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Project FZR 250 overbore -> 300+

Discussion in 'Your 250cc Projects' started by ruckusman, Nov 14, 2018.

  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Well as luck would have it, the planets look like they are going to align in coming months - space in the garage, some spare $$ and the time to devote to doing this, plus if I post this thread it might just spur me on to action.

    The purpose is to keep thing doable with the minimum of cost and easy to source parts, as close to plug and play as possible, with the boring and machining being close to what you'd expect in a normal engine rebuild.

    This should potentially be applicable to the CBR250RR, the ZXR250R & possibly the 4 cylinder Suzuki 250s

    I've done a lot of late night reading to keep myself amused and when you start getting carried away, things can get very expensive and complicated very quickly, which defeats the purpose of the exercise.

    I've got a few kooky ideas which I'll detail as the thread progresses, some may be feasible, others not., I'll keep this first post short so that you don't realise immediately that I'm nuts, give it time :prankster::prankster::prankster:

    @my67xr & @maelstrom have endured a few of those - apologies guys

    First a few inspirational threads which started it all.

    @gregt
    https://www.2fiftycc.com/index.php?threads/fzr150-bucket-race-motor.8949/

    Additionally this thread shows some impressive gains through friction reduction, polishing various parts and careful assembly - some of which I will be attempting.
    @Mngforce & @dave-moss-tuning
    https://www.2fiftycc.com/index.php?threads/dave-moss-cbr250rr-mc22-racing-in-california.8371/

    So the basic plan is to remove the OEM sleeves, have the barrels bored larger and fit L.A. Sleeves FL-52 which fits inside the dimensions Gregt worked to in his build.

    As gregt has already accomplished this - we know it's doable - it's also done extensively with the YZF750 and YZF1000 barrels as a comparison example.

    https://www.lasleeve.com/tech/all-purpose-sleeves - all purpose flange sleeves tab - FL-52 price for these is $52USD each plus shipping.

    Piston candidates were a little more difficult to locate, pistons in the range of 52mm - 54mm are scarce, and if they do exist they tended to be incorrect for various reasons.

    I've finally located two good potential candidates.

    YZF-R125 piston - 52mm - this page shows the OEM piston dimensions
    https://www.ebay.com.au/itm/125cc-5...mm-Pin-for-Yamaha-WR125R-WR125X-/151797497474

    yzf-r125-piston.jpg

    Below is a high compression version, which has the higher crown shape and should, all going well be able to maintain at least the majority of the OEM combustion chamber shape.

    https://www.racingplanetusa.com/piston-airsal-racing-high-compression-52mm-yamaha-p-167531-1.html

    There is a potential second piston candidate for 54mm bore which looks interesting - 800 Thai Baht ~$35AUD

    http://www.hispeedpiston.com/ThaiProduct/piston/RacingPiston/RX/RX145461/

    They have rearranged their website and some of the graphics of piston dimension have disappeared, however this is what they used to have - all of the basic dimensions look good as a candidate
    Piston_Dimensions.jpg

    There's much more to come, I will replacing seals, bearings, roller bearing - if anyone knows which need to be OEM and which ones can be from the local bearing suppler chime in, valve stem seals, gaskets etc, so all info appreciated - chime in

    peace out

    Glenn
     
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  2. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    It will be interesting.. it isnt the simplest way to get more bang for you buck as the larger rotating mass will potentially limit upper rev range and overall power but increased Cubes means more torque so swings and roundabouts I guess.
    I was thinking that Head Gasket may well be an issue but you could probably get away with multi layer copper and O ring'd head..
    I look forward to the next instalment :)
     
  3. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Well spotted - piston mass has me concerned given that the OEM pistons are so light - that's a bridge I'll have to cross

    The head gasket is an issue as the larger bore infringes the sealing ridge in the OEM gasket and I'd though that the solution will likely be a copper o-ring.

    To that end I have a page link which also introduces another potential change - offset cylinders.
    In all of my reading I was pondering the potential for friction reduction, power output increases year on year, and offset cylinder are much more common nowadays - well lo and behold @Mngforce had undone that precise modification and done o-ring cylinders because of blowing head gaskets, because they hadn't retimed the cams to prevent the valves hitting the piston - that's obviously preventable.

    http://www.akhara.com/afm/020825-fzr400rebuild/index.html

    This got me thinking about a different approach - seeing if I can have eccentric locating dowels made which doesn't require complex mods made to the barrels and cases and is therefore easily reversible in case of problems or adverse effects.

    I'm thinking in the vicinity of 2mm - 3mm.

    It has dual potential benefits, first is reducing piston to cylinder wall side thrust loading during the combustion stroke, and the second is that it actually increases intake stroke duration.

    Google desaxe for loads of info on offset cylinders

    This is a good paper
    https://www.fev.com/fileadmin/user_...pactonPistonAndPistonRingFrictionBehavior.pdf
     
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  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    • Valve pockets should be checked with plasticene. Valve recesses are often a pain in the neck when trying to swap in different pistons, and getting pistons with blank tops is sometimes the only option.
    • Compression is going to be much higher than standard with the larger displacement so expect to use a flatter topped piston.
    • As Andy mentioned, reciprocating weight is very important to avoid broken rods. I would consider coated Ti gudgeon pins since you might have saved a bundle by getting cheap pistons. See https://www.highpowermedia.com/blog/3342/piston-pins-material-choices.
    • From my experience, this kind of work requires design, design, and then design. My approach would to be get the big bore functional and then work on a matching head and cam.
    • I wouldn't go near the offset idea, too much work to be done already without worrying about that.
    • Cometic do custom head gaskets
     
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  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    My Bike:
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    This company makes a good selection of both cast and forged pistons in sizes between 52mm - 54mm, but because they've only got blank heads I decided that was a serious amount of outside machine work that put it outside the project aims

    In fact there's some really good candidates amongst them, but they're not on the menu right now

    http://www.daytonaindonesia.com/product-subcategory/piston/cast-piston/101
    http://www.daytonaindonesia.com/product-subcategory/piston/forged-piston/102


    I did a quick measurement and calculation of the volume of the protrusion over the compression height on an OEM FZR piston, then the change in swept volume to compressed volume, as luck would have it, removing the protrusion above the 18mm compression height would keep the compression ratio approximately the same

    So there is the possibility of even using a standard compression flat top R125 or T135 piston - that would change the combustion chamber shape entirely though - I am trying to find second hand OEM pistons to see the potential there

    Stock valves on those two are within 1.5mm of FZR valves, layout and included angle is at this point unknown and not in any specs that I've read so far and valve pocket depth in the crown looks different
     
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  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Speaking about the head cfm and torque etc. If you mess around with the figures Superflow's web site https://www.superflow.com/aspx/news.aspx?id=15 you get some interesting results.
    Assume the 10 inches of water values and calc cfm to yield 44hp with 250cc engine
    Total HP 44.72
    Cpower 0.43
    cfm = 26
    and plug that cfm number in to see at what rpm that gives
    Crpm 2000
    cubic inches 3.81 (per cyl)
    cfm 26
    RPM = 13634
    Not too bad, so lets make the displacement 300cc (4.57 in^3 per cyl)
    Crpm 2000
    cubic inches 4.57
    cfm 26
    RPM = 11361
    Off the top of my head the drop to 11361 won't be a problem because the standard head can fill the extra 20% capacity under 11000. I predict you will get a dramatic improvement in grunt and more peak power anyway.
     
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  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Okay those Daytona pistons are the business. As you said it is going to cost a buck to machine the tops and best done by a company that does them all the time. Having looked at those flow numbers I think the Fizzer head flows enough to make it a winner even if you do your budget "Ruckus Stage 1".
     
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  8. minimac

    minimac Active Member Premium Member Contributing Member

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  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Daytona are pretty good manufacturer's, i have a couple of their Minimoto race engines, Daytona Anima 190 4V OHC engine's



    kit-piston-daytona-anima-190.jpg

    Takegawa make a 54mm forged piston, they're around $230 US each though

    01-02-6027.jpg
     
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  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Guys keep the discussion and suggestions coming as that is exactly what I was seeking to inspire with this

    For what it's worth the Daytona pistons are not relatively expensive - cast pistons ~$45AUD - forged pistons ~$75UAD - now that may seem cheap still, but consider their main market - Indonesia, I suspect that is a very expensive part for them relative to their incomes.

    @maelstrom - well spotted, I was thinking in stages with this - 52mm piston - first stage - check the outcome - then perhaps towards a larger bore and other work - that doesn't bust my budget as progressive steps.

    @my67xr - I ogled many of those takegawa pistons, very pretty indeed and when I found Uma racing pistons, out of Malaysia, I thought I'd hit pay dirt, but however they don't list much if anything in the 52mm - 54mm range.

    Then came Daytona, that was actual paydirt - now here is the interesting development, only in recent months have they listed pistons with machined crowns on their website - they are even the same price as the piston blanks.

    I had wanted to run around with my arms in the air saying hey guys I've found the perfect setup, but need to get the proof of concept completed first - I think there is a very real possibility that with a large enough order and the file for the machining tested and supplied to them they could potentially machine the pistons in house ready for fitting - commonality between FZR, CBR, ZXR & GSX would be a bonus as it would increase the potential demand.

    But I don't want to get ahead of myself - basic setup @ 52mm bore first
     
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  11. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Something else you will want to investigate is Piston Crown cooling, especially if you are machining the crown for clearance, fit etc. I havent actually looked at the oil circuit in an FZR before.. or if there is even a diagram / explanation of the system.
    If you are machining the crown it will reduce the amount of material with the potential for things like holes in the top etc being the consequence.

    Depending on the sleeves it would be interesting to see how far you can take the standard bore out. I have purchased a "big bore" kit for my CB400 F1 that takes it out from 408cc to 466cc with a 3mm over standard bore. It doesnt leave a lot of meat and almost no taper at the bottom to assist in assembly. Heat apparently was an issue with the early Yoshimura Big Bore kits that they sorted by adding an oil cooler. The CB400 is air cooled. These were on bikes that were being pushed pretty hard.. I wont be fitting an oil cooler on mine initially as it will be ridden in a normal sedate manner :)
    So you may want to look at an oil cooler as well to supplement the water cooling...as long as an Oil Cooler can be adapted.
     
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  12. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    An oil cooler in an easy add on to the FZR engine, there's already a double ended banjo oil pipe running down the front of the engine
    (This crusty looking siezed 3LN engine was for sale at Yahoo Aleado for $60 AU)

    i-img640x480-1534562865hymjk788652.jpg


    UMA Forged piston's, blank top's for the Wave SRL110 are 52mm
    https://www.umaracing.com.my/piston/itemlist/category/65-forged-piston


    Also have a talk to Jaime at Classic Honda 50's he know's a lot about all sort's of racing part's.
    A Horizontal 50cc engine with an 88cc kit uses a 52mm piston.
    I'm pretty sure they are in Cessnock NSW

    https://classichonda50saustralia.com.au/store/index.php?search[keywords]=52mm+piston&_a=category
     
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    Last edited: Nov 15, 2018
  13. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    There are jets which spray the underside of the pistons on the FZR fortunately

    I reckon you could take the standard sleeves out 3mm, not certain what the longevity would be though.

    I have been investigating putting an FZR600 oil cooler on, but it look like it wouldn't fit inside the side stand part of the frame - I only have the 3LN1 engine in the frame right now

    Perhaps someone with a 3LN3 or later can chime in an let me know what the clearance is when removing the oil filter
     
  14. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    That engine is magnificent, it looks like it has actually been used as a boat anchor

    I tried getting in touch with Uma for some dimensions - no response unfortunately

    Those pistons look interesting, but I skipped past a lot of potential pistons with valve pockets for 2 valve heads

    Good website, I'm going to stickybeak there for a bit
     
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  15. minimac

    minimac Active Member Premium Member Contributing Member

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    You might want to look at jetskis and ATV parts houses also. It's amazing what parts can be swapped out.
     
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  16. Bryn duFresne-Mann

    Bryn duFresne-Mann Active Member Premium Member

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    Very interested here! I spent a bit of time looking into the big bore idea- but finding piston dimensions was a huge issue- clearly looking in the wrong catalogs!
     
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  17. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Realistically I'd like to find some conrods out of something more recent to take advantage of advances in metallurgy - I've been attempting to find the rod dimension of the YZF-R25, but I'm damned if I can find them.
     
  18. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I also spent a a lot of time looking in the wrong direction, the Asian market is awash with small bore scooter and bikes.

    Like a dog with a bone, one which I spent far too long chewing, was valves - the 3.5mm stem diameter was only used for a short time.

    @gregt reckons that 1mm larger is possible, they're out there, but with 4.5mm stems

    I'll have more to say on this possible modification further down the track
     
  19. Murdo

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

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    From what I've seen of FZR heads there shouldn't be much need to increase the size of the valve heads for the slight over bore you are going to. How much bigger are the valve heads of the 400cc FZR?
     
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  20. Bryn duFresne-Mann

    Bryn duFresne-Mann Active Member Premium Member

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    Given the (more than likely) drop in RPM... my spider senses tell me that this kind of build is likely not going to exceed 16k rpm... is a larger valve head really that necessary?
     
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