Scored piston - repair cost? (CG 125)

[Christian 2.0]

Hi,

Recently my CG125-BR 1999 began smoking furiously out of the exhaust, specifically when accelerating. Quick look in the mirror, blue smoke - oil. Figured the head gasket had gone, so caressed her home gently. What was really unfortunate is that for the next few days I literally had no other choice than to ride the bike for a few miles here and there. Topped up the oil before each trip, still smokey and sounded like it had a sore throat, no real power loss and still responding well.

Anyway, managed to find some time the other evening, took the top end off, found that the head gasket had gone. Bought a new one, fitted it and hey presto! Still smoking.

Had a chat with the chap at the garage today who said I've shot the piston, which will mean boring the cylinder and getting a new piston/rings etc. It's also likely that the cylinder head is warped and will need skimming.

How much can I expect to pay for the repair? Obviously the CG engine is so simple and easy to work on, though I don't have the facility to do the repair myself.

I have had the slap on the wrist for using the bike whilst damaged.

Has anyone got a rough idea how much this is likely to cost? I anticipate somewhere between £150-200, is that reasonable?

[P.]

check it yourself...new piston and rings is about £30.

garage folk are nice, some are honest, some are bastards.

Get photos and put them on here..

[N cee thirty]

as paddy said a new piston and rings is like £30

this time last year i had the same problem and ran it for a couple hundred miles to work and back smoking before we changed the piston

was fine after,we didn't even change the gaskets
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

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[Nexus Icon]

What's the head made of on a CG nowadays? Is it really likely to have warped?
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[sickpup]

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[Teflon-Mike]

For a ballpark:
https://www.ridersmotorcycles.co.uk/scripts/prodList.asp?idcategory=49&curPage=2
TO FIT: CHINESE 125CC PUSH ROD CG125 COPY ENGINES HONDA CG125 UP TO 1998
TOP END GASKET SET £4.50
CYLINDER HEAD COMPLETE £55
CYLINDER BARREL KIT £41.50
Cylinder 'kit' comes with piston, rings gudgeon pin, circlips, base and head gasket.
MIGHT be all you need.
Head is built up with valves, springs and collets.
That kind of money, these chinky bits can be cheaper then machine shop time to get barel bored and head skimmed.
I'd budget aprox £30 for a new piston, £30 for a rebore, £50 for a head skim and valve & seat grind.... elsewise.
Check e-bay, Riders aren't the only folk offering these parts, though they are prety competative.
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[unitynotsocri...]

My heads even more warped after crashing a cg,

REMEMBER,if you've got the money regrind the valves and fit new valve guides and valve guide seal.it'll run really crisp at lower revs.its an extra 35 quid .
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nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[Christian 2.0]

Many thanks for the replies.

@Paddy: Unable to take pics, the bike's strapped up in back of van waiting to be taken in tomorrow.

As for everyone else, learned some useful information. Appreciate it. Will post back here when the job is complete with a breakdown of final cost for others' benefit.

Cheers

[Christian 2.0]

Had the bike back today.

Total cost parts and labour (as well as a bit of servicing) came to: £147, which is pretty much what I was expecting.

Other than not pinning the throttle back all the time and taking it easy for the first 100 miles, is there anything I should be avoiding whilst wearing the new piston in?

[P.]

[unitynotsocri...]

dont go on a very long journey,change the oil after 500 miles(check mesh filter)and dont strain the engine by chugging it at low revs.
Did they do the valve guides as well?
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nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[Christian 2.0]

Cheers Paddy, avoiding cars is one of my favourite pass times.

[unitynotsocri...]

they should be fine at that milage,dont be stingy using cheap oil change it every 1000miles and it should run till 12 to 15 k without any major service.
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nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[badmanrising]

brought bike non runner took carb and top end off and noticed piston had nearly fused with rings expect new pisto needed and part it goes into but what i need to know do i also have to replace top part of head that houses springy things they look alright little dark on inside of cover looks like dark oil stain i expect that was to do with inside of piston

[badmanrising]

brought bike non runner took carb and top end off and noticed piston had nearly fused with rings expect new pisto needed and part it goes into but what i need to know do i also have to replace top part of head that houses springy things :D they look alright little dark on inside of cover looks like dark oil stain i expect that was to do with inside of piston

[Pol Anorl]

make a new thread in the workshop instead of gravedigging, you will get more replies.
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[spannermonkey...]

Ivor Searle in Soham in Cambs. Charge £25 for a skim on a stripped head and about £41 for a full head rebuild if you can't remove valve gear and for a re hone £25, depending how deep the score is, it could be honed if within limits, so new rings only.

Otherwise new piston and rings I would go 2 sizes over. Don't bother going one size over as your score is probably deeper and you'll waste money. so go .50mm over sized.

It's cheaper to take the engine parts loose.

Take the cylinder with new piston with your piston clearance to a machine shop.

When you strip the head for the skim and barrels, wash it all really well after any work as you will find loads of debris from the machine shop.

Lap your valves in but don't go beyond the valve seat/face limits as per the manual. Otherwise it won't hold compression as good if you exceed this. Replace valve stem oil seals.

You can do a confidence check at home, once you rebuild the head lay it upside down and with the spark plug in. fill the head chamber with a really thin oil and leave to stand. If you loose oil a valve is leaking. I left my cylinder head over night and lost nothing. Just a quick check really.

Use engine oil when you install your rings and piston to reduce any chance if snagging it and will slide better.

Once you put your new head on, your valve clearances will be tight as the valves have recessed into the head, so they will need adjusting.

Then run it in with a mineral oil and don't semi or full types as they have great anti wear properties and a rougher bore will seal better than a smooth one resulting in a better piston ring seal. Run it in until the engine starts to free up as per the book and don't over rev it as you'll undo all your work and wreck the bore.

Good luck. I've just done my old ZX7r top end rebuild in the past many other engines.
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[Pol Anorl]

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You do know it was bumped five days ago...
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