose the highest gear which can run to 75% of max rpm without exceeding the speed limit.

Next, start at 25% of the max rpm with light throttle and accelerate at wide open throttle to
75% of max rpm. Then engine brake with the throttle closed, back to 25% max rpm. Repeat
this 5-6 times.
 Example: 8000rpm max would start at 2000rpm and accelerate to 6000rpm then
engine brake back to 2000rpm.

je suis charlie

gruntguru - I tried to do this, but I think it was too late, because I did it about 2000 km after rebuilt. Or maybe problem is not with piston rings

That is literally called the "Italian tune-up". The thought is that running an engine under heavy load clears out carbon buildup and deglazes cylinder walls.

Honda has a recall out on their engines currently. It calls for replacement of piston rings. I don't think they recommend honing the cylinders.

Not the Italian tune-up - this is the age old procedure for initial bed-in of new rings. From a reputable source Link

BTW the Italian tune-up does work. Also known as a dyno decoke. Apply full load at peak torque rpm until the exhaust clears. Follow up with oil change and new spark plugs.

je suis charlie

Machine shops without HVAC are pretty rare stateside anymore, and OEs haven't selectively fit pistons in ~40 years that I know of. Regardless, if a shop is measuring pistons then they're not following piston manufacturer's spec for bore size (clearance) or finish so I wouldn't expect high quality work.

I still suspect that your problem isnt in the long-block. If you somehow were burning 1.5-2 liters tho, I wouldn't expect break-in to solve anything and would start by checking the condition and orientation of the rings. That said, if your 2k kms has been mostly short stop&go trips around town then its far from broken-in. I usually recommend new engines be babied on a nice long 2k+ km, mostly freeway roadtrip or motored and run-in via a dyno if money allows. Slamming transients on new ring packs is a great way of destroying engines and verboten in development.

Most of my experience with select fit pistons is in dirt bikes. The Japanese OEM's have A through D sizes for pistons and cylinders. You can't order a specific sized cylinder so you would need to order a cylinder, check the stamp, then order the correct piston. Instead the dealers stock the smallest D size piston and that gets used in all cylinders.

"if a shop is measuring pistons then they're not following piston manufacturer's spec for bore size (clearance) or finish"

logical fallacies - causal fallacy or maybe false dichotomy ?

Neither, due-diligence.

Today I saw video on Youtube and decided to try my luck, when it gets warmer outside, and try to change valve stem seals without removing cylinder head. I think simple method with rope/shoelace inserted in cylinder through spark plug hole with piston at TDC should work just fine, so this way I can save my time and money. And if new seals won't help, then it will be clear, that problem is with piston rings or cylinders

I thought the usual trick was a spark plug adapter for an air compressor to hold the valves closed while replacing the seals.

You might also be able to hear/feel air leaking past the valve stem seal.

3DDave - yes, method with air compressor also should work, but I don't have air compressor in my garage and I don't want to buy it just to use it once for this job

They are available for rent.

3DDave - yes, I know, but i don't see difference between these two methods

You don't need TDC with the air pump and you can confirm the valve stem is leaking without replacing it.

Is that worth the risk? Any loss of air pressure means the head is coming off.

3DDave - how You can see valve stem leakage with compressed air in cylinder if valve is closed? Cylinder head was checked before installation, and there was no leakage between valves and valve seats

Valve stems will leak with compressed air. They are not meant to seal.

An observation I have made working with 2-stroke diesels. They have an air box between between the combustion chamber and crankcase. There is no path for combustion gasses to get to the crankcase through the piston rings yet the oil still turns black. As it turns out, the majority of the blow-by is through the valve guides. I think you will find that this holds true for most engines, especially turbocharged engines.

Hello to all,

So, as I planned, I changed valve stem seals without removing cylinder head, almost all of them were not "fully seated" and also found intake manifold gasket oil leak (there is variable valve solenoid on intake manifold), so replaced this gasket also.
Assembled everything as it was, mounted timing belt, and... Surprise! Engine spins so hard with wrench, that I thought that something fall inside cylinder and blocked piston. Before dissasmebling head I checked timing marks and engine was spinning as it should, without too much force.
Removed timing belt, placed piston between tdc and bdc and tried to rotate camshafts by hand, and intake camshaft was very very hard to rotate.
After this I removed camshafts and hydraulic tappets, installed camshafts without tappets again, so now they not touching valves and should spin freely, but intake cam spins quite hard compared to exhaust cam. Tried to remove intake camshaft caps and even with one cap installed it still turns quite hard.
Any ideas what happened?

Edit:
Found the problem - damaged camshaft journal

Hello,

After few hundreds km valve stem seals popped off again. First time I used oil to fit them, second time I installed them dry, because I thought that maybe they popped off because of being lubricated inside. Both times I installed them with socket and they fit pretty easy without too much force. Anyone had similar situation? Because I don't know what to do, to keep them in place

Have these seals got a wound spring retainer to hold and retain an internal rib in a corresponding groove in valve guide?

Politicians like to panic, they need activity. It is their substitute for achievement.

Pud - no, there is no spring on seals to hold them in place. Also there is no groove on valve guide. Valve guide surface is smooth

What model and year Alfa?
The ones I'm //familiar// with would have had replaceable liner kits. 1950, 1960s, 1970s.

Did you say at the rebuild the valve stem seals were found out of place?

regardless, I wonder if the "new" guides were machined properly.
Diameter within .002", and groove type features.
Possibly just a roughened surface, although I think that would be wishful thinking for seal retention.

Did you use genuine OEM valve seals?

What is the un-installed seal OD? If the genuine seals have no clamping/booster springs on the OD. maybe a few coils cut from the appropriate size fine wire coil spring could be ddded.

Glue. I'd look for one that has a forever operating temp over 300° F.

Tmoose - it's 2000 Alfa 156. When I was rebuilding engine, I sent cylinder head to machine shop to resurface it and they also changed exhaust valve guides and exhaust valves, they removed old valve stem seals, so now I don't know if they were out of place or not. I used non OEM valve seals, because they cost about 10x more than aftermarket brands, and as I saw in catalog, all brands have same dimensions

Same dimensions != same performance

I could not find any Alfa 156 valve stem seals on line that were not pictured with metal shells or other features on the OD to enhance the grip of the seal on the guide.

Do your seals lack that kind of feature?


https://alfa-restoration.co.uk/shop/images/thumbs/...

https://www.kmotorshop.com/document/shop/701.289/t...

https://www.ebay.com/itm/263719475450

https://www.bestpartstore.co.uk/engine/valve-stem-...

Tmoose - sorry, I misunderstood you. These seals in your link are same as mine

Reading the posts, including ones from the OP on the Alfa owner's site, it appears possible the valve guides that were installed do not match the OEM guides. The engine seems to be a niche engine; there were multiple mentions that many of them did not have seals on the exhaust guides and many did not have any guide seals at all.

Since the engine shop tossed the original parts it's not possible to know if the replacements were a match for them. It's possible it's now a frankenmotor.

3DDave - yes, machine shop replaced exhaust valve guides and exhaust valves, but intake valve guide seals also popped off, and as far as I know, intake valve guides are still original

There is a type of seal often called an umbrella seal. These ride up and down with the valve stem and don't attach to the guide.