More Bad News About Grubee G4 Gearbox

Maybe able to use lighter springs instead of drilling holes.
No matter what anyone sayes about the earlier Grubee tranny's their pretty strong.
Lighter springs:You could try that & reduce the idle speed,BUT to my way of thinking since the new springs now engage earlier the whole setup will be under more stress(as the clutch shoes now more quickly engage with the clutch drum)
Without physically seeing & playing with the components the problems you've described have basically been that of under-engineering....it's too weak.
I goy my Titan PTO drum beefed-up with TIG welding & a replacement spare shipped free of charge(excluding freight ofcourse)
 
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Chinese Pig

It does look like they put lipstick on this pig?

This clutch bell housing thing is old with them. Can't remember the box that had a pressed bell and they all cracked?

It would look like the freewheel needs to be in the driven sprocket, but that would require them to actually engineer something original. I don't think there is one for them to copy out there large enough for the rag joint to fit inside?

The whole width thing seems to be a non starter? Then the drive sprocket hanging out in mid air? Pretty disappointing.

Jim
 
It would be less than honest not to say that the G4 is about as much use as t*ts on a bull!
 
Guys, I don't have one to study- but I am thinking of getting one. Can somone explain or point out the part that is tack welded to me please?
 
Guys, I don't have one to study- but I am thinking of getting one. Can somone explain or point out the part that is tack welded to me please?

The centrifugal clutch expands as it spins faster to grab onto the clutch bell. The clutch bell is tack welded onto the bell housing rather than being either continuously welded or pressed into shape as a single piece of steel.
My advice to you would be to stick with the superior older Grubee gearbox because the G4 is a much worse kit than its pedecessors.
The top speed is way down on the G4 because they got the gear ratios wrong,
It pulls away nicely but so would any GB with that ratio. As for its width well you will know what I've been saying when you buy one. Yes it is quieter but that's its only good point and most gearboxes are quiet at the sort of speed this thing crawls about at. I recommend giving the whole kit the elbow it so richly deserves Holbrow. There isn't a rear sprocket that fits it and the 11T drive sprocket will last a week before it disintegrates from the force of engagement that it isn't designed to withstand.
At the moment there isn't a drive sprocket designed that works on it - it probably needs a 14T drive sprocket cos the 11T cetainly won't work unless you find a way of fitting a 36T rear sprocket that lets the chain pass all the obstacles that will be in its way.
This gearbox will NEVER work as well as the older models and anyone fool enough to buy it will quickly find out this for themselves.
 
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I hear what you are saying- and I believe you Irish John. Looks as if the kit does have some serious issues, however, I see alot about it that I do like. (simple, quiet, lightweight). Aside from the tack welded clutch bell, does anything else appear to be wrong with the primary reduction set? Do the bearings appear adequate? Are there two bearings on the clutch bell shaft? That is probably what is making the whole thing be so wide- is getting enough room on that shaft to properly support it. The final drive from the primary down to the wheel does not concern me much- as I doubt I would use what came with the kit anyway. I'm used to starting from scratch with these things and doing whatever fabricating I have to. I would almost say that is a bad batch of really substandard freewheels that is stripping out like in those pictures- a good quality hardened freewheeel ought to stand what this rig will put out. Have you counted the # of teeth on the two belt pulleys in that primary? I'd like to know the actual ratio is to do some calculations.
 
I hear what you are saying- and I believe you Irish John. Looks as if the kit does have some serious issues, however, I see alot about it that I do like. (simple, quiet, lightweight). Aside from the tack welded clutch bell, does anything else appear to be wrong with the primary reduction set? Do the bearings appear adequate? Are there two bearings on the clutch bell shaft? That is probably what is making the whole thing be so wide- is getting enough room on that shaft to properly support it. The final drive from the primary down to the wheel does not concern me much- as I doubt I would use what came with the kit anyway. I'm used to starting from scratch with these things and doing whatever fabricating I have to. I would almost say that is a bad batch of really substandard freewheels that is stripping out like in those pictures- a good quality hardened freewheeel ought to stand what this rig will put out. Have you counted the # of teeth on the two belt pulleys in that primary? I'd like to know the actual ratio is to do some calculations.

The sprocket it needs on the drive shaft would most probably be too large to fit without hitting the engine casing. The 11T freewheels are not a bad batch cos I stock them and have a big supply from several batches. They are all badly made from soft steel and not made to acceptable cycling industry freewheel standards as I've said elsewhere. You'll get them to work on the old GB if you loctite the flange closed but the teeth will wear out at about 4000 - 6000 kms because the steel is so soft. They will not take the torque from this GB ipso facto.
What the GB needs is to be designed to be thinner and the reduction ratio needs to be changed. By the time you do all this I can't see why you wouldn't fabricate your own gearbox from scratch so you get what you want.
As for its weight advantage I can tell you that there is none - in fact it has to sit so high and with its excessive width you have serious balance and handling discomfort.
There are probably a myriad of other problems that will show up in time because it was never tested anywhere else. I'm suspicious about the drive sprocket out on the end of that long shaft but how will it get tested when it won't go for anytime without the sprocket disintegrating? The only other sprocket that fits it is a rigid (non-freewheel) 10T but that makes the speed problem worse. I won't be wasting much more time on it but by all means buy one and spend an inordinate amount of time reaching the same conclusion. Without changing the reduction ratio you will get nowhere. Change the reduction ratio and you'll be making a working GB out of a huge ungainly monster that won't fit on a bike without making people laugh at you.
You're flogging a dead horse when you sound like you could probably make a belt driven gearbox of your own from scratch.
 
Irish John- Ok- you make some really good points there. I have built several similar belt reductions from scratch- but with a slightly different twist. Instead of the clutch being directly on the motor output, I have done it before by going off the motor's output shaft
with a belt pulley- to a larger belt pulley on a 5/8" jackshaft- then a regular comet 5/8 centrifugal clutch with a #35 chain on down to the rear wheel hub. This works surprizingly well as long as you have a freewheel on the bike hub so you aren't backdriving the jackshaft. I used a left handed freewheel on the heavy duty hub from Staton Inc. I took regular #35 two piece 'quick change' kart racing sprockets and machined an aluminum carrier plate that matches a shoulder on the freewheel- and use a backing plate to bolt the original freewheel teeth between to secure it. Doing that, I can change the sprocket on the rear hub to get any ratio I want within reason. The nice anodized sprockets look good too. My problem with the whole set-up is it too is a bit wide, making pedaling awkward, and the set-up is fairly heavy. What caught my eye about the G4 is the nice, compact, custom sized belt sprockets. Belt sprockets like those are VERY hard to find off the shelf in that pitch and those ratios- especially the larger one. I have hunted them so hard I would almost say they don't exist off the shelf. The ones I was forced to use are larger than I would have liked, and are made of nylon with an aluminum hub- and I still could not get them in the ratios I really wanted. They are also a square tooth design which is not as efficient as curvilinear. Can you possibly count the teeth on those G4 pulleys so I will know what ratio it is so I will not make a similar mistake?

I think I'll take your advice and leave the G4 alone right now. I think they had a durn good idea- but ruined it by not doing all their homework. I really appreciate the info.
Thanks.
 
The 11T freewheels are not a bad batch cos I stock them and have a big supply from several batches. They are all badly made from soft steel and not made to acceptable cycling industry freewheel standards as I've said elsewhere.

Is the steel CAPABLE of taking a temper, but it just hasn't been tempered ?

Have you considered disassembling one, and tempering the thing, yourself ?
 
Irish John- just so I'm sure I understand, you're saying the G4 has TOO MUCH primary reduction- and that the chain sprocket on the output of the reduction box cannot be made large enough (and still fit) to get the ratio where it needs to be? I would really like to know how many teeth each of the belt pulleys in that reduction has- can anyone count them for me next time they get a chance?
 
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