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Cylinder hone after 10k km 2

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Deividas

Deividas

Automotive
Dec 14, 2014
106
Hello,

Half year in weekends I was rebuilding my old Alfa Romeo engine. Cylinders were re-bored and honed, new larger pistons with new rings installed, main and conrod bearings replaced, new valves, valve guides, valve stem seals installed, all other seals and gaskets replaced. And, as it was my first engine rebuild, in break in period I used 5w40 synthetic oil, and as I found out later, it was not good idea. Oil was changed after 1000 km to same 5w40. Right after rebuild, engine was using oil, I thought maybe it's due to break in period, but now, after few thousands km, engine still consumes a large amount of oil, about 1,5 - 2 litres for 1k km.
I can't understand where is the problem and I planning to try disassemble engine again after winter, when it gets warmer outside. I think, that there can be issues with oil rings, and my question is, do I need to get cylinders honed again, if I will replace piston rings? I know, that it's recomended to hone cylinders when changing rings, but if cylinders were honed few thousands km ago?
 
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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.
 
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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?
 
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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.
 
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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.
 
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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.
 
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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.

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.

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

Who assembled the engine ?
 
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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
 
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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
 
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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?
 
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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.

PXL_20210619_205300158_kxxnpa.jpg
 
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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
 
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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
 
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"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.
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.

 
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("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?
 
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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
 
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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
 
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