when to re-build a 2-stroke engine.

[Irezumi aka Reuben]

Im on my first 2-stroke having had a 4-stroke before but am wondering what I should be looking for in terms of an engine re-build.

The bike is a Suzuki GP125 so is air cooled. It's quite smokey at first(white smoke from the exhaust) but this clears up a fair bit after and it isnt in plumes so im sure is just the normal old 2-stroke engine. The bike feels ok in terms of its running as well.

Im going to do an engine re-build when I can afford it(next few months) but what should I look out for incase I need to take the bike off the road?

I have been told that a new piston/ring was put in 5000 miles ago but have no way of ensuring this.
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Pictorgraphicalfantastical

[alains]

generally you need to de-carbon around 8500 miles . at this occasion first time you change rings , then the second time both rings & piston , and third time barrel+piston+rings . most of two strokes have their barrel cover with nikasil which avoid a re-boring .
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the worst day fishing is better than the best day working

[stinkwheel]

Nah, a GP125, bog basic 2-smoke with cast-iron liners IIRC. If it seems down on power, struggles to go up hills and smokes a lot, it probably wants some attention, otherwise I would stick to a decoke every 5-10k miles or as necessary.

The textbook way would be to keep a log of the compression readings and do the top-end when you get a significant drop in these.

It is worth pulling the top-end apart at maybe 20k and fitting some new small-end bearings (if fitted) as they last roughly that long.

All of the service intervals should be shown in a workshop manual.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Irezumi aka Reuben]

Well its done 28k and if it has had a new piston/ring when the previous owner said (I very much doubt this) then it should be ok for a bit. Ill take the head off and poke around, I just dont want to have to have it overbored, its old so no nikasil cylinder coating sadly.

Or I might just change big-end, small-end, piston and ring as its cheap and should only take a couple of days anyway. And my old-man would end up doing most anyway

Cheers
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Pictorgraphicalfantastical

[alains]

if you find a forged piston such as wiseco , vertex and more , even if it's a bit more expensive , go for it !! and mind seals & gasket
the big end does not have to be changed only the small end (bearing+pin+clips) .
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the worst day fishing is better than the best day working

[stinkwheel]

I would rather not have nikosil coated barrels anyway. Plain barrels just need to be rebored whereas if a plated barrel is worn out you have to pay through the nose to have it replated.

Last iron barrel I had rebored cost £15, a nikosil one would have just about been into 3 figures.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Irezumi aka Reuben]

Another question concerning my bike is the lighting, or lack of. I'm pretty sure that your from an era where 6 volt electrics were alot more common Stinkwheel, and quite obviously utter crap. It's got all the electrics in the headlight unit (as they did in ye olde times) and I was wondering if there is any way to improve this? Revving the engine more helps, but something that makes the light shine brighter for without moving so fast would be good!

P.S. Everyone should buy a GP125, twoup power wheelies in second if you sit back! Much to my dads shock after the near crash from the first gear wheelie
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Pictorgraphicalfantastical

[stinkwheel]

As far as I can make out, 6 volt direct lighting is totally shit and there is very little you can do about it without wholesale replacement of the charging system.

You can't even change it to DC properly because there aren't enough phases to give a fully rectified output on account of there being only one coil.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Irezumi aka Reuben]

Ok thanks, I'll just avoid unlit roads
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Pictorgraphicalfantastical

[cagiva gezzer]

You can get halogen bulbs for 6V systems. My mate needed to get one for his MT5 when he upped the speed from 31mph to 38mph...
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"because one stroke isnt enough and four strokes waste two"

[Kickstart]

Hi

Might also be worth considering a 6V LED brake / tail light, as it will be less of a drain on the lighting circuit.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[stinkwheel]