Unusual Noise From The Gearbox

[manx2day]

Hi, wonder if anyone out there can help me... My gearbox in my '07 Pro is making some funny noises when running.

I have recently had the kick-start gear and idle gear replaced as the kick-start gear had sheared 2 teeth and cracked the clutch case. All replaced and sorted before the Reeth. During the last day of the Reeth the chain came off and wrapped itself round the front sprocket. All sounded fine for the rest of the day. When washing the bike i noticed that the front sprocket was stopping when i turned it, like it engaged a gear but would spin freely again.

Now there is an unusual crunching/grinding noise from the gearbox. On the stand and in neutral (definately in neutral because it makes the "neutral noise"!) it begins to spin the rear wheel, like it's in gear. Off the stand and again in neutral the bike jumps like it's trying to engage a gear.

Could it be something floating round and binding in the gearbox and how expensive could this be?

Cheers

[laser1]

Sounds like you need to open her up and find out whats going on. You may have some problems that will only grow in expense if ignored. I dont know how comfortable you are working on your bike, but heres a couple of options.

Have the shop do all the work - make sure you wash the bike before you take it in. Nobody likes working on a dirty bike. I would say you looking at 8 to 10 hours of labor. (It would take me about 10 )

Pull the motor yourself and have the shop split the cases and do the tranny work. Put the motor back in yourself. To me, that is more than 1/2 the work. Note: The tranny is easy to test on the bench.

If you are an experienced wrench, watch the Jim Snell video's on the TriaslpartsUSA tech page and work through it yourself.

[sectionone]

Before you decide to split the cases, I would check a couple of things just by removing the clutch cover. First check if your idle gear are kick start gear have been damaged again. If you installed the kickstart lever too far forward you could have chipped the gears giving you the grinding noise. Next, try rotating the shift adjuster eccentric to try to fix the gear engagement issue.

[manx2day]

Just been looking at the bike and the kick start gear and idle gear are fine, still brand new. Only trouble now is that the kick start WON'T engage now i've put the clutch cover back on. Didn't even fiddle with that! I do think that there is something in the gearbox. The magnet on the filler screw has attracted an awful lot of filings and when i move the bike in gear i can hear an AWFUL grinding. I'm not confident enough to split it myself, so it's going to the shop tomorrow. Another expensive fix no doubt! Already spent

[manx2day]

Just thought i'd say that my bike is back together. Apparently a bearing had collapsed on the main gear shaft. It got caught up in the gears, ruined the shaft and a couple of gears. Haven't got the bike back yet and don't know what the damage to my bank account will be but i have a feeling it's gonna be expensive. The engine had to be stripped (obviously) and the parts replaced. I'll be glad when i start it up and it doesn't crunch!!

[garethr]

My sons chain came off on his little GasGas 50TXT Boy on the weekend. It all bunched up around the front sproket, but I managed to stand on the chain and pull it out. When I put the chain back on he rode about 5 yds and the bike made an awful crunch click noise. I thought at the time it was knackered chain that wasnt meshing with the sprokets anymore. I've taken the chain off and rotated the front sproket by hand and I can feel something catching and clicking inside.

Sounds similar to the problem you describe here. I'm now in the process of removing the engine to take to the dealer. :-(

What did it cost you in the end??? Did you just take the bike whole!?

[jse]

Just thought i'd say that my bike is back together. Apparently a bearing had collapsed on the main gear shaft. It got caught up in the gears, ruined the shaft and a couple of gears. Haven't got the bike back yet and don't know what the damage to my bank account will be but i have a feeling it's gonna be expensive. The engine had to be stripped (obviously) and the parts replaced. I'll be glad when i start it up and it doesn't crunch!!

You are probably lucky you didn't break the centercase when the chain packed in. The forces involved in a gearbox from a sudden lockup of the countershaft are absolutely huge, especially in a Trials engine with the very large inertial energy stored in the big, heavy flywheels we use.

As a somewhat related aside, and in the area of TMI regarding chains and sprockets, because we use chain tensioners on our bikes, we almost never run into a fairly common problem with MX bikes, that being, centercases splitting at the countershaft case bosses because the chain was not allowed enough slack. Sometimes, if the rider was fortunate, the chain would pull apart before the cases split, so I would always look for the telltale signs of stretch fatigue on the links for a diagnosis. MX riders, like Trials riders, usually adjust the chain with the bike up on a support with the swingarm below "level" and sometimes forget that the rear axle pivots, not in a circular arc (the pivot center is the swingarm shaft center, not the front sprocket center), but a parabolic arc which causes the chain to tighten tension at the "level" point. Hmmm, I guess the point of this rambling is to offer that it is better to error on the side of a little too loose than a little too tight when making chain adjustments.

Jon