Rings/Bores: Running in?
Discussion
Why is it supposedly neccessary to run rings in to the bores in a particular way? I know that matching the bore hone to the rings is critical to provide seal and offer adequate lubrication without there being excess which would be combusted.
Let's say for a particular motor, I'd been told to get the motor cranked up and get moving. Once it's up to normal operating temp, use something like fourth gear and give it several bursts of acceleration up toward the higher end of the useable rev range. Why?
My thoughts (unknowledgeable as they are) would be that under load the piston would be forced against one cylinder wall but the exerted pressure of the rings would not change as they have a certain amount of float within the lands. Surely being stationary and running the engine to a high engine speed would achieve the same result?
And as for 'glazing the bores', though it's often talked about, no one has ever been able to explain this phenomenon to my satisfaction.
I can't ever remember leaving a car or bike showroom with instructions like this. What's it all about you engine guru's?
Let's say for a particular motor, I'd been told to get the motor cranked up and get moving. Once it's up to normal operating temp, use something like fourth gear and give it several bursts of acceleration up toward the higher end of the useable rev range. Why?
My thoughts (unknowledgeable as they are) would be that under load the piston would be forced against one cylinder wall but the exerted pressure of the rings would not change as they have a certain amount of float within the lands. Surely being stationary and running the engine to a high engine speed would achieve the same result?
And as for 'glazing the bores', though it's often talked about, no one has ever been able to explain this phenomenon to my satisfaction.
I can't ever remember leaving a car or bike showroom with instructions like this. What's it all about you engine guru's?
Your bores are like mountain peaks with valkleys in between. Contact area with the rings is minimal. Initially you want a burst of revs to force the rings into contact with the bores to wear a few peaks down, increasing contact area to seal the rings properly. To much oil and low revs won't allow initial wear to take place. Once you've done the initial bedding in drive more or less as normal. Varying the revs allows for high vaccum under closed throttle conditions. This draws oil up to the bores preventing overheating and cooking of your nice new rings. It also allows you to load the rings, pressing them onto the bores.
Boosted.
Boosted.
Boosted LS1 said:
Your bores are like mountain peaks with valkleys in between. Contact area with the rings is minimal. Initially you want a burst of revs to force the rings into contact with the bores to wear a few peaks down, increasing contact area to seal the rings properly. To much oil and low revs won't allow initial wear to take place. Once you've done the initial bedding in drive more or less as normal. Varying the revs allows for high vaccum under closed throttle conditions. This draws oil up to the bores preventing overheating and cooking of your nice new rings. It also allows you to load the rings, pressing them onto the bores.
Boosted.
Ta for the reply Boosted; you always seem to come across as knowing your stuff.Boosted.
Now, I would have thought that it's solely down to the piston to spread the side load against the cylinder wall when giving it beans or under hard engine braking. I'd expect (perhaps incorrectly) the rings to be exerting the same pressure against the bore no matter what because of the float allowed within the piston lands.
If we assume that those initial bursts of acceleration are going to bed the rings into the cylinder then surely this will only have effect on one side of the cylinder and unload that opposite. Is that not fair comment? And can you explain glazing?
Gas pressure in the cylinder above the piston puts pressure on the rings so this pressure would be fairly equal all around the piston top. The piston is a convenient place to mount rings but doesn't apply sideways/sealing pressure to the rings.
As for glazing I've never experienced that but imagine it caused by overheated oil carbonising on the sides of the bore. If so, it'll be dead smooth and hard. The rings will never bed in to that surface. There will probably be less oil retention in the crosshatching as well. Somebody will know about this and be along in a moment
As for glazing I've never experienced that but imagine it caused by overheated oil carbonising on the sides of the bore. If so, it'll be dead smooth and hard. The rings will never bed in to that surface. There will probably be less oil retention in the crosshatching as well. Somebody will know about this and be along in a moment
Boosted LS1 said:
As for glazing I've never experienced that but imagine it caused by overheated oil carbonising on the sides of the bore. If so, it'll be dead smooth and hard. The rings will never bed in to that surface. There will probably be less oil retention in the crosshatching as well. Somebody will know about this and be along in a moment
Hmm, well maybe not then; Anyway, your explanation is what I'd envisioned as being probable. So, thanks for your contribution there. I once remember Pops Nash (NCK) telling me that they ran rings into a fresh hone by giving the motor a few hammerings up the 1/4 to prevent glazing??What I'm trying to get to the bottom of is my unusually high oil consumption in a new motor (5.4 RV8/4000 miles) with a good leak down test result. Oil burning is certainly apparent during acceleration.
The motor was initially run-in in the manner described using a dedicated mineral 'running-in' oil for 640 miles; followed by a similar distance on another mineral oil before going to a full synth. I've even spoken to the engineers at 'Comma' about the dilemma. You'd think that if the 'apparently' important bedding in phase of applying bursts of acceleration had not been conducted early on then it could be remedied by carrying out the procedure at a later stage. I must point out that it was conducted as soon as we were up to temp (one dark 10 pm night on an airfield).
Any thoughts?
I think the issue with bedding in versus bore glazing is that when they're new the bore and rings only fit each other roughly, and on a microscopic scale they both have a coarse grinding surface. The point of bedding in is that the bore and the rings rub against each other and each one wears the other to fit it more and more closely. As they do this the rough surface of each component gets polished smooth so they form finer and finer grinding surfaces, if this works perfectly then both are worn smooth at the same rate and by the time they have been worn to completely smooth polished finish the two components have also worn to a perfect fit.
This is why you need to roughen the bores (take the glazed surface off) if you fit new rings - you have to start with both components having a similar coarse grinding surface otherwise the one with a smooth surface won't make any impression on the other.
The problem with this bedding-in process is that the rings will only bed in against the bore while they have gas pressure behind them, but meanwhile the bores are steadily being polished by the pistons too. So there is a danger that the pistons will polish the surface of the bores smooth before the rings and bores have been bedded in to each other. This is the 'glazing' that occurs if the engine isn't loaded sufficiently during the initial part of the running in.
This is why you need to roughen the bores (take the glazed surface off) if you fit new rings - you have to start with both components having a similar coarse grinding surface otherwise the one with a smooth surface won't make any impression on the other.
The problem with this bedding-in process is that the rings will only bed in against the bore while they have gas pressure behind them, but meanwhile the bores are steadily being polished by the pistons too. So there is a danger that the pistons will polish the surface of the bores smooth before the rings and bores have been bedded in to each other. This is the 'glazing' that occurs if the engine isn't loaded sufficiently during the initial part of the running in.
GreenV8S said:
I think the issue with bedding in versus bore glazing is that when they're new the bore and rings only fit each other roughly, and on a microscopic scale they both have a coarse grinding surface. The point of bedding in is that the bore and the rings rub against each other and each one wears the other to fit it more and more closely. As they do this the rough surface of each component gets polished smooth so they form finer and finer grinding surfaces, if this works perfectly then both are worn smooth at the same rate and by the time they have been worn to completely smooth polished finish the two components have also worn to a perfect fit.
This is why you need to roughen the bores (take the glazed surface off) if you fit new rings - you have to start with both components having a similar coarse grinding surface otherwise the one with a smooth surface won't make any impression on the other.
The problem with this bedding-in process is that the rings will only bed in against the bore while they have gas pressure behind them, but meanwhile the bores are steadily being polished by the pistons too. So there is a danger that the pistons will polish the surface of the bores smooth before the rings and bores have been bedded in to each other. This is the 'glazing' that occurs if the engine isn't loaded sufficiently during the initial part of the running in.
Ta Pete, glad you came along.This is why you need to roughen the bores (take the glazed surface off) if you fit new rings - you have to start with both components having a similar coarse grinding surface otherwise the one with a smooth surface won't make any impression on the other.
The problem with this bedding-in process is that the rings will only bed in against the bore while they have gas pressure behind them, but meanwhile the bores are steadily being polished by the pistons too. So there is a danger that the pistons will polish the surface of the bores smooth before the rings and bores have been bedded in to each other. This is the 'glazing' that occurs if the engine isn't loaded sufficiently during the initial part of the running in.
Now I've only seen rings with a smooth bearing surface and assumed their edges would be shearing off the peaks of a hone during the running-in process. Enough to leave a valley sufficient to carry oil for lubrication without their being excess that will be combusted (too coarse a hone for example).
I'd certainly never considered the piston itself to contribute to glazing; no matter what the silicone content it'll be softer than the cylinder and it's contact area is relatively large. As your bores see 100,000 miles there's often evidence of the hone being polished away but I'd guess that's inevitable after so many millions of piston sweeps.
If my problem lies in the rings/bores it seems unlikely there's a remedy that doesn't employ an engine pull-down. And that is Totally Arse
Pete, regarding the pistons polishing the bores, if this were the case you'd only get glazing on the thrust faces. I don't know if glazing could be all round the bore but I would have thought that to be more likely? I don't think pistons can cause glazing but it's an interesting thought.
^ You need to put load on the engine soon after startup and make it do some work. Then do a drive with varied revs, throttle action. That way it'll probably be run in before you get to a motorway. Light cruising is the worst way to run an engine in imo as there's no real pressure forcing the rings into contact with the bores.
Boosted LS1 said:
^ You need to put load on the engine soon after startup and make it do some work. Then do a drive with varied revs, throttle action. That way it'll probably be run in before you get to a motorway. Light cruising is the worst way to run an engine in imo as there's no real pressure forcing the rings into contact with the bores.
Like:One person in the car to crank up and warm the motor, monitor the indications and keep his foot on the gas at 2K rpm for the sake of the camshaft lobes whilst another person does a walk around and checks for leaks. After 10 minutes drive the car onto an airfield 1 mile away and stretch the motor with accelerative blasts in 3rd/4th gear being mindful not to labour the motor or exceed approximately 5K rpm? Something like that?
Did it! Still burns oil like a Whale rendering Try Pot!
Thank's for your continued input though Boosted, it's appreciated
. I'm just wondering if there's some cause other than that which we've talked through.Bruce
Boosted LS1 said:
^ You need to put load on the engine soon after startup and make it do some work. Then do a drive with varied revs, throttle action. That way it'll probably be run in before you get to a motorway. Light cruising is the worst way to run an engine in imo as there's no real pressure forcing the rings into contact with the bores.
2Munkys,how many miles as the motor done?what grade/type initial fill of oil have you used?not fully syn i hope
That Daddy said:
2Munkys,how many miles as the motor done?what grade/type initial fill of oil have you used?not fully syn i hope
.Oh, and it's done about 4,500 miles to date.
Edited by 2Munkys on Friday 14th March 09:26
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