Topic: I have a #$%* cloud that follows me everywhere.

[mrblasty]

Last weekend my bike gave me a scare, a valve adjuster backed off and was making a loads of noise.
Last night I went through the whole tune up routine and installed my new dyna-s got everything dialed in.
Today I take the 750 out on the open road, It's running better than it has since I bought the thing back in september, at one point in mid-shift I heard a wicked clunk.  The bike was working like it should, at one point I get off the bike and notice oil all over the rear wheel and the chain had gone slack.
Limped the bike home, pulled the drive gear cover and found a massive crack running pretty much the whole width of the cavity.
What the hell is with that? I just dumped $250.00 bones into ignition, tune-up parts, oil change, new bars, mirrors, grips, fairing.  Now a new motor.
This sucks.
I have attached a few pics of the damage.
The chain scraps at the front of the cavity were there when I replaced the chain a few months back and the chain looks good. Will JB weld fill that?
What do you guys make of the chain slack? my rear doesn't look like has moved. 

[supersport_CB400F]

If you have a crack in the casing then it’s shagged …#$%* happens one step forward two back 

[ofreen]

I can't tell for sure what you've got from the picture.  Is that the crack at about 8 o'clock from the sprocket?  For one thing, there is a lot of mung in the countersprocket recess.  There is not much clearance there as it is even when it is clean.  Possibly a rock or some other debris got between the sprocket and the case.  I suggest cleaning that area out, take the sprocket and chain off, and post another picture.  A lot of cases have been repaired with JB Weld in that area, so maybe you'll be able to do that, too.

Where are the sprocket retainer bolts?

[scunny]

that sucks, I don't know about this jb weld, never seen the stuff but I'm sure you can get it welded.

[Japbikemike]

Blasty, time to take Jarod up on his chopper motor offer, eh?

I'm still messing with my carbs from "the tumble".

[mrblasty]

I looked at it last weekend, had to pass on it then, but now I may need to rethink it.
Still need Transportation.

[Sam Green Racing]

I can't tell for sure what you've got from the picture.  Is that the crack at about 8 o'clock from the sprocket?  For one thing, there is a lot of mung in the countersprocket recess.  There is not much clearance there as it is even when it is clean.  Possibly a rock or some other debris got between the sprocket and the case.  I suggest cleaning that area out, take the sprocket and chain off, and post another picture.  A lot of cases have been repaired with JB Weld in that area, so maybe you'll be able to do that, too.

Where are the sprocket retainer bolts?

I don't know about the sprocket bolts, wheres the sprocket gone ?

[ofreen]

The chain scraps at the front of the cavity were there when I replaced the chain a few months back and the chain looks good. Will JB weld fill that?
What do you guys make of the chain slack? my rear doesn't look like has moved. 

Your original picture appeared to show the countersprocket retainer as being a little bent up.  Also, the retainer bolts weren't there.  Were they both in place when you removed the countersprocket cover?

Your new pictures show what appears to be another scrape to the right of the two chain scrapes leading down to a gouge by the widest crack.  It looks like something was wedged in there by the chain and sprocket, causing the break.  

How much chain slack did you get?  Does the countershaft turn freely?

It looks to me that if the damage is confined to the cracks shown in your picture that you may be able to repair it with JB Weld.

[Sam Green Racing]

Ofreen, what hapened to the original picture and was the sprocket still in place ?

[mrblasty]

Sorry guys, the first photo did show that the counter sprocket bolts were missing,I took them off.
I was going to remove the gear before the pic but didn't get that far.

[Sam Green Racing]

What size front sprocket do you use ?...If it is 18 and you have been running a slack chain it could have jumped the front sprocket and smashed the cases.
There's not a lot of room for mistakes with the 18 toother.

Sam.

[cb650]

What size front sprocket do you use ?...If it is 18 and you have been running a slack chain it could have jumped the front sprocket and smashed the cases.
There's not a lot of room for mistakes with the 18 toother.

Sam.

This was my first thought too.
Dad swears by JB weld. I've never used it.  I think it could be welded though.


                     Terry

[mrblasty]

I checked the gear and it is a 18 tooth,  What are my options on other gears?

[6pkrunner]

16 and 17 teeth versions are offered. And if you really clean the area well and chisel a V groove the length of the crack and fill it with JB weld it will save you for quite a while. But it has to be super clean with no contaminants or it'll be a waste of time.

And with a 48 tooth rear and an 18 tooth front you've got a 2.66 final drive ratio
Dropping down to a 17 will give you a 2.82
and the old 16 tooth will give you an even 3.00 final drive ratio. The 17 48 is a real nice setup.

[cd811]

some guys go down as low as a 15 ...will make it scream..I had a 16 and at 55mph it was screaming...I changed to a 18..more better
a lot of guys have repaired the hole( a lot of people have #$%*ed up)(like me)..some thin sheet metal and jb will work...I got a set of cases that I repaired(the right way)alum wielded that I never used..if you want them let me know

[mick750F]

   The '77-'78F's had a 14/43 set-up...one of the reasons they were/are quick...relatively. From my experience this also made them a bit buzzy at highway speed. I recently changed out my chain and took the opportunity to change the gear ratio. I went with a 15/44 set-up which is noticeably less "buzzy" but is still quick...relatively. I'm not sure if these front sprockets are available for the earlier 750's...don't know the subtleties of how they mount...but I though I'd throw it out as a possible option for anyone looking to get quicker.

Mike