Author Topic: CB400F Engine rebuild  (Read 6358 times)

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #30 on: October 27, 2020, 03:17:01 PM »
There is quite a lot of play on my Countershaft bottom gear and a small amount on Mainshaft top gear.

Is this normal or do they need replacing/rebushing?

Gareth

1977 CB400F
1965 T100SS

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #31 on: October 28, 2020, 11:13:49 AM »
There is quite a lot of play on my Countershaft bottom gear and a small amount on Mainshaft top gear.

Is this normal or do they need replacing/rebushing?

Can anybody give me some advice on this? New gears are available from CMSNL but over £200 each! Any idea how much it's likely to cost to get the bottom gear rebushed?
Gareth

1977 CB400F
1965 T100SS

Offline Laverda Dave

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Re: CB400F Engine rebuild
« Reply #32 on: October 28, 2020, 07:42:48 PM »
I can't really offer any advice other than I thought it was common on  most Jap bikes of that era to have a lot of backlash, I certainly remember it was mentioned a lot it road tests at the time.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline cliff7

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Re: CB400F Engine rebuild
« Reply #33 on: October 28, 2020, 08:28:57 PM »
On the notes I got with my 400, the previous owner but one mentions fitting a new bush to first gear. Unfortunately there is no receipt for this and I can't get hold of him. So not much help except it can be done.

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #34 on: October 28, 2020, 10:57:13 PM »
Ok. Thanks for the replies. Ive checked several gearboxes  and first gear is the same on all of them
so I wanted to check if that was excess wear or not. The bushes don't look very worn so it may be ok.
I don't suppose anybody has the bore size of a new gear do they?
Gareth

1977 CB400F
1965 T100SS

Offline K2-K6

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Re: CB400F Engine rebuild
« Reply #35 on: October 29, 2020, 09:52:36 AM »
Difficult, without being there, to accurately feel what it's like.

As Dave mentioned,  there's a fair amount of movement in gearboxes but in the right direction.  They are after all fairly crude, but effective,  by nature of design.

What shouldn't happen is for you to move the gear radially as the teeth would vary in mesh to it's pair, which is not acceptable.

Because of their compact nature,  some gears are in effect stabilized by it's neighbouring gear which is moved into "dog" engagement with it. Left in neutral,  you can't fully see that support,  but of course the gear takes absolutely no torque load until it's in use for that ratio.
Also a straight cut gear imparts no sideways loading to the gear itself, so no inherent drive to push it out of alignment.

To summarise,  you shouldn't be able to take one individual gear and move it radially on it's shaft so that it goes away from running concentric. That's worn, but slight wobble will be present for many.

A bit long winded,  but hopefully give you a little help to check.

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #36 on: October 29, 2020, 11:16:21 AM »
Difficult, without being there, to accurately feel what it's like.

As Dave mentioned,  there's a fair amount of movement in gearboxes but in the right direction.  They are after all fairly crude, but effective,  by nature of design.

What shouldn't happen is for you to move the gear radially as the teeth would vary in mesh to it's pair, which is not acceptable.

Because of their compact nature,  some gears are in effect stabilized by it's neighbouring gear which is moved into "dog" engagement with it. Left in neutral,  you can't fully see that support,  but of course the gear takes absolutely no torque load until it's in use for that ratio.
Also a straight cut gear imparts no sideways loading to the gear itself, so no inherent drive to push it out of alignment.

To summarise,  you shouldn't be able to take one individual gear and move it radially on it's shaft so that it goes away from running concentric. That's worn, but slight wobble will be present for many.

A bit long winded,  but hopefully give you a little help to check.

Thanks. There's no noticeable movement radially but I can rock the gear on the shaft, worse on the large 41 tooth gear, but that might seem worse because of the bigger diameter.
I'll try to take a video later.
Gareth

1977 CB400F
1965 T100SS

Offline K2-K6

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Re: CB400F Engine rebuild
« Reply #37 on: October 29, 2020, 01:59:35 PM »
There's a consideration too about where the load travels if you want to look while in there.

The "bushed" gears only ever run on their bushes by rotating on the shaft when NOT in use as a ratio. Once you select that gear to use it in drive train then either it or it's neighbouring gear slides to connect via the face dogs.  Then the torque passes through the teeth and as far as the dogs,  then divert into that paired gear and so onto the gearshaft to give output.

It doesn't much matter with some free play as it'll orient itself on the dog faces once changed,  it's initial alignment comes from it's opposing gear, and it, having straight teeth that take out misalignment when spinning together.

If you put it in the gear ratio in question,  then look at the load path it'll show this.

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #38 on: October 29, 2020, 03:12:06 PM »
There's a consideration too about where the load travels if you want to look while in there.

The "bushed" gears only ever run on their bushes by rotating on the shaft when NOT in use as a ratio. Once you select that gear to use it in drive train then either it or it's neighbouring gear slides to connect via the face dogs.  Then the torque passes through the teeth and as far as the dogs,  then divert into that paired gear and so onto the gearshaft to give output.

It doesn't much matter with some free play as it'll orient itself on the dog faces once changed,  it's initial alignment comes from it's opposing gear, and it, having straight teeth that take out misalignment when spinning together.

If you put it in the gear ratio in question,  then look at the load path it'll show this.

Cheers. Makes sense. 👍
Gareth

1977 CB400F
1965 T100SS

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #39 on: October 30, 2020, 08:28:48 PM »
« Last Edit: October 30, 2020, 08:31:52 PM by taysidedragon »
Gareth

1977 CB400F
1965 T100SS

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #40 on: November 12, 2020, 11:27:16 AM »
All the parts I need for the rebuild have arrived and the gear bush is sorted.
Primary drive rubbers and gasket set not in picture. Let the fun begin! 😁 [ Guests cannot view attachments ]
Gareth

1977 CB400F
1965 T100SS

Offline Laverda Dave

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Re: CB400F Engine rebuild
« Reply #41 on: November 12, 2020, 12:01:45 PM »
All those parts look reassuringly expensive  :)
Don't forget the Hondabond for the case joint!
Time to make a cuppa and get started on the adventure  :D
Good luck and keep the progress photos coming.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Nurse Julie

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Re: CB400F Engine rebuild
« Reply #42 on: November 12, 2020, 12:17:53 PM »
Luverly..... Enjoy
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline taysidedragon

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Re: CB400F Engine rebuild
« Reply #43 on: November 12, 2020, 03:13:29 PM »
All those parts look reassuringly expensive  :)
Don't forget the Hondabond for the case joint!
Time to make a cuppa and get started on the adventure  :D
Good luck and keep the progress photos coming.

Yep. Got a tube of Hondabond HT. Forget to put it in the pic.
I haven't added up the cost yet, but got the Kawasaki primary chain from MSP, piston set from Cruzinimage
and o-rings etc from  Nurse Julie so did quite well on prices. 👍🔧🏍
Gareth

1977 CB400F
1965 T100SS

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Re: CB400F Engine rebuild
« Reply #44 on: November 12, 2020, 04:26:03 PM »
All the parts I need for the rebuild have arrived and the gear bush is sorted.
Primary drive rubbers and gasket set not in picture. Let the fun begin! 😁 (Attachment Link)

Eye candy - lovely what make are the pistons and who did you source them from I'm pretty certain I might end up needing some early next year.
?
Honda CB500 K1 (new pit dug out ready)
Honda CB400 four super sport (first money pit)
Link to my full restoration http://www.sohc.co.uk/index.php/topic,23291.0.html

 

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