Author Topic: CB750F2 .... silk purse from a sows ear.  (Read 31630 times)

Offline andy120t

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #180 on: February 21, 2019, 04:22:36 PM »
I love the look of the the black 750 - it sort of reminds me of the Harley in Black Rain ... (sorry, I know I'm not making any friends here!)...
andy120t

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Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #181 on: February 27, 2019, 08:52:39 AM »
Right...the weather has risen above 'bloody freezing' in the shed, and we are back in business with the rebuild project.

Not quite at the point where I can start painting stuff....but it is warm enough to do things!

Yesterday, we dug out hte solvol and the front mudguard and polished it back to a respectable state. There are a couple of minor marks, but it actually looks prety good for an old piece of chrome. There is a bit of rust on the inside, but most of it shifted just fine. I don;t want to underseal the inside of the guard, but I will dab on some rust treatment to kill the rust, then give it a coat of clear lacquer to seal and protect it. I left the rubber bobbins in place on the guard as they are a bit 'solid' but not cracked. Taking them out would have ruined them for sure.

I have got myself into the habit of checking if things can be got before I make a mess of them....

Next...I need to order myself a set of gearbox bearings so I can rebuild the cases. The big question now is do I paint the cases together.....or before I rebuild. Much rubbing down to be done to shift those flakiy bits and prep the surface. I suppose I had also better get a gasket set sorted...and from what I read on here...that's another minefield!
CB750F2 - in pieces
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Offline Nurse Julie

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #182 on: February 27, 2019, 09:14:19 AM »
Paint all cases prior to rebuild. Always looks better and much easier to get in the oven and cure in bits rather than a whole, rebuilt engine  ;D ;D
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Offline K2-K6

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #183 on: February 27, 2019, 09:28:50 AM »
On the underside of the mudguard,  we discussed recently as to how it can be protected.

Oddjob was doing an original to help conserve it,  and ended up with zinc heavy paint as I recall.

I've never thought "underseal" was for protection of metal and to prevent rusting.  It's just to protect the paint from being chipped and breaches occurring in the protection that offers.
Any mild steel on old cars that's just been coated with straight underseal always rusts like hell in my experience.

Most effective appears to be zinc heavy painting,  and maybe something like coated with silver hammerite to give something of a waterproofing in that underside of mudguard area.

Thread is somewhere but couldn't find.

Offline K2-K6

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #184 on: February 27, 2019, 09:33:17 AM »
Found it,  this is the one I was thinking about.

http://www.sohc.co.uk/index.php/topic,17179.msg148069.html#msg148069

 :)

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #185 on: February 27, 2019, 05:33:13 PM »
hmm...that zinc paint looks like it will do the job. Will add it to the ever growing list of things to spend money on :) But I want to preserve the important parts that give the look I want. And that means a nice shiny chrome front guard.

Odd really...as I remember back in the day the fashion was to bin the chrome front guards and fit fibreglass ones with all sorts of horrid aerofoil shapes on them. Then...as the forks now lost the thing that braced them..namely a heavy steel mudguard...they fitted a fork brace.

Mind you...Suzuki ones just used to rust out completely in the centre....

Julie....gotcha on the paint. Damn thing doesn;t fit in the oven....but I have a plan B .....
« Last Edit: February 27, 2019, 05:34:57 PM by SumpMagnet »
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Nurse Julie

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #186 on: February 27, 2019, 05:38:17 PM »
Not many domestic ovens take a complete CB750/4 engine and none take almost 100kg or whatever it is. All I know is they are bloody, bloody heavy.
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Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #187 on: February 27, 2019, 08:12:58 PM »
bloody heavy indeed! Last motor I swapped was a Z750 lump, and I did that on my own. Took two of us to carry the CB750 out to the shed. A wrecked motor would make an excellent ship anchor.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Nurse Julie

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #188 on: February 27, 2019, 08:50:51 PM »
bloody heavy indeed! Last motor I swapped was a Z750 lump, and I did that on my own. Took two of us to carry the CB750 out to the shed. A wrecked motor would make an excellent ship anchor.
Plenty that we have through here for overhaul HAVE been used as ships anchors !!! It's the Barnacles that give it away  ;D
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.
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LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
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Offline K2-K6

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #189 on: February 28, 2019, 08:42:30 AM »
About the front mudguard,  the Honda type usually rust through in that sandwich area above the brace and around the rivets.  normally seen by rust bubbling through the top surface, by which time it's too late.

Maybe worth thinning the paint first and try getting it to run inside that joint with it upside down.

Offline Moorey

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #190 on: February 28, 2019, 09:21:38 AM »
I clean off the rust and use old oil. Warm the steel and the oil and it does get under the bracket and into the rolled edges of mudguards hang it up let it drain and give it a wipe and do it once a year.

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #191 on: February 28, 2019, 09:32:10 AM »
Yep...that double skinned brace area was where they all go, not just the Honda ones. You see the upper chrome layer go wrinkly, then crack and flake. Poke it and you can see the tyre.

Good ideas on getting something in there to keep the air/moisture out. I will do that before I wrap it up and put it away for fitting later. Need to send the forks off for chroming and get new seals, dustcaps and clips and get some satin black for the leg lowers. Oh...and some new head bearings. Then the front end is done.

Then I got to strip, clean and paint the swingarm and centrestand. Not sure about the swingarm bushes they feel OK....so will probably leave them.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #192 on: March 06, 2019, 04:57:30 PM »
No stopping me now ....well...not with those brakes anyway!

Figured I would make a start on the brakes as I need to get the calipers cleaned up ready for paint and I wanted to see what state thigns were in. As the bike arrived last summer, the brakes simply did not work. They were broke.

Popped the top on the master cylinder, and the rubber etc was all pretty good. Unlike the brake fluid. I say fluid...it was JELLY! I have never seen brake fluid do this, and to be honest....I never want to again.

A soak in fresh fluid and a lot of elbow grease cleaned it out, but I soon found out that the seals on the master cylinder were shot. Normally it's a breeze to pop out pistons just by pumping hte lever....but not here. Turned out there was another plug of sludge sitting in the caliper too. You can see it here where it oozed down once the piston was out...



Other than that, there was not much wrong here. The hoses and seals will all be changed for the simple reason of safety, but the pads were noi more than 50% gone, the sliding pins all did...and there was even grease in there! Small trasce of corrosion inside the caliper, but nothing that won't clean up. Dust seals were good and doing there job and the pistons was spotless.



Should all clean up nicely....
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #193 on: March 30, 2019, 05:04:26 PM »
God knows I should have known ... but a 'simple' job on an old bike just never really ends up being simple.

But...I had a bit of spare time this afternoon, so I thought I would strip down the front master cylinder. I have saved a bit of cash up, and will be ordering a rebuild kit for same, some bits for the front calipers, and the seals/clips for the forks. At some point, I will send the stantions off for rechroming, as I prefer that to buying pattern. Philpotts have done an excellent job on fork legs for me before, and I have seen some pretty thin chrome on pattern replacements in the past.

So...just whip the thang apart, then tidy up the shed as it's got damn messy over the winter... and then I can put my feet up.

Read the book ...and dug out the circlip pliers.

So...step one : Carefully prise out the rubber dust seal.

Nah....it's goosed. Split and crumbly. So it gets ripped out in pieces. Chucked in the bin. There is going to be one in the rebuild kit anyway, which will be fitted when I put it all back together.

Step 2: Remove the circlip that holds the piston in place.

Out with the circlip pliers, which will not fit in the space around the piston. Great. Figure if I push the piston down, it might let me get in there. Carefully clamp the thing in the vice with rags and bits of wood to protect the ally, and push down with a piece of dowel. Which promptly snaps. The piston springs up and squirts a little residual brake fluid in my face just to remind me whose boss here. Out with the angle grinder..... no....not in revenge. A little light modification to the circlip pliers and they fit in where I need them to, and out comes a circlip with a light dusting of gunge, rust, and stuff. Stuff being the technical term I am applying to the jelly the old brake fluid appears to have turned into.

Step 3: Remove the plain washer and slide the piston out.

You wot! The plain washer apprars glued in place, and the piston will slide in and out...but won't actually COME out at all. Whatever black arts were employed to place it there, I have yet to learn the counter spell to have it come out.

Does it just pull out?
Is there something else holding it?

I have studied the parts and the diagrams like a Buddhist priest looking for enlightenment...but in the end, I have just dumped a slug of WD40 in there and left it to soak.

As far as I can see, there is a pair of rubber seals, which fit on the piston, and the piston is held in place by the plain washer....which in turn is locked in by the circlip. So it should be clip out...and the piston ought to have popped loose under pressure from the spring. Hmmmm.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline hairygit

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #194 on: March 30, 2019, 05:39:48 PM »
The washer may well have rusted, or electolytically fused itself to the alloy of the master cylinder. If it's rusted, try applying heat to the outside area of the cylinder, being alloy it may expand faster than the steel and loosen it's grip. The easiest option if that doesn't work is one of DSS replica cylinders.

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