Ring seating, heat transfer

[hoodeng]

I will trawl further through the books,but i have read in one somewhere the percentages of heat dissipation in the cylinder/head/piston environment.

Nm9 noted the hone marks being more worn at the top of the bore,these are not high spots, they are where the ring is forced into the bore by initial combustion,this can get quite pronounced in old engines ,years ago i remember ring manufacturers offering 'ridge dodger rings' these rings had a reduced diameter step down at the top of the ring,they were commonly used in in frame repairs, and saved the time of using a ridge cutter and dressing the bore.

I use cylinders from a manufacturer made in the 90's that if they are not in torque plates and a ring is installed in the bore you can see light between the o/d of the ring and bore surface ,put them in torque plates and the contact is continuous,this one series of engine could be prone to blowby if bore and hone practices were not strictly adhered to.

Cheers.

[modok]

i know what he means.
I see the UNEVEN WEAR in the top ring travel, on engines not honed with torque plates.
Including OEM
The difference is plain to see, and plain to measure

But there isn't any correlation, that I have found, between that and "ring seating problems"

Bore guages and surface RMS, not telling the whole story.
Dyne testing would be a big clue IMO

[digger]

according to mahle 60% of of heat loss on a gasoline engine without any oil sprayers is via the ring belt (rings and lands). they dont go into detail regarding the breakdown between rings and lands or individual lands but you can bet the top half of the belt is the majority

[hoodeng]

I found the following in the 'Mahle Piston Manual' , i know i have seen a percentage graph somewhere,that somewhere eludes me right now so this will have to do for now.

The Mahle manual goes right into the importance of cooling jets and channels but this is more in relation to high duty diesel., oil is a conductor not an insulator.

Cheers.

[modok]

How about articulated piston?
Skirt sold seperately

[hoodeng]

Not adhering strictly to topic in this case but related is Modok's reference to articulated pistons,these are also called Composite pistons and Cross-head pistons,their design brief is in diesel ,one of their main advantages is in the crown being manufactured from steel or high grade cast iron the skirt section is forged aluminium or nodular graphite cast iron. The crown also has the underside extended to include the gudgeon bosses ,as the crown and pin carrier are unitized this transmits all combustion load directly into the gudgeon pin into the rod. The skirt is now only a guide structure and not taking any combustion loading.
These pistons are typically always oil cooled internally through a number of gallery's or channels, they can have sprayers on the top of the rod or jets in the crankcase.

The ring pack can either be carried in the crown or the trunk ,either way top ring temp is kept in a relatively temperature controlled environment .
These types of assemblies can weigh between 10 to 30% higher than a traditional one piece piston,but their service advantage is worth the extra cost and complexity.

A few of the above quotes are from the 'Detroit Series 53 service manual' or the 'Mahle Piston Manual'

Cheers.

[nm9stheham]

Nm9 noted the hone marks being more worn at the top of the bore,these are not high spots, they are where the ring is forced into the bore by initial combustion,this can get quite pronounced in old engines

Yes I know what you are speaking about, but as Modok noted, that is not what I was referring to. It is the worn vs less worn areas that you see looking around the top of the bore at the same bore height. Maybe the wear of these high spots around the periphery should be referred to as 'break-in' rather than 'ring seating'? My point is the some extended run time will make these wear down some and the ring seal will be better. Plenty of engines never see a torque plate, IMHO probably the great majority that get rebuilt do not.....

[nm9stheham]

Ran across this while looking at some other stuff today... it shows the heat transfer from piston being by far due to the top rings. That is pretty interesting IMHO.

Look at page 12 of thisl ink; it shows 70% of piston heat going out of the ring/land area. This is from a diesel engine, but I would not think that an SI engine would be very far different. Most of the heat outflow is due to the much hotter temps the higher you go on the piston, not that the transfer coefficient is necessarily better.
http://web.mit.edu/2.61/www/Lecture%20n ... transf.pdf

[jed]

A cast piston taht is open behind the oil ring, with wide rings on it, the rings will be doing a lot more cooling than if you have a forged piston and skinny rings.

According to the chart on page 12 the oil rings transfer more heat than any other ring.
I don't quite understand how because the oil ring rails, when considering surface area, have the least contact
area of the other 2 rings.
And after reading all the posts how can top 2 rings transfer/dissipate heat through so little a surface area?
And while talking about ring seating, which I don't use any more I talk about ring sealing, what are symptoms
Of rings not seating?

[Truckedup]

And after reading all the posts how can top 2 rings transfer/dissipate heat through so little a surface area?
And while talking about ring seating, which I don't use any more I talk about ring sealing, what are symptoms
Of rings not seating?

And this is sort of why I started this thread...More of my vintage Brit bike crap....A friend just completed engine work on 75 Norton 850...He was careful to have the jetting and timing correct..The piston clearance, cast pistons, was adequate...Cast iron rings because that's what they use for a street engine....He took it out for a test ride and I could hear him drilling around the country roads... then it got quiet.... A piston seized in the bore, classic four corner damage...No signs of detonation but looking at the rings closely, the wearing of the black finish,the top ring was only partially seated..So it seems the piston got too hot.....considering all else as in order, it must be the rings not transferring heat....The only other available is a Napier second ring in the first groove...but the two top rings appear the same ....

[jed]

What the rings don't touch....is another issue.
what I would consider "rings seating" is about what the rings do touch.

When the rings touch the cylinder and they SCUFF, the raised edges of the scuff marks only serve to hold the rings off the wall.
A Good cylinder surface is fresh material shaped in to provide boundary lubrication. It's about oil, and about oxide.
Old hands will say something like "exposing fresh material, open the pores of the metal" maybe something about work hardening, and....if that's right or not, I don't know, but basically that the right kind of ideas. The surface of any metal is oxide, so you need to make a surface conductive to lubrication with oil, and conductive to forming a new oxide layer.

The top statement is thought provoking. "What do the rings touch"??? Not the cylinder wall per say but the peaks of the
cross hatch. And accordingly the rings are running in the boundary lubrication mode. When I think of a ring traveling over a cylinder I prefer to use the word lapping not scuffing. And the oil in the valleys of the
cross hatch are providing a very small amount of oil for lubricating the rings and piston and providing a fluid to aid the lapping process.


Most automotive enthusiasts are familiar with “Fluid Film Lubrication”. We have all poured motor oil into our engines at one time or another and can we all can imagine the slippery substance that all the lubricated moving parts in your engine are riding on. Some of us can even imagine the pressurized hydrodynamic fluid film that the crankshaft journals are riding on. That is the “Fluid Film Lubrication” that we all know. “Boundary Lubrication”, on the other hand, is still a bit mysterious to most car enthusiasts. “Boundary Lubrication” occurs when the Fluid Film of oil cannot support the heat, speed and/or load between two parts any longer. At this instance the two parts actually come in contact with each other. When this happens you must depend on the Boundary Lubrication Additive Package that is in your oil. In Torco’s case, it is our proprietary anti-wear/anti-friction additive system “MPZ” that addresses the very necessary “Boundary Lubrication”. In a nut shell, the additive system causes a chemical reaction on the surface of the two parts at the instance they come in contact with each other. This chemical reaction changes the chemical make-up of the surface and allows the anti-wear additives to form an anti-wear barrier. In turn, this anti-wear barrier prevents the two parts from wearing, scuffing, gulling and even welding on each other when the Fluid Film is no longer present. This is “Boundary Lubrication” Important Fun Fact: Fluid Film Lubrication accounts for about 5% of all the friction that occurs in your engine. Boundary Lubrication accounts for about 75% of all the friction that occurs in your engine.

[twl]

And after reading all the posts how can top 2 rings transfer/dissipate heat through so little a surface area?
And while talking about ring seating, which I don't use any more I talk about ring sealing, what are symptoms
Of rings not seating?

And this is sort of why I started this thread...More of my vintage Brit bike crap....A friend just completed engine work on 75 Norton 850...He was careful to have the jetting and timing correct..The piston clearance, cast pistons, was adequate...Cast iron rings because that's what they use for a street engine....He took it out for a test ride and I could hear him drilling around the country roads... then it got quiet.... A piston seized in the bore, classic four corner damage...No signs of detonation but looking at the rings closely, the wearing of the black finish,the top ring was only partially seated..So it seems the piston got too hot.....considering all else as in order, it must be the rings not transferring heat....The only other available is a Napier second ring in the first groove...but the two top rings appear the same ....

I would say bore distortion, and fresh hone with minimal "contact surface", along with getting on the throttle too hard before full warm up of the cylinders. Adds up to too rapid piston expansion, and is quite common on aircooled vintage engines.

Also, we commonly saw boring/honing done too fast, where the unfinned sections of barrel liners expanded from heat more than the sections with cooling fins, thereby causing tapered bores which were tight at the bottom by at least half a thou after they cooled down.

Were the barrels bored/honed on torque plates?
Was the bore/hone done slowly enough to prevent overheating of the unfinned(exposed) section of the barrel liners?
Did he allow a decent number of minutes for a full warm-up before hammering the throttle?

[jed]

I agree the piston got hot, you say to hot, if a normal break in procedure was followed and the engine did not over heat,
for who knows for what reason, I would say the cylinder needed another .001/.002 clearance.
The piston was doing its job of transferring heat from the combustion process and grew faster than the cylinder which did not have enough clearance to accommodate the expansion.
There are 4&6 cylinder engines that specific extra clearance on those cylinders and .001 can do wonders at keeping
Problems at bay.

[modok]

A cast piston that is open behind the oil ring, with wide rings on it, the rings will be doing a lot more cooling than if you have a forged piston and skinny rings.

According to the chart on page 12 the oil rings transfer more heat than any other ring.

Seems nonsensical doesn't it.....but, I know the answer to that riddle, is oil. The oil ring takes what oil is thrown on the cylinder and spreads it out, and moves it through the piston also. It moves oil.
bearings are cooled by the oil moving THROUGH them, and pistons are no different.
How did mahle TEST this?....knowing would probably make it more clear what the results actually mean.

[modok]

A brand new fresh engine WILL run hotter.....why?
Clean engine parts absorb more heat, as the surface has not yet developed an insulating layer of carbon.
Same reason new CLEAN exhaust pipes radiate far more heat at first, which on a motorbike might be a concern also.

Cylinders run cooler after they are glazed.
I don't really know why, but they do. Perhaps once the surface is glazed with a flat coating of oxide they simply absorb less of the heat from combustion, and/or the ring friction is reduced.

All of this is in the TOP end, besides cam/lifter...... the bottom end of the engine won't run hot when fresh, so, it can be easy to end up in a condition where the bottom end is cold....not throwing enough oil where it needs to go.