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Pinned Hone & Fit New Rings

Discussion in 'Tech Tips' started by maelstrom, Nov 9, 2014.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Hi All,
    I often see posts about having to do top end overhauls on the forum and I thought it might be useful to give some information on this. Most of this is based on my own experience and I will provide links for other sources. Sorry, but I have zero flexibility when it comes to the tolerances and methods that I discuss here. This is controversial and what can I say? Maybe take it all with a grain of salt. I have thought about this for a long time and I figure that it is best to help a few people out and just say sorry to the others. No offence is intended. :)
    Personally, this area of engine rebuilding takes me an awful lot of time, so I will try to cover just a few of the important points that relate to fitting new rings.

    When it comes to a smooth and clean running powerful engine there is not much that is more important than a good piston to cylinder seal. I firmly believe that few people understand how important this is to engine performance. I will make reference to this point later. This seal can be long lasting and reliable but it is a very fine line between good and terrible. To create this seal the rings need to be bedded into a finely honed cylinder bore.


    worst.jpg
    I never imagined that I could find a pic of something as bad as this. This is not a finely honed cylinder bore. This engine is ruined even before it is assembled. It will never run well and by the time it does run in, it will be worn out. If you walk into an engine reconditioning shop and you see something like this then do a u-turn and walk away.


    Acceptable.jpg
    This is more like it. This has the makings of a good reliable engine, but I still prefer a finer cross hatch than this, and I am trying to find a suitable example. I know I saw a good one from the new Norton factory, but I can't find it now.


    Laser.jpg
    And of course technology marches forward at what seems like an ever increasing rate. This is laser honing from http://www.gehring.de/en/technology/laser-honing/. You can see that after the etching process it is finished with a superfine hone.

    So let's begin with the piston and bore. For the sake of this article I will use the information from a Kawasaki ZXR250 workshop manual.
    PistonTolerances_ZXR250.png
    Note that the manual does not give the maximum piston-skirt to cylinder bore clearance, or wear limit. Using the maximum limit on both items would yield 0.29mm. Given that this is a very large clearance, I would strongly recommend that you strictly follow the wear limits for the piston and bore separately.

    To even begin to work with this level of precision requires accurate instruments. The bore inside diameter is specified down to microns, or thousandths of a millimetre. Those values are so fine that they will be affected by ambient temperature. Fortunately though, we are only dealing with the fitting of new rings so we can get away with some relatively inexpensive equipment. Or, as very wisely suggested by a forum member here, make use of your local machine shop. They can measure your parts for you very easily and for a nominal fee.

    Cleaning:
    It is assumed that you have disassembled the engine as necessary. The first step is cleaning. There are many ways to do this but you must be very careful with the pistons. The ring lands, or grooves, are very precise and must remain parallel and within tolerances. Physically scraping carbon deposits out of them should be avoided for that reason. I would suggest ultrasonic cleaning or soaking in a solution that is specifically designed to dissolve carbon deposits without damaging aluminium. Removing the piston pins should be done with the factory tool or similar (not hammered out). Once they are clean the process of measuring can begin. I suggest that after the horrible cleaning work is finished, that you stop work and make yourself a nice, comfortable, well lit and clean area to work in. Make a sign “No Filth Permitted Past this Point”.

    Piston Diameter:
    The point at which the piston skirt diameter is measured is described in the service manual, in this case 5 mm from the base (always perpendicular to the piston pin), and of course this should be done with a micrometer. This is because pistons are tapered from their smallest diameter, at the top, down to their base.

    Cylinder Bores:
    Again the positions at which the bores should be measured are described in the manual for your model. In the case of the ZXR250, they are, 10mm and 60mm from the top edge in both fore-aft and left-right directions for a total of four measurements. Unfortunately the workshop manual does not specify a value for maximum taper nor ovality. Well, not one that I can find at least. However, the Honda workshop manual for the CBR250 gives a limit of 0.05mm and this seems like a reasonable value. Since we are only hoping to replace the piston rings these measurements can be performed with a telescoping gauge and a micrometer, not a digital vernier. Even the best vernier calipers, (and that includes digital ones) are only accurate to 0.02mm, which is unacceptable. Metric micrometers are dead easy to use and are not expensive.

    Taper:
    This is the difference in value between the two points, the first 10mm from the top edge of the cylinder and the second 60mm, in the same axis. As mentioned I suggest 0.05mm as a maximum. Since there are four measurement points you are making two comparisons.

    Ovality:
    This is the difference in value between the two axis. One parallel to the piston pin and the other perpendicular. As before there are two point of comparison, the first 10mm from the edge and the second 60mm. Again I suggest 0.05mm as a maximum.

    Clearance:
    Now for each bore subtract the piston diameter from the largest diameter that you have for that cylinder in the perpendicular to piston pin axis. This is your piston-cylinder clearance. See the 1st table above for the details.

    Small End:
    Again I cannot find the section in the Kawasaki manual for these measurements. More work to be done.

    Cylinder Deglazing:
    Now we are entering the twilight zone. I am taking about deglazing a cast iron cylinder sleeve here not a Nickasil coated aluminum one. Please refer to this document http://www.brushresearch.com/pdf/NOP.pdf I first read this in 1975 (yes, that is right, no internet) and have used Flex-Hones for deglazing cylinders since. There is also other technical documentation from the same source http://www.brushresearch.com/literature.php?type=2
    Use a 320 grit Flex-Hone to deglaze the cylinders (This is quite a light grit, more on that later). I attach to a drill and I have done so many of these that I just know what speed, and the rate of up and down motion to use. I run slower than is shown in the videos. Do a few strokes to get your cross hatch angle right first. You will get the hang of it quickly as it is not difficult. Follow the instructions to the letter and watch the videos. I like to use 10 weight oil, ATF is fine. After honing clean, clean and clean again. Edit: Murdo and Risky prompted me about this important point, as advised in the instructions, you need to test that the bores are totally clean from residual grit. I use paper towels and Murdo and Risky have suggested their techniques, all good.
    Brush Research, Sunnen and every other credible source that I have seen, advise to clean with hot soapy water, and they know more than you or I.

    Piston Rings:
    Rings_ZXR250.png

    Piston rings are made to suit the corresponding size pistons. One does not try to stuff oversized rings into a standard sized bore, so if you have a standard set of pistons you will be buying a new set of standard rings. Step one is to measure the thickness of the new rings that you have bought to make sure that they are not duds.

    Gapping the Rings:

    You need to fit the rings into the bore and use the piston to gently push the ring squarely down into the bore. Find the point at which the ring gap is the smallest and this is where you will continue to check the gap. Remove the ring and adjust the gap by filing the ends. Take the smallest amount off then check again. Since you have an old bore, you will probably not have to increase the ring gap as it will already be larger than the minimum value.

    Ring Groove Clearance:
    Next fit the rings to your perfectly clean pistons and use a feeler gauges to measure the ring/groove clearance. It must be the same all the way around the groove. To quote the workshop manual “The rings should fit perfectly parallel to groove surfaces. If not, the piston must be replaced”.

    Assembly:
    Follow the workshop manual. Get a friend to help you fit the cylinder block over the pistons. You do not have enough hands. Be patient and methodical. It is going to take a lot of time. You will not be able to “throw it together”. If you need a tool then stop work and buy it or make it.

    Running In:
    Here is the nasty part. Sorry, you are not going to run in your new rings. You are going to give your bike a good run. Here are some references. I do not necessarily agree with everything they say and there is a bit of variation in views but I am sure you will get the gist..

    http://www.mobiloil.com/USA-English/MotorOil/Synthetics/Synthetic_Oils_FAQs.aspx
    MYTH: You should break in your engine with conventional oil, then switch to a synthetic like Mobil 1™ oil.

    http://www.cbr250.net/forum/cbr250-performance/612-engine-break-myth-pros-respond.html

    http://www.motorcycleextremist.com/Motorcycle-Engine-Break-in-the-Right-Way!.html

    http://www.mototuneusa.com/break_in_secrets.htm

    You have a very small window of opportunity to make that 'seal' that is so precious to engine performance. The one that I mentioned at the start of this article. Just how fine can that seal be? Well get your head around this. The factory tolerance for the piston/cylinder tolerance of a freshly bored and honed Kawasaki ZXR250 is . . . wait for it . . 10 Microns. That is one hundredth of a millimetre. For any Americans that might be reading, that is 0.00039 inches. That is the maximum variation allowed. You can get a cylinder bored and honed to that degree of accuracy at other places besides the Kawasaki factory but it is not easy.

    Now here is what I suggest. There are a couple of variables. The first is heat and the second is how badly worn was your cylinder? If it is a very hot day and your bore clearance is still quite tight then I would wait until it is cooler or night. We want to get the engine up to operating temp and use about 60% of rpm to do that. Do NOT ride in traffic with stoplights etc. Once the engine is up to full temp we want to do a few full runs up to redline in say 3rd and 4th gear. The engine is not working too hard but you are using the full rpm range. Remember you have a worn engine and you need these rings to bed into your fine cross hatch quickly (remember it was 400 grit). It is never going to happen if you trundle around. I would want to let the bike cool completely down and repeat this cycle about 4 times. So over a period of days would be good. That is it job done.

    Big Jets:
    Now that your bike has compression again and a good seal you will need to get rid of those “big jets”. This is my pet hate; some of you may have noticed already. Lots of owners riding around with big jets. Their bikes run like rubbish and all that sooty carbon is like pouring sand into your top end. Then they post pics of their black spark plugs on web forums to show other owners who also have sooty plugs and they all assure each other that this is good. Run the smallest jets that yield maximum power, not the biggest ones that you can stuff in there and stop posting pics of your sooty spark plugs on the internet please. There, I said it, and I feel better now :D

    cheers
    Blair

    More Information:
    Here is a great article on some developments in this field.
    http://www.enginebuildermag.com/2002/11/the-smooth-science-of-cylinder-honing/
    Interesting to hear that what Brush Research have been saying for decades is now accepted. This article is talking about new cylinders not old worn ones. The case exists that if the cylinder is not too badly worn that starting with a coarser grit, say 240 and finishing with a 400 might be better than my suggestion of just using a 320. That could very well be the case, and I would not hesitate to do that if I thought that it was the best choice for my engine. But when it comes to recommending a procedure for the average owner who just wants to fit new rings, I prefer to stick to what I know has worked.

    Also here is CP Pistons guide, again this is for a freshly bored cylinder.
    https://www.cp-carrillo.com/files/1-Landing Pages/Pistons/faq/cp_instructionsheet_v4262012.pdf

    Piston Ring Tribology: http://www.vtt.fi/inf/pdf/tiedotteet/2002/T2178.pdf

    Assorted articles on honing:
    http://www.docs-engine.com/pdf/1/honing-cylinders.html

    The Smooth Science of Cylinder Honing - Engine Builder Magazine
    http://www.enginebuildermag.com/2002/11/the-smooth-science-of-cylinder-honing/

    Break-in your piston rings:
    https://www.enginebuildermag.com/2018/05/how-to-break-in-your-piston-rings-the-right-way/

    And for technical junkies:

    https://www.highpowermedia.com/RET-Monitor/tag/pistons-rings
    .
     

    Attached Files:

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    Last edited: Dec 1, 2018
  2. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Agreed Blair.
    One other thing I would point out is cleaning the bore after honing with very hot soapy water, then using a white piece of rag soaked in engine oil to collect any remaining bits of grit. Wipe through the bore and if any stains on the rag you will need to wash it again. As Blair said, clean, clean and clean.
    No point in building dirt/grit into and engine.
    The running rich will be washing the oil from the bores and allowing the piston to touch the cylinder wall causing more wear.
     
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  3. risky

    risky risky

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    my final clean is auto tranny oil on clean wipes. each there own. any grit or discolouration and do again.
     
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  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Thanks guys, I edited the post. What Risky and Murdo said is spot on. You need to test for cleanliness not just think that it is clean enough. I have left a lot of instructions out about using the Flex-Hone. I wash with solvent first. Then I follow with hot soapy water and use paper towels for checking, dry and then keep repeating until they are perfectly clean.
    You have to read all the details and instructions on the Flex-Hone site and you need to also carefully read your workshop manual.
    cheers
     
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    Last edited: Nov 9, 2014
  5. RosscoM

    RosscoM Active Member Premium Member

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    just on cleaning the bore, as a tradesman I have always used Prepsol, I fail to see how a lubricant will clean better than a solvent designed to clean, and lint free cloth so no bits of paper or cloth get left in the bore, and when assembling the bore over the pistons, use plenty of lubricant, go overboard with it...
     
  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I added a link and comment to an excellent article on cylinder honing to the end of the original post.

    .
     
  7. RosscoM

    RosscoM Active Member Premium Member

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    I wonder what laser honing would cost... with most 4 cylinder 250's, it may be cost effective, we're talking about an 18000 rpm engine...
     
  8. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    I was taught to use the oil on white rag as the oil would collect any dirt/grit and the oil film would stop rusting from the hot water wash. Good thought on prepsol, will try it on the next bore I do.
     
  9. tintankaussie

    tintankaussie Well-Known Member

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    Excellent reading,I have tried both methods (A+B) B on my gz with very good results,just clicked over 900km-starts first pop and pulls like a train for a single 250-On the other hand the gsx that my mate re-built before i got it rides like a pig in mud.Starts first go but no grunt (torque) head gasket to thick(home made)didnt hone the bore,just chucked new rings in to stop the smoke.So im looking for another engine (gsx-250) to rebuild my self the way i do it and swap it over then follow method "B" as it works for me...Ken
     
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Hi Ken,
    I don't know what you mean by A or B. There really is no 'method' in putting new rings in an old bore without de-glazing first. All that means is that someone does not know what they are doing. Glad to hear you got your GZ running sweet. Now you just have to do it again on the GSX
    cheers
    Blair
     
  11. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    This process would be used after boring for the fitment of new pistons. I get the impression from the website that they only supply the equipment and probably to OEMs. You would expect that someone would make use of this technology in the service industry but perhaps the costs make it prohibitive. However, this raises a very important issue, and that is, getting these services done at the required level of accuracy. It is a bit of a paradox because often our little motorcycles are not worth much, but their level of technology is very high. The technology used in the manufacturer's production plants often leads the service industry by decades. As in, your local engine reconditioning shop may still be using 1970's equipment and they may have the same mindset.

    This means that if you do want to have your four cylinders bored and honed to a "factory" level that it is most likely going to be expensive and difficult. That can also be exacerbated by your location. For example, I am in the middle of nowhere (Thailand) and I would have to ship my cylinder block to the USA or the Europe to have it bored and honed. The irony of that situation is that many automotive manufacturers are setting up plants here but outside of their factories the local service industry remains, for the most part, in the stone age.
    cheers
    Blair
     
  12. tintankaussie

    tintankaussie Well-Known Member

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    I read all the links in the first post-The "a and b" method is referring to running in the engine after the work has been done...Ken
     
  13. RosscoM

    RosscoM Active Member Premium Member

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    There's plenty of state of the art engineers in AU, even here in Newcastle, I use a mob called HB sales, I gave him the new os pistons and rings, told him it was an 18000 rpm engine, and he bored to suit each piston, each piston came back numbered to the bore, with the new rings on them, all the local V8 boat guys use him too... I'm going to be taking him some Fizzer camshafts soon to restore, the previous idiot left them out of the engine in the weather and dry...
     
  14. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I absolutely agree that there are businesses in Aus that are capable of doing this standard of work. I have had it done in the past (that person has now retired). However, since I started this thread, I feel obliged to at least try to keep it on the right track. If you would like to recommend a business that you have experience with and that you know can bore and hone cylinders to suit new pistons and maintain a level of accuracy as specified by the manufacturer then please post the finished measurements stating:
    1/ What the measurements were taken with
    2/ Maximum taper
    3/ Maximum ovality
    4/ Requested skirt clearance - Min & Max
    4/ Final skirt clearance - Min & Max
    In all positions and axis as specified in the factory workshop manual.
    I am afraid that anything less than that is just hearsay and should not be considered as good advice for others. On the flip side it could be a great resource for all the owners out there if they knew where they could get good quality work done.

    Here is a quite a good video showing a cylinder being measured.
    Since the origin is the US it is imperial and the tenths he is referring to are ten-thousands of an inch. Which is equal to 0.0025mm.

    Millennium Technologies were used by G-Force Engine Development for the cylinder work on their racing 400 Hondas. http://mngforce.typepad.com/
    cheers
    Blair
     
  15. RosscoM

    RosscoM Active Member Premium Member

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    great video... when they manufacture the mass produced garbage we all own ;) they machine measure, its why cranks have sizes stamped, and bearings are colour coded, doubt they actually measure ring gaps, more likely rely on the quality of supply... they might measure 1 in a 1000 for quality assurance... cost effective...
    When you've replaced 30 camshafts with no lobes left inside 20,000 km, or rebuilt 40 engines due to cold piston rattle, you don't tend to speak so highly of the "manufacturers quality"... it might be what you get...:( the video is race quality machining/measuring, only quality comes into this equation...
    cost + quality/quantity v warranty cost + reputation/unhappy consumer
     
  16. cal

    cal Well-Known Member Premium Member

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    thanks for the info, wish we could be this precise at work when re-building a late model LS V8 motor.... unfortunately it would cost our customer too much lol.... would love a dummie motor at home to practice honing on :)
     
  17. risky

    risky risky

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    HB SALES in newcastle at wickham are spot on.the vw trike motor was balanced and machined by them.not cheap nor expensive for work done and far better quality than a place further down the road.
     
  18. Phil

    Phil Senior Member Premium Member Contributing Member

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    My mechanics father bored my x7 engine and fitted new o/s piston and rings. Watched him perform this task many times, alas he has retired and moved to Thailand.
     
  19. monsigna

    monsigna Active Member

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    What a great write up, I've changed piston rings in the past. But nothing this technical. Very useful information. I will see how/if my restoration runs. If i hear knocks/rattles, then the lump will be sent for total rebuild.
     
  20. Fox McScrooge

    Fox McScrooge Well-Known Member Premium Member Contributing Member

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    I
    Hi Blair,

    Great article mate. Really useful links and advice.

    I used Millenium Technologies to get my NSR barrels replated and ported as well as the heads skimmed. Very happy with the results. It's not easy to get 60 HP plus out of an MC28 without extensive mods, pod filters, a big bore kit and/or running and MC21 wiring harness and ignition. Mine is putting out early 60s with an airbox still in place. They didn't go overboard with the porting either. Basically just got rid of any irregularities, matched the ports and flowed the exhaust port outlets and matched them to the exhaust manifolds I sent with the barrels.

    Cheers
    Jim
     
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