Fat Tire Bottom Bracket Blues

[outlawbiker]

Im so close to finishing off this Marcargi Slugo SS with a 4 stroke shift kit,however the bottom bracket cartridge isn't the right width for this monster. I cant get a straight answer out of elitist bicycle shops,maybe one of you can help me find what i need.

from the outside lip to the other lip of the bottom bracket is roughly (Fig.A in pic) 5in or 127mm. from the tip of the spindle/shaft where the crank arms mount is roughly (Fig.B) 10in or 254mm. the shaft has to have a key way in it for SBP's freewheel/sprocket. Also the distance between the bottom bracket and crank arm (Fig.C) is about 2 1/2in to 3in or 63mm to 76mm and needs that space to adjust for the freewheel sprocket. because the fat tire, i have to bring the freewheel sprocket out about an inch or 2 away from the bottom bracket so the chain can clear the tire. I cant find anything like that anywhere.

whats happening is the one that came with my shift kit is too short,and only screws into the bracket about half way, the solution i was told was to stuff washers in to fill the rest of the distance towards the outside of the bracket.This has cause the whole crank/spindle to torque and tweak up and down when I give the bike gas, because there is no bearing on the other side to keep the spindle from "flopping" around when under load/stress.

 

[5-7HEAVEN]

Like you, I'm realizing I could align my drive sprockets better if I had a wider bottom bracket(BB). Mine is 128mm; I'm looking for a wider one, too.

In my search, I found this: http://custommotoredbicycles.com/wi...r_clearing_4_stroke_motors68mm_bottom_bracket

They sell a 152mm bottom bracket. They also have 13.25" or wider shafts.

Call them. They might be able to cut the shaft to your exact needs.

BTW, your BB might be missing a bearing. It's not supposed to wobble, even under engine load.

 

[5-7HEAVEN]

I think this is what you need.http://sickbikeparts.com/bottom-bracket-cartridge-170mm-fat-tire-bike-83-110mm-bb/

Fatty bikes need that 83-110mm wide cartridge. Normal one is about 68mm.

 

[outlawbiker]

I think this is what you need.http://sickbikeparts.com/bottom-bracket-cartridge-170mm-fat-tire-bike-83-110mm-bb/

Fatty bikes need that 83-110mm wide cartridge. Normal one is about 68mm.

I have talked with Jim over there and he said that wont work. If i can remember correctly i think it was because the right side (sprocket side) of the shaft isn't long enough or it doesn't have the keyway cut on on it for the woodruff key for the freewheel sprocket.

Im thinking of getting one from the first person you mentioned, taking the axle to a lathe and cutting in a new C-clip groove in the the shaft unless i can get them to do it.

Of coarse money is always the issue here, so im trying to figure out what to do while i wait to get enough money together for this fix. So any other ideas till then would be helpful too.

 

[5-7HEAVEN]

I'm unsure why you'd need that sprocket adaptor or a keyway. SBP's fatty cartridge is designed for 2-stroke shift kits. Therefore, it's meant for the engine chain to clear the fat tire. I use part of SBP's shift kit on my bike, but not all the components. My driving sprocket bolts onto the freewheel and right-side crank arm. Then my drive sprocket is bolted onto and spaced away on that same freewheel, on the inside towards the bottom bracket. Maybe what you could do is position your chain ring sprocket directly onto the freewheel and the your driving sprocket inside, towards the bottom bracket. You'd have to bolt and space out the sprockets together on the freewheel. The driving sprocket would have to be smaller, like 30t or 32t, to clear the frame.

Do you have the correct BB for your fatty bike?

I noticed on SBP's website that they said fatty bikes need special attention.

 

[5-7HEAVEN]

My bottom bracket was wobbly also, and I was never able to tighten down the the left-side. Years ago, I had installed the BB conversion in my steel Diamondback cruiser frame. So I unscrewed it from the BB and loosened the four through-bolts. After cleaning the threads, the BB went back together. Then I tightened the through-bolts. No wobble, and everything's flush now.

Maybe ya just need to clean out the threads in the BB and reassemble.

But ya still need the wider BB.

The one I have in my cruiser frame is 8.25"or 206mm long, end to end.

 

[KCvale]

This Slugo was tricky but I just used the bikes BB.

Just make the bottom of your 4G case level buy drilling 4 new mount holes in the 4G, and the pedal goes right under it.

I don't recall any issues off hand on the right side other than you are going to want to put a tension wheel on it...

Heck, I even got the chain guard back on with some tin-snip 'snippy-snippy' hehe ;-}

I might have had to drill new engine mount holes farther forward so the right side pedal cleared the pull start but I can't recall.

I documented the whole build with pics here.
http://kcsbikes.com/topic.asp?TOPIC_ID=836

Give it a read if you want more info, it should help you.

 

[outlawbiker]

Hey KC, how did you adapt SBP's sprocket and freewheel to the Sluggo's standard crank shaft? my SBP freewheel adapter has a cut keyway in it, and so did SBP's bottom cartridge axle with a key.

 

[KCvale]

Hey KC, how did you adapt SBP's sprocket and freewheel to the Sluggo's standard crank shaft? my SBP freewheel adapter has a cut keyway in it, and so did SBP's bottom cartridge axle with a key.

The Slugo has a wide 3-piece BB.
I just did the freewheel like a 2-stroke install...
Screwed the right pedal into the freewheel/sprocket combo, and then just attached the pedal.

What you are thinking of is the normal 4-stroke kit that uses an adapter between the freewheel and the crank arm.

 

[outlawbiker]

oh no, you mean there is a difference between the 2 stroke and 4 stroke kit freewheel adapters? so i need to buy a 2 stroke freewheel from SBP? or what im saying below?

EDIT, because i have wide cranks, i assumed i was going to just use those, i never looked at the crank arms from the SBP kit, i think i get it, their crank arm screws into the freewheel, but there is a square cut into their crank arm that will fit on the end of the normal 3 peice crank keeping it on there properly? i need to go back thru my spare parts boxes and look for those crank arms,if thats the case ive got everything i need

 

[outlawbiker]

I just got done looking at the parts, i get it now! i didnt look at them the first time around. but now i cant get the cartridge out to put all the stock crank back in. Its so tight im standing on the wrench with the cartridge removal tool and it wont budge. its not offten i tear into these things,which way to these loosen?

Left is loose on these? or is it right is loose?

EDIT: Right is loose on that side, what a fight it gave me. now how the **** do i get the freewheel adapter out of the freewheel so i can screw on the crank arm?

 

[KCvale]

Correct, you don't need the 4-stroke adapter, with the stock Slugo BB shaft in the you can screw the FW right onto the right pedal.

EDIT: Right is loose on that side, what a fight it gave me. now how the **** do i get the freewheel adapter out of the freewheel so i can screw on the crank arm?

With the freewheel removal tool.

http://sickbikeparts.com/freewheel-removal-tool/

Use it to hold the freewheel from spinning while you unscrew the adapter from it.
Then you can use the straight crank arms and not those funky wide Z crank arms too.

While you are at it you really might want to think about painting the shift kit base parts black to match the bike as it looks a little silly beige ;-}

And don't forget, you need to drill new mounting holes in the 4G, you tilt it up so your left pedal clears it by just going under it.

That is pretty tricky to do... you'll want to make a template of the bolt pattern by tilting the 4G up until the left chain is tight.

You will also need to mount a chain tensioner on the back of the engine mount plate, a slot works great.

The stock exhaust won't fit and you don't want either but if you use a non EPA 2-stroke like I did you need to a cut/weld on it so the right pedal won't hit it.

I told you it was tricky but you can turn a Slugo fat tire into a 7-speed dual disc shifter ;-}

 

[outlawbiker]

thanks KC, this was my first shift kit, so after discovering my mistakes, i feel like an idiot, cant believe i over looked the threaded crank arm + freewheel. think i made more of a fool out of myself than i got accomplished on this build,ha!

Yea,im gonna paint the parts later, i was just trying to get everything to work first,then pull it all apart then paint and reassemble. If you could tell, i got the matte black slugo to give it that more "rat rod" look, so ill do up the shift kit the same.

Im really fighting hard to leave the trans in the same spot,i dont want any more aggravation with this project,but ive got a super wide angled crank arm for that side that may look stupid but will save me time and anger over looks. If i get a little more adventurous or disgusted enough with my lazyness and half assedness ill attempt the same trick you did.

For the little time that i did have this bike running and trying to learn how to shift was amazing,its like nothing else in the MB world ive driven in the past 10 years, floats down the road like a 70's caddy, having disc brakes on a MB are amazing too! This really feels like a great bike. Only other thing is, i think the clutch engages at too high of an RPM,its really screaming before it "hooks up",ill have to look into that,and the first 3 gears seem to go by very quick,like i dont even need them, i could start in 4th or 5th and the bike pulls fine off the line,I dont know, im still trying to get used to the gearing.

 

[KCvale]

thanks KC, this was my first shift kit, so after discovering my mistakes, i feel like an idiot.

Don't feel that way...
I hand already built ~Dozen shifters before I took on the Slugo and knew all the parts and how to use them.

Im really fighting hard to leave the trans in the same spot,i dont want any more aggravation with this project,but ive got a super wide angled crank arm for that side that may look stupid but will save me time and anger over looks. If i get a little more adventurous or disgusted enough with my lazyness and half assedness ill attempt the same trick you did.

It will look and feel silly but will work just fine.

...and the first 3 gears seem to go by very quick,like i dont even need them, i could start in 4th or 5th and the bike pulls fine off the line,I dont know, im still trying to get used to the gearing.

Jump gears shifting, like just using even numbered gears as the bike is geared for people power, your engine doesn't need all those gear steps.

Yes, gears change everything, once you learn to operate it you'll never want to go back to direct drive again ;-}

 

[outlawbiker]

ugh! i got it all back to stock, went to a bike shop and they backed out the freewheel adapter for free,then the bolts that hold the 2 sprockets and freewheel are too long,they are hitting the frame when i put the crank arm with the freewheel on. so i turn em around and the socket heads are now inside,facing the frame,no problem,ive got clearance now, i go to throw the nut on to tighten the crank arm on and it bottoms out the crank arm on the frame and can no longer spin.but the freewheel can.

cant put spacers on, it would cause the same thing, cant slide a bearing on,would cause the same thing, i dont know how KC did his,im lost,yet again.

 

[5-7HEAVEN]

From the first picture, it seems you need a wider bottom bracket.

In the second picture, it seems you need to have the socket heads facing out. If the bolts are too long, find shorter ones or trim to fit.

You could also clearance the pedal arm, where it contacts the nuts.

If you mount the sprocket on the inside of the freewheel, ya might not have to clearance the pedal arm.

That is after you trim the bolts a few mm.

 

[outlawbiker]

its soooooo close to working,its just the mater of like 1/8 of an inch that the whole thing presses to far on the shaft when i tighten up on the axle nut that keeps the arm from falling off the shaft.

Ive tried to run thru this in my head all night in bed, how can i get a spacer between the bearing cup,and the inside face of the crank arm and i cant think of anything because no mater what i put in between,its still going to pinch and cause the crank arm to lock up.

the only thing i didn't try was mounting the freewheel under the big sprocket like KC did, i didn't notice that till last night when i was trying to play detective and magnifying all the photos of his build. I dont know if that would make a difference.

I can only hope that KC,the master of the slugo,can teach me his ways!

EDIT: I shouldnt say its just the crank arm pinching or binding up, it could also be the inside face of the freewheel that doesn't spin also that could be making contact with the bike. If it was just the crank arm i could unscrew it,grind off the 1/8 or 1/4 inch of material on it to give me that clearance i need, but im not sure what is making the contact.

EDIT #2: Maybe i can mill out the material where the nut meets with the square hole in the crank arm,like counter sinking it,so the nut doesn't have so much room to tighten,so it doesn't push it all the way on the shaft creating that pinch.

 

[KCvale]

I can only hope that KC,the master of the slugo,can teach me his ways!

You assembled you freewheel dual sprocket combo wrong.

 

[outlawbiker]

yea, i had to reverse the bolts to face the outside so the bolts didn't hit the frame.

EDIT, ill try to do it the other way,like yours,where the freewheel is mounted on the other side
,there was a couple clearance issues that i didn't take into effect

EDIT #2. said screw it, i took the sprockets off and only left just the freewheel and crank arm, slid that on the shaft and tried tighten it up with the axle nut,and sure enough, its the freewheel thats rubbing, the only thing i cant do is try to hog out the back of the freewheel where the 4 indents are for the tool to unscrew it,ill hog it out with a dremel or something to get it to clear the bottom bracket/bearing cup

 

[outlawbiker]

i fixed it! i had to grind the crap out of the back of the freewheel so it would clear, just got back from a test drive. it feels like its surging,dont know if its the carb or the clutch slipping. i think i got a bad clutch or its just not ment for this set up.