admacp

The clutch works perfectly the first time you use it from cold and also if it is left even for a few minutes. It doesn't work at all (no difference in feel on the clutch lever) after it's first use (i.e if you stop at a section and pull the clutch in all is fine. If you use the clutch a second time or more in the section then the clutch doesn't work at all - the bike keeps going!!!) Leave it a minute or two and the same scenario happens. We have tried new fluid, bled it loads of times, tried a complete new clutch and replaced the seals in the clutch casing. The only thing we haven't tried is the seals in the master cylinder - that is probably our last hope!

Nope! Been meticulous with all the parts (followed the parts book assembly!)

The new clutch was ordered as a sealed pack and included the steel plates and the fibre plates. We tried putting the old clutch back in and it was slightly better but not much. We also tried various podsitions of the lever "play" and the best was to have the adjuster on the lever screwed almost in to a point where the lever couldn't even touch the handlebar grip (didn't slip even when that far in?). We are pretty sure that it requires Dot 4 fluid as my own 04 bike has Dot 4 mentioned on the reservoir (his 03 doesn't say anything).

My mates 03 gas gas 250 is having random clutch troubles. The clutch works fine on first use but doeas not work at all if it is "pumped up" a couple of times as you would normally use it in a section. There is always pressure at the lever and doesn't feel different during use. It works fine one minute and then not at all - the bike just keeps going with the clutch in. To date we have bled the system at least 4 different times (new Dot 4 fluid), fitted new seals inside the casing & fitted new clutch plates. Anybody had any experience of this or got any ideas how to fix this random fault?

Jarvis won the event!

Go to http://www.gasgasmotos.es/web/eng/frame.htm and click on the link for trial (top left hand column)then select the bike and year in the right hand drop down box and then look for it at the bottom of the pge. It is a downloadable file in .pdf format.

Is anyone able to tell me the proper method of measuring & refilling front fork oil for an 03 pro 250 and an 04 pro 280. I beleive you can measure down from the top of the stanchion tube to the oil level but I am not sure if this is the recommended way. What weight of oil (for both bikes) does anyone recommend. Thanks

Excellent reply - very helpful and very detailed - thanks!!!

I had the piston & barrel checked by 2 different machine shops with their own micrometres and they both gave the same results to within a thou which is accurate enough I would think.

Thanks HondaRS. On thinking about it, you can't just go up a couple of sizes from measurements taken on the worn piston as a new "B" size piston (to match my own "B" size) will have a larger diameter. Really what info I need then is - what size is a new "B", "C" AND "D" piston so that I can check that buying a new "B" size will still fit my barrel correctly. Any ideas where I could get that info from? It is a Mahle piston and I have checked their website and note that Gas Gas is not listed in their list of Manufacturers they supply!

That's a bit OTT!!! Any help on this matter is valuable as I and I'm sure others are, learning a fair bit from all of the replies to any of the questions on this forum.

I had the barrel measured "properly" today and it read 76mm exactly (280 pro '04 model). The piston measured 75.91mm which gives a distance of 0.09mm (or 0.00354 thou). I have ordered the biggest size piston available (I 've gone up from a "B" size to a "D" size. Can anyone tell me the difference in sizes between the "B" and the "D" pistons. I was told it was 1 thou but now whilst reading info on the american gas gas website I note they mention each size increase is 0.05mm (or 0.002 thou). Therefore if I am going up 2 sizes, that equates to 0.1mm (not 1 thou) and I am worried now that the piston will be too tight in the barrel.

I've checked the small end bearing and it's fine. My last hope is that HondaRS's theory is correct and a set of piston rings will cure it or at least help it. I find it hard to believe that so much wear has occurred in such a short time. HondaRS - I checked the piston clearance at the point you mentioned and that is where the 4 thou size was though I had to be reasonably forceful (shoogle it about a bit but it did go up the gap about an inch maximum at this size!) Is there any way of knowing if the rings are badly worn before buying them? I would have guessed that there would be quite a bit of blowback down the side of the piston, past the rings, making the piston black - but there isn't much sign of it. Finally, I rocked the flywheel gently from side to side and there is a slight tapping sound with a very small movement somewhere along the line. I've checked the big end, small end etc. and there's no vertical play therefore my only conclusion is that the movement is indeed the piston rocking slightly in the barrel.

I have just checked the carb and all of the jets are as standard spec. and there is no evidence of any dirt or blockages inside. The only thing I have not checked is the fuel but I doubt if that will make the difference as I previously mentioned that my mate's 250 is fine with the same fuel. I have checked the spark plug and it's pretty black so it doesn't look as if it is running lean. Apart from piston slap has anybody got any more ideas?

I`ll try messing around with the jetting and report back. It starts rattling (definately not pinking but is a similar noise to tapping the exhaust with a spanner) just after returning the choke which is long before it heats up to temperature and is not 100% consistent with engine revs and can be slightly variable. The rattling continues throughout the whole rev range. As far as petrol goes - I am running regular unleaded which is the same as my mates 250 and his runs with no problems.

Thanks guys. I could do with knowing the recommendations for jetting the carb for the uk at sea level as a starting point - anyone got those? opdeweegh1 - did you cure the rattle? If so - did changing the jetting help! I am starting to think about something like jetting as the bike is immaculate and I would be very disappointed with the engine if it is "worn out" already ('04 model)! I assume that as the piston heats up - it would expand and the rattle would get less but there doesn't appear to be a rattle at startup on idle until a few seconds have passed.

Can anyone tell me the max. clearance between cylinder & piston using a feeler gauge. I have a really annoying rattle which I cannot find. (I don't have access to any proper measuring tools or bike dealers) The bike is a 280 Pro and is a 2004 model. The barrel & piston look in excellent condition (B size) and I have measured the clearance as 4 thou (which is 0.1mm). Is anyone able to tell me if this figure is ok and if not if it is the likely cause of the rattle (piston slap). The rattle is not present until a few seconds after starting (first throttle blip) & does not go away - seems to be worse on closing the throttle. When buying a piston in the uk, do the piston sizes go up in increments of thousandths or millimetres and what is the maximum size they go to (I think they are available up to a D size but I don't know the actual size increase over a B size. Thanks to anyone who responds

I don`t have access to accurate measuring gear for the clutch pack measurement. I have measured the depth though from the clutch hub to the front of the "fingers" and the dimension is way below the recommended figure of 17mm. Mine is only 14mm! I believe that the difference can be brought down by the use of thinner steel clutch plates/shims but how do you know what size to get? I don't see a note of the size of the existing ones anywhere. Is there a "rule of thumb" (e.g. a 0.1 mm thinner plate will give 2mm to the overall dimension therefore I would need to replace 2 plates). If you don't know the original size then how do you know what size to get the new ones (other than buying a set of the thinnest ones and try replacing one at a time).

I know the bearings and circlip you are referring to, I have already replaced one of them as there was a needle "missing" when I had a first look. It is the needle roller bearing that is in behind those and is embedded in the crankcase half. You have to split the crankcases to get at it - that is the bearing I am referring to.

Hi Subira - I don't understand the "bushes" you are referring to! My '04 has a needle roller bearing (same as in the Parts Book) which is a one-piece job. I can't see any other bushes as the primary gear shaft slots through the bearing to connect the clutch hub. There is a fair bit of "movement" I think, on this bearing. Prior to you replacing the bearing on your bike - was there a noticeable "rattle" noise coming from the engine? I have an annoying rattle which I hope is coming from this potential bearing problem.

I have a feeling that there is way too much free movement to allow heat buildup. I think I am going to change the bearing for safety's sake. Has anyone any experience of renewing this bearing and if any tools are required?

Checked the clutch hub today on my '04 280 pro and noticed that there is a reasonable amount of movement in the whole assembly. Does anyone know if there is supposed to be a certain amount of movement in the whole clutch basket? (It's more than I imagine would be tolerence but less movement than an imminent failure!). There are no loose bolts - feels like the whole unit is moving as one piece. If not, I have a feeling that the needle roller bearing that's in behind the hub (the one serving the primary shaft and fixed in the crankcase itself) is probably worn. If it is this bearing, does anyone know if you need special extractor tools to remove it and generally if it's a real pain to work on?

Ok guys - got the gearbox fixed and everything appears ok (so far!). The circlip to me was wrongly fitted in the factory. The rounded/bevelled edge was facing towards the direction in which the gear cog could "move", effectively slipping over it's seating in the groove. I would assume that the flat, sharp edge should be the side that is stopping the gear cog as it would be more difficult to be pushed out of it's seating. Unfortunately, some of the other circlips in there were also facing the wrong way!!! It was interesting to read that there is a flat side/sharp side to the clutch plates. If they were fitted the "wrong" way round (which is the right way round anyway?) would that have any effect on the clutch action?

I was swithering over the purchase of a gas gas 280 pro (04 model) for quite a while but a lot of people told me (and I have read a few tales of woe) that they are troublesome - in particular the gearboxes have a tendency to give problems. Guess what, I bought one only 3 weeks ago and...........the gearbox has gone bang on only my 6th or 7th time out on it! I have stripped it down and found that 2 of the gear cogs have sheared teeth. The cogs are combined (i.e double gears ) which are fairly expensive. I reckon I have tracked the problem down to a circlip which has "jumped" out of it's slot on the gear shaft and allowed the gear to move freely only about 2-3mm which in turn, loses about 30% of it's contact area with the other opposite gear cog and resulted in broken teeth on both of them. Is this the main problem that is affecting the Gas Gas gearboxes or do you think I have been very unlucky? I don't know whether to trust it now (what's to stop it from happening again?) and am wondering if the Gas Gas is the right bike for me.

I am very pleased with the responses to questions on this forum - well done everyone - it`s a gret help. My question is regarding the rear shock. The suspension feels quite stiff. I have set the spring length to 140mm and also tried it at 142mm and I have set the adjuster at the bottom of the shock to full soft as advised but it still seems pretty stiff - no chance of bottoming it out I would imagine. I have a yellow spring (is that standard?), I have cleaned & greased all of the bushes (inc. the swingarm) and they are all in perfect condition. The shock is not leaking or bent and moves without sticking. I just think that it may not be travelling the full length of travel and "packs" quickly. The bike is a 2004 280pro. I weigh around 12 stone. Anybody else think the back shock on these bikes is quite harsh? Should I contemplate a softer spring (if there is one available)?