CG125 Woes

[heytc]

I'm getting out of my depth with a bike I've recently bought.
It's a CG125 br-j that was been sat idle for 10 years before I bought it. I'm pretty much a novice mechanic so hadn't realised that a bike sitting idle is the worst thing for it.

When I got it home I cleaned out the carburetor and was able to start it up. It sounded great and rode fine for the first half mile then lost power and stopped and I had to push it home.

I was able to get it started again when I changed the spark plug but it ran terribly, backfiring and not idling.

However today it has lost compression - it was reading about 150 from cold the day before. Today it is about 85 and about 95 when I added a little more oil. From my Haynes I take it that the piston or piston ring has gone.

So the advice I'm looking for is am I going to be able to sort this myself ? If it is piston rings that have gone is that all I would have to get ? Any gaskets or anything else ?

Cheers for the advice in advance

[Alexio]

Good to hear more CG's getting some love. If it was sat for 10 years did you check / change the fuel, oil, tires, inner tubes, chain, battery and... well I guess there's a hundred things you could check?

I suppose after all this time a piston ring could be worse for wear and deteriorate rapidly after use again. I've heard it isn't that hard but I don't know if you need to drop the engine out of a CG or not to do a top end rebuild / change the piston rings? I really need to know as well because I want to change mine as soon as I can.

New gasket would definitely be recommend yes.
____________________
will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?

[heytc]

I've changed the oil and its got a new battery. It will be getting a new front inner tube. I hadn't thought about getting new tyres for it. Maybe I should - does tyre rubber age badly ?
Beginning to get the feeling that if it can go wrong it will....hopefully the CG's reliability will help me out though.

[spiderwheels]

[heytc]

I've got to admit that the oil change was after my very brief journey on it. The mechanic I bought it off took it for a short spin round his yard so I thought that a similar short trip would be ok.
Feeling fairly dim but ya live and learn.

[Alexio]

I'm sure it'll be fun to take the engine apart anyway
____________________
will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?

[spiderwheels]

[heytc]

Thanks for the replies.
I will follow the Haynes manual and have a look inside.

[neatbik]

CG engines are very easy to work on and parts arent a lot of money.
You can drop the motor out of the frame in 10 minutes.

Best thing i think you can do is strip the top end down and have a look at whats going on. Feel free to post pics of what you find and people on here will help you.

[pepperami]

if you do delve into your bikes guts... .... lots of posts & pictures please..
i`m waiting to pick up an old CG and the more i can learn about them the better


i picked the CG because they are a simple bike....... lets hope that you find out that they are nice and easy to work on, so you can tell us lots!
____________________
I am the sum total of my own existence, what went before makes me who I am now!

[skatefreak]

Yeah, go for it.
Certainly cant do to much harm!
I took my engine appart and it was in the kitchen for over a month waiting for a gasket and such... When i got it back together and in the bike hearing it go again was amazing

Am back at square one but new head gasket in there and i know a heck of a lot more now

Lots of pictures please !

-Jvr

[heytc]

Thanks for all the encouragement.
Well I've opened up the bike and had a tinker but still haven't solved the problem.

As requested photos were taken. Here's the cylinder barrel on first inspection -

https://farm3.static.flickr.com/2688/4410034156_ee2f812f50_o.jpg

The barrel itself seemed pretty good to my untrained eyes. Smooth without anything that I could see wrong -

https://farm5.static.flickr.com/4061/4409269845_82814fc1cb_o.jpg

https://farm5.static.flickr.com/4072/4409269611_f22af5c1a8_o.jpg

https://farm3.static.flickr.com/2750/4409269283_5e4c8b13ab_o.jpg

Same with the piston rings. They looked fine to me but maybe I'm missing something -

https://farm3.static.flickr.com/2786/4410035784_94c6631927_o.jpg

https://farm5.static.flickr.com/4047/4409270247_40fa1b8037_o.jpg


While i was turning the engine over with the kickstart I could hear the air coming out of the cylinder hissing. Sounded like it was coming from a couple of places really and I was definate that one of them was the inlet valve because if it put my hand over the inlet hole then part of the hissing stopped.

The valves as they were -

https://farm5.static.flickr.com/4058/4410035478_5529f5796d_o.jpg

Decided to put new valves in coz at least part of the problem was there. New valves installed using grinding paste -

https://farm5.static.flickr.com/4055/4410036102_a62be973d4_o.jpg

So new gaskets installed, new valves installed, cleaned up the carbon and taken off the old gaskets, the piston rings look ok to me (is the lower one supposed to stick out slightly less ? ) but the compression is still barely anything and I can still hear a hissing coming out.

Any thoughts on what I'm missing ? What else can cause catastrophic loss of compression ?

Enjoying messing with my bike and learning loads by taking it apart - wish I could get it running lol.

Many thanks for reading

[temeluchus]

Have you checked the valve adjustment?

May be you have a loose rocker and its gone VERY tight.

As long as you've checked the bores (look fine) rings (also look fine), valves (which you've done) this is the thing I would check.

Whilst screw and locknut rockets tend to go loose, it wouldnt be impossible for them to go tight.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[heytc]

Thanks for the reply.
The rocker arms seem to be moving fine as far as I can see. The pushrod guide was missing but I got the part from David Silver spares.
I will try to take a short video turning the engine over to show the pushrods in action.

[temeluchus]

have you actually checked the clearances?

check it out here:
https://hondacg125.awardspace.com/valve_clearance.htm

Wont take too long, one of the advantages of a bum basic pushrod and rocker engine!
____________________
Some shite cruiser. Now with guns and FREEDOM!

[vcrmoss]

[spiderwheels]

Nice pictures.

It could be the rocker adjustment but looking back at how it failed you said it was riding fine and then suddenly stopped. That seems too sudden to be rocker adjustment (unless the locknut wasn't done up properly of course..)

How's the big end bearing? Does the con-rod move up and down with the crankshaft fixed at TDC?

[temeluchus]

i suspect big end failure would be obvious and noisey
____________________
Some shite cruiser. Now with guns and FREEDOM!

[spiderwheels]

[temeluchus]

there would be some pretty dramatic clanking if a big end bearing failed THAT badly to cause the engine to conk out like that!
____________________
Some shite cruiser. Now with guns and FREEDOM!

[heytc]

Many thanks for the replies.

I have rechecked the valve clearances and they did need some readjustments but didn't solve the problem unfortunately.

Here's a youtube video of the rocker arms in action, the video is sideways I'm afraid -

https://www.youtube.com/watch?v=rrSeLARI0PI

Also some video of the piston travelling up and down to see if anybody could spot anything.

https://www.youtube.com/watch?v=VhwxaLfopaI

The piston is totally solid when it is in place and doesn't feel like there's something wrong to me. I'm reluctant to take off the cylinder barrel to look at the con-rod because it was a difficult job getting the piston back in last time (Haynes says to push the rings in with fingers - not likely, ended up using some metal cut from a drinks can as a makeshift piston ring compressor)

[heytc]

I forgot to mention - the sound of the air getting out might be coming from the holes that the pushrods go into. Difficult to tell but sounds like it.

[heytc]

Update -
Believe I've worked out where the problem is. Thought it might be worth slightly overtightening the cylinder head bolts to see if that helped - and it did slightly taking the compression upto 60.
So it seems to be the gasket where the leak is.

How smooth do the connecting faces have to be ? Do they look smooth enough in the photos ? Are there techniques for getting an effective seal ?

I may even solve this

Thanks again

[Alexio]

Are you using a new gasket and proper gasket sealant?
____________________
will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?

[heytc]

Using a new gasket but not using any gasket sealant - Haynes didn't tell me to. Sounds promising