scraping noise from engine, thud and revs drop

[nathaniel2910]

Hi guys and gals.
I believe this is my first time posting here,
so bit of background im from the uk, studying automotive engineering.
I have been building and fixing 125's for a few years,
anyway my problem is i have recently purchased 1 and a half gs500's both 2003 models,
Unfortunately the bikes have been used as a training school bike,
its got 37,000 miles on the clock and has a engine knock,
it sounds worse than a knock though.
the engine idles at 2,000 which is a little high but its not a problem atm,
the knock can be felt throughout the bike and sounds like something catching metal on metal,
having stumbled on a youtube video of a similar knock it got me wondering more and i have stripped the left side of the engine case off, i believe it is the starter clutch behind the fly wheel, now i have never taken a fly wheel off and im unsure what to find behind it as i have yet to come across a picture of the starter clutch on the engine without the flywheel on, also i am unsure if the large cog behind the flywheel, the starter clutch should move as it does it has atleast 5mm of play towards and away from the flywheel.

also to note when the scrape/knock happens the revs drop to 1,500-1,600.
any info or help would be greatly appreciated

okay so i forgot to actually post this and have come across a few video
after watching this video of a similar starter clutch okay so its not the best video but it does show the blots and the fact the starter clutch is mounted on the flywheel.
http://www.youtube.com/watch?v=2CGfStxPaF8

also adidas guy's flywheel removal video pretty much explains how to remove and fit the flywheel
http://www.youtube.com/watch?v=GxS5yZ44AHU

its really now just is the noise deffinatly the starter clutch bolts or is it something else

[adidasguy]

Since you have the cover off, you might look at the 3 bolts that hold half the starter gear assembly to the flywheel. Are those 3 bolts in there? Do any look like they have been working their way out?
If the magnets look good then it could be the starter assembly coming loose from the flywheel.

The starter gear is on a 1 way clutch and otherwise is free to turn on the crank shaft. Some in/out movement is possible but should not be very much. Maybe a mm or two.

When the flywheel comes off, the starter gear should come with it. It slips in and there are 3 springs and rollers that make the starter clutch. If you pull the gear from the flywheel, you have to stick those parts back in. I have done it but not something I enjoy. Not that it is difficult, just takes patience to get the springs and rollers back in as you slip the gear back in there. (And if you do pull the starter gear off, watch for the springs and rollers falling on the floor or going flying somewhere.)

[nathaniel2910]

cheers for the reply, yeah i can see the bolts its the first thing i noticed, two sit flush with the inner side of the flywheel and one is maby 1mm further in so slacker.
im betting that one head has sheered off and thats the noise of it bouncing about and getting stuck between the flywheen and casing.

[adidasguy]

Pull the flywheel and take the starter gear with it as one assembly.
I show how to do it in my video.
Be sure to use a cut off hard steel bolt for the spacer. There really is a TON of force there to remove it. Soft steel will just squish up in the crank shaft. By hard steel I really mean a hard steel bolt - like one from a bike used for an axle or bolt for the rear shock. Home Depot soft steel Chinese bolts will just squish down in there.

[yamahonkawazuki]

Pull the flywheel and take the starter gear with it as one assembly.
I show how to do it in my video.
Be sure to use a cut off hard steel bolt for the spacer. There really is a TON of force there to remove it. Soft steel will just squish up in the crank shaft. By hard steel I really mean a hard steel bolt - like one from a bike used for an axle or bolt for the rear shock. Home Depot soft steel Chinese bolts will just squish down in there.

would grade 8 bolts work?