GN 250: Very poorly engine

[JohanR]

I have a suzuki gn250, and use it to get to work and back. About 8 miles each way, rarely reaching 60 mph, certainly not for any length of time.

I went for a longer trip a few months ago with some sustained periods of 60+, and came back with mr AA.

I was on a dual carriageway at about 65 mph. The bike lost power over about 20 seconds, and once pulled over refused to start. Pressing the start button did nothing - no noise, no lights, no nothing. Once the AA arrived he managed to start it with a battery pack, but the engine made a horrible noise. It's been a while now, so I can't remember exactly. Maybe a harsh rattle.

I left it for a while, but now decided to see if I could find out exactly what's wrong. I might not be able to fix it, but I'll get as far as I can. This is the first time I've done anything to an engine apart from use it.

The engine is now inside, and I just took off the cylinder head cover. There are two cam followers (tappets?), and while one looks superficially ok, the other has a nice bit of metal attached to the end. I've tried to get some photos.

https://www.dropbox.com/s/8ev9824dqdbl5s6/2013-01-19%2016.39.25.jpg

https://www.dropbox.com/s/tt44j5gkait3h2j/2013-01-19%2016.38.33.jpg

A bit of a silly question - but I know almost nothing here - but how bad is this? What caused it?

I assume this isn't the actual problem, so the next step is to get access to the piston...
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[mentalboy]

I don't think you need to go much further yet.
The bearing surfaces that your camshaft sit in look mullered. Let's have a pic of the shaft. I'm not sure if these run on shells but if you're in luck they will.

I'd say the muck on that follower is from a shell but we'll wait for pics.
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Make mine a Corona.

[JohanR]

Apologies for the quality. If these are too poor, I'll try and get hold of a proper camera.

The first 3 are from the cylinder dead, the last is from the cover. I've removed most of the 'stuff' from the follower, you can see the remains. Strangely, it feels more like plastic than metal.

(searching google for 'gn 250 camshaft shell', this thread is the 6th link!)
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[mentalboy]

You'll need to get that camshaft out. It's probably fooked, the bearing faces will need cleaning up - they should be nice and smooth - any remaining grooving is not a good sign.

The bearing recesses in the head/rocker cover should have whats left of some metal shells in them which will need prising out - if they haven't already gone!
Again any scoring is very,very bad.

If the shells have spun round they will almost certainly fook the ally bearers first, closely followed by the cam shaft.
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Make mine a Corona.

[JohanR]

Ok, I'll get on with that and see what I'm left with.

I've missed something... I need to rotate the cam chain in order to undo the bolts on the sprocket, but it won't move. Is this normal?
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[unitynotsocri...]

stop it,it hurts,reckon trashed head,camshaft and onlz god knows whatelse.I would get another engine or do a full strip n rebuild.
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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

[numpty2]

It looks pretty terminal.
You should start looking for a replacement engine, or at least a replacement complete cylinder head.
But bear in mind that there are many people who will try and sell engines that are in the same condition as yours, and claim it is a sweet runner.

I had a GN250 for a few years, and did over 20k on it. I had read that the top ends fail after 40k, so I sold it at around 42k before anything went wrong. Your top end has gone!
They are a nice & cheap budget commuter, but perhaps it is time to let this one go.
I think yours will be off the road for a while. Perhaps you should get another bike first to use as your commuter. Even a 125cc would be fine for your 8 mile commute. And then think about whether you want to fix the GN250. It might be a fair bit of work & expense.

[JohanR]

Crap.

I did look at getting another engine earlier, but they're not much less than the bike was in the first place. And as you say, it could be in the same condition anyway.

There are new heads on ebay for £180. Seems a bit much to throw at it given what else would/might be needed.

I think I'll carry on with finding out what's wrong, but now for interest, and to learn a little more about engines, rather than with an intent to fix it.

Thanks for the help, even if it's just to say 'stop!'.

So... should I be able to rotate the cam chain sprocket?
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[mentalboy]

[bladerunner]

Looks like proper oil starvation that! Have you drained the engine oil to see what crap likely stuck on your pickup filter etc?
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[JohanR]

I've taken out the sparkplug and removed the cam chain tensioner. I'm trying to rotate it both directly at the sprocket, and by the main chain sprocket.

It will turn slightly, but only about 1/4 inch in either direction before locking with a light 'clunk'.

I haven't drained the oil yet. It had an oil change a few months ago, and had the recommended amount put in. I haven't noticed any oil spills under where it used to stand, so I'd assume it's still in there.

I'll wait till the weather is a bit warmer before draining it though.
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[mentalboy]

Make sure chain hasn't gone so slack that it's binding on itself, if it is then you can solve this by taking up the slack at the top end on the side that the chain is moving downwards, may need rocking back and forth to free up.
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Make mine a Corona.

[bikenut]

oh dear thats not good.....

notice the broken wavvy spring washer to control rocker arm end float, lube problem........... :(