looking for box muffler for 48cc Grubee, lawnmower style

Discussion in '2-Stroke Engines' started by happycheapskate, Dec 1, 2009.

  1. happycheapskate

    happycheapskate Active Member

    If this thread is in the wrong place, sorry. I am new, and i think it should fit here. Please be friendly. I love bicycles and i'm glad to join the MB club.

    I have a 48cc Grubee Skyhawk, on a beach cruiser. I am looking to find a muffler that will bolt onto the stock motor, which is just like a big weedeater or lawnmower pancake or box muffler. I don't want pipes and stuff hanging off. I may have to make one out of a junction box and some fiberglass. I don't know. I'm looking for something that will just bolt on or that can be welded onto the cutoff stock exhaust pipe, to help other noobs and people with odd bike frames that the stock muffler doesn't fit without hitting the frame downtube.

    I may just cut it off, or bend it with a torch, but I doubt it will last too long then.

    IF you are on the same quest, please join the thread and share.

    If you find a supply of bolt on box mufflers, you'll be my hero.

    The only downside of this style muffler will be it will eventually clog up (carb spray and a drain hole might help) and it may get your leg dirty from soot blowing. I think it would not be a problem though, and want to try it.
    I can always just put a regular muffler on later.


  2. happycheapskate

    happycheapskate Active Member

  3. biketec

    biketec Member

    I couldn't make your link work but I think I know what your talking about so I tried to put on a stock HS box muffler on and it will fit if you get longer studs and drill out the mounting holes on the muffler just slightly and mount it upside down looks kinda cool and would love to hear how it sounds/Works kinda like a mini exp.chamber. I have pix if you would like to see what I'm talking about!:detective:
  4. professor

    professor Active Member

    It has come up recently about using the cigar shaped Briggs muffs -, they really work good (especially using 2 in line) however, the guys say they clog up in a 2 stroke.
  5. motorpsycho

    motorpsycho Active Member

    i tried using a pancake style lawnmower muffler on the end of my expansion chamber. The results were good as far as noise control and backpressure (increased bottom end torque).
    BUT, this muffler will collect a lot of oil over time and i think it will clog up after awhile. I used mine for about a week, and i didn't like the way it looked (nice chrome pipe with a plain steel lawnmower muffler just didn't look good to me).
    so i modified the stock muffler to go on the end of the expansion chamber.
    i gutted the stock muffler, drilled a few holes in the baffle plate, and cut the end at a 45 degree angle.
    works like a charm and looks good too.
  6. happycheapskate

    happycheapskate Active Member

    Please share more details. This sounds like a lead. But I don't know what an HS is. I cannot picture the part you describe. Longer studs are available fairly easily for the Grubee Skyhawk. Just source some allthread type rods or long screws as long as they are threaded all the way down.

    Be 100% sure its the same size and thread or you'll ruin your motor! (or cost more to fix than its worth).

  7. 210061741

    210061741 Guest

    Anyone ever try an X-Port and an X-Box.

    Google it.
  8. happycheapskate

    happycheapskate Active Member

    Why don't you share a favorite link to a product or home made how-to page, please? I don't know what an X Box is but I suspect you don't mean the video game console.
  9. 210061741

    210061741 Guest

  10. happycheapskate

    happycheapskate Active Member

    re: x box


    This is about the right concept, maybe more advanced than I was thinking. The ports don't match, and the grubee fins won't let you mate a flat surface to the engine.

    But this is about the right idea. Perhaps you could cut a gasket facing out of a peice of steel and weld it to a cut off Grubee pipe, then mount the muffler safely away from shoes and legs and frame.

    I'm going with bending my stock pipe out just enough to fit, but I'm interested in other solutions because the heat will probably wreck the paint.

    I mounted the front of the engine one a plate and riser washers, bolted through the frame, so I get more room than normal.


    I also plan to get a metal junction box, cut a hole and screw holes in the flat plate to mate with the carb, tack a couple little wires or something over the hole, then use a cut down Briggs lawn tractor foam as a filter. The box will have nickel sized knock outs and screw onto the plate. Screw these cheesy little filters.

    If you are building a rat bike and have a welder, you could try this with an old stock muffler for the mounting face and a few inches of the tube:

    Weld a heavy steel food can to the pipe, with the big open end away from motor. make baffle plates out of about 10 or 12 lids, littlle lock washers, and 2 long screws. Paint it black with barbeque grill paint. I bet it would sound tough and you could adjust it by the plates and the spacing of the closest plate to engine for backpressure.
  11. happycheapskate

    happycheapskate Active Member

    uploading photos, found bolt on muffler!

    I found this for $4 at a small hardware shop (try true-valu or something)

    MaxPower (sold at lawn mower repair shops too)

    Note, you will have to buy replacement screws/allthread to make longer studs, and you may have an interference with the fins on the motor.

    Edit: REMOVING ANY FIN surface on an air cooled engine is a very bad idea, and is not necessary for this modification, see next few posts for success.

    (Warning: do not do this. I did not. It is not necessary) I plan to hacksaw off a little bit of the 2 fins that it touches or see if i can press in the back of the muffler a little bit. It may even just fit up after I get the new studs, hard to tell how tight the back is sitting on the motor gasket till I put a little pressure on it.

    Note, the raised area on the front where the bolts come through and the nuts go down, leaves room for a matching plate (a junction box cover will work but the galvanize will burn off p u) to deflect the heat out to the sides.

    Note, this works with a beach frame, but might be too close for a standard frame with motor clamped on down tube (then you could just use the stock muffler)


    This muffler should not clog up because its just a box with 2 baffle plates in it and a bunch of holes drilled in the front.

    Its part 4135 Maxpower, and replaces Briggs 4-8HP muffler 297274
    Last edited: Dec 5, 2009
  12. happycheapskate

    happycheapskate Active Member

    The bolt holes are perfect for it. The muffler's hole is round and bigger than the motor exit port, but the gasket has it covered just right.

    I'm bolting it up and we'll see if it needs the fin modification or not, and how it sounds. (probably louder than stock, but low enough to pass cops if you don't drive it in parking ramps or near office buildings. You CAN pedal, so just get out of the parking area before opening it up.
    Last edited: Dec 4, 2009
  13. happycheapskate

    happycheapskate Active Member

    The exit port is a rounded rectangle, so it is highly likely that some pocketbike or other china mufflers will fit, but you should be able to see the muffler in person with your bike before you buy, or test fit against home-made mockups. Don't forget fins/head and your bike frame for clearances!
  14. happycheapskate

    happycheapskate Active Member

    Here is another smaller one that will work, for $3, but will require you to hacksaw off the threaded portion and drill your own holes!


    Note this one has one baffle plate exactly in the middle, welded all the way around. It has one hole in the center, exactly the size of the drillings on the front, plus about 20 little holes on the same baffle plate, around the edges. This will have a lot of backpressure! You can modify that by expanding the hole with a larger bit if needed. This one would probably be very quiet and look good.

    Note! the gasket shown is presumeably an extra carb gasket that came with the Grubee kit. The motor gasket has a rounded rectangle hole the size of the port, but will work.
    You will have to Hacksaw and File off the pipe threads on the muffler (easy) and mark and drill the bolt holes (harder but should be able to for anyone, use small pilot bit first, then drill out, and do the back holes before the front. Get them straight or you will possibly bend the studs.

    I'm going with the black box type first since I have the clearance and want to run wide open all day with it, but I'll do the silver one too just to get back with you guys, and see which runs better.

    The Part Number for the silver one is 4131 maxpower, replaces briggs 298830.

    If you have a welder, you could weld ears to a 1" x 1/2" pipe thread pipe fitting, machine out the inside diameter a little (the threads are too tall but seem to be the right pitch), and file the facing to be a smooth fit. This will position the muffler out quite a ways which may hit your frame. The black box is abotu 1"-1.5" thick not counting the raised area at the gasket facing (1/8")
    Last edited: Dec 4, 2009
  15. happycheapskate

    happycheapskate Active Member

    For the Win!




    I beat the back of the muffler box in carefully with a ball peen hammer, careful not to damage the gasket area. Just a few mms as necessary to clear the fins on the engine. If you accidentally bend it in (gasket face), you may be able to save it by bending back out with a small open end wrench, a little at a time.

    I used 6-1.0 x 50mm high grade hardware screws, with lockwashers on the out facing side, which matched right up.

    You should calculate how deep a screw by itself will sit into the block before bottoming out. Mark with a magic marker. Now make sure the stack height of the lockwasher, washer(s), and muffler (after beating for clearance of fins)
    do not allow the remaining threads to exceed this depth! If you have to hacksaw the screws short, you MUST use a die to clean up the threads, or at the very least put on a nut you can stand to lose and file the threads clean on top of the nut. If you have a bad thread, you can damage your engine permanently. If the screw is too long (remember the box mashes a little bit) you might break off a screw or break the block.

    Be careful.

    I cannot warranty how this will pass any laws, noise regulations, epa or inspections, or not damage your bike.

    Your mileage may vary! (literally, this is obviously not a stock muffler, so I don't know by what amount your mileage may change.)

    So far it looks swell, though, my shoe clears it and there is some room so it doesn't melt the frame or something.
    Last edited: Dec 4, 2009
  16. motorpsycho

    motorpsycho Active Member

    the only problem i see is that you MIGHT not have the advantage of the headpipe which will give you bottom end torque. the longer the headpipe is, the more bottom end torque you will get. (i think) you have no headpipe at all with that box.
    but, things that come with a box style muffler (think weedeater) were meant to run at w.o.t. all the time.
    you may have good results with it as far as top end goes, but you may loose bottom end torque.
    who knows, maybe it'll be just fine.
    i wonder what it will sound like?
    i'm sure that it will have a good sound (raspy or louder than stock).
    i personally love the sound of my expansion chamber and modified stock muffler...sounds like a yz-80 dirt bike. the way that i have the baffle stuffed inside of my muffler, the big open end on the muffler body is kind of an echo chamber which makes it sound really cool.
  17. happycheapskate

    happycheapskate Active Member

    We're about to find out!

    I don't do videos, but I'll report back with the initial results tonight or tomorrow. I'm about to double check everything and go fire it up out in the country. You are right that the box muffler probably won't boost the low end torque, but I expect to pedal to 15mph or so routinely, and then rely on the motor for all faster speeds.

    The smaller round muffler would probably have more backpressure for those interested in this mod.

    NOTE: try cross referencing the muffler number for the black box and see if you can find a round one with heavy baffles. There may be some available for generators and 5-7 hp machines (like tillers) that will include a pipe with gasket face and ears, and a big can muffler.
  18. happycheapskate

    happycheapskate Active Member

    Success! This worked very well and was a 100% success.

    I can recommend this to grubee 48cc owners IF: they live somewhere that tolerates ATVs, dirtbikes, or large lawn equipment.

    I can say DON"T do this mod if you drive in "bedroom community" neighborhoods (or somewhere that the cops hate scooters bicycles etc).

    This muffler worked well, purred taking off from idle, and had a good hearty chainsaw buzz at 30mph. It seemed to let the motor run free, so I didn't run WOT yet, still on the break in tank, so i did the first 5 miles at 1/2 speed and the next 15 at 3/4 speed or less.

    I need to do the clutch adjustment. I couldn't do it without running the motor since I didn't know how to tell if it was loading the clutch or not even with the lever in.

    The front brake (caliper style with v lever) worked but was sorry compared to any v-brake for sure. It will do with the the super duty coaster brake.

    With the big cog, it wanted to pull my axle forward, so I am going to have to get a chain tensioner or scrape the frame dropouts good for traction.

    I am very happy with the bike and surprised at how much power the little motor has. I am very pleased with my grubee kit after I got the bugs worked out of it (clutch arm was improperly assembled and required machining to install on the clutch throw shaft/tube.

    The wind resistance into the muffler at speed seemed to make the engine run even harder! I like it. I strongly recommend carefully routing your wires (I spliced into the CDI wires with my kill switch, and capped the white wire.) to preserve them from engine heat, even though I didn't sense the down tube getting warmer than I could touch easily. you may have a different frame, and it might be hotter when you ride.
  19. happycheapskate

    happycheapskate Active Member

    As for volume of sound, it didn't make my ears ring even standing next to the bike, but it did seem loud like a heavy duty brushcutter weedeater, or hand held leaf blower.
  20. happycheapskate

    happycheapskate Active Member

    At idle to about 1/2 throttle, it was a very tolerable sound and not too loud, but after that it sounded like a loud dirtbike. I didn't have any vibration problems.

    Note: the muffler flows easily, so the engine will not slow down as rapidly as with a stock pipe, if you just turn down the throttle lever.

    I strongly!!! recommend drilling the handlebar and correctly installing the throttle/grip. If you don't (like if you file off the peg), your whole handle grip can come off the bike.
    If you don't want to drill the bar, cut the throttle grip short for 2 fingers, and install at least a half size standard grip and end cap! (like a grip shift in a way).