Bought bottom end from Boy Go Fast, should I be worried?

Discussion in 'Motorized Bicycle General Discussion' started by fischer550, Apr 23, 2014.

  1. fischer550

    fischer550 Member

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    So oddly enough, a big piece of metal from the crank case, (the actual case itself, not the interior parts) cracked off. Sick of this motor and all of its problems, I bought a new bottom end unit from ebay user boygoesfast. http://www.ebay.com/itm/191078362791?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 It was only 75 bucks shipped, which I thought was pretty good. I also have a ported cylinder coming in, so that will be my top end. I've seen a lot of bad reviews for this guy, do you think I will receive a poor quality item? I want a good running motor, is he known for having bad motors? Also, what is with the bend in the clutch arm?
     
  2. Greg58

    Greg58 Well-Known Member

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    I have a bgf 48 cc and I think Map Bike has a 66cc, mine has been good and is almost three years old. I got the angled clutch arm from bgf several years ago to go on my grubee, the arm angle and length keep the clutch cable aligned with the cable boss better preventing cable wear at that point. Also keeps the cable end out of your leg when pedaling.
     
  3. mapbike

    mapbike Active Member

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    I've never hqd a bad experience with bgf, bought my first engine from him in 2009 and its stillgoing strong, I have done some upgrades to it but it was not because anything was wrong with but only because I wanted to experiment with some other parts and pieces, on another bike I'm also still running an engine from bgf and it has been going strong since 2010, its also a 66cc, bgf will work with someone and make a solid effort to make any legit issues right if he is addressed nicely and honestly, but if someone is being a jerk and starts acting out of line with him he will not cooperate, can't say I blame him either, many of the bad reports are do to people acting like an idiot with him and he just brushes them off, I've had a couple parts that were broke when I got them for shipping damage in the past and all they ask is for me to please take a picture and email it to them so they could see the problem, I did as they ask and they immediately at there cost shipped me a new part and thanked me for my honesty, im sure many people have tried to rip them off so you cant blame them for wanting proof.

    I have heard that the engines he is selling now are a "hybrid" PK80 because instead of having a 40mm stroke they have a 38mm stroke, Fred the maker of the Fred heads and other parts has said they are good engines and he has bought and built some himself, all china girls are a crap shoot to some extent but it is a fact that some factories in China are known for producing a better engine than others on average and it seems that the engines bgf has are good ones.

    Im partial myself to the engines and lowers tha dax and Neil ( motorbicycleracing ) sells, they are the best balanced engines I've personally had but the bgf engines I have are not the same engine he is selling now, mine are the old style and although they have been good strong engines they are not as well balanced as some of the engines that are coming out of China now days.

    Best wishes and just build that lower up right, make sure the carb is tuned right and by all keans install a quality upper bearing and not the stock china bearing, notch the piston to clear intake port if you have the ability and tighten everything correctly and you should have a good engine.

    Map
    .wee.
     
  4. fischer550

    fischer550 Member

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    So is a 38mm stroke better than a 40? And also, the motor has the piston attached so do I have to make any changes?
     
  5. mapbike

    mapbike Active Member

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    I would replace upper wrist pin bearing with higher quality one myself but some have good luck with the stock bearing so thate just a matter of whether you're willing to chance it being a good one or not, be sue to look close and realiz the there are tiny pins in the ring groove on the piston and each ring must have the pins placed in the gap of the ring before jug/cylinder can be place over piston and you will have to squeeze the rings and rub a good dose of oil inside cylinder to help it all come together, its a simple process but just ne sure the ring gaps are aligned with the little dowel pins in the pistons ring grooves or you'll break the rings trying to get jug on.

    Also look to make sure locking clips on each sode of wrist pin are both seated good in the grooves, some have had issues with them not being in the groove and if they come out has s big trouble and a jacked up engine real quick.

    Map
     
  6. fischer550

    fischer550 Member

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    Thanks for the info map bike. Again though, is a 38mm stroke better than a 40mm? What do you mean by "hybrid engine"
     
  7. Theon

    Theon New Member

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    More stroke more torque and slightly more displacement.
    So no 38mm stroke is not better.
    By Hybrid I think MAP is referring to rod length.
    I'd have got the MBR 40mm stroke motor myself.
    But depends what you expect,
    I want at least twice the standard HP, and 9000 RPM revs.
    can be done with a 38mm stroke, but better off starting with the better bottom end.
    If you just want a standard 2 1/2? HP motor, it'll be fine.
     
    #7 Theon, Apr 24, 2014
    Last edited: Apr 24, 2014
  8. mapbike

    mapbike Active Member

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    By hybrid I meen what I have read about them being a combination between the grube type engine and a typical PK 80 type.

    Im no expert on all these things but I read where Fred maker of the Fred heada and other parts including some high end engine builds refers to the bgf engines as hybrids because of the stroke and piston type combination, he actually uses the bgf lowers for one of his moderate performance builds and he says they're good built lowers so I would no be sfraid of them and as far as performance is concerned Im gonna say you will not likely notice a difference between the 38mm stroke engine and the 40mm stroke engine for a typical build, probably a really high end build might show some performance difference but the way most of us build our engines up I dont think a power difference will be noticed at all, I'd build up the bgf engine expecting it to be just fine, and if it just so happens to have a fairly true crankshanft and the balance of the lower is pretty good it will perform better than a 40mm stroke engine that has an untrue crank and bad balance, high amount of vibration is a performance limiting factor on whichever engine we get, a better balanced engine allows it to rev better and higher if it is set up right, as it has been said by many for a long time here on this forum, " all of the china made engines are a crap shoot" it does seem that we are getting some better quality engines here lately but no matter which " brand" or type of china girl engine we buy we can be assured that we may get a good one that runs for a long time or we may get a lemon......
    Main thing is just build it right by matching the components and run a quality oil and treat it like what it is, a cheap china made engine for using on a bicycle that was not designed for and engine, build your bike to be safe with good tires , good brakes and make sure everything is greased very good and stays tight and secure, get rid of cheap thin fenders and mounts, use thick thorn resistant tubes in the tires and make sure chain is aligned and stays at a proper tension, all these things will give you a safer bike and a better chance of having a bike that you can usually have fairly good reliability from, just remember you should give it a good visual inspection before each ride and ride it like a motorized bike and not like a motorcycle and avoid. Deep pot holes that can break frames and taco wheels.... use a mirror and watch out for the cars and trucks that dont see you well and realize how fast you are coming their way, people aren't suded to having a bicycle approach them at 25-30+mph and are prone to pull out in front of you, this is where xefensive riding and good brakes can save your hide.....

    Best wishes on the build, im looking forward to hearing abour it and seeing it as it comes together.

    Map
    .wee.
     
  9. Jumpa

    Jumpa New Member

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    if you look at the honor of the eBayers who give BGF the bad feedback they are mostly low by honor I mean feedback Honor is used ion the americas army game I play sorry same concept most are because the user is too stupid to know how to turn a wrench They put it together wrong get air leaks and want to place blame someplace and he is the closest person !
     
  10. fischer550

    fischer550 Member

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    Wow thank you for the help mapbike! I have the bottom end coming, a ported cylinder coming, a high compression head, tuned pipe, and a racing carb (with smaller jets for high altitude) so I hope it runs good
     
  11. fischer550

    fischer550 Member

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    So, I asked bgf what the size of the stroke was, and he replied "it is the 2-stroke 66/80cc
    the 66/80cc is the 47mm on the piston". What are you referring to when you say store size?
     
  12. Theon

    Theon New Member

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    If he wont tell you its stroke it will be a 38mm.
    I can't agree sorry MAP, but the 40mm stroke in my opinion makes a noticeable difference to the torque.
    It is only really 5% more, but 5% more displacement x 5% more stroke, so more than 5% increase in power.
    but the main thing is you will likely find that to get the compression up on a 38mm stroke motor you will need to deck the barrel if you want to set the squish.
    Hence the 38mm stroke motors come with a slant head to try and correct the compression.
    If I was just building a low power cruiser, then 38mm is OK, but if you want to try and get what you can from your motor then every 5% helps.
     
  13. Greg58

    Greg58 Well-Known Member

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    I wouldn't worry about the stroke at all, if you are like most people here a good riding and fairly dependable bike is what you want. A basic engine with just a few upgrades will scare you on a bicycle! When you get it you can measure the piston from bottom of skirt to the top of the pin to see what the stroke is, the 38mm stroke piston should be 15/16. The picture below is from piston bikes web site.

    http://motorbicycling.com/attachment.php?attachmentid=69519&d=1397927455
     
    #13 Greg58, Apr 24, 2014
    Last edited: Apr 24, 2014
  14. Theon

    Theon New Member

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    Piston pin height has nothing to do with stroke.
    It is to do with rod length.
    You can have either piston with either crank as long as you have the right rod.
    A 'Hybrid' engine usually refers to the use of a 40mm stroke with the longer rod and therefore higher piston pin.
     
  15. fischer550

    fischer550 Member

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    Thanks Theon, do you think the hybrid will have more or less power?
     
  16. Greg58

    Greg58 Well-Known Member

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    Theon that's what I was saying, the piston with the pin higher in the piston would be for a longer rod/stroke engine. The piston on the left is for the shorter stroke engine, put it in a 40mm stroke engine and it will hit the head. Therefore piston pin height has everything to do with stroke.
     
    #16 Greg58, Apr 24, 2014
    Last edited: Apr 24, 2014
  17. maniac57

    maniac57 Old, Fat, and still faster than you

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    What Theon meant was you can have EITHER PISTON ON EITHER STROKE with the correct con rod. Stroke does not matter IF it has the right rod for that style piston.
    The stock engines come both ways depending on source and con rod.
     
  18. Theon

    Theon New Member

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    Sorry Greg but rod length and stroke are not related.
    You are more likely to get a short rod on a long stroke motor, but you can also get a long stroke and long rod.
    As you can get short or long rod on 38mm stroke, the GT5 has short stroke and long rod so high wrist pin piston, however I had a 38mm stroke motor with a short rod before.
    Infact I have had motors of all four configurations.
    Long rod is 90mm, Short rod is 86mm I believe.
    Hence the difference in wrist pin height.
    I only have short stroke log rod and long stroke long rod cranks on the bench at the moment but they both take the same piston.
     
  19. mapbike

    mapbike Active Member

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    Theon agree with me or not makes no difference to me, The stroke of the engine being only 2mm difference on the average china girl build will not be noticeable in the torque or overall power, an engine with the shorter stroke can still be a very strong and torquey engine, I used to build some strong small block Chevys back in the day and the only difference between a 350 cid and a 327 cid engine is that the 327 has a 1/4" shorter stroke, and you can get crazy freaking power and better high rpm potential with breaking a rod with the 327 using stock rod length vs the 350 using stock 5.7 length rod.

    The point I have been making is that you need to understand not everyone is interested in a 10, 000 rpm all out china girl build and everytime you comment on a thread. Oncerning the china girl engine that is the type of advice you always give, maybe you should think simple a little more and understand that everyone isn't a race engine builder and what. Ounts the most is making sure people understand the simple basics of building their engine so that it runs as good as it can in the mostly bone stock arrangement, hepling people to build their bike up hinking safety above all out performance is what we should peobably concentrate on the most so someone isn't overwhelmed right from the get go with all the loads of high performance mods and junk that most people dont need or even know how to accomplish in the first place... there is an old saying tbat goes like this" keep it simple stupid" I think this needs to be our frame of mind when people are just getting into the hobby and dont even have a clue how these engines work yet.

    Peace, map
     
  20. mapbike

    mapbike Active Member

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    Nope long rod engine has 110mm rod
     

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