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Discussion Bore Glazing & Honing

Discussion in 'Tech Tips' started by Joker, May 14, 2015.

  1. Joker

    Joker See "about me" for contact details. Contributing Member

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    So, considering there is a lot of passion for this subject - I figured I'd start a thread on it for some healthy discussion.

    To start off, I've made it pretty clear in other places I have a real problem with this concept of "glazing" and "honing" as some kind of "necessity". I think it is a very high risk activity, often misunderstood/misrepresented and one that should be rarely required.

    Rather than re-state some things that others have said, there's many articles on the topic with vastly differing opinions. As has been said in another forum:

    "Unless one knows what their on about and are up-to-date with current technology, glazing could be an easy 'fits all' approach to diagnosing problems with these (diesel) engines. The word glazing conjours up all sorts of visual imagery that appears 'visually plausible' as an explanation for many undesirable effects, and therefore a convenient truth for the ignorant or person desperate to attribute their problems to something they can 'see'."

    This may also add some clarity:

    http://www.partinfo.co.uk/files/SB2136 - DIESEL ENGINE OIL CONSUMPTION.pdf

    First point: notice the reference to Diesel engines. DIESEL.

    Second point: Try this for something to think about (noted it does not contain references but contains some very interesting challenges on the topic):

    http://www.snowvalley.20m.com/bikes/dnthone.htm

    Also have a read of this article describing the causes and the differentiation between "glazing" and "polishing".

    https://coxengineering.sharepoint.com/Pages/Boreglazing.aspx

    Open for further discussion. I am in the process of putting together a mechanical engineering explanation in an attempt to combat some of the "age old" misconceptions about these processes, the causes of them, how common they should be and why. I'll post it up when I pull it all together but until then feel free to add some thoughts.
     
  2. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Stu, how do mate..FZR grrrrrrr - where's the bandit!!!!!

    Need to start this by saying this is what I've learnt,,read over the years, spoke to many, put into practice, learnt from mistakes, misunderstood and then do what I know works best..a few pics of the latest one attached!

    If you change either the bore or the rings then hone..read all three articles posted above and all are right to an extent..but one is based on iron rings..which no 250cc 4cyl engine has..they will work on that bike though as the ring material will be softer than the bore material..hence the rings wear 'into' the cylinder as opposed to vice versa..all the 250 4 cyls have chrome (or chrome based top rings - pretty hard) - the idea is to make the finished ring and bore to be as round and 'finished' as possible allowing for a short 'break in' (read tolerances to conform too) to match each other and seat well..and maintain oil to lubricate the rings allowing a good seal...if the plateau finishes on both are not compatible..read ring/and or bore wear and worse still low compression..the cylinder has peaks and troughs but so do the rings (unless concentrically cut are far less than round over their working area)..the idea is to make them broadly compatible to make a perfect seal after wearing in to their respective match..each breaks into the other and the quicker you get to that point the less the overall wear). NOTE -this cant be done in manufacture even given modern machining practices..engines are air pumps and all we try and do is minimise loss/ leakdown through rings, valves, piston/cylinder clearance and come out where were at..sometimes not where we want to be granted!! Minimise leakage past valves/rings..keep compression where it needs to be..and know that the closer you match tolerances the better..but always ALWAYS make sure the two surfaces can seat effectively and then hone to suit..chrome rings and our barrels (FZR/CBR/ZXR/GSXR) will all be 320 hone followed by a finish with an 800grade emery wheel lubricated with whatever engine oil the engine will use..(3HP gain boydie!!!!) emery wheel diameter at 3mm overbore size set at 4-500rpm..five or six passes down the bore followed by 5-6 up the bore in reverse..my local machine shop thinks i'm lacking somewhat lol..assuming piston cylinder clearance at 0.07 or less and for maximum compression nearer 0.03..top ring gaps up and down the bore even..compression on a used engine will be about 120-130psi per cylinder after rebuild..rising to about 160-170 after 500 miles or so..same engine honed will yield about 190-210 psi when correctly honed and broke in hard..i shall try and upload those pics!!!

    Hope all's well mate..never ridden the FZR but just read an article comparing it to the gsxr..i'm gutted :( But will post for all who will take the Michael until boydie brings the honours home!!!!

    Controversial topic me thinks..but good to have it on the forum,

    All the best mate and good to see you up and running again boss,

    Cheers si
     
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  3. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Files to large grrrrr...IT..never any good :(:(:(
     
  4. Mclaren

    Mclaren Well-Known Member Contributing Member

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    Before u do anything get a bore gauge a proper one and only if u can use it right (had apprentices that couldn't get a root in a brothel with fist full of 50's) measure before touching bore
     
  5. kiffsta

    kiffsta Senior Member

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    Email it to me simon
     
  6. Joker

    Joker See "about me" for contact details. Contributing Member

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    Well, after reading around I wasn't surprised to find a lot of opinion but I was surprised at how hard it was to find some clear engineering articles on this topic. I suppose that explains why it can easily become confusing.

    So, I admit I am not an expert in this particular field and I don't care to brag about some imaginary background of engine building experience in the hope to add validity to what I am saying. I'm just not like that. Instead, form your own opinion - but when you do, I hope that some engineering background will help. Below is an engineering thesis that attempts to shed some light on this topic. (attached in case the link breaks too. Note it is a big article):

    http://www.diva-portal.org/smash/get/diva2:124049/FULLTEXT01.pdf

    Now I'm not going to rattle off all the findings of this research, because like any thesis it has certain limitations and these are clearly listed (and there are a lot of concepts to understand). It does highlight the complexity associated trying to understand this phenomenon, and I believe it alludes to several basic factors that cultivate "bore glaze":

    1. Rough surface finish in the bore (creates areas that oil/deposits can "settle" without being moved through the engine)
    2. Low rates of oil film replenishment (ie lower piston speeds mean the oil film between the piston and the bore isn't being renewed as often)
    3. The presence of soot/ash/engine additives in the engine (therefore diesel engines could be particularly susceptible)
    4. Low engine temperatures (condensation of insoluble materials that form deposits)
    5. Prolonged oil film exposure to combustion gases (related to engine speed, the slower it is the longer the oil film is exposed)

    Acknowledging that normally run engines are at an extremely low risk of glazing, the only time I can think of to hone is when you've just cut your bores to oversize and you need to make them SMOOTHER...

    @Simon I'll message you about the bandit situation mate.
     

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  7. Joker

    Joker See "about me" for contact details. Contributing Member

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    Honing: The Very Annoying Discussion Summary.

    For those at home, I have been ranting about this for some time in various places on the forum which you may or may not have read. Perhaps my skeptical, challenging engineering brain has been totally frustrating and annoying for some. But that's how I've been taught to think - never believe what you are told until you understand it.

    So with much research, many conversations and probably to the relief of many readers and fellow forum members I will admit I have been both right and wrong in the various things I have said. So, with all the learnings I figured I'd post up a summary for others to read, understand, comment on and share. Perhaps you knew it all along and I just didn't understand you, sorry about that - I sorta get off with the fairies a bit now and then when I am thinking out loud.

    SO.....here goes. When you’re changing rings, there’s a few things to remember.

    1. The bore and old rings are highly polished surfaces that are bedded in together. The word “glaze” is often used because of the polished appearance, but there’s not usually a physical deposit on the bore itself. The historical origin of the word ‘glaze’ came from a yellowish deposit left on the bore of old diesel engines that had issues.

    2. It is possible the bore surface, if left untreated could be uneven or out of round depending on the type of life the engine had and the condition of the old rings.

    3. The new rings are not cut to a fine surface finish, they’re quite rough.

    4. When you “bed in” or “wear in” two lubricated parts, you want them to “grind” together and wear in evenly. This will result in both surfaces slowly being “polished” or refined together.

    5. If rings and a bore aren’t worn in evenly, the lubrication seal formed by the oil between the moving parts (bore and piston) will not be sufficient. This carries a high risk of blowby and compression loss.

    Now for some definitions:

    HONING is a process used after a re-bore to refine the surface finish. A re-bore is quite a rough cut, so honing is used to refine that cut back to a condition where the engine can be bedded in with new rings properly. This is actually making the surface finish SMOOTHER.

    CUTTING THE GLAZE is a term used to prepare a bore for the installation of new rings. It means basically roughening up the highly polished surface of the bore evenly. This (perhaps confusingly) can (and is commonly) achieved by honing, but there are several alternative methods. The confusing thing is, proper honing is used to make the surface of the bore smoother, however when used for cutting the glaze it is the exact opposite - used to make the bore surface rougher. It's exactly the same process though, but has different purposes.

    The reason you roughen the finish of the bore when replacing rings is because of the difference in surface finish between the new rings (rough) and the re-useable bore (smooth). If you attempt to bed in rings without making the surface finish of the bore rougher, the rings might too easily slide over the smooth surface and not wear in at all (or wrongly), or the roughness of the rings might start to grind back the surface of the bore. This is where the risk of blowby and compression loss is notable.

    At the “micro” engineering level, correct lubrication is all about the oil boundary layer or “film”. Essentially, a film of oil is formed between the bore and the rings, and the movement of the piston up and down introduces shearing forces into that film of oil. If the surface finishes are too different and not “worn in” what could happen is the shear forces are too close to the bore wall (or on it), meaning the oil doesn’t “stick” to the bore and the oil film (necessary for correct lubrication) will not achieve its purpose ie it will not be an "oil seal". There may be insufficient oil in the area, or the oil could slide over the surface of the bore which could also cause incorrect lubrication. What is ideal is having the shearing forces towards the centre of the oil film, with each side of the oil film “sticking” to the bore on one side and the rings on the other. This means that the oil slides over itself rather than over the surface of the bore (or rings) with the motion of the piston – which is correct lubrication (ie it is a lubrication "seal"). For that to happen, the rings and bore need to be bedded in evenly together.

    So with all this said, you don’t need to hone. You could use another method to prepare the surface of the bore – but you should probably still prepare the surface, because if you don’t you risk compression loss and blowby: both of which will significantly reduce your engine performance.

    THE END....?

    (yes I'm done, seriously.)
     
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    Last edited: Nov 30, 2016
  8. Joker

    Joker See "about me" for contact details. Contributing Member

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    As an update I'm on engine number 4 without honing (been using 800 grit sandpaper instead to dull the metal for the cutting in of the new rings) and am yet to experience oil burning (ie smokey engine) or compression issues. So yes I do practice what I preach :)
     
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  9. kiffsta

    kiffsta Senior Member

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    Holy thread revival Batman !!!
     
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  10. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    So how many psi are you getting from your run in engine's ?
     
  11. gregt

    gregt Well-Known Member Premium Member

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    All basically correct, I can't argue with your results using 800 grit if it works.
    My customers expect the best so where I consider a "deglaze" neccessary, it's off to my favourite reconditioner for a Sunnen hone. When it comes back to me I know the bores are straight, parallel and round....

    What I will add is the more frequently found now case of a nicasil bore...Yes a hone is possible if the bore looks a little scuffed but not so bad it needs replating. It has to be a diamond hone - which requires a lot closer attention to setup than usual so time costs will be higher. A good tip for nicasil bores too is to use castor base oil as assembly lube. This greatly assists breakin and stops cold picking up occurring.
     
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  12. Joker

    Joker See "about me" for contact details. Contributing Member

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    lol yeh I just put another fizzer engine back together and I remembered my previous ranting. At the time it was all a bit "theoretical" but now having been through the process with no issues I thought it was important to follow up with the result of it.

    For sure, if you're doing it professionally you want to use the best process you can as it ensures your risk/liability is mitigated.

    Also, I haven't actually compression tested any of the engines - I should check that. I just know they all haven't needed choke to start yet.
     
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