Worn rings, end gap and blowby

[Circlotron]

Are some engines more prone to cloverleaf shaped bores than others? If so, what contributes to this? Block rigidity? Coolant flow and block temperature gradients? Change in head stud tension vs temperature?

[ptuomov]

Are some engines more prone to cloverleaf shaped bores than others? If so, what contributes to this? Block rigidity? Coolant flow and block temperature gradients? Change in head stud tension vs temperature?

I don’t know. I’d also be interested in the answer.

I assume (but don’t know) that the head bolt tension can cause the fresh bore to have a fourth-order cloverleaf shape if the block is bored without a torque plate.

I assume that when the engine is run cold, there’s sulfur related bore wear in the cold areas of the bore wall that could explain cloverleaf shape wear. This especially with Nikasil like played bores which are otherwise very difficult to wear down. Getting the engine to operating temperature quickly and using aluminum cylinder towers/liners might help here.

[RDY4WAR]

Something else that must be considered is water. Water is produced in the chamber as a by-product of combustion and also enters from the atmosphere. From the oil point of view, high amounts of water dilution in the oil is common with engines that are short-tripped or experience very short run times where the engine doesn't reach sufficient temperature to evaporate the water.

I collected an oil sample from a local middle school teacher's car who drove <1,000 miles a year, only 31k miles on a 2001 Buick Lesabre. She had a 0.75 mile commute and only drove because she had to carry books, papers, etc... I only looked at the car because it was puffing blue smoke on cold starts (from worn valve seals) and noticed the oil was jet black. It had been more than a year since she changed it, but had only put 1,100 miles on it. She'd always went by the 3k mile rule which for her could've been >3 years. The short commuting meant the engine never got up to temperature, ran rich trying to warm-up, and produced a lot of water dilution in the oil. At just 1,100 miles, the oil was 7% water, and I can only imagine how bad it would be at 3k miles. That GM 3800 had more wear than a 300k mile motor with >10% leakdown in 2 cylinders (8% avg) and a 30% spread in compression. The rings were coked. Extensive treatment with heavy solvents helped to some degree, but not fully restored.

This can also be an issue with drag cars that run for <3 minutes at a time, never get over 180*F, and then shut off to go on a trailer and in storage for possibly weeks at a time between events or months during the winter. Everything that water touches will begin to oxidize.

This brings up my question in relation to all of this. What effect will carbon buildup around the rings, ring lands, and skirts (from poor maintenance) have on cylinder liner wear? Obviously it would accelerate it, but to what degree? If the rings are stuck in the grooves due to oil/sludge/carbon buildup, how does that effect the pattern of cylinder wear?

[ptuomov]

memberlist.php?mode=viewprofile&u=29448

RDY4WAR — I believe the sulfur problems I mentioned above come from sulfur in oil and fuel interacting with water that condenses into oil. Sulfur oxide. That’s how sulfur corrosion gets out of hand if the engine doesn’t regularly get to operating temperature that boils out the water.

Cutting edge recent research from 1925:
https://www.sae.org/publications/techni ... nt/250030/

[PSA]

Exactly right. If the bore shape is clover leaf, only portions of the ring will make contact with the wall surface, allowing blowby areas and causing severe ring hot spots. Now the very hot ring grows in size, increasing pressure against the wall and closing the end gap.

The additional point is that cloverleaf bore shape aligns the ring gaps between the first and second ring with relatively high probability.

If the bore is worn to cloverleaf shape, the piston cooling is really compromised, too, as you say — unless we have piston oil cooling jet. One more reason to have piston oil cooling jets.

Piston oil cooling jets will lower piston temperature by about 27F deg, which is not much when applied to a 450f deg piston temperature. But better than nuttin.

I believe it can be different how much it cools depending on how it's used. The difference on some of the diesel engines I worked with was less than 20 seconds at full power without and 1-10.000 hours with.

[David Redszus]

Ring blow by
Stuck rings that do not move to seal properly allow hot combustion gases to blow past the rings causing them to
overheat and to remove the oil film from the wall surface.

Blow by gases
In normal combustion processes, NOx is formed from the nitrogen in the air. When combined
with water it will form nitric acid (HNO3) in the crankcase. Nitric acid will cause bearing corrosion if
not controlled. Nikasil surfaces can resist nitric acids in low concentrations.

If the fuel contains sulfur, its oxides when combined with water, will form sulfuric acid (H2SO4) in the
crankcase if not controlled. Nikasil surfaces will be attacked by sulfuric acids.

Both acids will attack various metals including iron, steel, bearing material, etc.

Engine oils have the ability to neutralize engine acids to some degree. This ability is indicated by
the TBN (total base number), or TAN (total acid number) as shown in oil analysis. But this
acid reducing property wears out in oils with extended use and high acid exposures.

Bore distortion
Engine bore distortion, its causes and remedies, were extensively discussed on earlier forum posts.
Perhaps a search of previous forums will indicate thus.

[jed]

Very interesting discourse concerning blowby. If this conversation was taking place 50/60 years ago the topic of
the cylinders glazed over would have come up. Has this condition gone away and no longer an issue concerning blowby,
excessive oil consumption and smoking.

[hoodeng]

I think cylinders started to get honed in the 30's before that they were a turned finish, soft iron rings made bedding possible. There is a story of a 30's Rolls Royce competition V12 of that period that had an oil consumption in the gallons per run.

Now, we expect zero consumption over the oil change period no matter what it is.

When the Harley Davidson Evolution engine was introduced in 84, oil consumption was now a thing of the past, the shovel engine could be anywhere between zero per oil change to a quart every thousand which would not raise an eyebrow. After extended service the evo would develop four longitudinal polished patches in the bore around 20mm wide adjacent the cylinder through studs, this raised concern to people servicing these engines as some kind of fault, Harley printed in their service manual that these could be expected and ignored. They made no difference to cylinder sealing with a before and after hone cylinder leakage test.

Cheers.

[PSA]

Very interesting discourse concerning blowby. If this conversation was taking place 50/60 years ago the topic of
the cylinders glazed over would have come up. Has this condition gone away and no longer an issue concerning blowby,
excessive oil consumption and smoking.

Glazing could still be a problem, but I believe a big part of it was too low load on the rings (idling) and a rougher finish. It loaded up the surface pretty bad.
Today (if done right) the Ra is better and the engine is heated up and loaded on the dyno right away.

[David Redszus]

Very interesting discourse concerning blowby. If this conversation was taking place 50/60 years ago the topic of
the cylinders glazed over would have come up. Has this condition gone away and no longer an issue concerning blowby,
excessive oil consumption and smoking.

Glazing could still be a problem, but I believe a big part of it was too low load on the rings (idling) and a rougher finish. It loaded up the surface pretty bad.
Today (if done right) the Ra is better and the engine is heated up and loaded on the dyno right away.

A single stage honing procedure will produce a surface finish with as many peaks as valleys, with similar height and depth.
A passing ring will fold the metal peaks over into the valleys, elimination the oil surface reserve. Now the burnished surfaces will overheat due to a lack of lubrication. The Ra might be smooth but the surface has poor oil retention. Not good.

If a very soft ring material is used, it might result in increased ring wear rather than folded metal peaks, a slightly lesser evil. But soft cast iron rings are often replaced with harder steel rings.

The answer of course, is a plateau finish that provides oil retention and a load carrying surface.

[Mark O'Neal]

Had a guy will a BBF engine in a rail.

Beginning of the season, worst cylinder leaked 7%. Ran 7.40s

End of season, worst cylinder leaked over 70%. Ran 7.40s.

[David Redszus]

Had a guy will a BBF engine in a rail.

Beginning of the season, worst cylinder leaked 7%. Ran 7.40s

End of season, worst cylinder leaked over 70%. Ran 7.40s.

So does that mean it was grip limited?

[jed]

Very interesting discourse concerning blowby. If this conversation was taking place 50/60 years ago the topic of
the cylinders glazed over would have come up. Has this condition gone away and no longer an issue concerning blowby,
excessive oil consumption and smoking.

Glazing could still be a problem, but I believe a big part of it was too low load on the rings (idling) and a rougher finish. It loaded up the surface pretty bad.
Today (if done right) the Ra is better and the engine is heated up and loaded on the dyno right away.

A single stage honing procedure will produce a surface finish with as many peaks as valleys, with similar height and depth.
A passing ring will fold the metal peaks over into the valleys, elimination the oil surface reserve. Now the burnished surfaces will overheat due to a lack of lubrication. The Ra might be smooth but the surface has poor oil retention. Not good.

If a very soft ring material is used, it might result in increased ring wear rather than folded metal peaks, a slightly lesser evil. But soft cast iron rings are often replaced with harder steel rings.

The answer of course, is a plateau finish that provides oil retention and a load carrying surface.

David I was wondering what was the source of this information???
This is something I have neaver heard of before. I suppose of all the possibilities it can happen. I

[PSA]

Glazing could still be a problem, but I believe a big part of it was too low load on the rings (idling) and a rougher finish. It loaded up the surface pretty bad.
Today (if done right) the Ra is better and the engine is heated up and loaded on the dyno right away.

A single stage honing procedure will produce a surface finish with as many peaks as valleys, with similar height and depth.
A passing ring will fold the metal peaks over into the valleys, elimination the oil surface reserve. Now the burnished surfaces will overheat due to a lack of lubrication. The Ra might be smooth but the surface has poor oil retention. Not good.

If a very soft ring material is used, it might result in increased ring wear rather than folded metal peaks, a slightly lesser evil. But soft cast iron rings are often replaced with harder steel rings.

The answer of course, is a plateau finish that provides oil retention and a load carrying surface.

David I was wondering what was the source of this information???
This is something I have neaver heard of before. I suppose of all the possibilities it can happen. I

Total-Seal have talked about all of this, among others.
Break-in is almost an art form today, but it can happen later as well.

[hoodeng]

Dynamic leakage is not the same as static leakage, you could leakage test an engine and get a high number, then when it is under full load it will give a lot lower leakage result. This is where manometer testing comes into play, you are now testing dynamic blow by. Manometer testing is probably more recognizable to diesel engine fitters.

On a V twin S&S Pro Stock Motorcycle engine [circa 2005] dynamic leakage is monitored on data as 'Pan Vac', on a sound engine on a good pass we used to see 20+" of pan vac, if this number tapered to 18" or less over the passes ET, rings were going to be most likely to have gone off. This engine displaces the same amount of crankcase air in one revolution as what the engine displaces, so 160" in this case, it had a Dailey oil pump which for the return had rotors not unlike a Roots blower, this would generate vacuum in the bottom end that was measurable and to be kept as high as possible.

Different engines with characteristics to themselves behave differently under load, i have seen some pretty slack engines give stellar results and fresh bullets disappoint. Some engines need to be as tight as a drum, others not so tight, but not thrashed junk either.

There was a story about Cosworth engines in the early years when they leased out engines to teams, of a person getting a walk and talk tour of their facility. As they were going through the engine reco section where everything was bagged and tagged and followed through every step of their overhauls,
the person getting the tour noticed an engine that was stowed off to one side, he inquired as to what was going on with that unit, the reply was "That one will not do what its been told to do"

Cheers.