Here's one I haven't seen before....

[speedblock]

Hey guys - this is something that hasn't happened to me before, so I thought I'd share the story.

I am at the start of a 75 GT750 restoration / rebuild project. The bike I'm starting with is very rough, and it's a combination of parts from several different years. It was cheap enough and had some decent pieces, so I figured it would serve as a start.

The motor is a 75 and had good compression, so I wanted to try to at least hear it run before I tear the bike apart. I did a quick carb clean, filled the crankcase with oil and let it sit a few days, and poured a little oil down the cylinders. My buddy and I got it to fire up, but it would rev to the moon with the throttle off and the slides closed. Suspecting a big air leak from the rock hard boots, I ordered some new ones and new clamps.

Got the parts the other day, and today I put them on and fired it up. Same deal - it wants to rev to the moon. I shut it down right away, and noticed something strange on the clutch side of the motor. Check this out:

img_1621.jpg

The bolt was actually on the floor under the bike. It blew out of there hard enough to knock a hole in that cover.

Needless to say, I'm done trying to get it to run - I was going to go through it anyway, this just makes me worry about what else might be going on in there.

...and if anyone in the NY area has a decent 75ish motor they don't need, I might be interested.

- Chris

[stevegt738]

That does not look promising.

[husson73]

happens sometimes on any bike, the screw or something else went away and make a hole on a clutch cover, or ignition cover or other

[tz375]

Ah, the self generating inspection hole syndrome.

That's unusual. Usually a loose bolt will just slowly wear a hole in the side and that bolt is usually rusted in place.

[oldjapanesebikes]

Possibly running backwards ? In which case, it possibly could spin the rotor (it is heavy) off the taper and then drive the bolt through the cover.

[tz375]

I think that if it ran backwards, it would tighten that bolt.

[demozg1000]

Aparently the bolt to the alternator rotor backed out. I have a spare cover.

[speedblock]

Dave's got a spare everything

What gets me is that bolt is only 1/2 an inch from the cover when it's tight. How the heck did it develop enough velocity to blow it's way out of there? And what kind of tremendous air leak to I have that makes the motor wind up to about 8000 RPM when I start it? Or maybe the air pressure blew it right through there once it loosened up enough ?

[demozg1000]

My guess
1 bolt loose
2 no woodruf key
3 motor rotates clockwise as viewed from shaft backing out screw
4 Most important PO was messing with charging system and left loose.

[Suzsmokeyallan]

Is the rotor slack? if its not the bolt wound its way out because it was slack initially. Once it hit the cover that allowed it to hook up somewhat on the head and unscrew itself even better.
Are the butterflies on the carbs closing off? if not it will rev up like you describe since the intake vacuum will pull the slides up.

[speedblock]

I didn't pull the cover yet to check the alternator. I've got the bike on a lift now and started tearing it down; I'll take a look at that tomorrow.

As far as the carbs go, the butterflies are shut and the slides are all the way down (airbox off so it's easy to see).

[tz375]

I would expect that it happened exactly as Allen described it. The bolt came loos and once it touche the cover, there's enough drag to unwind until it popped out.

[speedblock]

A quick update: I took off the cover the other night and the alternator came out with it. Not only was that bolt loose, but the 3 hold down bolts are completely missing. The motor's coming out and I'll go through the whole thing. Going to need a good crank guy.

I'm still unsure on the high rev issue, but I'm pretty convinced it's got to be crank seal related. There has got to be a huge vacuum leak somewhere.

[ja-moo]

I never try to run an "unknown" motor for just this kind of thing.........