Author Topic: Replace Sprocket? - 1978 CB750F  (Read 1787 times)

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Offline Imago

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Replace Sprocket? - 1978 CB750F
« on: July 12, 2012, 11:45:43 AM »
I'm replacing the rear tire, (for the first time) have loosed the adjusters and removed the cotter key and the big nut, but how do you get the axle out?

My shop manual doesn't show how and a search here mostly refers to wheel bearings.

Does it turn from the other side, (I've put a bar on that head and it seems frozen)  or do you drift it out from the retaining nut side?

I don't want to wail on it too much or it will start to mushroom.
« Last Edit: July 12, 2012, 12:17:08 PM by Imago »

Offline Imago

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Replace Sprocket? - 1978 CB750F
« Reply #1 on: July 12, 2012, 12:15:24 PM »
Got the axle out by using a drift... now what do you think of this sprocket... replace?

Offline ChuckG750f1

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Re: Replace Sprocket? - 1978 CB750F
« Reply #2 on: July 12, 2012, 12:24:28 PM »
I would do both sprockets and chain while you're at it.
Life is hard; it's harder if you're stupid.
- John Wayne

1976 CB750 f1
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bollingball

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Re: Replace Sprocket? - 1978 CB750F
« Reply #3 on: July 12, 2012, 12:35:31 PM »
That sprocket looks bad. But I could tell better if it were clean. I am with chuck change it all and look at the brakes and the cush drive and wheel bearings. When I do this I like to change ever thing so I know where I'm at. No telling what a PO has done. As far as the bearings go I replace them with double seals

Ken

Offline ofreen

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Re: Replace Sprocket? - 1978 CB750F
« Reply #4 on: July 12, 2012, 12:43:34 PM »
Yep, sprocket and chain are past their pull date.  The advice given above is good, especially the suggestion about checking the other components.  There is a fair amount of corrosion apparent.  The seized axle is a good clue.  If the chain is a 630, may as well convert to 530 while you are at it.
Greg
'75 CB750F

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Offline Imago

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Re: Replace Sprocket? - 1978 CB750F
« Reply #5 on: July 12, 2012, 12:48:23 PM »
That sprocket looks bad. But I could tell better if it were clean. I am with chuck change it all and look at the brakes and the cush drive and wheel bearings. When I do this I like to change ever thing so I know where I'm at. No telling what a PO has done. As far as the bearings go I replace them with double seals

Ken
Good advice, and I already have new sprockets and 630 chain so I'll put them on with the new tire.

I'm trying to get the bike roadworthy to go to a vintage bike show and shine on Sunday... Do you know offhand which sealed bearings I should buy for the '78 750F with disc brake?

The bearings on the outside of the wheel feel ok however I'll replace them, but there is a pipe or shaft inside that the axle runs through that feels loose... is that normal? I suppose I'll know better when I get it apart.
« Last Edit: July 12, 2012, 12:51:35 PM by Imago »

Offline Shane72

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Re: Replace Sprocket? - 1978 CB750F
« Reply #6 on: July 12, 2012, 12:53:43 PM »
I'm replacing the rear tire, (for the first time) have loosed the adjusters and removed the cotter key and the big nut, but how do you get the axle out?

My shop manual doesn't show how and a search here mostly refers to wheel bearings.

Does it turn from the other side, (I've put a bar on that head and it seems frozen)  or do you drift it out from the retaining nut side?

I don't want to wail on it too much or it will start to mushroom.

Definitely don't want to peen the axle, but you do have to drift it out somehow...and some penetrating oil might also be indicated.

I'd start with a dead-blow hammer with non-metal head--the heaviest one I could find.  This tool will come in handy throughout a lifetime of bike work.

If that doesn't do it, I'd then move to a heavy (3-pound) hammer with a piece of hardwood over the axle.  Orient the hardwood piece such that the grain is in line with the hammer stroke.

If that doesn't shift it, try a blank of steel between the hammer and the end of the axle--this should prevent mushrooming of the axle.

One way to keep the axle from moving too far at once (and to protect the threads) is to leave the large nut mostly threaded on.  Just leave 3/16" or so of space for the axle to break free without flying too far.  That said, be very careful to not damage the threads if using this method--your hammer strength may be too much.

All the best,

Shane

*Edited to add*  I see you got the axle free before I posted.  Good job, and I'll read more closely before posting next time!   ;)
« Last Edit: July 12, 2012, 08:05:20 PM by Shane72 »
I mount and balance MC tires--while-you-wait service by appointment.  Send me a PM.

Offline Imago

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Re: Replace Sprocket? - 1978 CB750F
« Reply #7 on: July 12, 2012, 01:31:43 PM »
Does anyone know off hand the numbers for double sealed bearings for the rear wheel... I understand there are 3 of them... and SKF's are good.

Offline Imago

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Re: Replace Sprocket? - 1978 CB750F
« Reply #8 on: July 12, 2012, 04:49:06 PM »
Does anyone know off hand the numbers for double sealed bearings for the rear wheel... I understand there are 3 of them... and SKF's are good.
I got the cush drive open, (it opened up very easily) and everything including the bearings actually look great and the grease like new... I'm not messing with it for now.

I'm not having any luck with my new tire irons however... I'm starting to mar the wheels getting them off so I think it's off to the Honda or Harley dealership for me... drat.

Offline ChuckG750f1

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Re: Replace Sprocket? - 1978 CB750F
« Reply #9 on: July 12, 2012, 05:09:40 PM »
Are you trying this alone or do you have another set of hands?  Two strong sets of arms really helps.  You can use a large C-clamp to break the bead.  It is essential to move the bead into the deeper center of the rim as you go, this makes the battle easier.  There is a good thread on this, I'll try to find it.
Life is hard; it's harder if you're stupid.
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1976 CB750 f1
1995 HD Softail Custom

Offline MCRider

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Re: Replace Sprocket? - 1978 CB750F
« Reply #10 on: July 12, 2012, 05:14:40 PM »
The pipe betwen the hub bearings is supposed to be loose. It spaces the bearings apart side to side, but does nothing else. The axle holds it steady.

The bearing numbers are the same except for an identifier for the double seal, like RR v R, or such. Your bearing supplier will know.
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1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
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Offline ChuckG750f1

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Re: Replace Sprocket? - 1978 CB750F
« Reply #11 on: July 12, 2012, 05:17:46 PM »
Ok, this thread is pretty good.  My advise is to give it a read.  I don't cut the old tires off.  Keep us posted.
http://forums.sohc4.net/index.php?topic=106283.0
Life is hard; it's harder if you're stupid.
- John Wayne

1976 CB750 f1
1995 HD Softail Custom