Another CG problem ...

riktus · Two Stroke Sniffer Joined: 05 Mar 2004 Karma :

Right, well I have an '89 CG, 22.5k on the clock, which I have been running (seemingly) happily for about 1000 miles, the only real problems being it dieing occasionally in heavy rain at low revs, and a rusty exhaust which needs replacing fairly soon.
Friday night, sitting on the dual carriageway at about the top speed, a bit off the highest revs in top gear there is a bit of a judder, and the bike seems to lose a bit of power. As I carry on, there is a more noticeable rattling noise from somewhere down below me, but I keep it going and get it home as I'm soaked and freezing.
On later inspection I discover the crankcase is nearly dry. I'm no saint when it comes to checking the oil, but I'm fairly sure I did about 3-4 weeks ago and it was still as full as when I'd changed it a month or so before that. Topped it back up, which reduced the rattling, but noticed some blue/white (oil?) smoke at high revs when stopped at lights etc. although not otherwise (then again I can't really look for smoke very well when I'm driving around). Checked it again this morning, and the oil level has dropped a few mm on the dipstick, and the exhaust smokes blue/white at high revs.

So ...
a) What's probably wrong with it (I presume something is buggered in the top-end, and oil is leaking and being burnt, but I don't really know what I'm talking about to be honest), and for that matter how much is it going to cost me.
b) What should I do with it - to work on it myself is going to require another 50 miles journey back home to get to the garage and some tools, as i really don't want to attempt it in the street in Bristol. Is it going to be fairly straightforward to get the thing apart and see what's wrong? The other option is I guess to bite the bullet and take it to a garage - so c) can anyone recommend somewhere in Bristol, preferably which will fit a student budget.

Cheers for your help guys!

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Sounds like it nipped up on you. It the bore is almost certainly a bit scored, who knows what the valves and bearings are like? the only way is to check it out.

I wouldn't bother with a garage, a full engine strip is gonna cost when you compare it with:

riktus · Two Stroke Sniffer Joined: 05 Mar 2004 Karma :

cheers stinky (that just sounds wrong), I'll get some more oil, and take it back hopefully next weekend and look at taking it apart I guess ... time to actually buy a Haynes manual i feel Razz

mr.z · World Chat Champion Joined: 04 Feb 2004 Karma :

As stinky said you miht as well forget geting a garrage to do it...

You could at the very worst go and buy a second cg and swap over parts as you need them.. buy a ratty but running cg, take it to bits, put it in boxes and take any bits as you need them... im hopeing to do that with mine at some point... which is one major advantage to owning a bike that costs about the same as supersports bikers insureance (or allot less

Dont attempt anything without a haynes manual or a torque wrench Thumbs Up

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riktus · Two Stroke Sniffer Joined: 05 Mar 2004 Karma :

Well, I got the top end off eventually a couple of weeks ago, and my dad removed the piston and cylinder while I was back at Uni. There doesn't seem to be anything obviously majorly wrong with it though, which is a little frustrating. However there were:
Oily deposits all over the inlet valve
Light scoring to the cylinder, and scoring to the inlet side of the piston (see pics)
Everything else appeared to be ok, so the current plan is to clean off the crap, lightly deglaze the cylinder with some fine wire wool, put some new rings on and put it back together. Any suggestions/anything stupid I've overlooked?

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Looks like a bit more than lightly scored on the piston mate. I would get a new one, they cost next to nothing (£10 from david silvers). Check the ring end-gap with a feeler guage as described in your manual when you get the new ones to check if it needs a rebore.

If the bore is as manky as the piston I would seriously consider taking it out to the first rebore or just buying a new barrel, it won't be too expensive either (a cylinder head is £45, a barrel would be much cheaper).

https://www.davidsilverspares.co.uk
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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.

riktus · Two Stroke Sniffer Joined: 05 Mar 2004 Karma :

Yeah the piston does look rather ratty, think the cylinder is supposed to look a bit better, but I haven't actually had to chance to take a look at them yet - those are the only pics I've seen. Checking the prices for everything (standard + oversize pistons and rings, cylinder barrel and gasket sets) with david silver spares at the moment, looks like this weekend is going to be cleaning the crap off and deglazing only Sad

I want my bike back! Evil or Very Mad

Thanks for your help stink,

Rich

Scooby · Scrappy Doo Joined: 26 Mar 2002 Karma :

I take it this is a pisstake...
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A big enough hammer fixes anything!

riktus · Two Stroke Sniffer Joined: 05 Mar 2004 Karma :

Umm, why?

Scooby · Scrappy Doo Joined: 26 Mar 2002 Karma :

Because it's fucked.
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A big enough hammer fixes anything!

Guest · Brolly Dolly Joined: 22 Apr 2004 Karma :

Yep, stinky's right again, that's more than a 'slight nip-up' Crying or Very sad

Rebore and new piston and rings and gaskets. If yer dad's such a dab hand at stripping it get him to clean up the valves and grind them in while it's apart. Thumbs Up

You might get change from £50 if you're lucky, at least now you know why you should check your oil level regularly, particularly on a little 'un that spends most of it's life having it's neck wrung Wink

mr.z · World Chat Champion Joined: 04 Feb 2004 Karma :

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

All the above said, a single cylinder OHV engine will run in a frighteningly sorry state. I know guys who run old brit bikes until the bore is so worn that they don't start anymore then just fit the next size ring. It will probably run OK with a moderatley scored bore but it will be down on power and will burn more oil than the Exon Valdez spilled.

You could definatley spend a friuitful evening in front of the telly with an old screwdriver, some wire wool, grinding paste and a lapping rod cleaning up and reseating those valves, especially if you have bought a top-end gasket set which will have new valve-stem oil-seals in it.

I would definatley throw that piston in the bin though!
____________________
“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.

riktus · Two Stroke Sniffer Joined: 05 Mar 2004 Karma :

Right, the piston and rings are definitely going to be chucked, i'll see what the responses are from david silver as to the price of a barrel, and have a look around at reboring places (any recommendations in the gloucestershire area?). Sent a request off for prices on engines from various breakers as well, see what that turns up. And the weekend will be spent cleaning and grinding Very Happy

Cheers Guest, zero and stinkwheel again, and you sure are a friendly bugger aren't you scooby.

Rich

Scooby · Scrappy Doo Joined: 26 Mar 2002 Karma :

Sorry mate, I really did think this was a pisstake thread. You posted pictures and a statement saying 'there doesn't seem anything obviously wrong with it' and nobody with any mechanical knowledge had replied, so I thought it was a topic that someone had posted as a laugh to see how many serious replies they got.

I was obviously wrong, sorry if I seemed a like I was having a go at you.

Ok, seriously, definitely needs new piston and rings. Not sure about the barrel can't really tell from the pictures, but a new barrel will cost a fair whack, consider getting it rebored. Don't worry too much about using an aftermarket piston, just make sure the rings are genuine and you shouldn't have any problems Smile

____________________
A big enough hammer fixes anything!

riktus · Two Stroke Sniffer Joined: 05 Mar 2004 Karma :

hehe, ok dude no worries, it was really an 'obviously wrong' as in i was expecting a valve seal blown or something more definite and drastic than wear/scoring on the barrel and piston, as it went quite suddenly.
So thanks for the input scoob Thumbs Up

, sorry for being a tight-ass Wink

Rich

pb399 · L Plate Warrior Joined: 03 Aug 2004 Karma :

Hey there, I had a similar problem with my cg125 (1991, 16.5k), loads of smoke at most rev speeds - it was getting hard to see at night when I stopped Very Happy

Anyway, stripped it down and found similar crud on the vales and top of the piston which cleaned off ok, and also had some scoring on the piston - not as bad as yours but still not that pretty. The bore looked pretty ok though so I just put a set of new rings on, put it back together and it runs fine - 300 miles since I did it, does at least 60mph (well it's still a cg!!) and no more smoke!

I reckon the cg engine isn't nearly as sensitive to this sort of damage as higher spec engines so if you're just wanting to get it running again you could probably get away with a new piston and rings (I know I did just the rings, but my cg was still running fine bar the smoke?)

also you could have a look at www.gear4bikes.co.uk for the gaskets at least - they're a bit cheaper (I think) than david silver...

pb399 · L Plate Warrior Joined: 03 Aug 2004 Karma :

Oh and don't forget to clean the exhaust port too if you're cleaning the valves - mine must have been about 2/3 of the size it should have been due to all the crap that was inside it! Rolling Eyes

pipnet11 · Brolly Dolly Joined: 17 Sep 2004 Karma :

If this is going to cost you any more that 70 quid Id be looking at a new(er) engine from a breakers, or even a whole bike. I got a crashed damages Suzuki GS125 for spares with engine fine for 90 quid. This also meant I had spares for most of the bike except the forks and tank which were a bit broke!

These little bikes are a hell of a lot more common in scrap yards than you might think, and even if you dont find a runner you can always just replace the barrel and piston (and head if its in better condition)

Even though it is true that these bikes will go when all common sense says they wont, it means the chance of sitting at th side of the road with a dead bike is significantly higher.
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