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NSR150SP top end rebuild kit - no more A/B/C pistons?!

Discussion in 'Technical and Troubleshooting Torque' started by Morbo28, Sep 1, 2008.

  1. Hi All,

    I am just about to order a top end rebuild kit for the NSR150SP. The only thing that stopped me from ordering it was that it seems there is no longer the A/B/C piston sizing from Honda.

    I am hoping someone in the know (Trev etc :grin: ) could let me know if they are aware of this.

    Basically the cylinder and the piston have marks on them indicating which size they are - OD of piston indicated as A B or C and inside diameter of cylinder marked as A B or C. Obviously you make sure that if you have an A cylinder and it's within tolerance, you install an A piston.

    Anyhoo, when ordering from PS, the dude said that now when he enters either A, B or C into the piston sizing when ordering, it automatically 'supercedes' to the C sizing. He said Honda often make changes and obviously they have done something which means that it is now only necessary to buy the C size piston no matter what marking the cylinder has on it.

    I said I would just triple check before placing the order as I just don't really understand how that could work. He suggested that perhaps they have made changes to the rings or something that means the small difference in diameter is no longer of consequence.

    What do you think of this? Just gotta get a bit more advice/do a bit more research before I order it I think.

  2. I got a "C" piston in from Thailand although I ordered a "B".
    It should still be OK as the clearances of the new piston and my cylinder are still within limits (just). I'd say an "A" cylinder and a "C" piston's clearances would be out of spec. I don't know why I was given a "C" piston. When I find out I'll let you know. Unmarked cylinders are "B" other wise they have "A" or "C" marked.
    "A" = 59.010 - 59.015mm
    "B" = 59.005 - 59.010mm
    "C" = 59.000 - 59.005mm

    As you can see it is possible to have an "A" & "B" or a "B" & "C" with the same dimensions. Couple a big "B" cylinder with a small "B" piston and you get the maximum clearance allowable. Larger clearance don't mean the engine won't go well but it may mean the bore wears quicker and is noisier as the piston tilts, slaps and rattles more.

  3. Sounds like it should be okay then.

    I have a B cylinder so I will go ahead an order the piston. I just needed a bit of corroborating evidence before I was keen to order since the guys said he couldn't order a B piston :)

    Cheers Bob!

  4. Just to expand a little on the piston/cylinder gradings and clearances.
    Here is an interesting site on 2 stroke pistons and cylinders www.dansmc.com/pistons.htm
    I'll email the url if the moderator doesn't let it through.
    Why the 3 gradings? My guess is there is some variation in mfg tolerances and the plating process is not as exacting as machining. There is no reason IMO to make three grades of cylinder, each with a size tolerance of 0.005mm difference, that is "A" = 59.010 - 59.015, "B" = 59.005 - 59.010 and "C" = 59.000 - 59.005
    The fact that there is an accepted range from 59.000 - 59.015 means the plating process is not as exacting as machining. After batches of cylinders were given the Nickle/Silver finish, workers probable measured them and put them in the three categories acording to their size. The pistons would have been machined in batches to match the three categories. The biggest piston to cylinder clearance in theory would be 0.050 and the smallest 0.040mm. This cuts down on wastage as discarding cylinders outside specs would be expensive. The pistons have to be machined anyway so why not just remove a little more from some batches.
    My new "C" piston has small but measurable variation in it's diameter and this is normal. High quality 2 stroke pistons are slightly oval and have a small taper. This compensates for the uneven heating of the piston, particularly near the exhaust port. In theory the piston to cylinder clearance should be best at normal operating temperature.
    If I were a worker at Thai Honda making NSR motors I could have gone through batches of cylinders and pistons to get the ideal clearances. This is what appentices at Holden did in the 70s & 80s to give Holden Racing Team the best blue printed motors and 10 or 15 hp more.
  5. That's a good point about why they might have decided on the three size grades - the unknown quantity of the cylinder coating.

    The site was quite interesting - especially about him never being able to just push the piston in with his thumbs. On cars I have worked on with three rings it always needs some gentle persuasion with the wooden handle of a mallet tapping it down.

    Oh and ps - do you go through the full engine run-in procedure when you rebuild your top end? (I know about the various POV on running in and the controversy about how to do it). How do you do it and what results have you had?
  6. Just anecdotal evidence that babying an engine can be just as bad as thrashing an engine too early. With the NSR I would bed the rings in by using no more than 7,000 rpm for 100 km then increase to 10,000 by 500 km. Depends on if the cylinder is new/recoated in which case I would take it easy for 1,000 km. By easy I mean not going over 8 or 9,000 rpm and not labouring up hill under full throttle on a hot day. Pussying around too much justs polishes the high spots and can glaze the bore. All the bikes and cars I have owned have been thrashed within an inch of their lives at some stage and in my opinion they go much better than the same vehicle driven very conservatively all it's life. I'm not talking about abuse of a motor but it's potential performance being fully realised. Some people don't know how to use a motor fully. I don't mind using a rev limiter. Some people have kittens when they get anywhere near the redline. I do have mechanical sympathy. I do, I really do....
  7. What "they" (Honda) have done is run out of stock.

    If they can now only supply C pistons then you need to find a C cylinder to match it. The C is the smallest size, so that a C piston in a B cylinder will have too much clearance for correct performance. Whether you will notice this I cannot say, but I wouldn't bother using a non-specified part.

    You might have to buy a complete engine to get going again...

    Cheers, and all the best

    Trevor G

    PS I sold the NSR 150 last week for $3750 - what a steal! Immaculate and just 5,500 km.

    PPS Did you ask to see if they could supply a C cylinder? That will get you going again...
  8. Okay well Rob's rebuilding a B cylinder with a C piston by the sounds of it, so I will see how that works out first :LOL: :LOL:

    It sounds like it will probably be okay, but if it isn't I can buy a new cylinder rather than a whole new engine.

    The thing that makes me think it's okay is that the service limits are all the same (as taken from the service manual). Below it shows that even if you had a C piston in an A cylinder, they would still be within service limits.

    [Letter] [Min Size - Max Size] [Service Limit]

    Code A 59.010 - 59.015 59.05
    No mark 59.005 - 59.010 59.05
    Code C 59.000 - 59.005 59.05

    Code A 58.965 - 58.970 58.92
    Code B 58.960 - 58.965 58.92
    Code C 58.955 - 58.960 58.92

    Hmmmm so I'll keep an open mind but it looks like it will all be okay.
  9. My supplier in Thailand can get new cylinders for $400. I don't know what Aussie prices would be. He said that the price from a Perth dealer was $1,000 but I don't know about that. The cylinder looks thick. Plenty of thickness for a steel sleeve IMO. In practice I don't think it will make much difference to the performance or the reliability. Sleeves are far easier to repair compared to coated cylinders. The Nickle Silver coating was probable chosen because it is cheaper to manufacture rather than for a performance advantage. In practice I think it is the wrong choice for a high performance production engine as the operating conditions can be too harsh for the coating to last more than 30,000 km. That point was made on the site I refered to a few posts back. The coated cylinders are fine as long as the engine is well maintained, the best oil is used and there are no seizures.
    Any significant break in the coating will require honing and recoating.
    I don't know how much boring and resleeving would be but it is probably cheaper than recoating. If the bike is going to be kept through several engine rebuilds then resleeving is a more practical and cheaper alternative.

  10. 1) Where do you get the sleeve? It has to have the ports cut in it. The cost of that would well and truly eat into the saving made by not buying the genuine article.

    1a) The porting is extremely precise - where would you get the map to cut the ports in the iron sleeve?

    2) What is the sleeve made of, cast iron as usual? Where do you get the pistons? The standard ones won't work.

    2a) If you managed to get pistons the right size (or had the sleeve opened up enough to allow for expansion with a genuine piston), your performance would be down somewhat...

    3) The reason plated cylinders are used is that they expand at the same rate as the piston, and so piston/cylinder clearances are microscopic, for best performance.

    Old thinking does not apply to modern engines.

    All the best

    Trevor G

  11. What you need to look at is the optimum piston to cylinder clearance (0.04 - 0.05 mm) and the service limit (0.08 mm) and factor that into any calculations.

    That way you would see that an A piston would be much too big for a C cylinder.

    Similarly, a new, minimum sized C piston at 58.955 would already have more than the optimum clearance in an unworn/unused, maximum B cylinder of 59.010 (clearance = 0.055 mm).

    Have you had someone appropriate measure or even inspect your cylinder? There are usually ridges at the top and bottom of the ring travel due to direction reversal.

    All the best

    Trevor G
  12. Interesting site at http://2wheelstuffs.blogspot.com/2005/11/two-stroke-top-end-rebuilding.html
    When after market companies make sleeves for 2 strokes they use a graph paper template cut to size and taped inside the cylinder. With carbon paper and index finger to rub over the port edges, the ports shape is marked on the graph paper. Because the ports will be cut in the liner from the outside, the diameter of liner is greater. The ports will have to be repositioned on a second graph paper. The shape and size of the ports will be the same but they will be spaced slighty further apart so they can be marked on the outside of the liner. Of course this would be expensive for a one off cylinder but subsequently cheaper as CNC machines can have the machining parameters in memory or recorded to disc.
    This is all academic as there is no need for liners at this stage. It's only to consider when recoating is unavailable or good cylinders run out.

  13. This is the expert opinion from Ian Williams Tuning http://www.iwt.com.au/

    "Hi Bob,

    We always have the bores replated, it is easily done and there is the same performance and cooling afterwards as when new. Resleeving can be done, and is generally more costly, but it is not easy on a powervalved motor and there is always a slight power loss afterwards.

    Regards, Ian Williams.

    Bob Moore wrote:
    Dear Ian,

    I am rebuilding a Honda NSR 150 SP motor. It is a single cylinder 2 stroke with bore and stroke of 54 x 59 mm. It has variable exhaust port valve and is water cooled. The cylinder has a Nickel/Silicon coating. It seems to have plenty of thickness on the cylinder. I seized the piston once on a track day but the piston and cylinder was lightly scuffed only and I repaired for a further 15,000 km of use. There is a small crack on the exhaust port bridge and a small patch where the coating is broken through. The motor was still going strong when the gearbox failed. I am wondering for long term use would a steel sleeve be better than the coated bore? Is it feasible to sleeve a watercooled, coated cylinder? How would a sleeve have the ports cut and matched? The motor is outputing 36 hp at the rear wheel with some performance mods.


    Bob Moore"

    Trevor, it may be very difficult to find a "C" cylinder and the only price I have for a new one is $1,000. I was quoted $400 for recoating a few months ago and Ian Williams price is $390 plus shipping. Used motors at wreckers are between $1,000 & $1,200 and that would not guarantee the cylinder or piston wouldn't be worn. There is only "C" pistons available, even in Thailand. The measured clearance between my "C" piston and worn "B" cylinder is within acceptable limits. I can't do better than that at this time and the situation is unlikely to get better with time. With heavily scored cylinders in the future the only option may be to sleeve them. Otherwise owners are faced with scrapping their bikes. Their will be no catastrophic failure of the engine if the piston to cylinder clearances are slightly larger than the optimal clearances in the manual.

    I'll leave it at that.

  14. Not sure how big the score is, but local platers claim that they can fill/deposit enough material even for major gouges. A plated cylinder can always be replated, and I would never consider sleeving a cylinder which was originally plated.

    Tyga are still listing some cylinders for just less than AUD$400.

    All the best

    Trevor G
  15. Most companies say they can repair and recoat heavily scored plated bores. They alloy weld-fill the damaged areas, skim bore, plate then hone to original bore size. Others say they repair some damage but if it is beyond alloy weld repair, they bore and insert an alloy sleeve. They then bore to size, plate, then hone back to original dimensions. A few advocate insertion of a steel sleeve when the bore is heavily scored. This seems to be because it is a cheaper alternative, how much cheaper, I don't know. If Tyga still has cylinders then that's good. Cost would be about $450 if is coming from Thailand. Repair here would be only a little cheaper depending if living near one of the cylinder repairers. I think there is one in Brisbane, Melbourne and Perth but I don't know of any in Sydney. There is a lot of companies replating in the USA. One does single cylinders for US$179. It would be OK for me as I have a friend who ships goods from the US on a monthly basis. I can send a cylinder internal US mail to his company for inclusion in one of his shipments. Others may find the shipping costs to and from the USA prohibitive. It would cost me about A$250 total.
    Trevor, a damaged plated cylinder cannot always be replated. Most of the time it can be, but not always. An alloy sleeve, bored and plated would be a perfect repair if there were no other option available. At the moment there are cylinders still available. These will run out sooner or later. In my case the cylinder is marginal. It can certainly be repaired and replated. I would only advocate resleeving when there are no other options. I would only advocate a cast iron sleeve as a last resort. Probably 5 or 6 years away from that. There is probably no compelling reason to keep an NSR 150 going when new parts become rare. Plenty of other bikes out there which are equal or better than the NSR. However, there are few that give the same bang for buck.

  16. Tyga lists the "B" cylinder as out of stock. They have 5 "A" cylinders and no "C" cylinders. The "A" cylinder can't be used with a "C" piston. Looking a bit grim for continued supply of NSR top end parts.

  17. Another soln could be to source a dfnt piston that will fit. Might have to play around a bit and do a bit of machining but if you got the right combo you could pump them out at say two std sizes.

    You'd get a bit more life out of each cylinder (I haven't seen how much meat there is in the walls but surely it could do a 20 thou overbore or two?) :?:

    (there's a little specialty business for someone)
  18. Think about the "World's Fastest Indian" reminded about the motto "If there's a will, there's a way". I had a Honda 125 single cylinder 4 stroke many years ago. I got it bored out to 138 cc and fitted a Yoshimura kit. That thing used to rev it's tits off and for a little commuter bike was indecently fast. I ran Honda 750 pistons with the crown machined to stop the valves touching. It had 12-1 compression. It blew a hole in the piston. I then bored it to 150 cc with a Bert Kingston kit. The compression was 13-1. It ran to 152 kph but eventually cried enough. Somewhere there is a piston that is probably close to the 59 mm bore. Wiseco doesn't make any NSR 150 pistons and probably won't in the future as this model wasn't marketed in the USA and their would be almost zero demand. Somewhere on the net I saw a big bore kit that took a Honda CR 125 motocross engine out to 190 cc. It was stroked and bored. I haven't found it again yet. The piston for this engine may be around 59 or 60 mm diameter. There seems to be plenty of thickness on the NSR cylinder to accommadate a 2mm increase in the bore so any piston with diameter up to 63 mm could be candidates with some machining. Yamaha had a 400 twin so the pistons may be close or be machined to fit. It depends on the wrist pin diameter as well. Honda had a NSR 400 triple. Kawasaki a 500 triple. There were several 2 stroke trail bikes such as Yamaha DT 175 and probable Suzuki and Kawasaki 175 singles as well.

  19. Is it possible to get the cylinder re-coated and then cylindrically ground to suit what pistons are available? Just a suggestion.
  20. The Nikasil coating builds up to make a thin layer that adheres to the aluminium like solder adheres to metal. Sort of similar to a case hardening layer but much thinner and done at a low temperature by a process called electroporesis? The cylinder, for instance would be thoughly cleaned then immersed in a solution of Nickel/Siliconcarbide. Electrodes are immersed in the liquid and the Nickel/Silicon Carbide adheres to the cylinder. The deposition time and thickness depends on the voltage but the resistance of the coating climbs as it gets thicker so is self limiting. Generally 200 - 300 volts is used I think. Too much voltage and the coating becomes coarse with tiny inclusions and open pore structure. The coatings are very even in thickness for the one batch of items but between batches the thickness can be highly variable. I don't think the process could be used to build up layer upon layer of Nikasil or very thick layers. I think the layer is normally betwen 0.010 and 0.015mm thick. Recoating brings the cylinder back to original. There is very light honing after coating to introduce a cross hatch pattern and perhaps to bring the piston to cylinder clearances back within spec. The hardness of the coating comes from the silicon carbide which is akin to carborundum, almost as hard as diamond. The Nickel is akin to glue which binds the silicon carbide to the surface layer. Because the Nicasil is so hard, the rings wear more than with a cast iron bore. Despite the hardness it is still flexible enough to expand and contract with the aluminium cylinder. In answer to your question, in my opinion, Nicasil coating cannot make a "B" cylinder into a "C" cylinder because recoating replaces the existing coating it is not done over the top of the coating.

    Bob Moore