Bought a Chinese 125cc :D

Lopéz said:
Looks smart, nice job!
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Cheers!

This was a little while ago now, as per the "stuff you did to your bike today thread" post I made at the time.

However, in true OcUK fashion, you guys we correct! The valve (intake) that I did not replace because I figured "If it ain't broke, don't fix it" lunched itself in very unspectacular fashion:
bentvalve.jpg


It slipped its collet, dropped into the piston, and smashed itself into the valve guide, which had a hairline crack. So i decided to refit a new valve, and see if it would still run.

It does run again, but sounds a bit funny at higher revs and is not liking trying to go over 6k, which I think is symptomatic of the cracked valve guide. Still, I know it works, and think I know what is wrong... SOOOOO - new plan!

I don't fancy replacing the valve guides, so lets replace the original head with a Suzuki GS125 head, with new valves included for £60! (oddly cheaper than the Chinese spare part??)

Now, it MAY work with the flat top piston that I have in there already (which survived remarkably well for being whacked), but compression might be a tad too low, as the GS uses a domed piston.. I do happen to have a domed piston as part of the kit I got with the Suzuki cylinder I already replaced, so, I will probably swap those over while the engine is split. MIGHT actually get me a bit more compression, and perhaps a slight performance increase.

This is all provided the head will fit, but as its already on a Suzuki barrel, I have high hopes :)



So, what did I learn? If you can replace a part whilst doing similar parts, do it... It saves time, money and hassle in the long run :D Also, if you have a K157FMI engine, replace the valves and associated parts.

Also, when I replaced the bent valve, I actually managed to do the work with the block still in the frame, so its much faster. I also did the whole rebuild a LOT faster than the first time. Should be able to get it done in about an hour this time. So, i guess at least I am getting more proficient at rebuilding small 4 stroke engines :D
 
Bike now has a Suzuki Head/Valves/barrel and piston. I also replaced the valve locks at the same time, as they were looking a bit worse for wear.
Took it out for a ride today, and it feels good. Didn't go far as I think I needs the valves adjusting.
I think its going to be a tiny bit quicker, as it has more compression, domed piston, and larger valves/ports.
It's never going to set the world on fire, but I think I might ride it for a bit, then see if I can find an old Honda 125 or something to have a play about with.
 
jigger said:
You have done one hell of a job with the bike. Bummer about the dropped valve.
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Haha, thanks :)
Its been fine for a bit. Ridden it to work a few times, done a few longer rides and been enjoying it.

Topping out at 55/56 and I need to make a better seal for the tacho drive in the Suzuki head. The plastic bushing I used as a spacer is warping in the heat and needs tightening up after a long ride.

To stop valve slap on the motor with the slightly taller Suzuki piston I had to make the barrel sit higher by buying some thicker gasket material and tracing/cutting a taller one to replace it.

I toyed with the idea of running a doubled up head gasket to increase the head height but it just looked too much to ask for a decent head seal under combustion with that setup. I did try it breifly and it held for a bit, but mainly I used it to calculate the height needed to stop the valve slap.
I think there may be room to extract some more power if I lower the height a bit, but it's running reliably so I am leaving it for now. :)
 
Well, I moved it on again last night for £250. It dropped a valve again on a shopping trip. I had bought performance valve colletts when i rebuilt it to replace the knackered ones. But I think the engine decided they were too good for it and spat one set out.
Still sold it on, learned a lot from it. Now saving up to get me an old Honda 125 or something to have a go with over the winter :D
 
Haha, indeed. It was always a learning exercise though. And I have already used the things I learned on my other bike and am now itching to find something more Japanese to play with.
 
@Diddums Yup, I will admit to being a little disappointed I did not prove everyone wrong. But I stand by the fact that if these are looked after from new, they would be MUCH more reliable. The problem is, they are bought new for sub 2k, sold on even cheaper, and people treat them like cheap throw-away items.
Would I buy one new, if I was on a budget, yes. Certainly. Drive it under warranty, give it some love, and it will do the job fine for all but the most hardcore 125 rider.

I think this was more of an uphill battle, but I suspect it owes me about £50 after parts, if I count up. Happy to swallow that for what I learned :)
 
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