Power, economy, oil...

[johnl]

JohnL - Thanks, some food for thought there. I cut my teeth on A Series engines as a kid many years ago, so do remember those pistons you describe.

So the decision I have then is to spend the time to mount the pistons in the milling machine, drill a total of twenty four holes (three per thrust side/piston, de-burr and clean...). Or just whack em in. Will let you know what I do.

Cheers
Vne

As I'm sure you know, slots or holes in the oil ring grooves are to allow excess oil to drain to the inside of the skirt, instead of 'filling' the space behind the oil rings. If the space behind the oil ring fills with oil then more oil will get past the oil ring and possibly interfere with the compression ring seal (which are not so good at 'scraping' oil from the bore), and then enter the combustion chamber. These holes (and maybe slots?) are very common, so much that I'd be surprised to not find them in any vaguely modern engine. So, I'm surprised that your pistons don't have them...

Long slots in the skirt are there (which they aren't these days, at least I've not seen such slots for many years) so that the piston can be run with a very tight tolerance to the bore, which eliminates piston slap when the pistons are cold, but not seize when the piston heats up and expands (the slots get squeezed tighter instead of the piston seizing, but which probably still increases piston drag to some degree). This makes for a slightly quieter engine when cold, but at the expense of a substantial reduction in piston strength, which might be OK for a low stressed / low revving engine, but not so much for 'modern' more highly stressed / higher revving engines...

Drilling holes in a piston that doesn't have them already shouldn't require a milling machine, just careful work with a hand held drill, or something like a 'Dremel'. You want to avoid 'nicking' the top or bottom horizontal faces of the ring grooves with the drill bit (especially the upper face). So, I'd use a drill bit with a diameter a bit less than the width of the groove, don't let the drill wobble, keep the bit at 90° to the vertical axis of the piston.

I'd grind some metal from the sides of the drill bit so that the bit diameter is slightly reduced, from the corners of the cutting edges and upward for a few millimetres. If you do this then the edges of the spiral flutes shouldn't contact the piston (if the drill doesn't go in dead straight). Avoid the bit contacting and cutting into the pin bosses.

Regards,
John.

[bazzbazz]

To my knowledge the blocks are the same.

[johnl]

and what are your thoughts on machining a wider groove in the pistons to allow for a deeper oil control ring

How much metal would remain in the ring land thickness after machining the oil ring groove wider? I suspect that might be the limiting factor (?).

Looking around on the interweb, from what I see it appears that the JTS pistons don't (surprisingly) have any holes in the oil ring grooves, and also use one piece oil rings (also surprising if true). Is this correct?

If so, then I'm not a fan. It's my understanding that one piece oil rings are generally inferior to three piece oil rings. As per my understanding, three piece oil rings are effectively two quite flexible rings separated by a spacer. One piece rings are stiffer, and as a result don't conform to the bore as well as three piece rings do, often permitting excessive oil to get past the ring.

If this were my project I'd be looking to fit three piece oil rings (if possible), and drilling the oil ring grooves.

I've never had my pistons out so I don't know what they look like. Are the TS oil rings similar to the JTS? Do the TS pistons have holes drilled in the grooves?

Regards,
John.

[bonno]

Hi JTS owners
Excessive engine oil consumption with JTS engine. Found an interesting thread on Alfa Owner forum in the UK, in particular the post, dated 15-01-17 on outcome.
http://www.alfaowner.com/Forum/alfa-147-156-andamp-gt/1023626-alfa-romeo-156-jts-oil-mystery.html

[johnl]

With more familiarity with the change in power characteristics (with the thicker oil), I now don't think that the engine has lost top end power. There is a definite increase in low rpm power, it's unmistakably there from idle and into middling rpm. This is especially noticable when moving off from rest with almost no need to carefully balance clutch and throttle movements as before, the car will just move easily without wanting to 'bog down' as the clutch is let out. It's also better able to climb inclines in a taller gear, and more responsive when increasing speed from cruising rpm.

This makes it feel 'as if' it has lost some power in the upper rev range, there is now not as big a change in acceleration as the rpm increases. It's a relative perception thing.

Regards,
John.

[Citroënbender]

What height middle ring?  The CF3 TS went from 1.5 to 1.2mm in its first design change note.

[bazzbazz]

Do you really think that a small change of viscosity will have a noticeable effect moving a 1300KG mass

If the engine is full of old crud/sludge oil that is more akin to Molasses, sure. (Just ask my oldest son, he's an expert on it!)

[johnl]

Do you really think that a small change of viscosity will have a noticeable effect moving a 1300KG mass

Yes, at least a fairly substantial viscosity change can.

The old oil was quite 'thin', seemingly quite a lot thinner than it was when new even considering that the oil was warm when I drained it, it ran out like black water. It was still thin in the catch tray after it had cooled down. Oil can both thin out or thicken up in use, I've seen both happen with used oil. I've changed oil many times over the years, and seen hot oil run out both thick and thin, this was definitely quite a bit thinner than I would think to be usual.

This page from BITOG:

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/652719/Does_motor_oil_usually_thicken

The new oil is quite thick for an engine oil. I think it's more than a small viscosity change from what was in the engine to what is in there now.

The compression rings rely on the oil film to properly seal the combustion chamber, whether the rings are in perfect condition, or less than perfect. The more worn or glazed the rings and / or the bore suface (or the more resistant the rings are to moving freely in their grooves due to gunky deposits in the ring lands), the more likely it is that the ring seal won't be all that good, and the more the rings will rely on the oil to help seal the chamber. This is why adding some oil into the combustion chamber for a 'wet' compression test will increase compression (telling you whether poor compression is due to bad rings / bore or leaky valves, i.e. the excessive quantity of oil around the rings will 'artificially' and briefly increase ring seal if the rings are poor, being diagnostic of bad rings).

Poor ring seal and the engine loses significant compression on the compression stroke, and loses cylinder pressure on the power stroke (blow-by). Both of these problems can, if bad enough, result in significantly less power being produced. A too thin oil (for the circumstance) will be less able to assist the rings in sealing, it will just get 'blasted' out of the ring / bore interface by the compression and combustion pressures. A thicker oil will (may) stay in place more effectively. If the rings are not perfect then thicker oil will probably help, and result in higher combustion pressures, and more power will be produced.

It is the increase in power due to improved ring seal, especially at lower rpm when there is more time for pressure to be lost on the compression and power strokes, that has the noticable affect on moving the car. It's less likely to have as significant an affect at higher rpm, because there is less time for pressures to be lost via the rings.

Hypothetically and veering way off topic, if it were possible to raise rpm to an impossibly high number then the need for piston rings would largely disappear because there wouldn't be enough time for significant pressure to bypass the piston, a tightish piston to bore clearance would be enough. Turbine engines largely rely on this, i.e. there is a small clearance between the turbine blades and the housing (i.e. no physical seal), but the turbine blades move so fast that the compressed gasses can't escape and are adequately retained within the spaces in which they need to be.

Regards,
John.

[johnl]

The engine I did the autopsy on shows significant contamination of the piston rings large amounts of thick gunk stuck in and around the rings that would definitely hinder the sealing performance of the rings

If the rings get stuck in the grooves, then they aren't able to push against the bore and of course sealing suffers. I suspect it's not uncommon for a diagnose of 'bad rings' to be made when in reality the rings themselves are OK, just 'glued' into the grooves, and a good cleaning would set all to rights...

Highly detergent oils might help (and maybe the more effective 'engine cleaner' oil additives out there). After changing the oil on my old Accord (first oil change in my ownership) using a highly detergent deisel engine oil, after about a week or so I started to notice an unexpected improvement in engine performance. At the time I speculated that the cleaning action of the oil might have removed gunk from the rings and lands, maybe...

A reasonably objective indicator that the thicker oil is doing something beneficial is the improved fuel consumption (and the improvement may or may not be as much to do with the oil being new as it is to being thicker, not really sure). A few weeks ago the indicated consumption was steady at 8.8L/100km, then it dropped to a steady 8.4L/100km after changing the upstream O2 sensors, now it is hovering between 7.6 and 7.7 L/100km after changing the oil. This is a bigger improvement with new / thicker oil than with new 02 sensors...

Regards,
John.

[johnl]

can we really afford to experiment with different oil weights or  formulations when the oil type is so specific  "10-60 SYNTH"

The 10 weight is to protect the camshafts and variator and the 60 is for the bottom end and oil burning. we could move between the oil weights and protect one more than the other. Keep the bottom end safe and sacrifice the top end or use a thinner oil and sacrifice the big end for the cams and variator

So if the 'cold thinness' "is to protect the camshafts and variator" from damage and wear, it's curious that when my old thinned out (quite) oil was changed to a substantially thicker new oil, the obvious variator rattle on cold start up (and sometimes hot) completely disappeared...

This would imply that with thicker oil, less of it might be draining from the internals of the variator after shutting the engine off, even if we assume that it may take a slightly longer for the variator to fully pressurise on start up. Assuming that the variator is being most worn / damaged during the time it is audibly rattling due to lack of oil, surely this would be more protective of the variator than allowing it to rattle away for several seconds with a thinner oil? Or, it might be that the thicker oil also mostly drains out, but whatever residual thicker oil still in there (and this is may well be more than with a thinner oil) acts to more effectively 'cushion' the internal impacts that cause the audible rattling...?

The cams. My understanding (FWIW...) is that it doesn't take much oil to lubricate the cam and tappet faces at start up, when rpm are particularly low. Just enough to keep the surfaces separated is enough, and even when a lot of oil is present most of it gets squeezed out due the considerable pressure that exists between the cam and tappet faces (the most highly loaded surfaces in any four stroke engine). From previous operation a residual oil film will remain clinging to the surfaces, and before start up there will be a significant 'reservoir' of oil at and around the point where the cam lobe is contacting the tappet face. A 'fillet' of oil will be sitting at / around this contact point, held by the clingy nature of the oil and the surface tension of it. At start up, as the cam lobe rotates this oil will be 'wiped' onto the lobe surface, lubricating it until more oil becomes present.

This would I think be more to do with the 'hot' rating of the oil, since most of the drainage would occur while the oil is still hot, so an oil that is thicker when hot (say 60 weight compared to say 40) may well be more protective at cold start up, because more is likely to be present at the cams / tappets at cold start (or at least avoiding not quite enough being present as might conceivably occur with a thinner oil).

All else being equal, the thinner the oil the less this will tend to occur, as thin oil will more readily drain away from the cam / tappet faces after shut down, as opposed to a thicker oil, which will less readily drain away. This residual oil (and more so the more of it) should be adequate to lubricate the cam and tappet surfaces for the first few seconds of start up operation, before oil is pumped at full pressure through the system and finds its' way onto the cams, and more so the thicker the oil may be. So, as I see it, it may well be more likely that a thicker oil will protect the cams / tappets at start up more effectively than a thinner oil. I could be wrong, I'm not a tribologist, but it seems logical if I'm not missing something...

My understanding of the purpose of 'multi weight' oils is simply that such oils thin out (with heat) less than do single weight oils, i.e. all oils thin out with heat, but multi weights less so (and less so the greater the spread between the 'cold' and 'hot' numbers of the oil). This means that a cold multi weight oil (with a low 'cold' number) will circulate more quickly at start up and flow a greater quantity of oil through the system more quickly, getting oil to the bearings rapidly (noting that there will be residual oil in the bearings too, probably more with a thicker oil...), helpful to avoid issues if the engine is used too hard too soon after start up, and perhaps for cold oil to spray onto the bore surfaces more quickly (and again noting that residual oil will cling to the bore walls and in the ring pack as well, probably more so with a thicker oil).

I can't see that using an oil with a cold rating of 20 as opposed to 10 (or even 5) is going to be problematic, 20 is still reasonably thin and will pump through quite quickly from cold, perhaps with the exception of use in very cold ambient temperatures. Using the thicker oil I've noticed no difference in how long it takes for the CEL to switch off, which is I think a function of the oil pressure coming up to X. It doesn't take more time, and seems to be a bit quicker if anything (totally subjective as this is...).

Still, it's not good for cold oil to be too thick, it places a significant load on the oil pump, and affects fuel economy, at least until the oil warms up. In extremely cold conditions it may just take way too long for the cold thickened oil to thin out enough to pump easily, appreciably longer than it may take for the coolant temperature to reach operating temperature.

Assuming this to be the case, a thinner cold rating could avoid problems if say the driver uses the engine hard once the coolant is up to temperature but the oil is still too cold (or if the driver just uses the engine too hard when nothing is yet up to temperature, as will be the case for some drivers...).

I suspect that the real reasons why FIAT specified an oil with a hot 60 rating (for "decidedly sportive use") might be so that more oil would be present at the cams / tappets at cold start (given stories I hear re cam lobe wear), or, was simply to reduce oil consumption that occurred with these engines when habitually driven fairly hard over time. For 'normal' use they specified a hot 40 rating, which turned out to be too thin to keep oil consumption at a reasonable level, even with gently driven engines. Could this also be related to ameliorating cam lobe wear, I have my suspicions.

As if I haven't blathered on long enough, it occurs to me that we should also keep in mind the difference between the 'cold' and 'hot' numbers in the oil spec. The greater this difference (e.g. 10W60 having a difference of 50, as opposed to say a 20W/60 having 40 difference) the more likely it is that the oil has a heavier dose of 'viscosity improvers' in the formulation. These chemicals are the first things to degrade in an oil, and the more there is / are the more the oil is likely to degrade in X conditions over Y time. This will cause the oil to lose some degree of its' 'multi weight' capability, whether by thinning out when hot or thickening up when cold, or both, I don't know.

All else being equal, two similar oils one with a wide 'spread' and another with a significantly smaller spread, the one with the smaller spread is likely to have less viscosity improving chemicals in it, and therefore more likely to last longer. It's my understanding that fully synthetic oils tend to be less affected by this degradation due to the superior qualities of the base oil, meaning less viscosity improvers tend to be used, but even so the affect still exists because they still have some.

Apologies for the long post...

Regards,
John.

[bazzbazz]

Que?  (as said by Manuel)

   

[johnl]

Que?  (as said by Manuel)

Hi Baz,
Que what? Can you not follow my admittedly long winded arguments, or implying that they are incorrect?

I don't mind if anyone disagrees with something I may write, it's always open for discussion.

In this case it was suggested that thin oil is good for the upper engine components but not good for the bottom end components, and conversely that thicker oil is good for the lower end but not good for the upper end. I've never heard this argument before, and can't see why it would be true. I just put forward an argument as to why I think this isn't necessarily so. If my argument is wrong then it would be interesting to be told why...

Regards,
John.

[bazzbazz]

Sportiva - tap tap tap (private joke)

[johnl]

10-60 SYNTH covers the specific demands these engines require

Agreed, but I'm not convinced that using a 20W/60 will cause any problems, if the engine is used sensibly (i.e. not revving it hard with cold oil).

Such an oil isn't all that much thicker at ambient temperature than a 10W/60. If the engine can cope with the relatively high pumping loads and lesser flow rate of an oil with a 'hot' rating of 60 (quite a thick 'hot' rating) up to maximum rpm with the oil at operating temperature, then I think it should also cope with a somewhat thicker 'cold' rated oil, if the engine isn't revved hard until warmed up.

I agree that a 'synthetic' oil (whatever that may mean with a specific oil, i.e. maybe 'hydrocracked' mineral oil, or better still PAO / ester based) is preferable to a more conventional mineral oil. I chose a mineral oil simply because it was cheaper at a time when funds were depleted (i.e. I was next to broke...). If cost were not an issue I would always use a PAO and / or ester based synthetic oil, but such oils are not inexpensive. I'm confident that a good quality mineral oil will be quite OK so long as it's not left in he engine for an extended oil change interval (I change at 10,000km, though the last change was admittedly a bit late).

I would and do avoid mineral oil in our Saab, as these engines are well known to be extremely hard on their oil. This is due to the oil passing through the bearings in a turbocharger, the very close proximity of the cat convertor to the sump (heat soak into the oil), and a marginal crankcase ventilation design. These factors conspire to make these engines sludge badly if mineral oils are used, and not changed frequently enough regardless of the oil used (again I change at 10,000km, but would do so more often if the car were used mainly in urban driving, even with a 'fully synthetic' oil, probably at 8000km).

Regards,
John.

[Citroënbender]

I cannot comprehend the disparity in comments by the original poster; in one instance a change of oil (old for new) results in claims of appreciably better performance - yet in another instance - the actual grade of oil used as replacement, the dismissal is effectively "near enough is good enough" with respect to its departure from OEM recommendation. 

While I accept that there are indisputably "black arts" (said tongue-in-cheek, the point being some things are such a convergence of miniscule differences that it's effectively impossible to scientifically reduce it all to measures and procedure) the avoidance of hard data in cases such as the above makes them at best entertainment.