markkeen123 Posted May 1, 2008 Report Share Posted May 1, 2008 hi i have a gas gas 280 pro whitch has developed an engine knock for no reason been riding the bike for a year or so and it has a knock like the big end is worn. i removed the barrel and inspected the piston little end big end anll were fine apart from the smallest amount of play on the little end i have tryed moving the needel in the carb up and there was no affect removed the water pump and started it and still does it any idear what could cause this wb thnaks Quote Link to comment Share on other sites More sharing options...
jse Posted May 1, 2008 Report Share Posted May 1, 2008 hi i have a gas gas 280 pro whitch has developed an engine knock for no reason been riding the bike for a year or so and it has a knock like the big end is worn. i removed the barrel and inspected the piston little end big end anll were fine apart from the smallest amount of play on the little end i have tryed moving the needel in the carb up and there was no affect removed the water pump and started it and still does it any idear what could cause this wb thnaks There should be no straight vertical play for the large or small end bearings. What was the clearance between the piston skirt and the cylinder about 20mm down from top of cylinder? You really can't tell what shape the piston and cylinder is by just looking at them. If you can see the problem, it's too late to fix. Check the air boot and the inside of the carb bell for signs of grit, if you find a fair amount, it is a good bet you may have damaged the bearings and piston (and possibly the cylinder) by silt passing through the filter. A good mechanic with a dial bore indicator will be able to tell you in a few seconds if the cylinder is damaged. Jon Quote Link to comment Share on other sites More sharing options...
petejohn Posted May 2, 2008 Report Share Posted May 2, 2008 Check the primary transmision gear. Think thats what its called located behind the clutch basket. The kickstart gear engages with this and can damage the gears causing a knock like you describe. Thats what was wrong with my sons 200 after spending ages looking for things more serious Quote Link to comment Share on other sites More sharing options...
ham2 Posted May 2, 2008 Report Share Posted May 2, 2008 Check the primary transmision gear. Think thats what its called located behind the clutch basket. The kickstart gear engages with this and can damage the gears causing a knock like you describe. Thats what was wrong with my sons 200 after spending ages looking for things more serious Ditto, most people I ride with who have owned a Pro have had this 'idler?' gear chip a tooth and the noise it makes sounds like a bottom-end rumble/knock. It can be serious if you get the shrapnel in the clutch or gearbox. Quote Link to comment Share on other sites More sharing options...
jse Posted May 2, 2008 Report Share Posted May 2, 2008 Ditto,most people I ride with who have owned a Pro have had this 'idler?' gear chip a tooth and the noise it makes sounds like a bottom-end rumble/knock. It can be serious if you get the shrapnel in the clutch or gearbox. Good idea, I'd forgot about that possibility. The damage to the kickstart and idler gear usually is a result of not locking the racheting mechanism before applying pressure on the kickstart lever. Otherwise, the gears get slammed together and as many times as we start our bikes a day, chipping a tooth can happen (goes for any Trials bike). If you need to replace the racheting mechanism, the new replacements have a more pronounced spiral on the shaft which engages the mechanism at a sooner point in the arc, which gives a better spin to the engine. Jon Quote Link to comment Share on other sites More sharing options...
ham2 Posted May 3, 2008 Report Share Posted May 3, 2008 Good idea, I'd forgot about that possibility. The damage to the kickstart and idler gear usually is a result of not locking the racheting mechanism before applying pressure on the kickstart lever. Otherwise, the gears get slammed together and as many times as we start our bikes a day, chipping a tooth can happen (goes for any Trials bike).If you need to replace the racheting mechanism, the new replacements have a more pronounced spiral on the shaft which engages the mechanism at a sooner point in the arc, which gives a better spin to the engine. Jon Hmm.not sure about the fallability of other trials bike brands but the Pro's certainly seem to be the worst for this fault. Just look at the width of the gear we are talking about,much narrower than the norm' (but that all goes toward the 'beauty' of the pro engine design) then look at the possibility that the whole width of the quadrant and gearing may/may not be fully engaged when you jab the kick-start....it's a potential problem waiting to happen (I'm avoiding saying ''design-fault'' 'cos everybody's a hind-sight design engineer these days). The more pronounced spiral that you mentioned is a great way to ensure a 'quicker' mesh-contact-area..but more importantly it shows that GasGas were aware of the problem and are looking to sort it. A little bird told me (i.e. I can't prove it ) that GasGas ,like many other engineering companies, already had a massive batch of the early 'suspect' gears sitting on the shelf so nothing would be improved until the stocks were exhausted. This little bird had 4 of these gears for 1 (new) bike. Quote Link to comment Share on other sites More sharing options...
ham2 Posted May 7, 2008 Report Share Posted May 7, 2008 Ditto,most people I ride with who have owned a Pro have had this 'idler?' gear chip a tooth and the noise it makes sounds like a bottom-end rumble/knock. It can be serious if you get the shrapnel in the clutch or gearbox. This is what I meant by serious... Quote Link to comment Share on other sites More sharing options...
jse Posted May 7, 2008 Report Share Posted May 7, 2008 Hmm.not sure about the fallability of other trials bike brands but the Pro's certainly seem to be the worst for this fault. The Pro is the most popular bike where I ride and I've only seen it happen once, but after seeing it on the forum, it's certainly something to keep an eye on. The combination of fairly high compression/heavy flywheel/high repeat use puts a high strain on Trials kickstart mechanisms. I always tell riders to start their bikes (any brand) like it was a Harley and they'll be o.k. Jon Quote Link to comment Share on other sites More sharing options...
ham2 Posted May 8, 2008 Report Share Posted May 8, 2008 The Pro is the most popular bike where I ride and I've only seen it happen once, but after seeing it on the forum, it's certainly something to keep an eye on. The combination of fairly high compression/heavy flywheel/high repeat use puts a high strain on Trials kickstart mechanisms.I always tell riders to start their bikes (any brand) like it was a Harley and they'll be o.k. Jon Hi JSE, I'm a little confused about the Harley reference? Do you have a good start up procedure you could explain please. Wayne Quote Link to comment Share on other sites More sharing options...
jse Posted May 8, 2008 Report Share Posted May 8, 2008 (edited) Hi JSE,I'm a little confused about the Harley reference? Do you have a good start up procedure you could explain please. Wayne If you've ever seen a rider start an older Harley, they will engage the racheting mechanism, push the lever lightly a couple of times to get it started at the top of the throw, raise up slightly and use body weight-not leg muscle-to get the engine mass rotating. In terms of proportional rotating mass, Trials engines are fairly similar. My old JTR370 (high compression 338cc's) taught me that and was an easy engine to light off once I learned. Jon Edited May 8, 2008 by JSE Quote Link to comment Share on other sites More sharing options...
ham2 Posted May 9, 2008 Report Share Posted May 9, 2008 I see,Ta! Quote Link to comment Share on other sites More sharing options...
fester Posted May 13, 2008 Report Share Posted May 13, 2008 i'll bet 10 to 1 that your spark arrestor screen is clogged solid,if thats the case it will run like a bat outta hell better hi i have a gas gas 280 pro whitch has developed an engine knock for no reason been riding the bike for a year or so and it has a knock like the big end is worn. i removed the barrel and inspected the piston little end big end anll were fine apart from the smallest amount of play on the little end i have tryed moving the needel in the carb up and there was no affect removed the water pump and started it and still does it any idear what could cause this wb thnaks Quote Link to comment Share on other sites More sharing options...
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