GN250 Phantom clanking noise.

[CrotchRocket]

G'day, my daily ride GN has got a clanking noise, most noticeable between 2500 and 4500rpm. I've rebuilt the engine twice trying to find it, brand new piston and rings (oversize 0.5mm), new cam chain, big end bearings are fine. Chain tensioner is fine, I split the crankcase and checked all the components of the gearbox against their service limits. The camshaft has some interesting wear patterns but the profiles are ok and the valve clearances are fine. If anyone has any idea's, they would be much appreciated. Possibly running it on 98 is not good for the engine? (1990 model)

Cheers

[SIKPUPY]

Have you replaced your rocker arms, these can cause you grief if they are worn and you can still buy them as a Genuine part from your favourite Suzuki dealership? They are not too expensive either.

The GN style of engine is not a quiet engine and they can tick on with noises for years and be reliable until one day, they die as all good things must come to an end eventually. You will be sad as most people who have had a GN miss them, I cant explain why but it just happens. I had one which used to clunk all the time and after about 25000km's the noise was no different.

You need to make sure that with this engine you keep the oil level up around the full mark as they only take 1.3L. The oil is part of the cooling system too.

I have one of these engines which is untouched and is as healthy as they come if you feel the need to come listen to it and compare it to yours. I know of one which has about 5000kms on it since new and I will be hopefully making a purchase on it in the next few weeks if it is as good as I have been told.

The first thing you need to identify is where the noise is coming from so you can work out what is going on. Does it happen when it is cold or when it is hot? This could also help.

Try this approach at trying to diagnose your problem. You may even get laid in the process.

There is a couple of easy ways to check it out. I would assume you have already done this but if you haven't it might proove useful, if you have, somoene else on PSB may benefit from it.

Go to your doctors(preferably one that bulk bills, you dont want to pay for stuff unless you have to) distract them and knock some of their shit off. My mum is one of those shiny bum boss people at one so its a little easier for me but everytime I go there I never succeed in getting stuff, plus its a little embarrassing when the nurse hands you a packet of viagra in front of your mum and you get the 3rd degree, what do you need that shit for, then you have to try explain its a want not a need............ Anyway, Pay special attention to their stethoscope thing, it may come in handy later. You could try tuning one of the nurses and ask nicely for an old one but I dont like your chances, especially if you rock up on the GN. I would suggest taking the GPZ900 for a faster getaway I have tried tuning said Nurses and admin chicks for years with no sucess.

So you have knocked a stethoscope off, now its time to put it to good use. Ask your neighbour if they have a spare welding rod laying around, pull that shitty little thing that they use to listen to your ticker with and jam the welding rod down the hole until it sticks in there.

Put said GN on the side stand and crank it up in Neutral, get one of your mates to rev the bike to the rev range where the bike is making said noises. Go to town with your newly acquired stethoscope thing by poking it all over the engine to see if you can hear which general direction. I highly reccomend that you do not put it near moving parts like chains and stuff that isnt guarded as it could get somewhat embarrasing. Make sure your mate stays the fuck away from the gear lever. There is a video on PSB and youtube somewhere about some moron cleaning a wheel with the bike running and in gear on the centre stand, he lost fingers and shit. If you are going to do this, please post on PSB for all to see.

Anyway, this should help identify the fault. If you are unable to diagnose it this way as the noise isnt there, it may pay to put it in 2nd or 3rd rev it up and put your foot hard on the brake so you can load the engine up. This alone should help indicate whether it is engine or the transmission side of things. I would not reccomend doing this for any extended period of time and you need to pay special attention to any moving parts that arent guarded. If you do it for a long time, your brakes can wear out and without the airflow around the engine you could potentially do some damage.

If you don't have the courage to knock the stethoscope off and you had no luck tuning one of the nurses, you can also use a big screwdriver which will help, Google using a screwdriver as a stethoscope and it should come up. It is no where near as good as the real thing but it may give you enough of an indication to the area where you need to concentrate on.

You could also just shell out the 30 bucks supercheap want for one Stanley Stethoscope - Mechanics - Supercheap Auto Australia On a serious note, they can come in extremely handy when trying to do this type of stuff

A more professional and detailed approach can be found here Engine Noise Diagnosis Explained | YouFixCars.com

I hope you find this somewhat helpful.

[SIKPUPY]

Oh try it with the clutch in or out. Sometimes the clutches are quite noisy.

[CrotchRocket]

uhm wow, cheers for the insight and master plan SIKPUPY. i think i'll take a blast to supercheap and get one. tuning nurses is blissfully easy on the ninja. that unfortunatly is in the shed waiting for a teardown after a PSB ride injured the old girl. can't say i blame her, compound a cooling issue with a bike that is near 30 years old and a drag race with some honda's and it ended up being trailered home. no worry though. the ninja is easy, i know whats broken. the GN is somewhat harder, the noise happens with or without the clutch btw.

[SIKPUPY]

Let me know how you go

[CrotchRocket]

Took it to Mark at Maddington Motorcycle wreckers, he checked the engine over himself when it was apart, and when i rode it over to him he said it could only be the big end. being as the con rod is not separable without separating the crank, he said he could give me a second hand crank and rod for $120. frankly what choice do i have?

[SIKPUPY]

Come past my joint and have a look at the crank and rod that is still sitting in a bike that I got given by another psb member. I don't know what the bottom end is like as it's still in the bike and it's a bit weathered as the head is off. Still has oil in it and it turns over. If this crank is all good you should be able to buy new bearings and then it will be good as new. You could always just ride it till it dies.

[CrotchRocket]

the crank bearings are a bitch to get to, not worth replacing, the crank is actually two halves that are pressed together in perfect alignment, to change the big end bearing i would have to separate the crank, change the bearing, then get it pressed back together. much easier and cheaper to buy a decent quality second hand crank. HOWEVER. I'm almost certain its not the big end. its too, random? like its a looseness associated with something other than the piston and crank.

[SIKPUPY]

There are 2 of these bikes available at a bike shop for 300.00 which I believe are basket cases, PM me and I can tell you where they are. I will get my mate who works there to see if he can check out the bottom end on them. I know both dont have barrels, however it may pay to change the whole bottom end instead?