G'day from Queensland Australia

[iron_monkey]

[I should have been more clear. The first motor, a 55cc chinese 2-stroke seized at 3780kms when it pulled one side of the gudgeon pin out of the piston and threw me over the handlebars. The second engine a 66cc chinese 2-stroke (sometimes wrongly called 70cc or even 80cc) started to make noises at 1300 kms and I replaced the rings and keep it as a spare. The thirds 66cc one was retired after 3400kms because I lost faith in it and didn'tr like the noises it made (I'll fix it one day). The fourth 66cc one seized at 2200 and became a garden onament. I could go on but it makes me ill with anger that the only problem with these motors is something I could easily fix in twent minutes if only had half a dozen Commandos and entry to the factory in China!
Irish john

what are your riding habits(speeds?) and what sprocket(s)?

 

[Irish John]

what are your riding habits(speeds?) and what sprocket(s)?

I ride sensibly and I ride long distances. The speeds vary but I don't ride flat out for any distance. I stop every 30 mins to let the motor cool. The sprockets vary cos there are several engines mentioned and they were different sizes but the rear was a 48T on the 50cc and 44T on the 70cc. I've also built several bikes and the engines were all crud although the StarFire motor was a bit less crud cos it lasted the longest. This should all be in the past tense because I've moved over to four strokes.
The HTs are fun if you like tinkering with them all the time but the quality is not worth the price (see my thread on Chinese Quality Fade).
I no longer have to buy expensive synthetic oil and I can fill up at service stations once a week and the price of petrol isn't too important for 2.5 litres.
If the HTs were German made I would still be using them - or rather I'd still be using IT.

 

[BoltsMissing]

Welcome to MBc

All the best,

BoltsM.

 

[iron_monkey]

I ride sensibly and I ride long distances. The speeds vary but I don't ride flat out for any distance. I stop every 30 mins to let the motor cool. The sprockets vary cos there are several engines mentioned and they were different sizes but the rear was a 48T on the 50cc and 44T on the 70cc. I've also built several bikes and the engines were all crud although the StarFire motor was a bit less crud cos it lasted the longest. This should all be in the past tense because I've moved over to four strokes.
The HTs are fun if you like tinkering with them all the time but the quality is not worth the price (see my thread on Chinese Quality Fade).

Everyone's definition of "sensible" is different.

Exactly what are the higher(or the highest) speeds(and the corresponding sprocket) were you cruising on for an extended period of time?

 

[Irish John]

Everyone's definition of "sensible" is different.

Exactly what are the higher(or the highest) speeds(and the corresponding sprocket) were you cruising on for an extended period of time?

Ok Iron Monkey, can't see where you're from but I used to cruise 25 kms down the freeway at a speed of 33 kms\hr maximising to 38 km\hr in places. I would stop half way for a smoke and let the motor cool cos I reckoned that was best for it. That was with a 44T on a 26" wheel and the largest of the HTs - the 70cc sometimes sold as 80cc but in fact is about 66cc. On a Giant Elwwod with the same rig but with 700C wheels I would cruise at 38 km\hr continuously because the engine wasn't at peak at that speed and the wheels were larger. That was the best HT rig I ever built.
Most of my memories of HT cruising was at max 25 km\hr cos they need to be run in for 500kms and I seemed to spend more time running them in and less and less time post-running in because they either needed new rings which meant running in again or the bearings started to go and I threw the engines out because I didn't want to have another engine seizure at speed when the wheel locks up and I went over the front before you could blink an eye and get the clutch pulled in. I also used a twist clutch cos it gave me more control and faster reaction time.

 

[iron_monkey]

Which bearings broke? Im guessing the crank ones as the connecting rod ones are relatively new.

I dont recall reading that piston rings being a frequent problem with these engines, its mainly the connecting rod bushing breaking up. You must be cursed; for my last HT before it was stolen; the engine(as opposed to kit parts and the bicycle) itself was maintenance free after fixing the usual quality control control problems (filing exhaust, loctite everything, etc). Then again it only racked up 300-400km before it was stolen, but thats metropolitan start stop/short trip usage.

 

[Irish John]

Which bearings broke? Im guessing the crank ones as the connecting rod ones are relatively new.

I dont recall reading that piston rings being a frequent problem with these engines, its mainly the connecting rod bushing breaking up. You must be cursed; for my last HT before it was stolen; the engine(as opposed to kit parts and the bicycle) itself was maintenance free after fixing the usual quality control control problems (filing exhaust, loctite everything, etc). Then again it only racked up 300-400km before it was stolen, but thats metropolitan start stop/short trip usage.

Read the thread on quality fade and it will give you an idea of what has been happening to these motors:
http://www.motoredbikes.com/showthread.php?t=9158&highlight=chinese+quality+fade
The early engines were much less bad (I would never say they were good) but the pistons were always a different shape to the cylinders which is why they took 500 kms to run in. There were 2 types of motor - ones with bush bearings and ones with needle bearings. I reckon I've ridden these motors more than most people on this forum (14,000kms at least) cos they were my main means of transport and I live in the country. I think the needle bearings may have been better but they wore out too. I've had stacks of rear engine mounts snapping the 6mm studs even though I never used the Chinese studs and always replaced them with Australian 12.9 hardness steel studs (6mm is too thin - 8mm would not snap). I've had one motor pull the gudgeon pin out of the piston, one bottom end bearing break, two top end bearings break and in latter years the rings began to go very quickly because the quality was faded. Replacing rings is no big deal but a broken ring or badly mounted ring will scratch the chrome cylinder lining and you can't really fix that although you can try honing it a bit. My supplier (the world's largest single supplier of HTs) seemed to know about the quality fade because he was concerned enough to seek a lift in the quality fade. Haven't tried any of his new batch to see what they are like. I could list plenty of components where the quality was deliberately faded over time and when they weren't much good to start with it becomes more serious sooner. Like good dentistry you get what you pay for and cheap price isn't necessarily cheap after it breaks.
You can do all sorts of things to improve the power of these engines but all it does is hasten the day when it breaks. I maintain that there was a really bad batch of rings made and that they threw a high percentage of these in with each batch they supplied. This is exactly what I have found happens all over China in the construction industry where I worked. There is no limit to what they will do because there are no laws against it. Unless there is some sort of punishment for doing something they will do it.
For a while I thought I was cursed but I've bought more engines than most people and that is why I have a low opinion of them. It is turbo capitalism at its very worst.

 

[iron_monkey]

These engines arent very well made from day 1 but from my experience most problems can be overcome. In fact if the engines are as fragile as the ones you had I dont think there would be a motoredbike community today. They simply wouldnt be usable and the vast majority of members would have given up in frustration like you; including me.

You seemed to have experienced almost every major problem that can conceivably happen. In fact the only major problem that i know that hasnt happened to you is disintegration of the flywheel.

Imo you must have bought from a very bad batch of engines.