Author Topic: CB750F2 .... silk purse from a sows ear.  (Read 31599 times)

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #135 on: October 04, 2018, 06:34:40 PM »
So that's part of the primary drive sprocket.....not one of the gear shafts. That makes sense.

Now I got to go find a replacement one. Happy days.....
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Trigger

  • Grogu
  • *
  • Posts: 8434
  • Engines built on reputation, not advertising.
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #136 on: October 04, 2018, 07:31:27 PM »
I see that kind of damage more and more these days. Test the shaft once out to see how true it is  ;)

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #137 on: October 04, 2018, 07:41:03 PM »
Oh....true...didn't think of that.

Thanks for cheering me up Trigger :(

But yes...if they put a load of brute force on the thing pressing down on the shaft, it may well be banana shaped. And if it is, then my gear mesh is going to go to hell in a handcart.
I was always told if something doesn't move and you think it should STOP. Find out why it won't move...don't just apply more force.

CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Trigger

  • Grogu
  • *
  • Posts: 8434
  • Engines built on reputation, not advertising.
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #138 on: October 04, 2018, 10:23:30 PM »
There are two types of primary sprockets, the early ones never had a circlip

[ Guests cannot view attachments ]

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #139 on: October 05, 2018, 09:44:49 AM »
So any later sprocket would fit. From the pics I was looking at...late K models have the circlip groove.

Whilst I am sure the earlier design is OK and teh clutch centre nut holds the whole assembly in place...I presume Honda changed the design for a reason. And I would much rather my clutch basket was held on the shaft rather than floating free.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Trigger

  • Grogu
  • *
  • Posts: 8434
  • Engines built on reputation, not advertising.
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #140 on: October 05, 2018, 10:24:36 PM »
The one you require was fitted to some K6 units, all F1/F2 and K7 and K8 units  ;)

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #141 on: October 06, 2018, 01:50:24 PM »
Brilliant. Thanks Trigger. Now I can go shopping!
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #142 on: October 09, 2018, 04:30:29 PM »
Been one of those days. 2 steps forward...2 rakes trodden on. That kind of day.

Stopped off on the way home to pick up some fresh drill bits to drill out the offending screws if needed ( my 6mm was blunt and I had snapped my last 4mm for pilot hole drilling to keep it centred. Helps get past the awkward bit where teh drill has to get trhough the centre of the cross ... and to the shed I went!

One last try with the impact driver and my largest hammer was called for, before I broke out hte drill and dived in.

Bang...bang...bang...shift. YES! it moved! One screw out.... on to the next.

Bang...bang...bang...shift. YES! The bigger hammer was a success and the overnight soak in penetrating oil had probably helped too.

No stopping me now!

Bang...bang...slip. That didn't feel right. Not to worry I thought, just means I have to drill this one out. Well....not exactly.



The bottom left screw head was still perfect. It was just full...of impact driver head. Bugger. Damn thing had broken up! A funeral service will be held later. IOty had been a loyal servant and had fallen in the line of duty... Now I got to go buy another one. No way was I going to try another impact bit, as none of the others fit the screw, and I was not going to even bother trying an ill fitting one. Just going to mash the screw to no purpose.



So...I figured I would move on to another less strenuous task where an impact driver was not going to be needed ( probably... ) and I started on the carbs.

Floatbowls came off easy, and still held liquid. Probably petrol once. Wouldn;t call it that now. But liquid all the same. Usually makes life a whole lot easier when they are not completely dry....unless they were properly drained. Which they were not.

Jets were a bit gunked up but they all shifted easily and the emuilsion tubes came out after. Not...with...as usually happens. I alwys get nervous with brass screws, as they snap easily under stress and strain. Bit like me.....

Next I popped the carb tops off and all looked pretty clean. Slides etc. are not an easy strip on this type of carb...All rods and linkages rather than old fashioned screw top carbs. I noticed the throttle cable bracket was a bit wobbly...and needed a tighten up. Nope. It was tight. Then I saw the issue.

The bracket is held on by a single screw and a cast in pin on the carb body. That pin was no longer part of the carb body. Worse...the stress had been applied to the cast boss on the carb body....and that had caused a crack in the carb body. Wish I had never looked now.



Now...I could fix the pin with a drill/tap and screw a peg in. Not sure about hte carb body though. I mean...I could bodge a fix with chemical metal/araldite....or I could get it welded up...or source another set of carbs. The question is...whether I can get a good set of carbs, what they will cost.....

Fixing would mean taking the carbs apart from the mounting bracket. I have never done this...and have...in the past...done EVERYTHING to avoid it. All the shafts and springs and whatnot all need to be properly aligned, and choke flaps ahve to come off...and so on. But any fix is going to need access to the side of the carb...and it's one of the inners...

But I need to make a decision on this before I go any further with the carbs, as any kind of cleaning and fettling is going to be a waste of time if the carbs are not usable.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline paul G

  • SOHC Master
  • Posts: 1748
  • No room left in the garage what now !
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #143 on: October 09, 2018, 04:46:32 PM »
It always seems to be surprise after surprise with these things and most of them are usually unpleasant ones. >:( >:(
Honda CB400 4
Honda CB550 K3 (sold)
Honda CB750 UK K1
Kawasaki Z650 C2
Kawasaki Z650 cafe racer (Sold)
Honda CD175 sloper

Offline K2-K6

  • Grogu
  • *
  • Posts: 5234
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #144 on: October 09, 2018, 05:17:35 PM »
May be proved wrong,  but never considered the carb's material weldable.  Not sure of the alloy but think it has a zinc content that oxidises at below weld temperature,  which prevents normal metal flow. That's the bad news  :(

The good is that the crack appears to be in an entirely non critical part for normal carb structural function. Doesn't look like it's used for the throttle slide to bare on,  so you should be able to make an epoxy repair into the crack to prevent air leak potentially affecting the mixture  :)

To get a realistic repair,  I'd clean it with carb cleaner,  warm it and get plain epoxy two pack to flow into the crack,  leave to set and clean off excess with a blade.  Don't try to flex the casting in any way at all,  it'll probably snap off.

Offline K2-K6

  • Grogu
  • *
  • Posts: 5234
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #145 on: October 09, 2018, 05:41:44 PM »
Just a thought on the impact driver,  it hasn't flicked it to doing up has it? Just sometimes they bounce past the centre point if you don't hold them against the screw tightly.  If it has,  that may have snapped the bit.

I usually pre-load it slightly by holding  the smallest amount of anti clock rotation on it before thumping it.

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #146 on: October 09, 2018, 07:12:23 PM »
No...the impact driver was fine. I do the same as you do K2-K6 ... I apply a little bit of twisting torque to the handle to make sure it is in contact with the screw surface it's going to press on. It also helps to let you 'feel' the thing turn when it starts to go.
I think the bit has just failed through long years of use. The large cross head is the one I used the most...and it's life is one of shock loadings. It's just called time.

Going to be a deep breath job if I have to seperate the carbs...but in order to fix the sheared pin part, I will need to do this.

No way I would try to move the thing back...made that mistake before. You think..I'll just ease it back...ping.

The slides don;t go that far up, so I will try an epoxy repair. I will also...assuming I get it all apart...stop drill the crack before I epoxy and maybe just 'V' the inner side a little to help the epoxy bond.

There also is a small grommet on the accelerator pump that has cracked and broken in two. It's part of part number 16201-393-004, and seems to form a seal and a support to the shaft on the accelerator pump. I can't tell if it is plastic or rubber.....but I think it was once rubber. It may explain why there is corrosion in the area below the diaphragm. Need to find a replacement for this while I am at it. Then order a set of carb rebuild kits..... but not until I have done the deed with the carb body!
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Bryanj

  • Grogu
  • *
  • Posts: 10694
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #147 on: October 10, 2018, 01:06:22 AM »
Got a set of 550k3 carb bodies you cab have cheap plus postage, i know that a lot of the internals are the same but not sure on the bodies. Have you got the pilot jets out to clean them? They clog up for a passtime, are a press fit and you need to twist and pull with vice grips

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #148 on: October 10, 2018, 08:31:55 AM »
Thanks Bryan....I'll do do e research and find out if the bodies are the same. Aside from the crack ..the carbs are not bad. Not taken the smaller jets out yet. Much still to do!
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline SumpMagnet

  • SOHC Pro
  • Posts: 683
    • View Profile
Re: CB750F2 .... silk purse from a sows ear.
« Reply #149 on: October 10, 2018, 12:43:49 PM »
Mixed dasy today. No work as I had a dentist appt...so some sneaky work was done on the motor.

Picked up a replacement impact driver as it was £8 to get the bit I needed....or £15 for a whole new one from Halfords with a lifetime guarantee. So....no brainer really. I got a few extra bits to replace ones that had been lost over the 30 years I had the tool...

It is only when you replace a worn out old tool with new that you realise how much slop has grown with time. New driver...3 taps...2 screws out. WOW. Didn;t even need a big hammer.

Flushed with success and with half an hour to spare, out came all the top bolts and into the prepared piece of card with the holes laid out...Flipped motor over. Lost the little screw in the top of hte neutral indicator thing I can't shift from the upper case...must go find that later. Undid all the bottom case bolts, breaking the torque in a sensible stress relieving pattern....gave the cases a few judicious taps on the big bits where the engine mounts are. Saw it shift. One section wouldn't budge. Resist the urge to 'pry' as I have seen a couple of minor scars on the cases where someone did...Find the bolt I forgot to undo after I slackened it...which forced me to turn the motor back over to get to it...then back over again...and hte cases parted like the Red Sea before Moses.

The Halleluia Chorus was playing on the MP3 and hte sun came out from behind the clouds.....

Nothing horrid met my eyes. I have not had time to check the shells or actually lift the crank out as I was now late for the appointment...but I am sure they understood. No time for photos either...so will do that later.
what I did have time to see was the state of hte crankshaft journals.

I had feared something looking like an aerial photo of a railyard.....rust....furrows....metal fragments. All these things were not there.

Instead, I could see a shadow line where the oil channel is in the shells, which was wiped with a lint free cloth....revealing a polished surface of shiny loveliness. I could not see a mark on the bearing surface. Not one. Which is how it should be. Running a fingernail across was smooth on all 4. That's a relief. Really is. Big ends all felt rock solid.

Of course...I haven't measured the clearances on the shells ( I have heard of Plastigage....understand the process...but it's not something I have ever done.  )

Also...I am reluctant to mess with the big ends, as they all seem smooth and free from any slack I can detect. Should I? Or should I not. Bottom end on this thing looks really tidy aside from the gorilla knackered primary sprocket shaft and some idiot marks on the cases .

Also need some gasket sealant for reassembly ( Hondabond isn't it ? ... won't have instant silicon stuff anywhere oil lives )

After the last couple of days of hassle...today has started well.

Aside from the dentist.
CB750F2 - in pieces
CB900F Hornet - the daily transport

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal