So I got the cheapest HT on ebay...

[FurryOnTheInside]

Yep, the US Dollar is darn strong right now, very handy for me when I am buying parts overseas but not so good for you.

Well, I was talking about the weak £ against every currency since the news that we're leaving the EU. If I was buying the American parts right now it would add maybe 15% or something to the parts cost; but it doesn't matter because it'll take me a while yet to save up for all the sick Sick Bike Parts and the cool cylinder head, and the currency will recover in time.
Anyway, the topic. Cheap and nasty kits.. I hope that someone will start importing Grubee engine kits into the UK or Europe because at the moment the standard here seems to be the cheapest unbranded Crappy Time. This side of the Atlantic is like being back in the time of the earliest posts on this forum, maybe worse. There is just one company I have been able to find offering what they claim to be a better engine kit (they call it the GT4, but not a Grubee ??) but they're charging three times as much as the other kits and the product appears to have not changed at all in the last three years.
What it means to me is that I really have to go all out to learn and apply the best of the modifications and fixes for these cheap engines that have been generously shared in the forums, and build a vehicle that utilises the few strengths and avoids the many pitfalls of these worst cheapest engine kits.

 

[Steve Best]

Furry, I hear ya. My wife left 12 years ago. I was broken up by it for a while, but now with a dozen motorcycles and quads around, and a few girlfriends that really like riding, I don't think about her much!

I like the human-ICE hybrid idea and I don't think that involves a shifter.
I like pedal assisting even while running the engine. With the single speed I can pull the clutch and pedal on the down hills and straights. The shifter needed a compromise ratio between the engine and pedals so you could still get it started. I could not keep a good pedal and engine ratio with that system because of the need for a certain starting ratio. I spun the threads off the pedal freewheel because of the force needed to start. I repaired the freewheel, but went to single speed and love it. I'd recommend you go 66cc single speed and go with 44t or less, depending if you have hills or flats.

The Cdn dollar / pound are not bad, either order the kit from http://www.motorizedbicycle.ca/ or have a Canadian send it to you.
The complete kit is 127 pounds at today's rate. The stock motor and ragjoint sprocket will take you 1000s of kms.
Use BMX bike chain, mod the head, drill the pipe flange out to portmatch, and rejet the carb. 55 kph and 50 km/litre.
Mount the motor low, silicon rubber dampers in the fins, even hide the motor with sideplates.
I ride on "NON-MOTORIZED" trails by just shutting off my motor and locking the clutch in. Totally accepted.

My ultimate bike will likely be a fully suspended MTB with 48cc single speed and mid-drive electric shifter (for low speed trails, sand and town). I think I can keep the weight under 30kg/66 lbs.

Steve

 

[FurryOnTheInside]

Furry, I hear ya. My wife left 12 years ago. I was broken up by it for a while, but now with a dozen motorcycles and quads around, and a few girlfriends that really like riding, I don't think about her much!

I like the human-ICE hybrid idea and I don't think that involves a shifter.
I like pedal assisting even while running the engine. With the single speed I can pull the clutch and pedal on the down hills and straights. The shifter needed a compromise ratio between the engine and pedals so you could still get it started. I could not keep a good pedal and engine ratio with that system because of the need for a certain starting ratio. I spun the threads off the pedal freewheel because of the force needed to start. I repaired the freewheel, but went to single speed and love it. I'd recommend you go 66cc single speed and go with 44t or less, depending if you have hills or flats.

The Cdn dollar / pound are not bad, either order the kit from http://www.motorizedbicycle.ca/ or have a Canadian send it to you.
The complete kit is 127 pounds at today's rate. The stock motor and ragjoint sprocket will take you 1000s of kms.
Use BMX bike chain, mod the head, drill the pipe flange out to portmatch, and rejet the carb. 55 kph and 50 km/litre.
Mount the motor low, silicon rubber dampers in the fins, even hide the motor with sideplates.
I ride on "NON-MOTORIZED" trails by just shutting off my motor and locking the clutch in. Totally accepted.

My ultimate bike will likely be a fully suspended MTB with 48cc single speed and mid-drive electric shifter (for low speed trails, sand and town). I think I can keep the weight under 30kg/66 lbs.

Steve

You make some interesting points, Steve, and I have looked into the starting ratio problem, but I was advised that it would be no problem with a reasonably low compression engine. That said, I don't think that the guys at SBP have actually tried a 45.92:1 ratio. I could get the head with a compression release, perhaps?? They are "a bit" expensive though! But yes it is a problem, needing to use such a high ratio and then still having to do mods to get some power out of such low RPM (3903:85).

I may indeed build a single speed but at the moment I am only really considering it as a future second bike project. I have an alloy, rigid, V brake frame that could maybe work with that if the GT5A won't fatigue it. I still have to convince myself that I won't be at risk by always having the engine chain connected, or mind that I can never pedal and coast without turning the chain.
I will never ever use a rag joint though, my wheels cost too much and the way I understand (or misunderstand) how it works tells me that the top hat is the only way to divide the force evenly between all of the spokes instead of just the ones at the top of the sprocket. I have long flat stretches of headwindy coast path and short but steep hills.. and I'm indecisive, LOL!


I will be interested to see how you fit a single speed fixed drive to a suspension frame.
Ooh, that reminds me. I wanted to ask you what you think about the SBP right hand side tensioner design. Used on the left it can swing to cope with the bump start/ engine braking reverse function business, but I don't know if it is very sound/efficient to have the tension applied by pulling the top and bottom of the chain together. It does need the frame to have clearance for the straight lower run of chain too, of course, but it might be a good idea. With a turnbuckle instead of the spring if it is on a rigid frame or the spring could be good for suspension and the varying chain length?

 

[Steve Best]

I'm not keen on spring tensioners except to act as dampeners on long runs of chain.
Chains need a certain minimum slack.
I opted for an eccentric bearing chain tensioner on the left side like this:

I actually had it (shifter since switched to single speed) on the drive side since that was the only place on the jackshaft plate I could drill and tap. It worked very well. no problems at all, minimal drag.

The right side had a levered tensioner like SBP but instead of a spring, it had a tension adjuster like this:

I apologize for the stock internet pictures, but I watered my camera and need another.
Expect a flood of picts when I get a new camera...

I experimented with ratios to no avail. With it close to good enough for pedaling it took a REALLY hard kick to start the engine. If you plan to mostly motor, a shifter is fine. The SBP and other steel kits are heavy too.

As for the rag joint, I am pleasantly surprised with how well it works.
It takes some careful setup.
1) true the wheel and tension the spokes
2) install the sprocket, ideally rubber on both sides of the spokes.
3) use locknuts and tension the bolts to get the sprocket true.
4) run the chain true (and I'd suggest 410 BMX chain) and as short as you can.
5) install the tensioner TRUE and TIGHT on the bottom side, as close to the rear as possible.
6) check the spoke tension and wheel true occasionally, don't over tighten.

This has worked for me for over 1000 kms on the 66c at constant speeds of about 50 kph.

As for safety? THIS IS A BICYCLE! Check it often and check it carefully.
I had a rear bearing go on the well used and watered cheap rear wheel about 500km in.
Bike shop repaired (replaced?) and greased and fine since.

Don't poo-poo the simple cheap stuff, don't over think it. Just build it as supplied and RIDE.
I'm getting 20-100 kms daily on the as supplied Chinese kit with a little careful set up.

Steve

 

[FurryOnTheInside]

I'm not keen on spring tensioners except to act as dampeners on long runs of chain.
Chains need a certain minimum slack.
I opted for an eccentric bearing chain tensioner on the left side like this:

I actually had it (shifter since switched to single speed) on the drive side since that was the only place on the jackshaft plate I could drill and tap. It worked very well. no problems at all, minimal drag.

The right side had a levered tensioner like SBP but instead of a spring, it had a tension adjuster like this:

I apologize for the stock internet pictures, but I watered my camera and need another.
Expect a flood of picts when I get a new camera...

I experimented with ratios to no avail. With it close to good enough for pedaling it took a REALLY hard kick to start the engine. If you plan to mostly motor, a shifter is fine. The SBP and other steel kits are heavy too.

As for the rag joint, I am pleasantly surprised with how well it works.
It takes some careful setup.
1) true the wheel and tension the spokes
2) install the sprocket, ideally rubber on both sides of the spokes.
3) use locknuts and tension the bolts to get the sprocket true.
4) run the chain true (and I'd suggest 410 BMX chain) and as short as you can.
5) install the tensioner TRUE and TIGHT on the bottom side, as close to the rear as possible.
6) check the spoke tension and wheel true occasionally, don't over tighten.

This has worked for me for over 1000 kms on the 66c at constant speeds of about 50 kph.

As for safety? THIS IS A BICYCLE! Check it often and check it carefully.
I had a rear bearing go on the well used and watered cheap rear wheel about 500km in.
Bike shop repaired (replaced?) and greased and fine since.

Don't poo-poo the simple cheap stuff, don't over think it. Just build it as supplied and RIDE.
I'm getting 20-100 kms daily on the as supplied Chinese kit with a little careful set up.

Steve

Thanks for taking the time to reply.
But I think you mixed up left and right?
I agree that springs are not as good as adjustable but rigid.. erm idk what to call it, flat bar brace with a slotted hole to adjust it. Certainly I want to remove the spring from the SBP left hand side tensioner. I would also like to use a turnbuckle or something similar (but tool free) to set the right hand side tensioner.

But what I meant about that right hand side tensioner was that it pulls the slack (return) side of the chain against the taught (power) side instead of it being braced from the frame, and I am not sure what effect that has.
It just had occurred to me that it could work well for single speed bikes too (on the left/only motor chain). And a suspension frame must need a spring somewhere unless it's a concentric pivot point and sprocket design, like the DMR Bolt or the (lovely, jackshafted) Brooklyn Machine Works full suspension frames.
Incidentally, the BMW frames have an eccentric bottom bracket for tensioning their pedal-jackshaft chain, then horizontal dropouts like the DMR to take hub gears/single speed or derailleur.

Okay where were we.. Oh yeah the engineedal ratio. I don't know what cranking pressure you had/have but you have me worried now. I don't really want to make it even more expensive by having to get the head with compression release. I don't even know if that would work (a little knowledge is a dangerous thing).
I won't use a shifter with a ratio much lower than the 45.92:1 that I am aiming for, though.. I need to keep pedalling even if the engine is doing most of the work. :/

I'm not bothered about weight.. It has an engine.

Yeah I'm not convinced about that rag joint. I get how to set it up. I just don't see how it distributes the force through all the spokes when only the top of the sprocket is being pulled by the chain.

As for safety. Who mentioned safety?! oh "at risk by having the chain connected" meant from the cops (mainly the trainees!), but yeah I would not like to break a ring or something unexpected and seize the engine, lock the wheel and go under a truck. You can't check for things that didn't happen yet! I like the ability to freewheel for more reasons than that though. I will have to see anyway. I have a £155 /$203 rear hub and it is far too wide to fit the kit sprocket, and a top hat won't fit either (old five bolt pattern disc mount not ISO six).

I'm not knocking the simple, but my cheap Chinese unbranded engine was supplied broken. Also I just have an idea of what I want and I already have several hundred pounds worth of parts that are specific to that.. I might as well use them for something.

 

[KCvale]

...The shifter needed a compromise ratio between the engine and pedals so you could still get it started.
I could not keep a good pedal and engine ratio with that system because of the need for a certain starting ratio.
I spun the threads off the pedal freewheel because of the force needed to start.
Steve

Say what...
Have you ever even used a 2-stroke SBP shift kit on a geared bike Steve?

Your starting gear ratio is whatever bike gear you want to get you rolling!
Then it's just Kick-Starting the engine directly with the pedals with no bike momentum to help.

A high compression head makes this Kick Starting harder.
The thing is, you don't need the extra compression power.

GEARS CHANGE EVERYTHING!

50KPH is only 31MPH, heck, I get that on a stock 48cc 2-stroke engine on a 3-speed bike, and it's a breeze to start!
A stock 66cc 3-speed will usually top out ~42MPH or 67KPH.

Want more power?
Put an expansion chamber exhaust on it.
It won't effect starting, but will make a huge difference once you start riding.

That is my first hand experience with many shifting builds.
Take it or leave it.

 

[FurryOnTheInside]

Say what...
Have you ever even used a 2-stroke SBP shift kit on a geared bike Steve?

Your starting gear ratio is whatever bike gear you want to get you rolling!
Then it's just Kick-Starting the engine directly with the pedals with no bike momentum to help.

A high compression head makes this Kick Starting harder.
The thing is, you don't need the extra compression power.

GEARS CHANGE EVERYTHING!

50KPH is only 31MPH, heck, I get that on a stock 48cc 2-stroke engine on a 3-speed bike, and it's a breeze to start!
A stock 66cc 3-speed will usually top out ~42MPH or 67KPH.

Want more power?
Put an expansion chamber exhaust on it.
It won't effect starting, but will make a huge difference once you start riding.

That is my first hand experience with many shifting builds.
Take it or leave it.

The "starting gear ratio" is the engine to pedal crank ratio, backwards.
I am trying to make sure it has a high engine to pedal ratio.
4592 : 100 (or 3903 : 85, 4133 : 90) so that the bike can still be pedalled, I can still keep warm and add my own 0.3hp, while the (modded for low revving) engine is powering the bike too. Like the single speed bikes do except they don't even need to keep engine speed low.
The gears I am going for (written backwards for starting)
48T : 9T (1:5.3333)
21T : 10T (1:2.1)
Internal (1:4.1)
Meaning one pedal kick of half a rotation would turn the engine 22.96 times.
I may need a low compression head /cranking pressure (planned anyway), I may need a compression release valve, or I may need to fit a pull start (and then sell the bike because I want to stop and start the engine while riding the undulating hills!).

I will be shifting to a low gear to start anyway, after getting the bike rolling, so that I am not engaging the hub freewheel; but that won't change the very high starting ratio.

 

[Steve Best]

Yes KC, my jackshaft shifter kit is a well worn SBP kit I picked up used.
New bearings and 5/8" shaft and I was running. Honestly, it worked best with the as delivered ratios.
I didn't check for top speed (oversight), but it would be over 50kph with the stock 48cc motor and the low cruising rpm was nice.
It came with 1/8" sprockets so I switched it to 1/8" wide chain and it worked well. No tensioners for either chain so I made my own, both worked well. I put several hundred kms on it, several long trips, but I missed the ability to pedal at speed. I'm looking for pedal assist, not power only. Your remarks are absolutely true and bang on, but not what I was looking for. I played with the gear ratios and by lowering them I had good off-road performance. which might work well for urban stuff too.

I did try to up the pedal to motor ratio, but it took so much force to start.
I understand where you are coming from, and why you prefer the shifter, but the simplicity,easy starting and ability to simply pedal assist lead me to personally favour the single speed for now. This is more of a stick-shift vs automatic debate in which there is no ultimate winner, just personal preference.

Steve

 

[FurryOnTheInside]

Yes KC, my jackshaft shifter kit is a well worn SBP kit I picked up used.
New bearings and 5/8" shaft and I was running. Honestly, it worked best with the as delivered ratios.
I didn't check for top speed (oversight), but it would be over 50kph with the stock 48cc motor and the low cruising rpm was nice.
It came with 1/8" sprockets so I switched it to 1/8" wide chain and it worked well. No tensioners for either chain so I made my own, both worked well. I put several hundred kms on it, several long trips, but I missed the ability to pedal at speed. I'm looking for pedal assist, not power only. Your remarks are absolutely true and bang on, but not what I was looking for. I played with the gear ratios and by lowering them I had good off-road performance. which might work well for urban stuff too.

I did try to up the pedal to motor ratio, but it took so much force to start.
I understand where you are coming from, and why you prefer the shifter, but the simplicity,easy starting and ability to simply pedal assist lead me to personally favour the single speed for now. This is more of a stick-shift vs automatic debate in which there is no ultimate winner, just personal preference.

Steve

Steve, can you tell me what your cranking pressure is/was?
You had the 17T-10T:44T sprockets, I assume. That's 30.67:1 or 15.33 crank revolutions per half turn kick. I can see that the force required to start "an engine" with that gearing is two thirds of the force it would take with the 45.92:1 ratio I have planned. Now, if I knew your cranking pressure, I might be able to get an idea of whether my planned build will really need 1.5 times the force to kick over.. Or what cranking pressure I would need for it to take the same force to kick over.