Topic: 78F2 gearbox noise? headache

[asom]

I'll be following this thread closely.  Good luck Jus.  I have the same bike and a similar/same problem. 

[CB750F2]

Jus, I saw your reply to Ron where you indicated that you wish that the float needles can be bought separately. They can be purchased in packs of six from www.z1enterprises.com. I have used them and they seem ok. Pat

[jus750]

Hey I just checked out there site, they have pretty good selection, If I cant get my needle's soon I think I will be buying them, I cant beleive 1 of mine is buggered it looks fine.
Thanks for everyones help, ounce I get it back togethger I will have to put it on youtube so people can see it idle and give me pointers. The bike has not been to a mechanic yet and I would like to keep it that way. 

[jus750]

Cheers ASOM I will post any advances, 14.5mm seams pretty precise for the measurement, what if they are 14 or 15mm. Im a linesman not a mechanic. I just want the thing to idle amooth, Im sure these jets and a bit of pacience will see me sorted

[jus750]

Okay got my new needles today, made a template to measure the float gap, set them all to 14.5mm, made sure idle circuit was clean. set the mixture to 1 3/4 turn on all 4, Stuck everything back together and Im pretty sure there is no change.Spewin What I did notice though is the noise from my gearbox is still there.( it has been there since my rebuild, 1 have done about 200klms, I was hoping it would go away) It has definatly got worse. When you turn the back wheel, there is a clunky noise  that comes from the gearbox, Im sure its not the sprocket. When I got the bike started today I put it in gear with the bike on the centre stand,and listened for the noise while the motor was doing about 3000rpm in 1st and the clunky noise can be heard. Dammit
so I have decided to pull the bike apart and look into the gearbox. I will be getting stuck into my idle problem but not right now, hopefully in a couple of weeks,Thanks for everyones help

[Terry in Australia]

G'Day Mate, before you do, check your starter clutch isn't shagged. Quite often that'll produce some nasty noises, and also, remove your starter motor and kick start it and see if the noise goes away. Much easier first step than pulling your engine apart! Cheers, Terry.

[jus750]

cheers terry, I'm a bit stumped on this noise.
here is what i have found.
if I rotate the back wheel backwards the noise disappears, when you rotate it forward there is a clunkety noise. the noise is not constant. you can spin the wheel a quarter turn and there will be no noise then there will be a few clunks, a quarter more then a few more clunks.
the chain is new, the sprockets are standard and almost new. When you watch the chain it is very smooth and doesnt jump around on the sprockets. Tension is even throughout movement.
When you slacken the chain the noise is quieter.
When I remove the chain the noise is gone I hooked my battery drill up to the sprocket and spun it , Its smooth as, with no noise.
There doesn't seam to be any play in the shaft. The sprocket is a bit loose on the shaft but I presume this is normal ?
any ideas ?

[Terry in Australia]

The CB750F2's have a problem with wear in the splines on the output shaft mate, the one on my F2 has a bit of slop in it so I used a bit of Selley's "All Clear" silicon sealant on the shaft, then slid the sprocket back on, and when it had cured, it appears to have taken the slack out, but of course, I should replace the shaft. (but I don't want to pull the fcuking enggine apart again, I've already done it twice, it's an annual fcuking event!)

How much slack have you got in your chain? If it's too tight (it tightens when you sit on it) it can destroy the output shaft bearings and when a bearing is on the way out, it usually goes "click click click"............. My "rule of thumb" is an inch of play in the centre of the chain with the bike on the centre stand, not particularly scientific, but it works for me. Have a good one mate, Cheers, Terry.

[jus750]

I tightened the chain as per the manual, To be honest the chain feels a bit tight. I have probably 15-20mm play 1 way 30-40mm all up, even when I slacken the chain to say 80mm play there is still a noise. When I push the bike outa the shed to take it for a ride the noise is very obvious. Taking the motor out is a pain, I know, but I don't think I can avoid it, It would be awesome if I could re tension the head at the same time, but seeing as i have to pull the thing apart its going to be all fresh gaskets.
questions. ?
would it be the output bearing ? ( when the output cog is turned with no tension on it feels good ?, its only when there is a bit of tension )
Are these easy to get and how much would I expect to pay and where is good to get em ?
I would probably have to split the cases to inspect this ?
Should I replace the other bearings ?
I presume it could only be a bearing is this right do you think?
pullin the motor means a lot of shed time

[jus750]

about to start pulling the engine reckon Im doing the right thing ?

[motomotard]

ok, have found the fuel tap needs to off on the bike otherwise the carbs overflow, having a bit more luck now, have found 2 carbs levels are now a bit low, im not stopping until I get this fixed. Here's some pics of me bike. Thanks for the fender Bender it looks awesome, just gotta get the little ding out

damn thats clean... wow

[jus750]

Gearbox noise fixed ?
I decided b4 the tear down to make a make shift chain out of a strap, tension it right up, spin the wheel and see if the noise was still there. Well guess what noise gone !. Tensioned it even tighter so it made a twang sound when you hit it, spun the wheel, still no noise.
Put chain back on set it to 25mm and still no noise. Pushed it around yard, Howcome whenever I push my bike at night in the backyard I run over doggy doodoo, everytime.Anyway no noise ?
Dont know if the chain is on opposite to how it was b4. Would this change anything?
Anyway Im back in business, just gotta  fix this idle and Im sweet.
still dont know how it is fixed it just is. All i did was remove the covers and drop the oil ?

[Terry in Australia]

Well done mate, glad you didn't have to pull it apart. Don't ask why, just be happy............. 

[jus750]

Dont worry Im happy, just gotta cut ouit 2 new gaskets and Im sweet, oil leak was on the alternator casing anyway

[Terry in Australia]

Yeah mate, that's common, make sure you put some sealant (non silicon, of course) around the rubber wiring plug or it won't matter how good your gasket is, it'll leak whenever you put it on the sidestand. Cheers, Terry.

[jus750]

Back to square 1
filled the motor with oil got everything back together, even synched the carbs.
spun back wheel and the noise is back ? ( clicking sound)
here is what i have found. The noise is inside the gearbox
if i put it into first, then neutral first again then neutral, a few times spin the wheel the noise goes (sometimes)
then i can put it in gear then neutral and it will be back ( not all the time but sometimes)
Strange thing is, with the bike running on the centre stand in 1st or second sometimes the noise can be heard.( sometimes)
any thoughts on what it could be ? could a shift fork cause this ?
I am going to pull the motor now and split the bottom case what should i look for ?
Note when i pulled the sump off there was a small amount of fillings, was not too worried, now i am

[Jerry Rxman Griffin aka MuthaF'er]

Is it THAT bad that you NEED to pull the engine?! ALL these bikes make some noise. If the noise was ALL the time, it created a nasty vibration, or was about to blow OR if you had another real reason to open it up then I'd do it. Otherwise just ride it. It's gonna cost some money (more than you think) and some of the parts may be impossible to find. Once you get into it you will go crazy and do all sort of other stuff. ~ $15,000 later I know but I'll have an almost NOS 75 750F  

I don't have that good of hearing so I don't have to worry about little annoying noises.

Couple other thoughts. If the engine was apart before by a previous owner then I'd consider breaking it down (half ass job??) more than I would otherwise but I'd probably still leave it alone in lieu of having a known serious issue. You may have to have your pistons machined for new aftermarket rings since no one has been able to source NOS rings! I just purchaed some D-I-Y custom molded ear plugs for $10. Consider that. OR, maybe Terry can make a house call 

[jus750]

I split the motor when I rebuilt it, a big end bearing was gone, so I swapped a crank from another motor.I'm no mechanic so maybe I dodged something up. Wish I could make my mind up, I think I will just ride it for a while.
Would be interesting to see what it is

[Terry in Australia]

I was lucky on the weekend mate, I decided to get my K1 running for summer so I did a heap of work on it, anyway, yesterday when I was riding it, I was sure I could hear a clicking noise from the gearbox, so I pulled up and put it on the centre stand. I spun the back wheel, but no noise? Hmmnnn.

I was about to take it off the centre stand and ride it home when I noticed a shiny mark on my centre stand, turns out the chain was rubbing on it because when I'd changed the exhaust, I left out the bracket that holds the stand away from the chain? I kinda like the idea of the stand working as a spring loaded chain tensioner, so I'm thinking of screwing or glueing a block of teflon to the stand, and see if that works? can't hurt........ 

[jus750]

Man I wish that was my problem. Your ride looks awesome. The more I think bout it the more it makes sence to pull it. Reckon I should