How to rebuild and balance these engines

Discussion in 'Motorized Bicycle General Discussion' started by taddthewadd, Feb 22, 2010.

  1. taddthewadd

    taddthewadd New Member

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    I have searched for these topics and couldn't find what I was looking for so here goes:

    I am wanting to balance and rebuild my engine. This kit is brand new out of the box and I want to start things off right with this one. I consider myself capable of this project but lack the knowledge of how to balance and rebuild these china engines.

    My hope is that someone or many will post something extensive that would include a step by step guide on disasembly of the engine, how to balance the crank, con rod, piston or what type of shop to go to for balancing, how to re-assemble the engine including proper torq specs on all hardware. Also any other tips or tricks related to this project that I missed. Pics would be nice too if possible.

    I thank you in advance and will be checking back frequently as well as posting responses to your ideas and info.

    I know that there is vague info on this in the forums but I thought others as well as myself would benefit from a more detailed guide on this. Thanks
     
  2. wildemere

    wildemere New Member

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    Read Gordon Jennings 2 Stroke Tuners Handbook or

    Performance Tuning by Graham Bell

    Its all in there. Then you will be the guru.
     
  3. taddthewadd

    taddthewadd New Member

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    Thank you wildemere. I checked into those books and they look like they will be a great read. After reading those books I will understand in detail how the general 2 stroke works. I think I am looking for something a little different though. I was hoping for some info from the forum on our specific engines.

    If someone out there has rebuilt and balanced our china engines will you please post a how to?

    Thank you in advance
     
  4. wildemere

    wildemere New Member

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    Tadd, as I say, its all in those old texts as they are from the era of racing 2 strokes. When reading these texts just remember a few things about the happytime, they are piston ported, 66cc or 48cc, 6,000 or 7,000 max rpm.

    They are not 12,000rpm+ race motors. There are no dowell pins, bearing retainers, shims, or anything that promotes power or reliability in these engines as delivered. Including any standards between numerous factories that bang these kits together. Power and reliability is as random as the build quality and gear noise/vibration.

    An engine tuner needs numbers to work from, a base standard or blueprint.

    And a dyno...

    It is not a Yamaha YZ or Honda CR where all these numbers are available in a workshop manual. That is why there is no "guide " to blueprinting these old fashioned, low tech engines.

    Regarding balancing, run the engine first, some HT's are smooth out of the box, others vibrate. If yours is not smooth then look into balancing. A 2 stroke single is never balanced, there is always a rocking motion.

    The other problem we have is a lack of a real blueprint. Things like port heights, durations, ignition settings, compression ratio and even torque settings are all up in the air. Evey barrell I have inspected is different slightly, eapecialy in the transfers

    Some forum members here are achieving great things though, through good research and trial and error. Other members make here great bolt on parts too.

    You can't make a guide for random chinese engineering, just do the best with what you got, run a spare bike or engine when pushing the envelope and have fun.
     
  5. Creative Engineering

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    taddthewadd,

    wildemere summed it up perfectly!

    These engines are different. Knowing the "how" by reading articles will make you informed so that you can modify your engine based on what it needs.

    Jim
     
  6. GearNut

    GearNut Active Member

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    Each engine is like a snowflake. No two are the same.
    You have to figure out the details of your snowflake to see what it needs for improvement.
    Each snowflake requires subtle differences in modification to reach your desired goal.
     
  7. BarelyAWake

    BarelyAWake New Member

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    "Balancing" a single cylinder two stroke may require mystical formulas and an alchemist's lab - but on the other hand have you considered the basics? These lil motors respond really well to even such simple things as a good port & polish, an expansion chamber, a better carb than stock, replacing the head and making your own intake manifold.

    Though many consider these "performance" upgrades it's true that much of it in reality is just "correcting" the sloppiness inherent in such low-cost, low quality Chinese engines. It's really not difficult in the slightest, ranges in cost from nothin' but your time to a maximum of about $200 - if you choose the absolutely nicest of aftermarket carbs and expansion chambers.

    Beyond the above? Much as I hate to say it as I'm guilty of being a borderline fanatic... it may simply not be worth the effort (beyond amusement ofc) as engines like the Morini are available. Starting out far better "balanced" than our poor lil HTs they may be worth considering if that's your goal.

    The reason there's no comprehensive "step by step guide on disassembly" of the engine is that it's so basic as to be four nuts to remove the top end - the rest not needing to be addressed as there's little to be done. A Dremel the fanciest tool ya need, patience the scarcest commodity - most if not all the information you desire to be found here on the forum.

    Of course we'll be more than happy to address any specific questions ya have ;)
     
  8. taddthewadd

    taddthewadd New Member

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    Thank you guys for the great info. I guess I was just getting too wrapped up in all of this. I tend to be a perfectionist. I do realize that these engines are old technology and the quality is hit and miss. I guess I was just looking for a way to change that. I do agree with all of you that sticking with the basics will be sufficient.

    This is what I plan to do:
    From SBP- hardware kit, expansion chamber, clutch cable, clutch cover, fuel filter, plug wire, and plug

    From Manic Mechanic- intake manifold

    From Pirate- possibly the racing carb and damp pro

    I might try the port and polish down the road somewhere too.

    I do have a few questions for you guys:
    Does anyone know all of the torq specs for the engine so when I replace everything with the SBP hardware kit I get it right
    Also what are your opinions on the racing carb from Pirate. Also does the damp pro really work from Pirate.

    Thanks,
    Todd
     
  9. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    The 49cc engines tend to be smoother running in general... leading me to believe that they have better balancing right out of the box.
    They lack the pulling power that the 66cc engines have, but on flat ground, they can keep up!
     
  10. BarelyAWake

    BarelyAWake New Member

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    I would heartily recommend a light port & polish, essentially cutting away flash and smoothing the bad casting in the intake and exhaust ports and the transfers - as well as the easier but essential matching of the intake and exhaust to their manifolds, including the gaskets themselves. Despite the relative "complexity" of a "serious" port n'polish, what I'm describing is truly easy for those with a lil patience and a touch of caution (like not cutting too much or scoring the cyl walls is all), yet the gain is usually quite pronounced.

    I figure it like this - tho alla goodies you describe are indeed worthy, their effect is somewhat lessened when bolted to a motor that's not been "cleaned" in this fashion.

    Examples of untouched sloppiness (click to view)
    [​IMG] [​IMG]

    after jus' a few minutes with the ol' Dremel ;)
    [​IMG]
     
  11. taddthewadd

    taddthewadd New Member

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    Thanks Barelyawake. I will do the port and polish like you said. I am just wondering what bits you used for your dremel. I have a dremel and a ton of bits, just wondering which ones work best. Also It was previously mentioned that disasembly of the engine is easy with the for nuts to remove the head but what about the clutch. I haven't looked in there yet and does the piston have rings and if so do I need a special tool for that? One last question when I put everything back together do I need to use all new gaskets? Thanks
     
  12. BarelyAWake

    BarelyAWake New Member

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    I just used a combination of these two kits, which one in particular just a matter of what will (or won't) fit... the "coarseness" dictated only by what stage it's at. A 1/2 round file helps too - but mostly as a sanding block for "buffing" out some of the lateral scoring left by the Dremel's habit of only spinning one way.

    Dremel 686-01 Sanding Grinding Kit
    Dremel 684-01 20-Piece Clean & Polish Kit

    The clutch is one of those things that if it works - best to just leave it be... but Jim's (Manic Mechanic) sweet animation sure is handy: http://motorbicycling.com/f30/animated-view-ht-clutch-assembly-countershaft-8939.html

    lastly - tho you'll prolly be able to salvage most of the gaskets if you've never run the motor before you disassemble it, odds are you'll mess up the base gasket at least. In any case gaskets are inexpensive and the stock ones aren't that great anyway - with that in mind I'd pick up spares and make whatever ones you feel comfortable doing, with a quality material found at yer local auto parts store ;)

    Ya don't hafta do alla this BTW (many don't bother) - tho it does help, I just think it fun as well as giving that hard-sought extra "oomph" outa these lil motors :D
     
  13. Cannonfish

    Cannonfish New Member

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    I'm about to undertake a similar operation (mild port and polish), and I am also wondering about dremel-tool attachments. I've been looking online and at local hardware stores, and I haven't been able to find any long-shank 1/8" diameter bits. My dremel-tool is too chunky to reach the transfer ports using the little standard-shanked bits.

    Do you guys have any idea where to find longer-shanked grinding/polishing bits for 1/8" dremel-tools?

    Thanks!
     
  14. BarelyAWake

    BarelyAWake New Member

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    For longer shanks - no, I've not much luck finding Dremel brand ones, tho I suspect there's gotta be something available for other rotary tools. There's the Dremel Flex Shaft attachment - but I've found the collet is what gets in the way so it's not much help.

    I just had a buddy tack weld (TIG) extensions on a coupla bits (in a V made with angle stock so it's true and straight) so I didn't look around much... defo give a shout if ya know/find an alternative :)

    If none of the above is possible fer folks, there's always the tedious but effective (dundundun) hand tool option lol, but I r lazy and hates that heh


    Oh and this is prolly obvious, but be careful with longer bits and drop the speed down accordingly (better for this app anyway). At the speeds a Dremel is capable of, even the slight imbalance cause by using the bit can get... exciting (may be why they're unavailable/hard to find) ;)
     
    #14 BarelyAWake, Feb 23, 2010
    Last edited: Feb 23, 2010
  15. taddthewadd

    taddthewadd New Member

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    Thanks again barelyawake. I am so excited about this hobby and now my new project (Port and polish). I know that I don't have to do it but tinkering on these is half of the fun. I was wondering though what is the purpose of the transfer port. I understand exhuast and intake ports but have never heard of a transfer port.

    Also just wondering if you have any info on some of my previous questions that haven't been answered yet? Here is the quote:
    "I do have a few questions for you guys:
    Does anyone know all of the torq specs for the engine so when I replace everything with the SBP hardware kit I get it right
    Also what are your opinions on the racing carb from Pirate. Also does the damp pro really work from Pirate."
     
  16. BarelyAWake

    BarelyAWake New Member

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    Tinkerin' on these is indeed at least half the fun - it's why I got into this blasted addiction FTW

    The fuel air mix from your carb goes through the crankcase too w/a two stroke engine, when the piston moves down it exposes the transfer ports and draws in the mix - to be compressed then detonated like you'd expect. This way the fuel/oil mix can be used to lubricate the crankshaft and assorted bearings - thus the marvelous simplicity (and disproportionate power/weight) of teh two smoker :D

    Pics of the transfer ports in our HTs (Grubee Skyhawk 66cc btw), the squarish indentation in the side of the case and passages next to the sides of the cylinder... also note the destroyed base gasket heh (click to view larger);
    [​IMG] [​IMG]

    A perhaps overly simplistic & general explanation (but better than mine lol) can be found here: http://www.vf750fd.com/blurbs/stroke.html a more in-depth definition and various alternatives wiki provides here: http://en.wikipedia.org/wiki/Two-stroke_engine

    The specific torque specs... varies depending on whom you ask - and the Chinese ain't tellin'. I try not to worry about it too much, mostly I get em "snug" and resist the urge to "check" them by just tightening them a lil more - which can lead to fastener failure and stripped threads. Despite the lack of loctite (I'm not a huge fan, personal bias tho) I've not had any problems with fasteners loosening or failing... I am however a big fan of lock washers, including replacing them after use and disassembly. I'm sure someone else will drop by with torque specifics, it's defo handy to know them - sorry I can't be of more help (betcha Pablo from SBP knows tho).

    TBH I'd care more if the engine cost more I think *shame*

    I've not checked out the "racing" carb from Pirate, I did however just get a CNS from Spooky... but I've not had a chance to run it yet. I've heard good things mostly, but anythings gotta be better than stock lol

    As for the 'Damp Pro' - well, it's 'nother product I've not tried as I simply lined the inside of just the clutch cover with a coupla coats of rubberized undercoating. Easy n'cheap and best yet unobtrusive, it works well to help shut up the clutch noise... the vibration? Only a sprung seat and good, soft handgrips will do anything to "damp" that with these motorized bikes.


    lol - 'nother missed question *second helpin' of the shame* ;)

    No, you'll not need any special tool for the piston rings - they're small 'nuff to easily compress w/yer thumbs (being sure to put the gap over the alignment pin) as you put the piston back in the cylinder. Gently get the first one aligned and in, then work the second. If it's tough, stop and look again 'cause yer doin' it wrong, it outa be easy.

    The pesky lil alignment pins;
    [​IMG]
     
    #16 BarelyAWake, Feb 23, 2010
    Last edited: Feb 23, 2010
  17. taddthewadd

    taddthewadd New Member

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    Thank you for taking the time. Great info. You are an asset to this forum. I plan on working on this soon.

    Anyone else want to chime in?

    BTW I am also working on a PVC gas tank. I have another thread about it called PVC gas tank. I will test it to make sure it will hold up to gasoline and post my findings. I plan to let it sit for a month with gas in it. Just thought you guys might be interested.
     
  18. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    I would say stay way from any "racing carbs" unless you are racing....learn to tune the stock one, and try the stock carb mod as outlined by Igor on this website. Also, before you shell out 50-70 dollars or more for one, and STILL have to tune it for it to work properly, consider the alternatives available on ebay for a few dollars, like a Mikuni, Del'Orto, or ect. from a small dirt bike.

    Damp Pro?!? How about .25 cents worth of caulking or silicone, works the same way and doesn't cost an arm and a leg.
     
  19. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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  20. taddthewadd

    taddthewadd New Member

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    Have you tried that carb mod from egor Bikeguy Joe? Are you suggesting it "at your own risk" or do you believe in it?
     

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