Clear up the HS142s for me?

So yours ended up being the version with the short tapered shaft? And it came with a Stage III gearbox instead of a T-Belt transmission?

As far as I understand it, there are 2 different "flavors" of T-belt transmission - there's one for the 5/8" shaft engine and one for the tapered shaft. The 5/8" shaft seems to be more common, and a lot of places don't specifically differentiate which particular engine they're selling (or of they do I just miss it, heh).

As long as you have one of these versions of the T-belt transmission, you're probably going to be fine. As long as it's anything besides the cheap gearbox/chainbox that a lot of the engines ship with. Mine shipped with a transmission module that was held together by a tiny #25 roller chain... all the engine's torque concentrated on that small of a chain I'm surprised it lasted as long as it did.

If any of this is totally wrong (had a few beers tonight), someone feel free to correct. Cheers!

The HS142 with a 5/8 shaft and the HS142 with the short tapered shaft both work equally well.

The 5/8 shaft kit is slightly narrower than the tapered shaft kit and usually does not necessitate the use of the wide pedal cranks.

The way I understand it,
The 80 tooth 4G tends to be faster at top speed with less slow speed torque.
The 100 tooth 4G tends to be slower at top speed with more slow speed torque.
The 100 tooth has a solid hub 100 tooth pulley.
The 80 tooth has a one way clutch in the hub of the 80 tooth pulley. These are notorious for failing and the hub free spins in both directions. The common fix is to weld it solid before it has the chance to fail.

The final output shafts are different between the 80 tooth and 100 tooth units.
You cannot simply swap out a 100 tooth pulley for the original 80 tooth pulley or vice versa.

The clutch bell on the tapered shaft units needs to be welded full circle to the input shaft. The factory tack welds will fail. This weld should be done before the factory tack welds fail to ensure that the clutch hub and shaft stay true to each other.

The clutch on the 5/8 shaft units rides on bronze Oillite bushings. These bushings tend to wear out quickly and require replacement at regular intervals.
The tapered shaft clutch does not suffer from this issue.
The 5/8 shaft clutch can be upgraded to ride on ball bearings if you are willing to file down the engine's 5/8 shaft to a smaller diameter.

Each kit has it's merits and pitfalls. Both are equally up to the task of propelling you down the road for 1000's of miles, they just need different maintenance requirements/ modifications.


Oh, and I am sipping a beer right now.

Hello Knightscape!
Where in Maine are you? I spent some time in Brunswick.. I too am putting together the combo you are working on. I did one last year and was not too happy with it due to the lack of clearance on the upper end. (see "From Barry's Shop in albums). Right now, I'm trying to figure out a way to make a 90 degree intake manifold and a 2 stroke carb to fix the clearance issues. Will keep you posted on my progress.

GearNut said:

The clutch on the tapered shaft units needs to be welded full circle to the input shaft. The factory tack welds will fail. This weld should be done before the factory tack welds fail to ensure that the clutch hub and shaft stay true to each other.

Click to expand...

forgive my stupidity but do you mean the clutch needs to be welded to the crank shaft ? if so wouldn't that mess with the cranks temper ? also what
if you need to replace the clutch ? just grind, replace an reweld?


sorry to butt in Knightscape it's just that i'm kind of in the same postion
though i haven't ordered my drive yet (i need to get it right since i'm
in australia) i looked into EZ Q-matic seems no one ships to aus. gasbike
will ship me a 4G but i need to know which one

sorry again Knightscape an everyone else i'm new here an i'm trying to learn

Yes the 4G's evolve from year to year and the 2014's will have a new 4G output shaft, plus new sprocket and pulley choices and maybe a new mounting base.

I have been working with Don Grube most every day via e-mail for a month now on a new 4G output design change for this years production run.

The new output shaft will be a ~4cm long 15mm wide (well, 14.95) keyed shaft with a 'flat spot' bevel at 180 degrees from the key for two new offset 9T and 10T 410 or 415 chain size with two corresponding set screws.

GearNut said:

The HS142 with a 5/8 shaft and the HS142 with the short tapered shaft both work equally well.

Click to expand...

The gasbike kit has the HS 142F with a tapered shaft and the clutch is already installed.
Note there is now an HS 142F.2 with a 12V magneto output for lights and such but I haven't seen one personally.

The way I understand it,
The 80 tooth 4G tends to be faster at top speed with less slow speed torque.
The 100 tooth 4G tends to be slower at top speed with more slow speed torque.

Click to expand...

The gasbike 20T/80TFW (the FW is Free Wheel) gives you a 4:1 gear reduction.
A 20T/100T gives you a 5:1 gear reduction.

That is initial gear reduction at the 4G, you then have to multiply that by your direct drive gear reduction for what actual 'on the wheel' reduction is.

The current 142F/4G gasbike kit has a 9T output sprocket and 50T rear sprocket.
Total reduction (80T/20T) * (50T/9T) = 22.2:1 output to the wheel.

The 20T/100T 4G is a 5:1 initial reduction but it has a 12TFW output sprocket, about as small as you can go for a freewheel sprocket and why they suck.
With the same 50T rear sprocket...
(100/20) * (50/12) = 20.8 which is actually geared higher than the 20/80 and why they use smaller rear sprockets.

The 100 tooth has a solid hub 100 tooth pulley.
The 80 tooth has a one way clutch in the hub of the 80 tooth pulley. These are notorious for failing and the hub free spins in both directions. The common fix is to weld it solid before it has the chance to fail.

Click to expand...

I haven't seen a freewheel belt pulley fail yet but certainly possible if you run the belt too tight.
What I have seen a couple of times is that freewheel sprocket fail but just a couple tack welds fixes that.

The problem with that fix is you loose the freewheel for pedaling until you spin the whole engine output all the way to the cent clutch bell.
Not fun if you run out of gas or something.

The final output shafts are different between the 80 tooth and 100 tooth units.
You cannot simply swap out a 100 tooth pulley for the original 80 tooth pulley or vice versa.

Click to expand...

That is all changing for 2014.

As mentioned there will be a new far more flexible output shaft for all 4G's based on a Freewheel main pulley including a new 100TFW that will pop right on a new 80TFW 4G and have a couple cheap simple output sprocket sizes.

One side note here is a 16T primary drive pulley option to make a 16T/100TFW 4G with the existing base and new output shaft for a whooping 6.25 initial gear reduction is on the table for a new 4G for shifting applications.

But back to knightscapes build....

You sure picked a tough build with the GT2 bike frame.
You will soon find that the HS 142F/4G 4-stroke kit will NOT go in easy on that frame.

My 4-stroke shifter build on one required a completely custom made base and mounts and other mods to fit it in, but they are sharp bikes if you can pull it off.



Best of luck on your build!

Thank you KCvale for all of your hard work working with Don Grube to improve the 4G kits!.

ajoh said:

forgive my stupidity but do you mean the clutch needs to be welded to the crank shaft ? if so wouldn't that mess with the cranks temper ? also what
if you need to replace the clutch ? just grind, replace an reweld?


sorry to butt in Knightscape it's just that i'm kind of in the same postion
though i haven't ordered my drive yet (i need to get it right since i'm
in australia) i looked into EZ Q-matic seems no one ships to aus. gasbike
will ship me a 4G but i need to know which one

sorry again Knightscape an everyone else i'm new here an i'm trying to learn

Click to expand...

Nothing needs to be welded onto the engine's output shaft. Only the clutch hub (inner part with the friction shoe assembly) attaches to the engine shaft.
The shaft that the clutch bell (outer part of the clutch) attaches to is held to the clutch bell by 2 tack welds. These tack welds are known to fail. Welding the bell full circle, or completely around the bell to shaft attachment point, greatly strengthens the attachment point and prevents the chance of failing.

GearNut said:

Thank you KCvale for all of your hard work working with Don Grube to improve the 4G kits!.



Nothing needs to be welded onto the engine's output shaft. Only the clutch hub (inner part with the friction shoe assembly) attaches to the engine shaft.
The shaft that the clutch bell (outer part of the clutch) attaches to is held to the clutch bell by 2 tack welds. These tack welds are known to fail. Welding the bell full circle, or completely around the bell to shaft attachment point, greatly strengthens the attachment point and prevents the chance of failing.

Click to expand...

thank you for clearing that up Sir


reading + insomnia(27hrs no sleep)= one stupid aussie (not thinking straight)

it's kinda obvious to me now since i've read about the bell before i should of realized.

anyways thanks again much appreciated

I have 3 4G's sitting here open in various stages of builds so I snapped this for you.



The circle is where the 20T pulley's shaft connects to the inside of the clutch bell housing.
I haven't seen one fail but to shore the weld gaps I would think some JB weld would be a safer attached option than throwing a welder to it.

I'm not worried about it but I'll pass that on to Don as a 'concern' while there is still time before the production run.

All fun stuff when you finish a build that not only looks like what you after but operates as well if not better than expected.

knightscape said:

Ajoh, given that I've just got the gasbike kit and it's all still parts, let me know if you want to see detail pics of any of it prior to assembly so you can know what you're getting into better than I did.

Click to expand...

thanks bud, KCvale kinda answered with the pic he has plus i have to go
a very different route (stupid queensland, australian law) re; how i mounting the engine

KCvale said:

I have 3 4G's sitting here open in various stages of builds so I snapped this for you.

The circle is where the 20T pulley's shaft connects to the inside of the clutch bell housing.
I haven't seen one fail but to shore the weld gaps I would think some JB weld would be a safer attached option than throwing a welder to it.

I'm not worried about it but I'll pass that on to Don as a 'concern' while there is still time before the production run.

All fun stuff when you finish a build that not only looks like what you after but operates as well if not better than expected.

Click to expand...

KC personally i wouldn't trust JB weld with high load ie, the clutch bell it just won't hold under that stress a TIG weld would be the best way of doing it
JB weld is better used to fixed cracks in intakes, intake ports (reshaping, filling, small holes etc) an other things that aren't under the stress that things like the clutch bell is under


when it comes time to order my 4G (they are out of stock atm) how do i make sure it's the right one? meaning the one for tapered shaft any help on that would be much appreciated (australia is to far to return it if it's wrong)

ajoh said:

when it comes time to order my 4G (they are out of stock atm) how do i make sure it's the right one? meaning the one for tapered shaft any help on that would be much appreciated (australia is to far to return it if it's wrong)

Click to expand...

When you order a kit it comes with the engine and 4G system, that is unless you already have a HS142 engine and order just the 4G without the engine included.

Bicycle-Engines dot com sells the 5/8 shaft kits.
Gasbike dot net sells the tapered shaft kits.

KCvale said:

My 4-stroke shifter build on one required a completely custom made base and mounts and other mods to fit it in, but they are sharp bikes if you can pull it off.

Best of luck on your build!

Click to expand...

Now that is a sweet looking ride! Awesome!

knightscape said:

I just counted teeth and the output sprocket in my kit is actually 10t and the rear sprocket is 48, just a wee bit taller gear making 19.2:1 reduction.

Click to expand...

Yes, 10T solid output sprocket on the newer 20T/80TFW as the freewheel is in the 80T pulley, hence the 80TFW designation.

The solid 80T, 90T, 100T, etc use a freewheel output sprocket and as mentioned 12TFW is about as small as you can go and they fail quite easily and you need a larger wheel sprocket to compensate.

It's tough to fit that new gasbike HS 142F 49cc with new 20T/80TFW/10T in a bike like the 26" Macargi Pantera 7S but it will fit if you have a welder, angle grinder with cutting wheel, big vice, and drill with proper decent bit and you tell me, I think they turn out nice like this one I just finished this week.





I don't have time go into detail right now so in short easy steps if you want to keep the bikes chain guard and not loose the ability to clean the stock air cleaner and cut down the choke lever I:

1. Undo the front chain guard screw and drop the dual mount down until the clearance above the chain is 1/2" or less including cutting off the bottom part if need be.
The goal here is to get the guard as low as possible so the engine mount base can go as low as possible.

2. Mark the frame mount spot on the front fender mound and drill a new hole for it's screw and get your chain guard back on.

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3. Take the whole front 4-bolt mount system off and discard if you like, you won't be able to get the front right motor mount drilled with it in the way and sticks out to far anyway.

4. Get yourself a muffler clamp that will fit the front down tube, in this case a 1 1/2" will squeak in but a 1 5/8" is easier to find and works just dandy.

5. Get yourself a piece of steel and make a piece a bit wider than the muffler bracket and about 2" up with a ~1/2" long spot to weld to the bottom of the stock mount with as little front space as possible.

6. Get the new front muffler clamp mount on and use the rear base adjuster to lower the base dead level with just a 'smige' of clearance between the chain guard and the base to eliminate any rattle noise.

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7. Get the funky wider pedal axle, bearings and pedal arms on.
I find putting both arms facing the same way so you can turn them both facing up and is how wide you can go.

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8. Set the engine with the 4G attached on the base and move it to where it actually fits in the bike.

9. Just holding it put the chain on to the back wheel sprocket.
Now just adjust engine laterally. If your system is anything like this one the 4G sprocket is in too far to fit past the tire to rear sprocket.
You cut the spacer bushing down some and flip the sprocket but thats it.

10. With the chain on and aligned, both pedals on pointing up for clearance, get you engine set for the perfect mount, mark it and drill a bit oversized mount plate holes and use wide washers so you have a bit of 'wiggle room'.

Here are a couple of pics of the mount.







Hope that helps.

I'm still running the 11T freewheel output that came with my 2010 model 5:1 4G. It's never given me an issue despite it's bad reputation.

I think it's because with a shift kit it doesn't have to freewheel - unless I'm pedaling without the engine running.

Here's the 2 stroke carb that I fitted to the HS-142. I pulled the starter one time last night and it ROARED to max power. Obviously, it needs some peeking and tweaking!